IgE antibodies specific for carbohydrates in a patient allergic to gum arabic (Acacia senegal)

Safety and efficacy of a feed additive consisting of acacia gum (gum Arabic) for all animal species (A.I.P.G. Association for International Promotion of Gums)

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of acacia gum (gum Arabic) as a feed additive for all animal species. Acacia gum is safe up to approximately 280 mg/kg complete feed for chickens for fattening, 375 mg/kg complete feed for turkeys for fattening, 400 mg/kg complete feed for rabbit, 500 and 600 mg/kg complete feed for piglets and pigs for fattening, respectively, 1,100 mg/kg complete feed for cattle for fattening and 1,250 mg/kg complete feed for veal calves and salmonids. No conclusions can be reached on the safety for long living and reproductive animal, until the genotoxic potential of the additive is fully assessed in the framework of its use as a feed additive. No exposure of the consumer to the additive or its metabolites is expected. Therefore, the use of the additive in animal nutrition is considered safe for the consumers. Acacia gum is a potential dermal and respiratory sensitiser. No conclusion can be reached on the irritating potential to the skin or eyes. The use of acacia gum in animal nutrition is considered safe for the environment. The FEEDAP Panel is not in the position to conclude on the efficacy of acacia gum.

Re-evaluation of acacia gum (E 414) as a food additive

The Panel on Food Additives and Nutrient Sources added to Food (ANS) provides a scientific opinion re-evaluating the safety of acacia gum (E 414) as a food additive. In the EU, acacia gum has not been formally evaluated by the Scientific Committee for Food (SCF), and therefore, no ADI has been allocated. However, it was accepted for use in weaning food (SCF, 1991). In 1999, the SCF considered 'that the use of acacia gum/gum arabic in coatings for nutrient preparations containing trace elements is acceptable provided carry-over levels in infant formulae, follow-on formulae or FSMP do not exceed 10 mg/kg'. Acacia gum was evaluated by JECFA in 1982 and 1990 and the specifications were amended in 1998. Based on the lack of adverse effects in the available toxicity studies, an ADI 'not specified' was allocated. Following the conceptual framework for the risk assessment of certain food additives re-evaluated under Commission Regulation (EU) No 257/2010, the Panel considered that adequate exposure and toxicity data were available. Acacia gum is unlikely to be absorbed intact and is slightly fermented by intestinal microbiota. No adverse effects were reported in subchronic and carcinogenicity studies at the highest dose tested and there is no concern with respect to the genotoxicity. Oral daily intake of a large amount of acacia gum up to 30,000 mg acacia gum/person per day (approximately equivalent 430 mg acacia gum/kg bw per day) for up to 18 days was well tolerated in adults but some individuals experienced flatulence which was considered by the Panel as undesirable but not adverse effect. The Panel concluded that there is no need for a numerical ADI for acacia gum (E 414), and there is no safety concern for the general population at the refined exposure assessment of acacia gum (E 414) as a food additive.

IgE reactivity to carbohydrate moieties of glycoproteins in wheat allergy

Carbohydrate moieties of different glycoproteins, such as cross-reactive carbohydrate determinants (CCDs) and galactose α-1,3-galactose, can induce IgE reactivity with varied clinical significance. In this study, the possible participation of glycan from wheat gliadin, with respect to its IgE-binding capacity, was investigated in children with food allergies to wheat. Total IgE and wheat-specific IgE quantification, documentation of history, and/or oral food challenge (OFC) were performed for 52 children. Subjects with positive wheat-specific IgE were characterized as the symptomatic group, never-exposed group, or asymptomatic group. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and glycan detection in gliadin were performed. IgE binding to gliadin and deglycosylated gliadin was measured by immunoblotting and ELISA. Gliadin-specific IgE was detected and correlated with wheat-specific IgE in the symptomatic, never-exposed, and asymptomatic groups. The glycan range overlapped significantly with the gliadin range. Deglycosylation of gliadin reduced the allergenicity of gliadin. In gliadin, the allergenicity of the glycan portion was greater in the symptomatic group than in the never-exposed and asymptomatic groups. We conclude that N-glycan in gliadin might exhibit allergenicity as a possible carbohydrate epitope in wheat allergy in children.

