Mapping of IgE epitopes in in vitro gastroduodenal digests of β-lactoglobulin produced with human and simulated fluids

Bioactive Dairy-Fermented Products and Phenolic Compounds: Together or Apart

Fermented dairy products (e.g., yogurt, kefir, and buttermilk) are significant in the dairy industry. They are less immunoreactive than the raw materials from which they are derived. The attractiveness of these products is based on their bioactivity and properties that induce immune or anti-inflammatory processes. In the search for new solutions, plant raw materials with beneficial effects have been combined to multiply their effects or obtain new properties. Polyphenols (e.g., flavonoids, phenolic acids, lignans, and stilbenes) are present in fruit and vegetables, but also in coffee, tea, or wine. They reduce the risk of chronic diseases, such as cancer, diabetes, or inflammation. Hence, it is becoming valuable to combine dairy proteins with polyphenols, of which epigallocatechin-3-gallate (EGCG) and chlorogenic acid (CGA) show a particular predisposition to bind to milk proteins (e.g., α-lactalbumin β-lactoglobulin, αs1-casein, and κ-casein). Reducing the allergenicity of milk proteins by combining them with polyphenols is an essential issue. As potential 'metabolic prebiotics', they also contribute to stimulating the growth of beneficial bacteria and inhibiting pathogenic bacteria in the human gastrointestinal tract. In silico methods, mainly docking, assess the new structures of conjugates and the consequences of the interactions that are formed between proteins and polyphenols, as well as to predict their action in the body.

An in vitro protocol to characterise the resistance of food proteins to intestinal digestion

In vitro digestion tests provide data on the form in which dietary proteins maybe presented to the gut mucosal immune system, one of many strands of evidence used in allergenicity risk assessment. A 96-well plate format in vitro intestinal digestion protocol has been developed with a high and low enzyme activity test executed at pH 6.5 and 8.0. It was applied to the systematic analysis of test proteins (including six allergens and one non-allergenic comparator) which were either completely resistant to pepsinolysis or gave rise to large persistent fragments following in vitro gastric digestion. Digestion was monitored using SDS-PAGE and densitometry. Proteins resistant to pepsin were also resistant to intestinal digestion irrespective of the protocol applied and gave rise to large persistent digestion fragments. In contrast persistent fragments from pepsin digestion were readily digested. Bile salts enhanced the digestibility of two highly resistant proteins, lysozyme ad β-lactoglobulin, changing the rank order of protein digestibility. Intestinal digestion tests that include bile salts provide a more physiologically relevant system for future investigation into how digestion products may influence the balance between tolerance and sensitization - and hence contribute to future development of a more effective allergenicity risk assessment process.

IgE-Binding and Immunostimulating Properties of Enzymatic Crosslinked Milk Proteins as Influenced by Food Matrix and Digestibility

Dairy foods are essential in the diet, although in some susceptible individuals they may cause allergy to cow's milk proteins. Therefore, alternative methods are sought to reduce their allergenicity. Transglutaminase (TG) is widely used in dairy products mainly to improve texture. Although it has been claimed that TG can be used to modify the digestibility and allergenicity of foods, its impact within a real matrix has been rarely studied. The aim of this work was to assess the allergenic potential of crosslinked skim milk (SM), milk casein fraction (CN), and whey protein (WP). To this purpose, inhibition ELISA with sera from milk allergic patients, in vitro activation tests of mouse mast cells and splenocytes, and simulated gastrointestinal digestion assays were performed. The results showed that cross-linking increased the binding of IgE to WP, but decreased IgE-binding to SM and CN. However, no differences were observed in the ability of cross-linked proteins to induce mast cell degranulation compared to native proteins. The cross-linking of SM and CN reduced Th2 cytokine release from the splenocytes of sensitized mice. All TG-treated samples exhibited more resistance to in vitro digestion than the untreated proteins and the human IgE binding capacity after digestion was higher. In conclusion, TG treatment of milk proteins does not reduce the risk of eliciting allergic symptoms in cow's milk allergic patients.

