Intra- and inter-laboratory validation of an innovative huFcεRIα-RBL-2H3 degranulation assay for in vitro allergenicity assessment of whey hydrolysates

Aptasensors application for cow's milk allergens detection and early warning: Progress, challenge, and perspective

Cow's milk allergy (CMA) is considered one of the most prevalent food allergies and a public health concern. Modern medical research shows that the effective way to prevent allergic reactions is to prevent allergic patients from consuming allergenic substances. Therefore, the development of rapid and accurate detection technology for milk allergens detection and early warning is critical to safeguarding those with a cow milk allergy. As the oligonucleotide sequences with high specificity and selectivity, aptamers frequently assemble with transduction elements forming multifarious aptasensors for quantitative detection owing to their high-affinity binding to the target. Current aptasensors in the field of cow's milk allergen detection in recent years are explored in this review. This review takes a look back at a few common assays, including ELISA and PCR, before presenting a clear overview of the aptamer and threshold doses. It delves into a detailed discussion of the current aptamer-based detection techniques and related theories for milk allergen identification. Last but not least, we conclude with a discussion and outlook of the advancements made in allergen detection with aptamers. We sincerely hope that there will be more extensive applications for aptasensors in the future contributing to reducing the possibility of patients suffering from adverse reactions.

An In Vitro and In Vivo Translational Research Approach for the Assessment of Sensitization Capacity and Residual Allergenicity of an Extensive Whey Hydrolysate for Cow’s Milk-Allergic Infants

Introduction: Hypoallergenic formulas prepared from hydrolyzed cow’s milk proteins are often used for the management of cow’s milk allergy (CMA) in infants. In this study, both in vitro assays and an in vivo mouse model for CMA were used to assess the sensitizing and allergenic potential of a newly developed, extensive whey hydrolysate (eWH). Methods: Gel permeation chromatography was used to characterize the molecular weight distribution of the peptides. Residual antigenicity was measured using a beta-lactoglobulin ELISA as well as with immunoblotting using anti-beta-lactoglobulin (BLG) and anti-alpha-lactalbumin antibodies. In vitro residual allergenicity was assessed using huFcεRIα-RBL-2H3 cells sensitized with anti-bovine BLG human IgE. In vivo sensitizing and allergenic potential was assessed in a CMA mouse model by measuring the acute allergic skin response, anaphylactic shock score, body temperature, serum mMCP-1, whey-specific IgE, and cytokines. Results: There was no in vitro residual antigenicity and allergenicity observed of the eWH. Mice sensitized with eWH showed no acute allergic skin reaction after challenge with whey, confirmed by an absence of whey-specific IgE and anaphylactic symptoms and decrease in body temperature and mMCP-1 levels. Conclusions: Results from our in vitro and in vivo translational approach to assess sensitization capacity and residual allergenicity indicate that the newly developed eWH is safe for use in CMA infants. This was subsequently confirmed in a clinical study in which this eWH was tolerated by more than 90% (with 95% confidence) of infants or children with confirmed CMA.

An electrochemical aptasensor for the milk allergen β-lactoglobulin detection based on a target-induced nicking site reconstruction strategy

Food allergy is an immune system reaction to a particular food, milk being the most common one. β-Lactoglobulin (β-Lg) is the main ingredient of milk protein and the main cause of infant milk allergy. On such an occasion, the determination of β-Lg is very important and the electrochemical sensors are a good alternative for this purpose since they are sensitive, selective and inexpensive. In this work, an electrochemical aptasensor was fabricated for the quantitative detection of β-Lg in hypoallergenic formula (HF) milk. A tri-functional hairpin (HP) was designed, which was composed of an aptamer sequence, a nicking site and a DNA sequence (T1). In the absence of β-Lg, the aptamer part hybridized with T1 to form a stable stem-loop structure. However, in the presence of β-Lg, the capture of the aptamer sequence towards β-Lg caused the reconstruction of HP and thus the nicking sites were exposed. Then, the nicking enzyme was activated and T1 could be released, which bound with the end of the hairpin 1-methylene blue (HP1-MB)/HP2-MB conjugation on the Au nanoparticle (AuNP) modified electrode surface. Thus, the insulating property of the electrode was enhanced and the current response of MB decreased, which built the quantitative basis for β-Lg detection. In this way, the proposed aptasensor exhibited a wide linear range of 0.01-100 ng mL^-1 and a low detection limit of 5.7 pg mL^-1. This aptasensor also displayed high selectivity, reproducibility and stability, and became a promising platform for β-Lg detection in real food samples.

