The effect of digestion and pH on the allergenicity of kiwifruit proteins

Site-specific glycosylation and single amino acid substitution dramatically reduced the immunogenicity of β-lactoglobulin

To reduce the immunogenicity of β-lactoglobulin (BLG), we prepared recombinant BLG which has both site-specific glycosylation and single amino acid substitution (D28N/P126A), and expressed it in the methylotrophic yeast Pichia pastoris by fusion of the cDNA to the sequence coding for the α-factor signal peptide from Saccharomyces cerevisiae. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that the D28N/P126A was conjugated with a ∼4 kDa high-mannose chain. D28N/P126A retained ∼61% of the retinol-binding activity of BLG. Structural analyses by circular dichroism (CD) spectra, intrinsic fluorescence, and Enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies indicated that the surface structure of BLG was slightly changed by using protein engineering techniques, but D28N/P126A was covered by high-mannose chains and substituted amino acid without substantial disruption of native conformation. Antibody responses to the D28N/P126A considerably reduced in C57BL/6 mice. We conclude that inducing both site-specific glycosylation and single amino acid substitution simultaneously is an effective method to reduce the immunogenicity of BLG.

Starch and protein hydrolysis in cooked quinoa (Chenopodium quinoa Willd.) during static and dynamic in vitro oral and gastric digestion

Quinoa is a pseudocereal that has a favorable nutrient profile and may be a beneficial addition to the diet. To evaluate potential health-promoting properties of foods, it is important to understand the rate of macronutrient hydrolysis, which is commonly quantified through in vitro digestion studies. Additionally, limited information is available comparing starch and protein hydrolysis of solid foods using static and dynamic digestion models. The objective of this study was to examine starch and protein hydrolysis in cooked quinoa using a combination of a static (saliva only) or dynamic (saliva + mincing) oral digestion model with a static (gastric fluids only) or dynamic (Human Gastric Simulator) gastric digestion model. Disruption of the pericarp of the cooked quinoa seeds during dynamic oral digestion released additional surface area, which led to faster gastric emptying during dynamic gastric digestion. Starch and protein hydrolysis were impacted by type of gastric model due to differences in pH and variations in structural breakdown. Starch hydrolysis was 29.04 ± 1.83% after 180 min dynamic gastric digestion compared to 2.85 ± 1.88% during static gastric digestion (averaged across both oral digestion models). The degree of protein hydrolysis was 4.85 ± 0.01% after 180 min in the static gastric model compared to 3.94 ± 0.18% in the dynamic gastric model (averaged across both oral digestion models). This information provides evidence on the role of food structure and breakdown (through use of static vs. dynamic oral and gastric digestion models) on quinoa starch and protein hydrolysis.

Development of Salmonellosis as Affected by Bioactive Food Compounds

Infections caused by Salmonella serovars are the leading cause of foodborne hospitalizations and deaths in Americans, extensively prevalent worldwide, and pose a considerable financial burden on public health infrastructure and private manufacturing. While a comprehensive review is lacking for delineating the role of dietary components on prevention of Salmonellosis, evidence for the role of diet for preventing the infection and management of Salmonellosis symptoms is increasing. The current study is an evaluation of preclinical and clinical studies and their underlying mechanisms to elaborate the efficacy of bioactive dietary components for augmenting the prevention of Salmonella infection. Studies investigating dietary components such as fibers, fatty acids, amino acids, vitamins, minerals, phenolic compounds, and probiotics exhibited efficacy of dietary compounds against Salmonellosis through manipulation of host bile acids, mucin, epithelial barrier, innate and adaptive immunity and gut microbiota as well as impacting the cellular signaling cascades of the pathogen. Pre-clinical studies investigating synergism and/or antagonistic activities of various bioactive compounds, additional randomized clinical trials, if not curtailed by lack of equipoise and ethical concerns, and well-planned epidemiological studies could augment the development of a validated and evidence-based guideline for mitigating the public health burden of human Salmonellosis through dietary compounds.