Immunomodulatory Role of BLG-Derived Peptides Based on Simulated Gastrointestinal Digestion and DC-T Cell from Mice Allergic to Cow's Milk

Peptides, but not whole protein, elicit an allergic reaction since food allergens should be consumed by digestion. In this study, we explored the remaining peptides after simulated digestion of cow’s milk in order to search for β-lactoglobulin (BLG)-derived peptides that could play an immunomodulatory role. As a major allergen in milk, BLG-derived peptides, 109 in total, were identified both from simulated infant and adult digestion in vitro. These peptides were mainly located in four regions, and they were synthesized as five peptides, namely, BLG_1–14, BLG_24–35, BLG_40–60, BLG_82–101, and BLG_123–139. Then, the effect of peptides on the Caco-2 cell’s transport absorption, the co-stimulatory molecules of DC, and the T-cell phenotype was explored. The results suggested all peptides showed better transport absorption capacity with the apparent permeability coefficient higher than 2 × 10⁻⁶ cm·s⁻¹. The ability of BLG_40–60 for promoting lamina propria-derived DC cell (LPDC) maturation was observed by the increase in MHC II. Moreover, BLG_1–14 and BLG_40–60 directed activation of T lymphocytes towards a Th1 phenotype. This is the first report of the immunomodulatory potential of peptides in the sensitization of allergic reaction, and one peptide, BLG_40–60, was regarded as an immunomodulatory peptide, one that should be further explored in an animal model in depth.

Investigation into predominant peptide and potential allergenicity of ultrasonicated β-lactoglobulin digestion products

The effect of ultrasonicated β-lactoglobulin on the allergenic potential of predominant peptide was studied in vitro digestion. Gastrointestinal (GI) digestion of ultrasonicated β-lg was fractionated into four fractions, which have different molecular weight and allergenic potentials. The lowest allergenicity of fraction was produced by ultrasonicated β-Lg after GI digestion, depending on the changes in the structure of β-Lg by ultrasonic and the promotion of its proteolysis, resulting in the production of numerous small peptides with significantly reduced IgE activity and basophil histamine release. Mass spectrometry analysis showed that ultrasonic can promote the further hydrolysis of large intermediate peptides, Y42, L54, L57/L58, L95, L104/F105, L122 were target residues that became more available to protease by the pretreatment of ultrasonic, thus have a smaller molecular weight with reduced allergenic potential. Ultrasonic processing of milk products alone could reduce the risk of an allergenic reaction in milk allergy patients to some extent.

IgE-Reactivity Pattern of Tomato Seed and Peel Nonspecific Lipid-Transfer Proteins after in Vitro Gastrointestinal Digestion

The influence of gastrointestinal digestion on the immunological properties of three different nonspecific lipid-transfer proteins (nsLTPs) described in tomato fruit has been assessed using an in vitro system mimicking the stomach and intestine digestion conditions. Tomato peel/pulp nsLTP, Sola l 3, was degraded after digestion, although the immunoglobulin E (IgE) recognition of intact protein and a 10 kDa band were still observed after 30 min of duodenal digestion in the presence of phosphatidylcholine. The tomato seed nsLTP, Sola l 7, showed a higher stability than the other seed allergen, Sola l 6, during digestion. Sola l 7 showed an IgE immunoreactive 6.5 kDa band in immunoblotting analysis, retaining up to 7% of its IgE-binding capacity in inhibition ELISA test after 60 min of duodenal digestion and keeping intact its ability to activate basophils after digestion. These results suggest that the tomato seed allergen Sola l 7 might be considered as an important allergen in the induction of allergic responses to tomato due to its high stability against gastrointestinal digestion.

