Latin name: Asparagus officinalis
Source material: Frozen stem
Family: Alliaceae (Liliaceae)
Asparagus is a widely grown vegetable. Together with Garlic, the Onion and the Leek, it belongs to the Alliaceae (previously known as Liliaceae) or Lily family, which contains ferns and vegetables and flowers such as tulips. The genus Asparagus is made up of some 300 species.
The well-known table delicacy Asparagus has been cultivated for more than 2,000 years and has been much esteemed from the time of the Greeks and Romans. It is an important commercial and garden crop in many parts of the world. Its relatively high price tends to make it a luxury.
Asparagus is native to the marshes of southwest Europe and may be found wild on the seacoast in southwest England. In the southern parts of Russia and Poland the waste steppes are covered with this plant. It is also common as a wild plant in Greece. Otherwise, it is found in cultivated beds.
Asparagus plants are perennials with edible aerial stems (spears). There are 2 main varieties of Asparagus, the tougher green one, and the more tender white one, which is preferred in Europe and grown in shade or underground to keep it from producing chlorophyll.
Asparagus is available fresh, canned or frozen and is often served as a side dish after being steamed or briefly boiled. The tough base of the stem is usually removed before cooking, and sometimes the plant is peeled as well.
The smell in one’s urine after eating Asparagus is caused by the substance methyl mercaptan. Asparagus is well known as a diuretic and laxative and has been used to treat gravel and dropsy. It has been a folk remedy for eye ailments, toothache, cramps, convulsions, and sciatica.
At least 6 IgE-binding components, ranging from 22 to 73 kDa, have been detected in raw Asparagus and shown to be very labile and quite sensitive to heat denaturation (1). However, the presence of a heat-stable allergen was suggested due to the fact that IgE-mediated allergy has been reported to canned Asparagus (2). Subsequently, a heat-stable lipid transfer protein was characterised (3-4). In addition, profilin and glycoproteins harbouring complex asparagine-linked glycans may also be involved in Asparagus allergy (4). In a study of 10 Asparagus-allergic individuals, IgE-binding components of 15 and 45-70 kDa were detected (5).
The following allergens have been characterised:
- Aspa o 1, a lipid transfer protein (3-4,6).
- Aspa o 4, a profilin (4).
- A Bet v 1 homologue is present (7-8).
Two LTP (lipid transfer protein) isoforms (Aspa o 1.01, Aspa o 1.02) have been isolated from Asparagus, and demonstrated to have an amino acid sequence similar to that of Pru p 3 from Peach. Each elicited positive SPT responses in 9 of 18 patients with Asparagus allergy (4).
An allergen has been detected that may be a plant growth inhibitor, 1,2,3-Trithiane-5-carboxylic acid, which is present in young shoots (9). This substance, identified as a sulfur-containing growth inhibitor in one study, was shown to be a first contact allergen from Asparagus (10).
An extensive cross-reactivity among the different individual species of the genus could be expected, as well as to a certain degree among other members of the family Alliaceae, such as Onion, Leek, Garlic, and Chives (2,11-12).
Cross-reactivity can be expected with other foods or plants containing profilin or a Bet v 1 homologue allergen (4,6-7).
Asparagus contains a lipid transfer protein (Aspa o 1), which will result in variable degrees of cross-reactivity with other foods containing lipid transfer proteins (3).
In sensitised individuals, Asparagus can induce symptoms of food allergy through ingestion, respiratory symptoms through inhalation, or cutaneous allergy through skin contact (1). Occupational contact dermatitis, contact urticaria, rhinoconjunctivitis and asthma have been reported (13-15).
Both delayed cell-mediated reactions and IgE-mediated reactions secondary to Asparagus have been described. IgE-mediated reactions can occur as food allergy or can be due to cutaneous or respiratory exposure, which is often occupational. Most reports of allergic reactions to Asparagus are from occupational settings. Anaphylaxis is the most common clinical picture of food allergy, while contact urticaria, rhinitis and asthma, appearing either isolated or associated, are typical clinical pictures of occupational allergy. Sensitisation to different allergens is the likely cause of the different reactions to Asparagus (4,16).
Significantly, there appears to be no single typical clinical pattern for the expression of Asparagus allergy. In a Spanish study of 27 patients who had been diagnosed in the previous 5 years with hypersensitivity to Asparagus, 10 were diagnosed with urticaria or allergic contact dermatitis. All of these 27 cases seemed to result from occupational exposure (80% packing employees and 20% housewives). IgE antibodies for Asparagus were detected in 19 patients. Five had associated symptoms of respiratory allergy. Ten patients were diagnosed with rhinoconjunctivitis, of whom 8 had coexisting occupational asthma, confirmed by means of bronchial provocation. With the exception of 1 patient with asthma who had experienced an episode of severe anaphylaxis, all the others consumed Asparagus without symptoms. The authors attribute this to the fact that the LTPs are located preferentially in the external layers of the plant, which were removed before its consumption. In a group of 3 subjects who were diagnosed with allergy from ingestion of Asparagus, in 2 the symptoms were those of anaphylaxis, and 1 experienced only oral allergy syndrome. None of these were occupationally exposed to Asparagus. The authors concluded that the Asparagus LTPs appeared to be associated with more severe symptoms, e.g., anaphylaxis (12).
