Published: 1 September 2016

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Soya-based Excipients — a Problem for People with Peanut Allergy?

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Prescriber Update 37(3): 42
September 2016

Peanuts are the seed of the legume Arachis hypogaea¹. The prevalence of peanut allergy is estimated at about 1% of the population². Peanut allergy causes more concern than most other food allergies as it is more severe and more persistent³.

Soyabeans are the seed of the legume Glycine max. Soya allergy usually manifests in childhood. The prevalence in adults is poorly described, but has been estimated at around 0.4%³. Isolated soya allergy seems to be rare; 88% of children with soya allergies also have peanut allergies³. Allergic symptoms to soya include atopic dermatitis and enterocolitis³. Anaphylaxis caused by soya is very rare. It has been postulated that the presence of anti-inflammatory chemicals in soya may reduce the allergic response³. In the few cases where death was reported after ingestion of soya the patients also had severe peanut allergies³.

Food induced allergenic reactions can be classified into two groups according to the type of immune reaction⁴.

• Immunoglobulin E (IgE) mediated symptoms (includes anaphylaxis).
• Non-IgE mediated gastrointestinal symptoms; these reach a peak approximately 48 hours after ingestion.

Several methods have been used for diagnosing suspected food allergy⁴.

• Skin prick testing; gives a large number of false positive results and shows sensitisation rather than allergy.
• Food-specific IgE measured by ELISA or immunoblotting.
• Double blind placebo controlled food challenge.
• Skin patch testing.
• Basophil activation test.

The results of some of these tests show only that a person is sensitised to an allergen, but is not necessarily allergic.

Cross-reactivity is less common than cross-sensitisation. Cross-sensitisation generally implies a positive skin test or IgE test but the patient is clinically tolerant, whereas a cross-reactivity implies that clinical symptoms are experienced⁵.

Cross-reactivity relies on the presence of conserved anti-body accessible surface structures of proteins and is often observed between members of the same protein family¹. Plants in the same genus such as legumes are likely to have similar proteins.

Peanuts contain 12 known allergens which are categorised into six families:^1,2

• the cupin superfamily (Ara h 1, 3)
• the prolamin superfamily (Ara h 2, 6, 7, 9)
• the profilin family (Ara h 5)
• bet v-1-related proteins (Ara h 8)
• oleosin/glycosyl transferase GT-C (Ara h 10, 11)
• defensin/scorpion toxin-like knottin (Ara h 12, 13).

The peanut allergens Ara h 8, 5 and 9 are responsible for allergic cross-reactivity across a wide variety of unrelated plants and are considered to be panallergens¹.

Several soya allergens share high sequence homology to their counterparts in peanut. Soya Gly m 5 (β-conglycinin, 7 S) is close to Ara h 1. Ara h 3 and soyabean Gly m 6 (glycinin, 11 S) share a similar 3D structure¹.

Approximately 50% of peanut-allergic patients have positive skin prick tests to other legumes, but less than 5% are clinically symptomatic upon ingestion of legumes^2,5

Peanut allergic people have a high theoretical risk of cross-reactivity to soyabean but double-blinded food challenges have shown a low rate of cross-reaction⁴. In a group of 39 peanut sensitised patients, 33 (87%) were also sensitised to soyabean and 11 (33%) reported symptoms to a wide variety of soya products¹. In a study of 32 children with peanut allergy, 10 (31%) had a positive skin test to soya whilst one (3%) had a clinical reaction⁵.

In a study investigating factors associated with the development of peanut allergy in childhood, consumption of soya was independently associated with peanut allergy⁶.

Refined soya and peanut oil contain low quantities of allergenic protein, depending on the refining process. No safe level for these residual proteins has been established. Neither is it clear that long-term consumption of medicines containing these oils will not induce allergy^7,8.

Whilst the risk appears to be low, the European Medicines Agency (EMA) has taken a precautionary approach in their guidelines on excipients^7,8. The EMA guideline recommends that medicinal products containing soya oil should include a contraindication for patients allergic to peanut or soya. In New Zealand, pharmaceutical companies are encouraged to follow this guidance, particularly if the allergenic potential of the peanut or soya based excipient has not been characterised.

References

1. Bublin M, Breiteneder H. 2014. Cross-reactivity of peanut allergens. Current Allergy Asthma Reports 14: 426.
2. Mueller GA, Maleki SJ, Pedersen LC. 2014. The molecular basis of peanut allergy. Current Allergy Asthma Reports 14: 429.
3. Masilamani M, Commins S, Shreffler W. 2012. Determinants of food allergy. Immunology and Allergy Clinics of North America 32: 11-33.
4. Verma AK, Kumar S, Das M, et al. 2013. A comprehensive review of legume allergy. Clinical Reviews in Allergy & Immunology 45: 30-46.
5. Kazatsky AM, Wood RA. 2016. Classification of food allergens and cross-reactivity. Current Allergy Asthma Reports 16: 22.
6. Lack G, Fox D, Northstone K, et al. 2003. Factors associated with the development of peanut allergy in childhood. The New England Journal of Medicine 348: 977-985.
7. European Medicines Agency (EMA). 2003. Medicinal products for human use; Safety, environment and information; Excipients in the label and package leaflet of medicinal products for human use. Volume 3B. URL: www.ema.europa.eu/docs/en_GB/document_library/Scientific_guideline/2009/09/WC500003412.pdf (accessed 14 July 2016).
8. European Medicines Agency (EMA): Committee on Herbal Medicinal Products (HMPC). 2006. Public Statement on the Allergic Potency of Herbal Medicinal Products Containing Soya or Peanut Protein. 12 January 2006. URL: www.ema.europa.eu/docs/en_GB/document_library/Scientific_guideline/2010/04/WC500089954.pdf (accessed 14 July 2016).