Improved antitumor activity and IgE/IgG-binding ability of α-Lactalbumin/β-lactoglobulin induced by ultrasonication prior to binding with oleic acid

Bovine α-lactalbumin (α-La)/β-lactoglobulin (β-Lg) was pretreated through ultrasonic treatment and subsequently binding with oleic acid (OA) by heat treatment. And, the antitumor activity, IgE/IgG-binding ability, and structural modifications were investigated. After α-La/β-Lg were treated by ultrasonic prior to binding with OA, the treated α-La/β-Lg showed high antitumor activity and IgE/IgG-binding ability, and significantly affected the structural modifications, which reflected by the reduction in α-helix content, the increase of molecular weight, intrinsic fluorescence intensity, and surface hydrophobicity. Molecular docking studies indicated that OA bound to α-La/β-Lg by hydrogen bonds and hydrophobic interaction. Therefore, ultrasonic prior to binding with OA could improve antitumor activity and IgE/IgG-binding ability of α-La/β-Lg as a result of structural modifications. And, ultrasonic prior to binding with fatty acid processing of milk products alone may increase the antitumor activity, this change may enhance the risk of an allergenic reaction in milk allergy patients to some extent. PRACTICAL APPLICATIONS: Fatty acids, natural ligands associated with the bovine milk proteins, and milk protein-fatty acid complex has a variety of functional applications in the food industry. This study revealed that antitumor activity, IgE/IgG-binding ability, and structural modifications of α-La/β-Lg induced by ultrasonic prior to binding with oleic acid. It will be beneficial to understand the mechanism of the functional changes of protein. Ultrasonic prior to binding with oleic acid will be more likely to develop a practical technology to improve the functional characteristics of milk protein and design the optimal nutritional performance of milk food.

Glycation of β-lactoglobulin combined by sonication pretreatment reduce its allergenic potential

β-lactoglobulin (β-Lg) was treated through different ultrasonic power and subsequently glycated with galactose to investigate its structural changes and immunological properties, and then evaluated by high-resolution mass spectrometry, enzyme-linked immunosorbent assay and basophil histamine release test. Ultrasonication combined with glycation (UCG) modification significantly reduced the IgE/IgG-binding capacity, and the release of β-hexosaminidase, histamine and interleukin-6, accompanied with changes in the secondary and tertiary structures. The decrease in the allergenicity of β-Lg depended not only on the glycation of K47, 60, 83, 91 and 135 within the linear epitopes, but also on the denaturation of conformational epitopes, which was supported by the glycation-induced alterations of the secondary and tertiary structures. This study confirmed that UCG modification is a promising method for decreasing the allergenic potential of allergic proteins, which is likely to develop a practical technology to produce hypo-allergenic milk.

The mechanism of reduced IgG/IgE-binding of β-lactoglobulin by pulsed electric field pretreatment combined with glycation revealed by ECD/FTICR-MS

Bovine β-lactoglobulin (β-Lg) is a major allergen existing in milk and causes about 90% of IgE-mediated cow's milk allergies. Previous studies showed that pulsed electric field (PEF) treatment could partially unfold the protein, which may contribute to the improvement of protein glycation. In this study, the effect of PEF pretreatment combined with glycation on the IgG/IgE-binding ability and the structure of β-Lg was investigated. The result showed that PEF pretreatment combined with glycation significantly reduced the IgG and IgE binding abilities, which was attributed to the changes of secondary and tertiary structure and the increase in glycation sites and degree of substitution per peptide (DSP) value determined by electron capture dissociation Fourier transform ion cyclotron resonance mass spectrometry (ECD/FTICR-MS). Unexpectedly, glycation sites (K47, K91 and K135) added by two mannose molecules were identified in glycated β-Lg with PEF pretreatment. Moreover, the results indicated that PEF pretreatment at 25 kV cm^-1 for 60 μs promoted the reduction of IgG/IgE-binding capacity by increasing the glycation degree of β-Lg, whereas single PEF treatment under the same conditions markedly enhanced the IgG/IgE-binding ability by partially unfolding the structure of β-Lg. The results suggested that ECD/FTICR-MS could help us to understand the mechanism of reduction in the IgG/IgE-binding of β-Lg by structural characterization at the molecular level. Therefore, PEF pretreatment combined with glycation may provide an alternative method for β-Lg desensitization.