These findings were further elaborated upon in a second report evaluating these 27 subjects: 8 had allergic contact dermatitis alone, 17 had IgE-mediated allergy, and 2 had both allergic contact dermatitis and IgE-mediated allergy. Positive patch tests with crude Asparagus extract but not with lipid transfer protein were observed in subjects with allergic contact dermatitis (n=10). Of 19 patients with IgE-mediated disease, 10 had contact urticaria after Asparagus handling. Of these, 5 subjects and 5 others without skin allergy showed respiratory symptoms. Eight were diagnosed with occupational asthma, and this was confirmed by positive Asparagus inhalation challenge, whereas the remaining 2 had isolated rhinitis. Four patients experienced immediate food-allergic reactions following ingestion of Asparagus; 3 reported anaphylaxis, and 1 experienced oral allergic syndrome. IgE antibody-binding proteins of 15 and 45-70 kDa were detected in 10 subjects. Of 10 subjects with skin reactivity to lipid transfer proteins, 6 showed bands at 15 kDa. The presence of IgE antibodies or skin reactivity for lipid transfer proteins was demonstrated in those with asthma (62%) and anaphylaxis (67%). The study concluded that Asparagus may result in occupational allergy, inducing allergic contact dermatitis as well as IgE-mediated reactions, that severe disease (anaphylaxis or asthma) is common, and that lipid transfer proteins appeared to play a major role (5).
In a study assessing the role of lipid transfer proteins in asparagus allergy, 18 patients with allergy to asparagus were enrolled. Asparagus allergy resulted in symptoms of asthma in 7, anaphylaxis in 1, rhinoconjunctivis in 1, oral allergy syndrome in 1, contact urticaria in 6, and contact dermatitis in 2. Three patients had a combination of two symptoms. IgE antibody testing was positive in all, varying from 0.43 to 12.7 kUA/l. The majority were exposed to Asparagus in an occupational setting (4).
Conjunctivitis, rhinitis, tightness of the throat and coughing during preparation of fresh Asparagus have been reported in 2 individuals. No symptoms occurred while the individuals were eating the cooked food. The authors suggest that the allergen was inhaled. Skin-prick tests with native green and white Asparagus were strongly positive, but negative with cooked Asparagus. Both patients had measurable levels of IgE antibodies against Asparagus (3.0 and 6.2 kU/l respectively). The Asparagus-specific IgE antibodies of the 2 patients were inhibited only by Asparagus, indicating that the patients were specifically sensitised by Asparagus and were not affected by cross-reactivity. No immunological cross-reactions could be detected (17).
Allergy to Asparagus may not always be obvious. In a 4-year-old child with multi-food allergy, significant skin reactivity was found to be directed at a number of foods, including Asparagus. However, IgE antibody testing was not able to detect Asparagus IgE above 0.35 kUA/l (18).
Acute urticaria after ingestion of Asparagus has been reported (19). Two patients were reported with IgE-mediated contact urticaria to canned Asparagus (2).
Occupational asthma and rhinoconjuctivitis within 10 minutes were reported to occur in a 28-year-old man due to inhalation of Asparagus allergens during cutting of the spears while harvesting Asparagus (1).
Allergic contact dermatitis and contact urticaria have been caused by Asparagus (9,20). A 53-year-old farm worker presented with a 3-year history of occupational allergic contact dermatitis to Asparagus (8).
Fixed food eruptions caused by Asparagus in a 50-year-old white woman were reported. She presented with 2 sharply marginated, round, slightly elevated erythemas on her right forearm and left chest wall that appeared a few hours after ingestion of tinned Asparagus and persisted for more than 4 weeks, then faded slowly without treatment, leaving circumscribed areas of hyperpigmentation. She later experienced another 2 episodes at exactly the same locations after eating either fresh or tinned Asparagus. These areas of erythema never developed independently of Asparagus intake (21).
A 55-year-old cook presented with seasonal (always in May) recurrent eczema on both hands, which prevented him from working. He also reported several episodes of dysphagia and dyspnoea after ingestion of asparagus. IgE antibody level to Asparagus was 15.1 kUA/l whereas IgE antibodies directed against other Liliaceae vegetables including Garlic and Onion could not be detected. Skin reactivity detected using prick-to-prick tests with native material of fresh, raw Asparagus and Asparagus cooked at 100 °C were positive, whereas Onion, Garlic, and Leek were negative. Epicutaneous patch testing with Asparagus resulted in a strong delayed-type skin reaction with a peak response on day 2 (22).
Asparagus is associated with the production of malodorous urine. This occurs in approximately 43% of people, and the propensity has been shown to remain with individuals for virtually a lifetime. Genetic studies suggest an autosomal dominant trait. Those who produce this odour assume that everyone does, and those who do not produce it have no idea of its potential olfactory consequences (23-24).
Compiled by Dr Harris Steinman, email@example.com
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