Electrophysiological Detection of Non-IgE-mediated Hypersensitivity to the Fragrance Eugenol (2-Methoxy–4-(2-propenyl)phenol, MW 164 D) in Human Rectal Biopsies In Vitro

Non-IgE-mediated hypersensitivity to fragrances cannot be measured by skin-prick tests or specific serum-IgE (RAST) tests, and the diagnosis is based on epicutaneous patch tests, which have a poor sensitivity and/or specificity. We examined rectal biopsies of 2 patients with an atopic condition, who had a history of intolerance to spices and foods containing eugenol, and compared them to biopsies of 6 other atopic patients without a history of eugenol intolerance. Four to 6 rectal biopsies per patient were mounted in Ussing chambers (serosal surface area 1.1mm²) with carbogenated Ringer’s solution at 37^o C. Short circuit current (Isc) was recorded, and Isc-responses to serosally applied eugenol were analyzed. Isc-responses to 10^–4 M histamine and 10^–4 M carbachol (a stable cholinomimeticum) were also determined, to test the secretory reactivity of the rectal epithelium. Rectal Isc-responses to histamine and carbachol were 228±20 resp. 191±26µA/cm² (n=5) in eugenol-intolerant patients, and 125±26 resp. 64±11µA/cm² (n=17) in tolerant patients. Addition of 2×10^–3 M eugenol induced a transient secretory response of 45±5 resp. 65±44µA/cm² (n=2) in intolerant, resp. tolerant patients. In both patient groups, Isc-responses to histamine and carbachol were reduced 10- to 20-fold after addition of 2×10^–3 M eugenol, indicating a toxic effect of this high concentration to the epithelium. After addition of 10^–4 M eugenol, Ics-responses to histamine and carbachol were comparable to control values in both patient groups. However, 10^–4 M eugenol itself induced a significantly larger (p=0.004, Mann-Whitney U-test) secretory Isc-response of 8.8±1.4µA/cm² (n=4) in eugenol-intolerant patients, compared to a minor Isc-response of 1.9±0.6µA/cm² (n=13) in eugenol-tolerant patients, the latter being comparable (p=0.71) to the Isc-response to the vehicle 0.1% ethanol (1.6±0.9µA/cm² (n=9)). These results indicate that the rectal Isc-responses to a low concentration of 10^–4 M eugenol quantitatively discriminate between eugenol-intolerant patients and eugenol-tolerant patients. We conclude that this test may provide a new sensitive and specific tool in the diagnosis of non-IgE-mediated hypersensitivity to fragrances like eugenol.

Keywords: allergy, diagnosis, electrophysiology, eugenol, intestine, spices