Allergic and immunologic reactions to food additives

For centuries, food additives have been used for flavouring, colouring and extension of the useful shelf life of food, as well as the promotion of food safety. During the last 20 years, the studies implicating the additives contained in foods and medicine as a causative factor of allergic reactions have been proliferated considerably. In this review, we aimed to overview all of the food additives which were approved to consume in EU and find out how common and serious allergic reactions come into existence following the consuming of food additives.

Gum arabic as a cause of occupational allergy

Background. Gum arabic is a potential sensitizer in food industry. Methods. We examined 11 candy factory workers referred to examinations due to respiratory and skin symptoms paying attention to exposure and sensitization to gum arabic. Skin tests, pulmonary function tests, and respiratory provocation tests were carried out as indicated by the symptoms and findings. Results. Occupational asthma, caused by gum arabic was diagnosed in 4/11 candy factory workers and two of them had also occupational contact urticaria and one had occupational rhinitis. One of them had oral symptoms associated with ingestion of products containing gum arabic. Conclusions. Airborne exposure to gum arabic may cause sensitization leading to allergic rhinitis, asthma, and urticaria.

Biological effects of gum arabic: a review of some recent research

Gum arabic (GA) is a branched-chain, complex polysaccharide, either neutral or slightly acidic, found as a mixed calcium, magnesium and potassium salt of a polysaccharidic acid. The backbone is composed of 1,3-linked beta-D-galactopyranosyl units. The side chains are composed of two to five 1,3-linked beta-D-galactopyranosyl units, joined to the main chain by 1,6-linkages. Pharmacologically, GA has been claimed to act as an anti-oxidant, and to protect against experimental hepatic-, renal- and cardiac toxicities in rats. These reports could not be confirmed by others. GA has been claimed to alleviate the adverse effects of chronic renal failure in humans. This could not be corroborated experimentally in rats. Reports on the effects of GA on lipid metabolism in humans and rats are at variance, but mostly suggest that GA ingestion can reduce plasma cholesterol concentrations in rats. GA has proabsorptive properties and can be used in diarrhoea. It enhances dental remineralization, and has some antimicrobial activity, suggesting a possible use in dentistry. GA has been shown to have an adverse effect on electrolyte balance and vitamin D in mice, and to cause hypersensitivity in humans. More studies are needed before the pharmacological properties of GA can be utilized in therapy.

The role of protein glycosylation in allergy

The asparagine-linked carbohydrate moieties of plant and insect glycoproteins are the most abundant environmental immune determinants. They are the structural basis of what is known as cross-reactive carbohydrate determinants (CCDs). Despite some structural variation, the two main motifs are the xylose and the core-3-linked fucose, which form the essential part of two independent epitopes. Plants contain both epitopes, insect glycoproteins only fucose. These epitopes and other fucosylated determinants are also found in helminth parasites where they exert remarkable immunomodulatory effects. About 20% or more of allergic patients generate specific anti-glycan IgE, which is often accompanied by IgG. Even though antibody-binding glycoproteins are widespread in pollens, foods and insect venoms, CCDs do not appear to cause clinical symptoms in most, if not all patients. When IgE binding is solely due to CCDs, a glycoprotein allergen thus can be rated as clinical irrelevant allergen. Low binding affinity between IgE and plant N-glycans now drops out as a plausible explanation for the benign nature of CCDs. This rather may result from blocking antibodies induced by an incidental 'immune therapy' ('glyco-specific immune therapy') exerted by everyday contact with plant materials, e.g. fruits or vegetables. The need to detect and suppress anti-CCD IgE without interference from peptide epitopes can be best met by artificial glycoprotein allergens. Hydroxyproline-linked arabinose (single beta-arabinofuranosyl residues) has been identified as a new IgE-binding carbohydrate epitope in the major mugwort allergen. However, currently the occurrence of this O-glycan determinant appears to be rather restricted.

Sensitization due to gum arabic (Acacia senegal): the cause of occupational allergic asthma or crossreaction to carbohydrates?