Pollen food allergy syndrome (PFAS): A review of current available literature

OBJECTIVE

Pollen food allergy syndrome (PFAS) is a complex syndrome posing a diagnostic and therapeutic challenge. Our objective was to summarize the available literature regarding its prevalence, pathogenesis, diagnosis, and treatment.

DATA SOURCES

A PubMed search was performed to include English language articles with the following search terms: pollen food syndrome, pollen food allergy syndrome, PFAS, oral allergy syndrome, OAS, food anaphylaxis, food components.

STUDY SELECTIONS

Human articles discussing PFAS.

RESULTS

Varying reports have been made of the prevalence of PFAS, ranging from 4.7% to greater than 20% in children and 13% to 58% in adults. Prevalence varies widely by geographic region. PFAS is typically the results of class II food allergens (e.g. sensitized to anaeroallergen, but reaction occurs due to cross reactivity from a food allergen). Commonly these reactions are limited to the oropharynx due to the lability of the proteins causing the reaction. As multiple families of proteins with varying stability cause PFAS, severe systemic reactions are also possible, as anaphylactic shock has been documented in up to 1.7% of reactions.

CONCLUSION

Pollen food allergy syndrome therefore cannot be dismissed as a benign food allergy, but it needs to be approached individually based on known risk factors.

The relevance of a digestibility evaluation in the allergenicity risk assessment of novel proteins. Opinion of a joint initiative of COST action ImpARAS and COST action INFOGEST

The current allergenicity assessment of novel proteins is based on the EFSA GMO guidance. Recently, EFSA launched a new guidance document on allergenicity assessment of GM plants (2017). This document describes, amongst other topics, the new scientific and regulatory developments on in vitro protein digestibility tests. The EFSA GMO Panel stated that for in vitro protein digestibility tests, additional investigations are needed before any additional recommendation in the form of guidance can be provided. To this end, an interim phase is considered necessary to evaluate the revisions to the in vitro gastrointestinal digestion test, proposed by EFSA. This prompted the establishment of a joint workshop through two COST Action networks: COST Action ImpARAS and COST Acton INFOGEST. In 2017, a workshop was organised to discuss the relevance of digestion in allergenicity risk assessment and how to potentially improve the current methods and readouts. The outcome of the workshop is that there is no rationale for a clear readout that is predictive for allergenicity and we suggest to omit the digestion test from the allergenicity assessment strategy for now, and put an effort into filling the knowledge gaps as summarized in this paper first.

Food Allergens: Is There a Correlation between Stability to Digestion and Allergenicity?

Food allergy is a major health problem in the Western countries, affecting 3-8% of the population. It has not yet been established what makes a dietary protein a food allergen. Several characteristics have been proposed to be shared by food allergens. One of these is resistance to digestion. This paper reviews data from digestibility studies on purified food allergens and evaluates the predictive value of digestibility tests on the allergenic potential. We point out that food allergens do not necessarily resist digestion. We discuss how the choice of in vitro digestibility assay condition and the method used for detection of residual intact protein as well as fragments hereof may greatly influence the outcome as well as the interpretation of results. The finding that digests from food allergens may retain allergenicity, stresses the importance of using immunological assays for evaluating the allergenic potential of food allergen digestion products. Studies assessing the allergenicity of digestion products, by either IgE-binding, elicitation or sensitizing capacity, shows that digestion may abolish, decrease, have no effect, or even increase the allergenicity of food allergens. Therefore, the predictive value of the pepsin resistance test for assessing the allergenic potential of novel proteins can be questioned.

