Geert Houben

Oral sensitization to food proteins: a Brown Norway rat model

Although several in vivo antigenicity assays using parenteral immunization are operational, no adequate enteral sensitization models are available to study food allergy and allergenicity of food proteins.

Establishment of Reference Doses for residues of allergenic foods: Report of the VITAL Expert Panel

In 2011, an expert panel was assembled to establish appropriate Reference Doses for allergenic food residues as a part of the VITAL (Voluntary Incidental Trace Allergen Labeling) program of The Allergen Bureau of Australia & New Zealand (ABA). These Reference Doses would guide advisory labeling decisions for use on food labels. Individual NOAELs and LOAELs were obtained from clinical challenges of food-allergic subjects. Statistical dose-distribution models (log-normal, log-logistic, Weibull) were applied to the individual NOAELs and LOAELs for each allergenic food. The Reference Doses, in terms of mg of total protein from the allergenic food, were based upon either the ED01 (for peanut, cows milk), the 95% lower confidence interval of the ED05 (for wheat, soybean, cashew, shrimp, sesame seed, mustard, and lupine), or both (egg, hazelnut) using all appropriate statistical dose-distribution models. Reference Doses were established for 11 allergenic foods ranging from 0.03 mg for egg protein to 10mg for shrimp protein. Reference Doses were not established for fish or celery due to poor model fits with existing data. Reference Doses were not established for other tree nuts beyond hazelnut and cashew because of the absence of data on NOAELs and LOAELs from individual subjects.

Allergen reference doses for precautionary labeling (VITAL 2.0): Clinical implications

BACKGROUND There has been a dramatic proliferation of precautionary labeling by manufacturers to mitigate the perceived risk from low-level contamination from allergens in food. This has resulted in a significant reduction in choice of potentially safe foods for allergic consumers. OBJECTIVES We aimed to establish reference doses for 11 commonly allergenic foods to guide a rational approach by manufacturers based on all publically available valid oral food challenge data. METHODS Reference doses were developed from statistical dose-distribution modeling of individual thresholds of patients in a dataset of more than 55 studies of clinical oral food challenges. Sufficient valid data were available for peanut, milk, egg, and hazelnut to allow assessment of the representativeness of the data used. RESULTS The data were not significantly affected by the heterogeneity of the study methodology, including little effect of age on results for those foods for which sufficient numbers of adult challenge data were available (peanut and hazelnut). Thus by combining data from all studies, the eliciting dose for an allergic reaction in 1% of the population estimated for the following were 0.2 mg of protein for peanut, 0.1 mg for cows milk, 0.03 mg for egg, and 0.1 mg for hazelnut. CONCLUSIONS These reference doses will form the basis of the revised Voluntary Incidental Trace Allergen Labeling (VITAL) 2.0 thresholds now recommended in Australia. These new levels will enable manufacturers to apply credible precautionary labeling and provide increased consumer confidence in their validity and reliability, as well as improving consumer safety.

Threshold dose distributions for 5 major allergenic foods in children

BACKGROUND For most allergenic foods, insufficient threshold dose information within the population restricts the advice on levels of unintended allergenic foods which should trigger precautionary labeling on prepackaged foods. OBJECTIVE We wanted to derive threshold dose distributions for major allergenic foods and to elaborate the protein doses at which a proportion of the allergic population is likely to respond. METHODS For 7 allergenic foods double-blind, placebo-controlled food challenges (DBPCFCs) with a positive outcome for allergic reactions were selected from the clinical database of children routinely tested to diagnose food allergy at the University Medical Center Groningen. For each allergen 2 population threshold distributions were determined with the individual minimal eliciting dose and the preceding dose of each DBPCFC for objective symptoms and any symptom (either subjective or objective). RESULTS Individual positive DBPCFCs were available for peanut (n = 135), cows milk (n = 93), hens egg (n = 53), hazelnut (n = 28), and cashew nut (n = 31). Fewer children were challenged with soy (n = 10) or walnut (n = 13). Threshold dose distributions showed a good statistical and visual fit. The protein dose at which 5% of the allergic population is likely to respond with objective reactions was 1.6 mg for peanut, 1.1 mg for cows milk, 1.5 mg for hens egg, 7.4 mg for cashew nut, and 0.29 mg for hazelnut. Thresholds for any symptom were on average 2 to 6 times lower than for objective symptoms. The 95% upper and lower confidence intervals of the threshold distributions were overlapping. The peanut threshold distribution on objective symptoms was similar to the distribution of another European center. CONCLUSIONS Threshold distribution curves and eliciting doses are a powerful tool to compare different allergenic foods and for informing policy on precautionary labeling.

