Phthalate esters reveal skin-sensitizing activity of phenethyl isothiocyanate in mice

Phenethyl isothiocyanate (PEITC) is a constituent of edible cruciferous vegetables and has received attention due to its potential cancer chemopreventive activity. Although its protein-binding activity is known, PEITC has not been studied as a contact sensitizer. We previously demonstrated that phthalate esters, including dibutyl phthalate (DBP) and di-n-propyl phthalate (DPP), enhance skin sensitization in a fluorescein isothiocyanate (FITC)-induced contact hypersensitivity mouse model. In this study, we examined whether DBP and DPP enhance skin sensitization to haptens other than FITC. During this study, we tested PEITC as a contact sensitizer. BALB/c mice were epicutaneously sensitized with a suboptimal dose of a hapten with or without a phthalate ester. Sensitization was evaluated as the ear swelling response after a challenge with the respective hapten. DBP and DPP did not enhance the sensitization to two T-helper 1-type (2,4-dinitrofluorobenzene and oxazolone) or three T-helper 2-type (trimellitic anhydride, methylenediphenyl 4,4′-diisocyanate, and tolulene 2,4-diisocyanate) haptens. In contrast, DBP and DPP enhanced the sensitization to two FITC analogues (eosin 5-isothiocyanate and rhodamine B isothiocyanate) as well as to PEITC. Adjuvant effects of DBP and DPP were observed in contact hypersensitivity to haptens other than FITC, including a food ingredient PEITC.