BACKGROUND

A pharmaceutical industry worker was exposed to dust of gum arabic in the tablet coating plant and complained of work-related shortness of breath, chest tightness, runny nose, itching and redness of the eyes. This case was investigated for allergy to gum arabic and compared with a control group. The aim of the study was to identify the IgE-binding components responsible for the work-related symptoms.

METHODS

Skin prick tests (SPTs)and specific IgE (sIgE) measurements with environmental and occupational allergens, spirometry and a specific bronchial challenge with gum arabic were performed. One hundred and nineteen control subjects underwent SPT with gum arabic and 43 controls were tested for sIgE. Crossreactivity between gum arabic and horse radish peroxidase was investigated by IgE CAP inhibition. A combined procedure of immunoblotting and periodate treatment was applied to identify the epitope nature of gum arabic.

RESULTS

Allergy to gum arabic was shown by SPT, presence of sIgE and a positive bronchial challenge with gum arabic. Sensitization to gum arabic was demonstrated by SPT or sIgE in 7 and 5 controls, respectively. The results of inhibition with horse radish peroxidase, immunoblotting and periodate treatment suggest that gum arabic sIgE of the patient and 1 SPT-positive control subject were directed to the polypeptide chains of gum arabic. In contrast, gum arabic sIgE of the other controls reacted to carbohydrate components.

CONCLUSIONS

Sensitization to gum arabic carbohydrate structures occurs casually in atopic patients with pollen sensitization without obvious exposure to gum arabic. This study suggests that allergy to gum arabic is mediated preferentially by IgE antibodies directed to polypeptide chains of gum arabic.

Final report of the safety assessment of Acacia catechu gum, Acacia concinna fruit extract, Acacia dealbata leaf extract, Acacia dealbata leaf wax, Acacia decurrens extract, Acacia farnesiana extract, Acacia farnesiana flower wax, Acacia farnesiana gum, Acacia senegal extract, Acacia senegal gum, and Acacia senegal gum extract

These ingredients are derived from various species of the acacia plant. Only material derived from Acacia senegal are in current use according to industry data. The concentration at which these ingredients are reported to be used ranges from 9% in mascara to 0.0001% in tonics, dressings, and other hair-grooming aids. Gum arabic is a technical name for Acacia Senegal Gum. Gum arabic is comprised of various sugars and glucuronic acid residues in a long chain of galactosyl units with branched oligosaccharides. Gum arabic is generally recognized as safe as a direct food additive. Little information is available to characterize the extracts of other Acacia plant parts or material from other species. Acacia Concinna Fruit Extract was generally described as containing saponins, alkaloids, and malic acid with parabens and potassium sorbate added as preservatives. Cosmetic ingredient functions have been reported for Acacia Decurrens Extract (astringent; skin-conditioning agent--occlusive) and Acacia Farnesiana Extract (astringent), but not for the other Acacias included in this review. Toxicity data on gum arabic indicates little or no acute, short-term, or subchronic toxicity. Gum arabic is negative in several genotoxicity assays, is not a reproductive or developmental toxin, and is not carcinogenic when given intraperitoneally or orally. Clinical testing indicated some evidence of skin sensitization with gum arabic. The extensive safety test data on gum arabic supports the safety of Acacia Senegal Gum and Acacia Senegal Gum Extract, and it was concluded that these two ingredients are safe as used in cosmetic formulations. It was not possible, however, to relate the data on gum arabic to the crude Acacias and their extracts from species other than Acacia senegal. Therefore, the available data were considered insufficient to support the safety of Acacia Catechu Gum, Acacia Concinna Fruit Extract, Acacia Dealbata Leaf Extract, Acacia Dealbata Leaf Wax, Acacia Decurrens Extract, Acacia Farnesiana Extract, Acacia Farnesiana Flower Wax, Acacia Farnesiana Gum, and Acacia Senegal Extract in cosmetic products. The additional data needed to complete the safety assessment for these ingredients include (1) concentration of use; (2) identify the specific chemical constituents, and clarify the relationship between crude Acacias and their extracts and the Acacias and their extracts that are used as cosmetic ingredients; (3) data on contaminants, particularly relating to the presence of pesticide residues, and a determination of whether Acacia melanoxylon is used in cosmetics and whether acamelin (a quinone) and melacacidin (a flavin) are present in the Acacias that are being used; (4) skin sensitization study (i.e., dose response to be determined); (5) contact urticaria study at use concentration; and (6) ultraviolet (UV) absorption spectrum; if there is significant absorbance in the UVA or UVB range, then a photosensitization study may be needed. It was also noted that other data may be needed after clarification of the chemical constituents of the Acacia-derived ingredients.