House dust mite (Der p 10) and crustacean allergic patients may react to food containing Yellow mealworm proteins

SCOPE Due to the imminent growth of the world population, shortage of protein sources for human consumption will arise in the near future. Alternative and sustainable protein sources (e.g. insects) are being explored for the production of food and feed. In this project, the safety of Yellow mealworms (Tenebrio molitor L.) for human consumption was tested using approaches as advised by the European Food Safety Authority for allergenicity risk assessment. METHODS AND RESULTS Different Yellow mealworm protein fractions were prepared, characterised, and tested for cross-reactivity using sera from patients with an inhalation or food allergy to biologically related species (House dust mite (HDM) and crustaceans) by immunoblotting and basophil activation. Furthermore, the stability was investigated using an in vitro pepsin digestion test. IgE from HDM- and crustacean allergic patients cross-reacted with Yellow mealworm proteins. This cross-reactivity was functional, as shown by the induction of basophil activation. The major cross-reactive proteins were identified as tropomyosin and arginine kinase, which are well known allergens in arthropods. These proteins were moderately stable in the pepsin stability test. CONCLUSION Based on these cross-reactivity studies, there is a realistic possibility that HDM- and crustacean allergic patients may react to food containing Yellow mealworm proteins.

Might gluten traces in wheat substitutes pose a risk in patients with celiac disease? A population-based probabilistic approach to risk estimation

BACKGROUND In patients with treated celiac disease (CD), the ingestion of gluten traces contained in gluten-free (GF) wheat substitutes (eg, GF bread, flour, and pasta) could cause persisting intestinal mucosal damage. OBJECTIVE The objective was to evaluate the proportion of CD patients at risk of mucosal damage due to the consumption of GF products in 4 European countries (Italy, Spain, Germany, and Norway). DESIGN A probabilistic modeling approach was used to assess the risk of gluten intake at the population level. The input variables were 1) consumption of GF products, 2) concentration of gluten traces in GF products determined by the sandwich R5 ELISA method, and 3) the gluten threshold for mucosal damage of 10 to 50 mg/d. Different population and product availability scenarios were examined for risk assessment. RESULTS The gluten content of 205 commercially available GF products ranged between <5 and 27.8 mg/kg. Overall, 99.5% of the analyzed samples had a gluten concentration <20 mg/kg. Most (94%) had a gluten concentration below the limit of quantification (5 mg/kg). The mean percentage of the CD European population at risk of mucosal damage resulting from consumption of GF products ranged between 0.01 (Germany) and 0.15 (Italy) and remained very low, even in the worst-case scenario (<1%). CONCLUSIONS The adoption of a single gluten threshold (20 mg/kg) for gluten contamination is suggested. GF products in Europe constitute a very safe option for patients with CD. The dietary follow-up of CD patients should focus on other potential sources of gluten contamination.

Prevention of work-related airway allergies; summary of the advice from the Health Council of the Netherlands

The Health Council of the Netherlands published a report in which the best procedure and method for recommending health‐based occupational exposure limits (OELs) for inhaled allergens were identified by evaluating the scientific state of the art. Many respiratory disorders in the workplace arise from inhalation of substances which can cause allergy. To protect workers against respiratory allergy, various preventive measures are taken, one of them being reduction of exposure by setting legally binding standards. These are based on health‐based OELs that specify a level of exposure to an airborne substance, a threshold level, below which it may reasonably be expected that there is no risk of adverse health effects. The Council is of the opinion that an OEL should prevent against allergic sensitization, as sensitization plays a crucial biological role and is a prerequisite for the development of allergy. Furthermore, the Council considers it most likely that the exposure level below which no allergic sensitization develops for most allergens is so low, that OELs are difficult to set with the current knowledge and technical feasibilities. An alternative approach is to accept exposure, which carries a small predefined risk in developing allergic sensitization. In addition, it is worth considering periodic screening of exposed workers on allergic sensitization, because timely intervention can prevent worse. The feasibility of periodic screening and what else is needed to comply with the most important criteria, should however be judged case‐by‐case.

Double-blind placebo-controlled food challenges in children with alleged cow's milk allergy: prevention of unnecessary elimination diets and determination of eliciting doses.