Lectin Digestibility and Stability of Elderberry Antioxidants to Heat Treatment In Vitro

Elderberry contains healthy low molecular weight nutraceuticals and lectins which are sequence-related to the elderberry allergen Sam n1. Some of these lectins are type II ribosome-inactivating proteins. The sensitivity of native lectins present in elderberry fruits and bark to the proteolysis triggered by in vitro simulated gastric and duodenal fluids has been investigated. It was found that these lectins are refractory to proteolysis. Nonetheless, incubation for 5-10 min in a boiling water bath completely sensitized them to the hydrolytic enzymes in vitro. Under these conditions neither total Folin-Ciocalteau's reagent reactive compounds, total anthocyanins and the mixture of cyanidin-3-glucoside plus cyanidin-3-sambubioside, nor antioxidant and free-radical scavenging activities were affected by more than 10% for incubations of up to 20 min. Therefore, short-time heat treatment reduces potential allergy-related risks deriving from elderberry consumption without seriously affecting its properties as an antioxidant and free-radical scavenging food.

Interfaces between allergen structure and diagnosis: know your epitopes

Allergy diagnosis is based on the patient's clinical history and can be strengthened by tests that confirm the origin of sensitization. In the past 25 years, these tests have evolved from the exclusive in vivo or in vitro use of allergen extracts, to complementary molecular-based diagnostics that rely on in vitro measurements of IgE reactivity to individual allergens. For this to occur, an increase in our understanding of the molecular structure of allergens, largely due to the development of technologies such as molecular cloning and expression of recombinant allergens, X-ray crystallography, or nuclear magnetic resonance (NMR), has been essential. New in vitro microarray or multiplex systems are now available to measure IgE against a selected panel of purified natural or recombinant allergens. The determination of the three-dimensional structure of allergens has facilitated detailed molecular studies, including the analysis of antigenic determinants for diagnostic purposes.

In vitro evaluation of digestive and endolysosomal enzymes to cleave CML-modified Ara h 1 peptides

Ara h 1 is a major peanut allergen. Processing-induced modifications may modulate the allergenic potency of Ara h 1. Carboxymethyl lysine (CML) modifications are a commonly described nonenzymatic modification on food proteins. In the current study, we tested the ability of digestive and endolysosomal proteases to cleave CML-modified and unmodified Ara h 1 peptides. Mass spectrometric analyses of the digested peptides demonstrate that carboxymethylation of lysine residues renders these peptides refractory to trypsin digestion. We did not detect observable differences in the simulated gastric fluid or endolysosomal digestion between the parental and CML-modified peptides. One of the tested peptides contains a lysine residue previously shown to be CML modified laying in a previously mapped linear IgE epitope, but we did not observe a difference in IgE binding between the modified and parental peptides. Our findings suggest a molecular mechanism for the increased resistance of peanut allergens modified by thermal processing, such as Ara h 1, to digestion in intestinal fluid after heating and could help explain how food processing-induced modifications may lead to more potent food allergens by acting to protect intact IgE epitopes from digestion by proteases targeting lysine residues.

Characterization of the allergenic potential of proteins: an assessment of the kiwifruit allergen actinidin

Assessment of the potential allergenicity (IgE-inducing properties) of novel proteins is an important challenge in the overall safety assessment of foods. Resistance to digestion with pepsin is commonly measured to characterize allergenicity, although the association is not absolute. We have previously shown that specific IgE antibody production induced by systemic [intraperitoneal (i.p.)] exposure of BALB/c strain mice to a range of proteins correlates with allergenic potential for known allergens. The purpose of the present study was to explore further the utility of these approaches using the food allergen, actinidin. Recently, kiwifruit has become an important allergenic foodstuff, coincident with its increased consumption, particularly as a weaning food. The ability of the kiwifruit allergen actinidin to stimulate antibody responses has been compared with the reference allergen ovalbumin, and with the non-allergen bovine haemoglobin. Haemoglobin was rapidly digested by pepsin whereas actinidin was resistant unless subjected to prior chemical reduction (reflecting intracellular digestion conditions). Haemoglobin stimulated detectable IgG antibody production at relatively high doses (10%), but failed to provoke detectable IgE. In contrast, actinidin was both immunogenic and allergenic at relatively low doses (0.25% to 1%). Vigorous IgG and IgG1 antibody and high titre IgE antibody responses were recorded, similar to those provoked by ovalbumin. Thus, actinidin displays a marked ability to provoke IgE, consistent with allergenic potential. These data provide further encouragement that in tandem with analysis of pepsin stability, the induction of IgE after systemic exposure of BALB/c strain mice provides a useful approach for the prospective identification of protein allergens.