Sensitization to cross-reactive carbohydrate determinants and the ubiquitous protein profilin: mimickers of allergy

BACKGROUND

During the last decade, evidence has been provided for profilins and cross-reactive carbohydrate determinants (CCDs) to be capable of inducing cross-reactive IgE antibodies with little clinical relevance.

OBJECTIVE

To investigate the prevalence of sensitization to CCD and profilin in isolated allergies (birch, timothy grass, house dust mite, pets (cat and/or dog), natural rubber latex (NRL) and hymenoptera venom). To study the contribution of anti-CCD and anti-profilin IgE antibodies as a cause of clinically irrelevant IgE for NRL and apple.

METHODS

For the first part of the study, 100 patients with inhalant allergy, 17 patients with NRL allergy and 40 patients with venom anaphylaxis were enrolled. Diagnosis was based on a questionnaire and a positive IgE determination and skin test for relevant allergen. Patients were identified as sensitized to CCD if they had a negative prick test and positive IgE for the glycoprotein bromelain. Sensitization to profilin was assessed by IgE for rBet v 2 (recombinant birch profilin). For the second part of the study, sera containing IgE against apple (n=82) or NRL (n=38) were classified as true-negative or false-positive according to the presence or absence of an oral allergy syndrome (OAS) or NRL-induced anaphylaxis. In these patients, sensitization to CCD and profilin was evaluated as described above.

RESULTS

No sensitization to bromelain-type CCD and profilin was found in isolated birch pollen or NRL allergy. In contrast, sensitization to bromelain-type CCD was found in 4/17 patients with isolated grass pollinosis, 5/24 patients with combined pollinosis (birch, timothy, mugwort) and 7/33 patients with venom anaphylaxis. Sensitization to profilin was almost restricted to patients with combined pollen allergy (5/24). In pollen-allergic individuals with a false-positive IgE against NRL the prevalence of sensitization to bromelain-type CCD and profilin IgE was higher than in NRL-allergic patients (P<0.00001 and P=0.0006, respectively). In pollen-allergic individuals with a false-positive IgE to apple, the frequency of sensitization to bromelain-type CCD was higher than in OAS patients (P=0.004). Clinically irrelevant NRL and apple were also found in four and five out of the seven patients sensitized to venom CCD, respectively. In pollinosis, clinically irrelevant NRL and apple IgE antibodies were inhibited by bromelain and recombinant birch profilin, whereas in isolated venom anaphylaxis these antibodies were inhibited by bromelain.

CONCLUSIONS

Patients monoallergic to NRL or birch pollen showed no sensitization to bromelain-type CCD or profilin. Sensitization to profilin and/or bromelain-type CCD, caused by pollen (timothy grass, mugwort) or hymenoptera venom allergens, can elicit false-positive IgE antibodies against NRL and apple.

Molecular and immunological characterization of a novel timothy grass (Phleum pratense) pollen allergen, Phl p 11

BACKGROUND

Allergy to grass pollen is typically associated with serum IgE antibodies to group 1 and/or group 5 allergens, and additionally often to one or several less prominent allergens. Most of the grass pollen allergens identified to date have been characterized in detail by molecular, biochemical and immunological methods, timothy grass being one of the most thoroughly studied species. However, a 20-kDa allergen frequently recognized by IgE antibodies from grass pollen allergics has so far escaped cloning and molecular characterization.

OBJECTIVE

To clone and characterize the 20 kDa timothy grass pollen allergen Phl p 11.

METHODS

Phl p 11 cDNA was cloned by PCR techniques, utilizing N-terminal amino acid sequence obtained from the natural allergen. Phl p 11 was expressed as a soluble fusion protein in Escherichia coli, purified to homogeneity and used for serological analysis and to study Phl p 11 specific induction of histamine release from basophils and skin reactivity in sensitized and control subjects.