BackgroundChildren with cow’s milk allergy (CMA) need a cow’s milk protein (CMP) free diet to prevent allergic reactions. For this, reliable allergy-information on the label of food products is essential to avoid products containing the allergen. On the other hand, both overzealous labeling and misdiagnosis that result in unnecessary elimination diets, can lead to potentially hazardous health situations. Our objective was to evaluate if excluding CMA by double-blind placebo-controlled food challenge (DBPCFC) prevents unnecessary elimination diets in the long term. Secondly, to determine the minimum eliciting dose (MED) for an acute allergic reaction to CMP in DBPCFC positive children.MethodsAll children with suspected CMA under our care (Oct’05 - Jun’09) were prospectively enrolled in a DBPCFC. Placebo and verum feedings were administered on two randomly assigned separate days. The MED was determined by noting the ‘lowest observed adverse effect level’ (LOAEL) in DBPCFC-positive children. Based on the outcomes of the DBPCFC a dietary advice was given. Parents were contacted by phone several months later about the diet of their child.Results116 children were available for analysis. In 76 children CMA was rejected. In 60 of them CMP was successfully reintroduced, in 2 the parents refused introduction, in another 3 the parents stopped reintroduction. In 9 children CMA symptoms reappeared. In 40 children CMA was confirmed. Infants aged ≤ 12 months in our study group have a higher cumulative distribution of MED than older children.ConclusionsExcluding CMA by DBPCFC successfully stopped unnecessary elimination diets in the long term in most children. The MEDs form potential useful information for offering dietary advice to patients and their caretakers.

The Key Events Dose-Response Framework: A Foundation for Examining Variability in Elicitation Thresholds for Food Allergens

Food allergies are caused by immunological reactions in individuals sensitized to normal protein components of foods. For any given sensitized individual, the severity of a reaction is generally assumed to be proportional to the dose of allergenic protein. There is substantial clinical evidence that “threshold” doses exist for the elicitation of an allergic reaction; however, the threshold (i.e., lowest dose that elicits a reaction) varies substantially across the sensitized population. Current approaches to protecting sensitized individuals from exposure to food allergens are highly qualitative (i.e., they rely on food avoidance). The Key Events Dose-Response Framework is an analytical approach for refining understanding of the biological basis of the dose-response. Application of this approach to food allergy provides a foundation for a more rigorous quantitative understanding of variability in allergic response. This study reviews the allergic disease process and the current approaches to identifying thresholds for food allergens. The pathway of key biological events occurring between food intake and allergic response is considered, along with factors that may determine the nature and severity of response to food allergens. Data needs, as well as implications for identifying thresholds, and for characterizing variability in thresholds, are also discussed.

Effects of the color additive caramel color III and 2-acetyl-4(5)-tetrahydroxybutylimidazole (THI) on the immune system of rats

Administration of ammonia caramel color (AC) to rats may decrease blood lymphocyte counts, specifically in rats fed a diet low in vitamin B6. This effect is associated with 2-acetyl-4(5)-(1,2,3,4-tetrahydroxybutyl)imidazole (THI). To characterize and compare the effects of AC and THI and to study the influence of dietary pyridoxine, two studies in rats were conducted. Weanling rats fed a diet containing 2-3 ppm pyridoxine and exposed to 4% AC or 5.72 ppm THI in drinking water for 4 weeks showed reduced cell numbers in spleen and popliteal lymph nodes, as well as in the blood. Flow cytometric analyses demonstrated a comparable reduction in B and T lymphocytes. In blood, spleen, and popliteal lymph nodes, CD4+ lymphocytes were more reduced than CD8+ cells. The number of bone marrow cells was not affected. Although thymus weight and cell number were not affected either, a decreased cortex over medulla area ratio and an increase in medullary cell density largely due to an increase in CD4+ thymocytes was observed. Decreased numbers of ED2+ macrophages were observed in the thymic cortex and in the spleen red pulp. All effects observed were either less pronounced or absent in a study with rats fed a diet containing 11-12 ppm pyridoxine. The effects of AC and THI on the immune system were similar. Whereas AC exposure was associated with changes in vitamin B6 status, THI did not induce obvious effects on vitamin B6 parameters. It is proposed that the effects of AC and THI on the immune system are not caused by a disturbance of vitamin B6 metabolism, but may in fact result from a disturbance of a specific PLP-dependent process.