Relationship between protein digestibility and allergenicity: comparisons of pepsin and cathepsin

An association between protein allergenicity and resistance to pepsin digestion in the gastrointestinal tract has been proposed. However, although widely accepted, such an association is inconsistent with known labile allergens and resistant nonallergens. Given the central role of antigen presenting cells, and in particular dendritic cells (DC), in the development of allergic responses, the stability of allergens to intracellular processing may be more relevant than resistance to extracellular pepsin digestion. We have characterised the expression by DC of cathepsins (proteolytic enzymes), and compared the proteolytic activity of the most highly expressed cathepsin with pepsin for a range of 9 allergens and 4 putative nonallergens. Cathepsin expression in bone marrow-derived DC (BM-DC) derived from BALB/c strain mice was characterised by flow cytometry; cathepsins D, E and S were identified, with cathepsin D being the most highly expressed. Digestion studies revealed that the majority of allergens (5/9) were pepsin resistant, whereas non-allergens (3/4) were labile. If the generation of pepsin-resistant fragments was considered as a feature of allergenicity, this increased to 7/9 allergens and 4/4 nonallergens. In contrast, most of the proteins examined were resistant to cathepsin digestion, with significant digestion recorded for only 2/9 allergens and 2/4 non-allergens. Chemical reduction (to mimic intracellular reducing conditions) increased the susceptibility of proteins to digestion by cathepsins, but did not improve discrimination between allergens and nonallergens on this basis. These data confirm that there is a general relationship between resistance to digestion with pepsin and allergenicity. The relationship is not absolute, but the information gained from this characteristic does provide useful information in a weight of evidence approach for allergenicity assessment. The most abundant cathepsin detected in antigen processing BM-DC, cathepsin D, is not an appropriate substitute for pepsin. The hypothesis that pepsin stability may be a surrogate for stability to digestion within DC may still hold true, but consideration of a single enzyme in this context is possibly an oversimplification.

Kiwifruit proteins and enzymes: actinidin and other significant proteins

Protein is a minor but significant component of kiwifruit. Crude protein is typically measured at about 1% of fresh weight; however, soluble protein is much less, around 0.3%. The difference can be accounted for by nonprotein nitrogen and insoluble protein, such as polypeptide chains forming part of the cell wall. Kiwifruit soluble protein is mostly accounted for by the proteolytic enzyme actinidin and its inactive forms, a so-called thaumatin-like protein and an unusual protein called kiwellin, which has no known function. Actinidin is the predominant enzyme in kiwifruit and can play a role in aiding the digestive process. There is also a wide range of enzymes involved in the ripening of kiwifruit, particularly enzymes involved in polysaccharide and oligosaccharide metabolism and in the development of flavor and aroma compounds. Whether the enzymatic actions of these have any effect during the consumption and digestion of kiwifruit is not known, although any noticeable effect is unlikely. Some enzymes are likely to have an effect on flavor, texture, and nutritional values, during storage, processing, and preparation of kiwifruit.

Effect of simulated gastro-duodenal digestion on the allergenic reactivity of beta-lactoglobulin

Background

Cow's milk (CM) allergy affects about 2% of infants. The allergenicity of dietary proteins, including those from CM, has been related to their digestibility although the generality of the link and its causality remains to be demonstrated. In this study we use an in vitro digestion system, to investigate the digestibility of β-lactoglobulin (blg) during gastrointestinal transit and to assess the impact of this process on blg allergenic reactivity in CM allergic children.