Cattle with a precise, zygote-mediated deletion safely eliminate the major milk allergen beta-lactoglobulin

We applied precise  zygote-mediated genome editing to eliminate beta-lactoglobulin (BLG), a major allergen in cows’ milk. To efficiently generate LGB knockout cows, biopsied embryos were screened to transfer only appropriately modified embryos. Transfer of 13 pre-selected embryos into surrogate cows resulted in the birth of three calves, one dying shortly after birth. Deep sequencing results confirmed conversion of the genotype from wild type to the edited nine bp deletion by more than 97% in the two male calves. The third calf, a healthy female, had in addition to the expected nine bp deletion (81%), alleles with an in frame 21 bp deletion (<17%) at the target site. While her milk was free of any mature BLG, we detected low levels of a BLG variant derived from the minor deletion allele. This confirmed that the nine bp deletion genotype completely knocks out production of BLG. In addition, we showed that the LGB knockout animals are free of any TALEN-mediated off-target mutations or vector integration events using an unbiased whole genome analysis. Our study demonstrates the feasibility of generating precisely biallelically edited cattle by zygote-mediated editing for the safe production of hypoallergenic milk.

Identification of IgE and IgG epitopes on native Bos d 4 allergen specific to allergic children

Alpha-lactalbumin (ALA) is one of the major allergens in cow's milk. However, research on its conformational epitopes has been relatively limited. In our study, specific antibodies against cow's milk ALA were purified from eight children by two-step affinity chromatography. Subsequently, mimotopes against IgG and IgE were biopanned from Ph.D.-12 and Ph.D.-C7C, respectively. Based on the mimotopes, linear epitopes were defined with the UniProt alignment tool. Conformational epitopes were computed using the Pepitope Server. Six IgE and seven IgG linear epitopes were identified. Meanwhile, five IgE and three IgG conformational epitopes were revealed with PyMOL. The results showed that common residues were identified in both IgE and IgG epitopes and some residues of the conformational epitopes were composed of linear epitopes on bovine α-lactalbumin. The results indicated that the data could be used for developing hypoallergenic dairy products on the basis of epitopes and providing a diagnostic tool for the assessment of patients who are allergic to cow's milk.

Mechanism of Reduction in IgG and IgE Binding of β-Lactoglobulin Induced by Ultrasound Pretreatment Combined with Dry-State Glycation: A Study Using Conventional Spectrometry and High-Resolution Mass Spectrometry

Bovine β-lactoglobulin (β-Lg) is one of major allergens in cow's milk. Previous study showed that ultrasound treatment induced the conformational changes of β-Lg and promoted the glycation in aqueous solutions, which is, however, less efficient compared with dry-state. In this work, the effect of ultrasound pretreatment combined with dry-state glycation on the IgG and IgE binding of β-Lg was studied. Dry-state glycation with mannose after ultrasound pretreatment at 0-600 W significantly reduced the IgG and IgE binding of β-Lg, with the lowest values observed at 400 W. The decrease in the IgG and IgE binding of β-Lg was attributed to the increase in glycation extent and the changes of secondary and tertiary structure, which reflected in the increase of UV absorbance, α-helix and β-sheet contents, as well as the decrease of intrinsic fluorescence intensity, surface hydrophobicity, β-turn, and random coil contents. Moreover, ultrasound pretreatment promoted the reduction of IgG and IgE binding abilities by improving glycation, reflecting in the increase of the glycation sites and the degree of substitution per peptide (DSP) value determined by Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Ultrasound pretreatment at 400 W showed the most significantly enhanced glycation extent. Besides, the results suggested FTICR-MS could provide insights into the glycation at molecular level, which was conducive to the understanding of the mechanism of the reduction in the IgG and IgE binding of β-Lg. Therefore, ultrasound pretreatment combined with dry-state glycation may be a promising method for β-Lg hyposensitization.