RESULTS

Phl p 11 cDNA defined an acidic polypeptide of 15.8 kDa with homology to pollen proteins from a variety of plant species and to soybean trypsin inhibitor. The sequence contained one potential site for N-linked glycosylation. Serological analysis revealed that recombinant Phl p 11 shared epitopes for human IgE antibodies with the natural protein and bound serum IgE from 32% of grass pollen-sensitized subjects (n = 184). Purified recombinant Phl p 11 elicited skin reactions and dose-dependent histamine release from basophils of sensitized subjects, but not in non-allergic controls.

CONCLUSION

As the first representative of group 11 grass pollen allergens, Phl p 11 has been cloned and produced as a recombinant protein showing allergenic activity. One-third of grass pollen-sensitized subjects showed specific IgE reactivity to recombinant Phl p 11, corresponding in magnitude to a significant proportion of specific IgE to grass pollen extract.

Allergenic components of a novel food, Micronesian nut Nangai (Canarium indicum), shows IgE cross-reactivity in pollen allergic patients

BACKGROUND

New foods may present a risk for food hypersensitive patients. Several examples exist of allergic reactions caused by cross-reactive plant-derived foods, and new foods should be scrutinised before introducing them to the market. We have evaluated the clinical and serological relevance of cross-reactivity between Nangai and pollen allergens.

METHODS

Cross-reactivity was examined with Maxisorp RAST (radioallergosorbent test), RAST inhibition and Western blot, using sera from patients allergic to grass, birch and mugwort pollen. None of the patients reported having seen or eaten Nangai previously. To determine the biological and clinical relevance of the cross-reactivity, histamine release (HR) test, skin prick test (SPT) and food challenge were used.

RESULTS

There was prevalence for reactivity against Nangai in the group of pollen allergic patients. This cross-reactivity seems to be related--at least in part--to carbohydrate epitopes. Three out of 12 patients tested with Nangai were positive upon open challenge, but using double blind placebo controlled food challenge (DBPCFC) this could not be confirmed in two patients. The biological effects of Nangai on allergic patients were confirmed using HR and SPT.

CONCLUSION

The Nangai specific IgE found among pollen allergic patients addresses the need for control of new or changed foods before introduction to the market.

Antibody binding to venom carbohydrates is a frequent cause for double positivity to honeybee and yellow jacket venom in patients with stinging-insect allergy

BACKGROUND

Up to 50% of patients with stinging-insect allergy have double-positive RAST results to honeybee and yellow jacket (YJ) venom. True double sensitization and crossreactivity through venom hyaluronidases are considered main reasons for this multiple reactivity.

OBJECTIVE

We investigated the role of antibodies against cross-reactive carbohydrate determinants in venom double positivity.

METHODS

CAP inhibition experiments were performed with crude oilseed rape (OSR) and timothy grass pollen extracts and a neoglycoprotein construct displaying a MUXF glycan, as present in pineapple-stem bromelain (MUXF-BSA). CAP to OSR was used as a rough measure for carbohydrate-specific IgE in individual sera.

RESULTS

CAP results to OSR pollen were positive in 2 of 14 single-positive honeybee venom sera, 2 of 16 single-positive YJ venom sera, and 33 (80.5%) of 41 double-positive sera (P < .00001, chi(2) test). CAP inhibition was performed in 16 selected patients with a CAP class of 3 or higher to both venoms. In 9 of 11 patients with a highly positive CAP result to OSR (CAP score to OSR > CAP score to second venom), pollen extracts, MUXF-BSA, or both were able to completely inhibit IgE binding to one of the venoms, whereas this was not the case in 5 patients with a negative or weakly positive CAP result to OSR (CAP score to OSR < CAP score to second venom).

CONCLUSIONS

The data suggest that carbohydrate-specific IgE is a major cause for the double positivity to honeybee and YJ venom seen in patients with Hymenoptera allergy. Because these antibodies may have low clinical relevance, they may severely impede the correct diagnosis of Hymenoptera venom allergy.