Methods

Blg digesta were prepared using an in vitro digestion protocol simulating either gastric digestion alone or followed by duodenal digestion with or without phosphatidylcholine (PC). Biochemical analysis of blg digesta was performed by SDS-PAGE and their concentration was measured by a sandwich ELISA. Assessment of their allergenic reactivity was done in vitro by EAST inhibition, specific basophil activation (basotest) and lymphocyte proliferation (PCNA-flow cytometry) assays using sera and cells from patients allergic to blg and in vivo by skin prick testing (SPT) of these patients.

Results

Blg was only broken down to smaller peptides after gastro-duodenal digestion although a sizeable amount of intact protein still remained. Digestion did not modify the IgE binding capacity of blg except for gastro-duodenal digestion performed in the absence of PC. These results are consistent with the quantity of intact blg remaining in the digesta. Overall both gastric and gastroduodenal digestion enhanced activation of sensitized basophils and proliferation of sensitized lymphocytes by blg. However, there was a tendency towards reduction in mean diameter of SPT following digestion, the PC alone during phase 1 digestion causing a significant increase in mean diameter.

Conclusions

Digestion did not reduce the allergenic reactivity of blg to a clinically insignificant extent, PC inhibiting digestion and thereby protecting blg allergenic reactivity. SPT reactivity was reduced compared to blg immunoreactivity in in vitro tests.

Mechanisms underlying differential food allergy response to heated egg

BACKGROUND

Egg white proteins are usually subjected to heating, making them edible for the majority of children with egg allergy.

OBJECTIVE

We sought to investigate the underlying mechanisms responsible for the reduced allergenicity displayed by heat-treated egg white allergens.

METHODS

C3H/HeJ mice were orally sensitized with ovalbumin (OVA) or ovomucoid and challenged with native or heated proteins to evaluate their allergenicity. Immunoreactivity was assessed by immunoblotting using sera from children with egg allergy. In vitro gastrointestinal digestion of native and heated OVA and ovomucoid was studied by SDS-PAGE and liquid chromatography. Intestinal uptake of intact native and heated OVA and ovomucoid by human intestinal epithelial (Caco-2) cells was investigated. Rat basophil leukemia cells passively sensitized with mouse serum and human basophils passively sensitized with serum from children with egg allergy were used to assess the effector cell activation by heated, digested, and transported OVA and ovomucoid.

RESULTS

Heated OVA and ovomucoid did not induce symptoms of anaphylaxis in sensitized mice when administered orally. Heating did not completely destroy IgE-binding capacity of OVA or ovomucoid but enhanced in vitro digestibility of OVA. Digestion of both OVA and ovomucoid diminished mediator release in rat basophil leukemia assay and basophil activation. Heating of allergens prevented transport across human intestinal epithelial cells in a form capable of triggering basophil activation or T-cell activation.

CONCLUSION

Heat treatment reduces allergenicity of OVA and ovomucoid. This is partially a result of the enhanced gastrointestinal digestibility of heated OVA and the inability of heated OVA or ovomucoid to be absorbed in a form capable of triggering basophils.

Oral allergy syndrome: a clinical, diagnostic, and therapeutic challenge

OBJECTIVES

To provide a review of the literature and discuss the clinical, pathophysiologic, diagnostic, and therapeutic challenges of oral allergy syndrome (OAS).

DATA SOURCES

English-language publications on OAS (and pollen-food allergy syndrome) were identified through MEDLINE and through the reference lists of each identified article and review.

STUDY SELECTION

Articles pertaining to OAS with respect to its varied clinical presentation, underlying pathophysiology, available and investigational diagnostic testing, and evidence-based treatment options were selected.

RESULTS

OAS occurs in patients with a prior cross-reactive aeroallergen sensitization and clinically presents with initial oralpharyngeal symptoms after ingestion of a triggering fruit or vegetable. Although controversial, these symptoms may progress to systemic symptoms outside the gastrointestinal tract in 8.7% of patients and anaphylactic shock in 1.7%. OAS's underlying pathophysiology may play a role in clinical presentation and outcome, depending on whether the cross-reactive protein is a heat-labile PR-10 protein, a partially labile profilin, or a relatively heat-stable lipid transfer protein. Diagnostic testing is variable based on the underlying food tested, but fresh food skin prick test typically has the highest sensitivity. Treatment centers on avoidance and the consideration of self-injectable epinephrine. Because of its relationship with a cross-reactive aeroallergen sensitization, subcutaneous immunotherapy and sublingual immunotherapy have also been therapeutically tried with mixed results.

