A Case of Immediate Hypersensitivity Reaction to Maltitol

Background Maltitol is a sugar alcohol that is frequently used as a noncaloric sweetener, although it is also used as an excipient, a plasticizer in gelatin capsules, and an emollient. It has not been previously described as an agent involved in immediate hypersensitivity reactions. Methods We report on an anaphylactoid reaction with pharyngeal occlusion suffered by a 60-year-old man after ingestion of a candy containing maltitol syrup. A prick-to-prick test was performed with the candy and maltitol powder. Other allergens were excluded as causative agents of the adverse reaction, although the patient refused to undergo an oral challenge test with the candy. A basophil activation test (BAT) was performed with maltitol powder, and a dose-response curve was generated. The test was also performed in 3 healthy controls. Results Both prick-to-prick tests were negative. The result of the BAT was positive at all the concentrations tested in the patient's blood and negative in all the controls. Conclusions The BAT can help to clarify the agents implicated in an adverse reaction and can reduce the risk involved in diagnosis. The BAT can also prove useful in the study of reactions caused by low-molecular-weight antigens, for which routine diagnostic tests are not feasible.


Background
Maltitol (4-O--glucopyranosyl-D-sorbitol) is a sugar alcohol (polyol) that is produced by hydrogenation of maltose obtained from starch ( Figure 1). It is frequently used as a noncaloric sweetener because it has half the calories of sucrose (table sugar). It is also used as an excipient in drugs, a plasticizer in gelatin capsules, and an emollient.
Sugar alcohols rarely cause hypersensitivity reactions, although there have been reports of reactions to mannitol [1][2][3][4] and erythritol [5]. Maltitol has not been previously described as an agent involved in immediate hypersensitivity reactions.

Patients and Methods
We report the case of a 60-year-old man with a history of hypothyroidism and cutaneous psoriasis. He reported an acute episode of dyspnea, facial flushing, and pharyngeal occlusion (anaphylaxis grade 2 of Ring and Messmer) immediately after licking a candy (Virginia's Coffee Candies5, Rodríguez S. A. Industries, Reus, Spain). He spat the candy out without swallowing and reported spontaneous improvement after 15 minutes. The candy was composed of maltitol syrup, hydrogenated fatty acids, and coffee. The patient reported that he usually ate the mentioned kind of candies and assessed good tolerance to one of the same candies five hours before the episode and to four units the day before. After the adverse reaction, the patient referred good tolerance to coffee and the other foods taken during the hours preceding the episode.
Prick testing was performed for common inhalants, Anisakis, Pru p 3, and a complete battery of foods, including egg, milk, nuts, fruits, legumes, fish, seafood, flour, and spices.
Prick-to-prick testing was first performed with the candy implicated in the adverse reaction.
The general blood analysis included immunoglobulins, 24-hour urinary catecholamines, erythrocyte sedimentation rate, tryptase, anti-thyroid antibodies, and total IgE and specific IgE for Anisakis and Ascaris. As the patient refused to undergo a controlled oral challenge with the candy, in vitro tests were performed in order to correlate the suspicious components with the clinical picture.
The basophil activation test (BAT) was performed with maltitol powder (Sweet Pearl P200) according to a previously reported technique [6,7]. Briefly, whole blood was drawn, and the analysis was performed within 24 hours. Maltitol was tested in a dose-response curve from 1000 g/ml to 100 g/ml. Double staining was carried out with CD203c-PE to detect basophils and CD63-FITC to detect basophil activation ( Figure 2). Serum saline was added as negative control (Figure 2(a)), showing the basally activated basophils, before adding any stimulus. The peptide fMLP was used as positive control (Figure 2(b)), to asses an adequate cellular reactivity. The positivity criterion was the same as that applied for other low-molecular-weight substances, such as drugs [6]. Therefore, to consider a result positive, the percentage of basophils that became activated after incubation with maltitol had to be at least double that of the negative control (basophil activation index ≥ 2).
The test was also performed in three healthy individual controls.

Results
The results of the prick and prick-to-prick tests were negative. Total IgE was 85.3 kU/l and specific IgE was negative for Anisakis and Ascaris.
The blood analysis revealed no pathological values, except for a slight increase in thyroid peroxidase antibodies (anti-TPO) (109 IU/L, normal values < 35 IU/L).

Discussion
In this case, the other main components of the candy had been tolerated by the patient after the reaction, and no other food allergies were found. So, maltitol was suspected as the cause of the anaphylactoid reaction.
Other low-molecular-weight sugars have been reported as allergens causing anaphylaxis [1][2][3][4][5]. In general, the capability of low-molecular-weight elements to cause sensitization depends on their binding to proteins to form a hapten-carrier complex. Thus, reactions have been reported between Dglucose and N-terminal amino groups of in vivo proteins, such as serum albumin, hemoglobin, and plasma proteins [8].
Nevertheless, sugars such as mannitol do not have the reactive group necessary for covalent binding to proteins and production of a stable complex [4]. In one case of anaphylaxis due to this sugar, the formation of a Schiff base with the reduced sugar form (D-mannose) and amino groups of proteins has been proposed as a mechanism of sensitization [4]. This base could expose the sugar epitopes, leaving them available as antigenic determinants to induce specific IgE production [4,9]. The hypersensitivity reaction could then take place by bivalent, or even monovalent, binding to mannitol [10].

Conclusion
The potential ubiquity of maltitol as well as the absence of feasible routine diagnostic tests to study the hypersensitivity reactions which it could cause means that it is difficult to diagnose as a potential cause of anaphylaxis. The BAT could be a useful and noninvasive technique for the study of cases such as the present one, in which the challenge test involved risk of anaphylaxis and was refused by the patient. Although we were unable to determine the underlying pathogenic mechanism of the reaction, our findings draw attention to the role of maltitol as a causative agent. Fluorescein isothiocyanate PE: Phycoerythrin.