Investigations on the carbohydrate moieties of glycoprotein allergens

Many allergens are glycoproteins and their carbohydrate structure can contribute to the IgE reactivity. Therefore it is of great interest to study the carbohydrate structures of these particular antigens. Here, we present an overview of methods combining basic procedures in glycochemistry with various applications of electrophoresis that allow investigating single allergens in crude extracts. Various allergen extracts, e.g. from tomato, grass pollen and bacteria were analysed and the suitability of the tests are discussed.

N- and O-linked oligosaccharides of allergenic glycoproteins

Cross-linking of cell-bound IgE on mast cells or basophils by polyvalent antigens causes the release of histamine and other mediators of the allergic response which then lead to the development of allergic symptoms. In this event not only peptide epitopes, but also carbohydrates can act as cross-linking elements. Since peptide epitopes of allergens are subject of most published studies, this review is focused on glycosidic epitopes. The current knowledge of the structures and possible epitopes of oligosaccharides linked to allergenic glycoproteins is briefly reviewed, showing that complex plant N-glycans containing alpha1,3 fucose and beta1,2 xylose are most frequently involved in the structures of IgE epitopes. In own studies a prevalence of up to 29% anti-glycan IgE was determined among pollen-allergic patients. The clinical relevance of these carbohydrate specific IgE antibodies is still a matter of controversial discussions.

Beta(1,2)-xylose and alpha(1,3)-fucose residues have a strong contribution in IgE binding to plant glycoallergens

Primary structures of the N-glycans of two major pollen allergens (Lol p 11 and Ole e 1) and a major peanut allergen (Ara h 1) were determined. Ole e 1 and Ara h 1 carried high mannose and complex N-glycans, whereas Lol p 11 carried only the complex. The complex structures all had a beta(1,2)-xylose linked to the core mannose. Substitution of the proximal N-acetylglucosamine with an alpha(1, 3)-fucose was observed on Lol p 11 and a minor fraction of Ole e 1 but not on Ara h 1. To elucidate the structural basis for IgE recognition of plant N-glycans, radioallergosorbent test analysis with protease digests of the three allergens and a panel of glycoproteins with known N-glycan structures was performed. It was demonstrated that both alpha(1,3)-fucose and beta(1,2)-xylose are involved in IgE binding. Surprisingly, xylose-specific IgE antibodies that bound to Lol p 11 and bromelain did not recognize closely related xylose-containing structures on horseradish peroxidase, phytohemeagglutinin, Ole e 1, and Ara h 1. On Lol p 11 and bromelain, the core beta-mannose is substituted with just an alpha(1,6)-mannose. On the other xylose-containing N-glycans, an additional alpha(1,3)-mannose is present. These observations indicate that IgE binding to xylose is sterically hampered by the presence of an alpha(1,3)-antenna.

Characterization of a core alpha1-->3-fucosyltransferase from the snail Lymnaea stagnalis that is involved in the synthesis of complex-type N-glycans

We have identified a core alpha1-->3-fucosyltransferase activity in the albumin and prostate glands of the snail Lymnaea stagnalis. Incubation of albumin gland extracts with GDP-[(14)C]Fuc and asialo/agalacto-glycopeptides from human fibrinogen resulted in a labeled product in 50% yield. Analysis of the product by 400 MHz (1)H-NMR spectroscopy showed the presence of a Fuc residue alpha1-->3-linked to the Asn-linked GlcNAc. Therefore, the enzyme can be identified as a GDP-Fuc:GlcNAc (Asn-linked) alpha1-->3-fucosyltransferase. The enzyme acts efficiently on asialo/agalacto-glycopeptides from both human fibrinogen and core alpha1-->6-fucosylated human IgG, whereas bisected asialo/agalacto-glycopeptide could not serve as an acceptor. We propose that the enzyme functions in the synthesis of core alpha1-->3-fucosylated complex-type glycans in L. stagnalis. Core alpha1-->3-fucosylation of the asparagine-linked GlcNAc of plant- and insect-derived glycoproteins is often associated with the allergenicity of such glycoproteins. Since allergic reactions have been reported after consumption of snails, the demonstration of core alpha1-->3-fucosylation in L. stagnalis may be clinically relevant.