CONCLUSION

OAS is a challenging diagnosis to the practicing allergist because of its many clinical, diagnostic, and therapeutic considerations. Understanding these challenges and their underlying mechanisms can facilitate a knowledgeable approach to treating an oral allergy patient.

In vitro digestion of Cry1Ab proteins and analysis of the impact on their immunoreactivity

A pepsin resistance test performed at pH 1.2 and with high pepsin to protein ratio is one of the steps of the weight-of-evidence approach used for assessment of allergenicity of new proteins. However, the use of other in vitro digestibility tests, performed in more physiologically relevant conditions and in combination with immunological assays so as to increase the value of the information gained from the studies of stability of a novel protein to digestion for the overall allergenicity assessment, has been proposed. This study then aimed to investigate the stability to digestion of Cry1Ab protoxin and toxin, insecticidal proteins expressed in genetically modified crops, using simulated gastric fluid (SGF) at different pH values and pepsin-to-substrate ratios, in the presence or absence of physiological surfactant phosphatidylcholine (PC). Electrophoresis and immunoblot patterns and residual immunoreactivity of digesta were analyzed. Although Cry1Ab protoxin is extensively degraded at pH 1.2 with high pepsin-to-protein ratio, it is only slightly degraded at pH 2.0 and conserved its immunoreactivity. Furthermore, Cry1Ab proteins were demonstrated to be stable in a more physiologically relevant in vitro digestibility test (pH 2.5, pepsin-to-substrate ratio 1:20 (w/w) with PC). Factors such as pH, SGF composition, and pepsin-to-substrate ratio then greatly influence the digestion of Cry1Ab proteins, confirming that new and more physiologically relevant in vitro digestibility tests should be also considered to study the relationship between the resistance of a protein to digestion and its allergenicity.

Capacity of purified peanut allergens to induce degranulation in a functional in vitro assay: Ara h 2 and Ara h 6 are the most efficient elicitors

BACKGROUND

Peanut is a most common and potent food allergen. Many peanut allergens have been characterized using, in particular, IgE-binding studies.

OBJECTIVES

We optimized an in vitro functional assay to assess the capacity of peanut allergens to degranulate humanized rat basophilic leukaemia cells, RBL SX-38 cells, after sensitization by serum IgE from peanut-allergic patients. We thus compared the activity of the main peanut allergens, i.e. Ara h 1, Ara h 2, Ara h 3 and Ara h 6, purified from roasted peanut.

METHODS

Sera of 12 peanut-allergic patients were collected and total and peanut-specific IgE were measured. They were used to sensitize RBL SX-38 cells and the degranulation was induced by incubation with ranging concentrations of a whole peanut protein extract or of purified peanut allergens. The mediator release was quantified by the determination of beta-hexosaminidase activity in the supernatant. The intensity of the degranulation was expressed as maximum release and as EC50, corresponding to the dose of allergen that induced 50% of the maximum release.

RESULTS

For each serum, only 10 IU/mL of human IgE was necessary to sensitize the cells and obtain an optimal degranulation. With all the allergens, the release was positively correlated with the concentration of allergen-specific IgE in the serum used to sensitize the cells. The medians of EC50 obtained for Ara h 2 and Ara h 6 were 2.1 and 2.8 pm, respectively, while they were much higher for Ara h 3 and Ara h 1 (65 and 150 pm, respectively).

CONCLUSION

The RBL SX-38 release assay proved to be sensitive, specific and reproducible. It allowed the comparison of the degranulation potential of different peanut allergens. For all the sera tested, Ara h 2 and Ara h 6 were more potent than Ara h 1 or Ara h 3.