Limited Lactosylation of Beta-Lactoglobulin from Cow's Milk Exerts Strong Influence on Antigenicity and Degranulation of Mast Cells

Background: beta-lactoglobulin (BLG) is one of the major cow’s milk proteins and the most abundant allergen in whey. Heating is a common technologic treatment applied during milk transformational processes. Maillardation of BLG in the presence of reducing sugars and elevated temperatures may influence its antigenicity and allergenicity. Primary objective: to analyze and identify lactosylation sites by capillary electrophoresis mass spectrometry (CE-MS). Secondary objective: to assess the effect of lactosylated BLG on antigenicity and degranulation of mast cells. Methods: BLG was lactosylated at pH 7, a water activity (aw) of 0.43, and a temperature of 65 °C using a molar ratio BLG:lactose of 1:1 by incubating for 0, 3, 8, 16 or 24 h. For the determination of the effect on antibody-binding capacity of lactosylated BLG, an ELISA was performed. For the assessment of degranulation of the cell-line RBL-hεIa-2B12 transfected with the human α-chain, Fcε receptor type 1 (FcεRI) was used. Results: BLG showed saturated lactosylation between 8 and 16 incubation hours in our experimental setup. Initial stage lactosylation sites L1 (N-terminus)—K47, K60, K75, K77, K91, K138 and K141—have been identified using CE-MS. Lactosylated BLG showed a significant reduction of both the IgG binding (p = 0.0001) as well as degranulation of anti-BLG IgE-sensitized RBL-hεIa-2B12 cells (p < 0.0001). Conclusions and clinical relevance: this study shows that lactosylation of BLG decreases both the antigenicity and degranulation of mast cells and can therefore be a promising approach for reducing allergenicity of cow’s milk allergens provided that the process is well-controlled.

Design, quality, safety and efficacy of extensively hydrolyzed formula for management of cow's milk protein allergy: What are the challenges?

Cow's milk protein allergy (CMPA) is one of the most common food allergies in infancy. Clinical food allergy guidelines recommend an extensively hydrolyzed formula (EHF) as the first-line treatment in nonbreastfed infants with CMPA. Designing and commercializing EHF poses both technical and regulatory challenges. Each manufacturing step, from sourcing of raw materials to release of the final product, needs to be managed in accordance with comprehensive quality systems. To avoid cross-contamination via externally sourced ingredients, suppliers should be carefully selected based on quality requirements. Strict zoning of the manufacturing areas according to contamination risk and air flow control are effective strategies to prevent accidental allergen contamination. Furthermore, dedicated manufacturing lines for hypoallergenic products are used to prevent potential cross-contamination from other products produced on the same line. The enzymatic hydrolysis, heat treatment and ultrafiltration used are specific to each manufacturer. Consequently, EHF are a heterogenous group of products with differences in the molecular weight profile of peptides, content of residual immunogenic cow's milk allergens, and residual in-vitro allergenicity. These differences are likely to affect clinical efficacy and safety. As not all commercialized EHF products have undergone formal testing in the laboratory and clinical trials, there is a need to develop guidelines for minimum technical and regulatory requirements for EHF products, including validated assays for ongoing quality control. Clinical trials assessing new EHF products for their hypoallergenicity and ability to support normal growth remain the definitive proof of efficacy and safety in infants and young children with CMPA.

Epicutaneous immunogenicity of partially hydrolyzed whey protein evaluated using tape-stripped mouse model

BACKGROUND

Hydrolyzed cow's milk protein formulas are widely used for infants with a history or risk of cow's milk allergy. Based on the current theory that food allergen sensitization occurs via the skin, we investigated the epicutaneous immunogenicity of partially hydrolyzed whey proteins, which are ingredients in infant formulas.

METHODS

BALB/c mice were exposed epicutaneously to whey protein concentrate (WPC) or partial whey protein hydrolysates (PWH1 or PWH2) on tape-stripped skin. Sensitization was assessed by evaluating serum β-lactoglobulin (β-LG)-specific antibodies, basophil activation, and cytokine production from β-LG-stimulated lymphoid cells. The anaphylaxis reaction was evaluated by measuring the rectal temperature and plasma level of mouse mast cell protease-1 after oral β-LG challenge. Immune cell accumulation in the skin was also analyzed.

RESULTS

Substantive sensitization and β-LG-induced anaphylaxis reaction were observed in WPC-exposed mice, whereas no significant changes were observed in PWH1- or PWH2-exposed mice. The basophil and eosinophil counts increased in WPC-exposed murine skin, not but in PWH1- or PWH2-exposed mice.