The Reduction in the IgE-Binding Ability of β-Lactoglobulin by Dynamic High-Pressure Microfluidization Coupled with Glycation Treatment Revealed by High-Resolution Mass Spectrometry

Our previous study indicated that pretreatment by dynamic high-pressure microfluidization (DHPM) and glycation with galactose was a promising method for decreasing the immunoglobulin E (IgE)-binding ability of β-lactoglobulin (β-LG). In this work, the conformational alteration of β-LG subjected to DHPM and glycation treatment was investigated in relation to IgE-binding ability by orbitrap mass spectrometry. After DHPM pretreatment, lower IgE-binding ability of glycated β-LG was observed with increasing pressures. Prior to DHPM pretreatment, 11 glycated sites were identified, while the number of glycation sites was increased to 12 after pretreatment. However, there was no significant difference of the glycation sites at the pressures of 50, 100, and 200 MPa, respectively. Average degree of substitution per peptide molecule of β-LG (DSP) was investigated to assess the degree of glycation per glycation site. All of the samples pretreated by DHPM exhibited a higher glycation level than those without DHPM pretreatment. The shielding effects of epitopes owing to glycation contributed to the reduction of IgE-binding capacity. Orbitrap mass spectrometry could provide a comprehensive understanding of the nature of protein glycation.

Protein degradation and peptide release from milk proteins in human jejunum. Comparison with in vitro gastrointestinal simulation

Human jejunal digests after oral ingestion of casein and whey protein were collected by a nasogastric tube and protein degradation and peptide release was compared with that found in the digests of the same substrates using a standardised protocol. No intact casein was detected in the jejunal nor in the in vitro samples taken during the intestinal phase, while β-lactoglobulin was found in one hour-jejunal samples in agreement with the in vitro digestion. In vivo and in vitro digests showed comparable peptide profiles and high number of common sequences. A selective precipitation step was used to strengthen the identification of phosphorylated peptides. Most of the sequences found in jejunum, some of them not previously described, were also identified in the simulated digests. Common resistant regions to digestion were identified, revealing that the in vitro protocol constitutes a good approximation to the physiological gastrointestinal digestion of milk proteins.

Reduction of whey protein concentrate antigenicity by using a combined enzymatic digestion and ultrafiltration approach

The global interest in saving food resources is leading to recycle wasted-food materials to extract useful nutrients. In dairy industry, the recycling of whey proteins determines their utilization in the healthy-addressed foods, which, however, can cause immunological responses in allergic subjects. In this work, a whey protein concentrate (WPC) was alternatively hydrolyzed with pepsin, papain, trypsin and rennin in order to attenuate or abolish the β-lactoglobulin (BLG) antigenicity. The electrophoretic profiles of both pepsin and papain WPC hydrolysates proved the disappearance of the BLG band, even though a slight antigenicity was still found by ELISA. Pepsin hydrolysates, filtered through a 10-kDa cut-off membrane, did not produce immunological response. A deeper investigation carried out on pepsin digested and ultrafiltered samples by LC-MS/MS showed the disappearance of the immunoreactive BLG-fragment IVTQMKGLDIQKVAGTW. The remaining peptides, partially overlapped to major IgE binding epitopes, were not able to give immunoreactivity response. The combined WPC pepsin digestion with ultrafiltration confirmed to be a user-friendly strategy to reduce markedly the WPC antigenicity. The improvement of this two-steps process could be used to produce novel hypoallergenic infant food formulas.

