Isothiocyanates are important as haptens in contact allergy to chloroprene rubber

Summary

Background

Contact allergy to chloroprene rubber products is well known. Thiourea compounds are considered the cause of allergy, despite being non- or weak sensitizers. Diethylthiourea is commonly occurring in this type of products and can decompose to the sensitizer ethyl isothiocyanate.

Objectives

To investigate the clinical importance of degradation products and metabolites from organic thioureas in contact allergy to chloroprene rubber with focus on isothiocyanates and isocyanates.

Methods

Patients with contact allergy to diphenylthiourea were patch tested with phenylisothiocyanate and phenylisocyanate. Patients with known contact allergy to diethylthiourea were retested with diethylthiourea, while chemical analyses of the their chloroprene rubber products were performed. The stability of diethylthiourea, diphenylthiourea and dibutylthiourea in patch test preparations was investigated. Liquid chromatography/mass spectrometry and solid-phase microextraction/gas chromatography were used for determination of organic thioureas and isothiocyanates.

Results

All diphenylthiourea allergic patients reacted to phenylisothiocyanate, 2 of 8 reacted to phenylisocyanate and 6 of 8 reacted to diphenylthiourea. All four diethylthiourea allergic patients reacted at retest, diethylthiourea was detected in all chloroprene rubber samples, with levels of 2-1200 nmol cm⁻². At 35 ᵒC, ethylisothiocyanate was emitted from all samples. Patch test preparations of diethylthiourea, diphenylthiourea and dibutylthiourea all emitted the corresponding isothiocyanate, with diethylthiourea showing the highest rate of isothiocyanate emission.

Conclusions

Thiourea compounds are degraded to isothiocyanates, which are generally strong or extreme sensitizers, thus acting as prehaptens. This process occurs in both chloroprene rubber products and patch test preparations. Positive reactions to phenylisocyanate indicate cutaneous metabolism, as the only known source of exposure to phenylisocyanate is through bioactivation of diphenylthiourea.

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