CONCLUSION

The epicutaneous immunogenicity of PWH1 and PWH2 is markedly decreased, which may reduce the risk of allergen sensitization. Further studies are required to investigate the clinical value of these partial hydrolysates for high-risk infants.

NPY-mRFP Rat Basophilic Leukemia (RBL) Reporter: A Novel, Fast Reporter of Basophil/Mast Cell Degranulation

Humanized rat basophilic leukemia (RBL) reporter cell lines are increasingly used for the detection of allergen-specific IgE and other purposes, such as the detection of allergens and standardization of allergen preparations. Existing reporter systems have many strengths and advantages but can be expensive or require longer incubation times. The new NPY-mRFP reporter cell line addresses such problems, as it requires neither expensive substrates nor overnight incubation for detection of activation. The fusion of Neuropeptide Y (NPY) with monomeric Red Fluorescent Protein (mRFP) results in localization of the fluorescent protein in granules.  As NPY-mRFP is preformed in granules, the reporter system activation can be assessed using fluorescence measurements after as soon as 45-60 min, as described in this chapter, without the need to add any substrates.

Aptamer based fluorometric β-lactoglobulin assay based on the use of magnetic nanoparticles and carbon dots

The authors describe a fluorometric aptamer based assay for detecting β-lactoglobulin by using carbon dots (C-dots) as a signal indicator. The aptamer was immoblized on magnetite (Fe₃O₄) nanoparticles (MNPs), and the C-dots served as a label for the complementary oligonucleotide (cDNA). The assay is based on the hybridization that takes place between aptamer and cDNA. In the presence of β-lactoglobulin (β-LG), the aptamer preferentially binds to β-LG, and this leads to a partial release of the C-dots-cDNA into the solution. After magnetic separation, the supernatant of the solution contains the released C-dots-cDNA which are quantified by fluorometry, best under excitation/emission wavelengths of 354/447 nm. Under the optimal conditions, the fluorescence intensity is proportional to the logarithm of the β-LG concentration in the 0.25 to 50 ng mL^-1 range, with a 37 pg mL^-1 detection limit. The method was successfully applied to the determination of β-LG in hypoallergenic formulations, and the results demonstrated that this assay is a promising tool in food quality control. Conceivably, it also provides the opportunity for detection of other analytes. Graphical abstract Schematic of a novel aptamer based fluorometric β-lactoglobulin assay based on the use of magnetite (Fe₃O₄) nanoparticles (MNPs) and carbon dots (C-dots). C-dots were used as a signal indicator and Fe₃O₄ MNPs acted as a magnetic separator. This assay exhibits high sensitivity and selectivity with a detection limit as low as 37 pg mL^-1.

A chimeric IgE that mimics IgE from patients allergic to acid-hydrolyzed wheat proteins is a novel tool for in vitro allergenicity assessment of functionalized glutens

Background

Acid-hydrolyzed wheat proteins (acid-HWPs) have been shown to provoke severe allergic reactions in Europe and Japan that are distinct from classical wheat allergies. Acid-HWPs were shown to contain neo-epitopes induced by the deamidation of gluten proteins. However, products with variable rates of deamidation can be found.

Objectives

In this work, we studied the effect of the extent of wheat proteins deamidation on its allergenicity. A recombinant chimeric IgE was produced and compared to patients’ IgE for its capacity to assess the IgE-mediated triggering potential of acid-HWPs.

Methods

Sera from acid-HWP allergic patients were analyzed via ELISA and a functional basophil assay for their IgE reactivity to wheat proteins with different deamidation levels. A chimeric mouse/human IgE (chIgE-DG1) specific for the main neo-epitope, QPEEPFPE, involved in allergy to acid-HWPs was characterized with respect to its functionality and its reactivity compared to that of patients’ IgE.

Results

Acid-HWPs with medium (30%) and high (50–60%) deamidation levels displayed a markedly stronger IgE binding and capacity to activate basophils than those of samples with weak (15%) deamidation levels. The monoclonal chIgE-DG1 allowed basophil degranulation in the presence of deamidated wheat proteins. ChIgE-DG1 was found to mimic patients’ IgE reactivity and displayed the same ability to rank acid-HWP products in a degranulation assay.

Conclusion

Increasing the deamidation level of products from 15% to 60% resulted in an approximately 2-fold increase in their antigenicity and a 100-fold increase in their eliciting potential. The chimeric ChIgE-DG1 may be a useful tool to evaluate functionalized glutens for their allergenic potential. By mimicking patient sera reactivity, chIgE-DG1 also provided data on the patients' IgE repertoire and on the functionality of certain repeated epitopes in gluten proteins.