Assessment of IgE Reactivity of β-Casein by Western Blotting After Digestion with Simulated Gastric Fluid

Cow's milk allergy is defined as an immunologically mediated adverse reaction to cow's milk proteins and it is usually, along with hen's egg allergy, the first food allergy identified in childhood.One of the main aspects to consider when evaluating the allergenic potential of food proteins is the effect of gastric digestion. It is known that allergens are usually able to survive the harsh acidic environment of the stomach, tolerate the presence of surfactants, and resist digestion by pepsin. They might also be digested into high molecular weight peptide fragments, which retain the same, or sometimes increased, IgE-binding. In this respect, western blotting is a highly sensitive and efficient technique that we have used to detect IgE-binding to the digests of milk and egg proteins. Given the importance of the resistance of food proteins to gastric digestion in their capacity to modulate the immune response, we describe in this chapter the assessment of IgE reactivity of a relevant cow's milk allergen, β-casein, by western blotting after simulated digestion under relevant physiological conditions.

IgE Epitope Mapping Using Peptide Microarray Immunoassay

IgE epitope mapping of food allergens contributes to a better understanding of the pathogenesis of food allergy and may become an additional tool for food allergy diagnosis/prognosis. Microarray platforms which allow for simultaneous screening of a large number of peptides corresponding to the sequences of food allergens are ideally suited for large-scale IgE epitope mapping. Here we describe the method of performing a reliable and sensitive peptide microarray immunoassay, which was developed in our lab and results in the identification of candidate IgE epitope biomarkers useful in determining allergic disease severity and prognosis, as well as in the prediction of treatment outcomes. A gastric digestion model that can be applied to prescreen peptides and reduce costs in the peptide microarray is also described in this chapter.

β-Lactoglobulin mutant Lys69Asn has attenuated IgE and increased retinol binding activity

β-Lactoglobulin (β-LG) is a member of lipocalin superfamily of transporters for small hydrophobic molecules such as retinoids, fatty acids, drugs, and vitamins. β-LG also is one of the major allergens in milk. Despite a lot of research on decreasing cow's milk allergenicity, the effects of mutations of β-LG on recognition by IgE from cow's milk allergy (CMA) patients have not been investigated. We describe here the expression in the yeast Pichia pastoris of a mutant bovine β-LG, in which lysine at position 69, in the main epitopes of the protein, was changed into asparagine (Lys69Asn). The purity and native like folded structure of the recombinant Lys69Asn β-LG was confirmed by HPLC, SDS-PAGE, mass spectrometry and circular dichroism. Lys69Asn β-LG has a fourfold stronger affinity than the wild-type protein for retinol, palmitic acid, and resveratrol, as determined by quenching of the intrinsic tryptophan fluorescence. At the same time the Lys69Asn mutant had a 9 fold attenuated, compared with the wild-type, affinity for IgE of sera from patients suffering from cow's milk allergy, whereas no difference could be detected between mutant and wild-type for binding of the IgGs of four monoclonal antibodies. The results of this study demonstrated the significant role of Lys69 residue on the binding and immuoreactivity properties of β-LG.

β-lactoglobulin mutation Ala86Gln improves its ligand binding and reduces its immunoreactivity

β-Lactoglobulin (β-LG) is a member of lipocalin superfamily of transporters for small hydrophobic molecules. β-LG is also one of the major allergens in milk. Despite a lot of researches on decreasing of cow's milk allergenicity, the effects of the mutation of β-LG on its recognition by IgE from cow's milk allergy (CMA) patients have not been investigated. We described here the expression in the yeast Pichia pastoris of a mutant β-LG, in which Alanine 86 was changed into Glutamine (Ala86Gln; a mutation on one of the major epitopes of the protein). The purity and native like folded structure of the recombinant Ala86Gln have been demonstrated using circular dichroism, HPLC, SDS-PAGE and mass spectrometry. The effect of the mutation on the binding of IgE from CMA patients to mutant protein was evaluated by ELISA methods and the results showed that the mutation of Ala-86 was associated with weaker binding of IgE from CMA patients to Ala86Gln mutant protein. Subsequently, the binding of various ligands such as retinol, palmitic acid, resveratrol and serotonin, with native, recombinant wild type and Ala86Gln mutant β-LGs were investigated by fluorescence spectroscopy and an improvement on the binding affinity of the mutated protein to various ligands was observed.