Rôle of a metabolite in allergenicity of Sudan I.

A metabolite of Sudan I (1-phenylazo-2-naphthol) was isolated after in vitro incubation with the supernatant of guinea pig liver homogenate (S-9). The metabolite was found to be 4'-hydroxy-1-phenylazo-2-naphthol by gas chromatography-mass spectrometry (GC-MS), and proton and carbon-13 nuclear magnetic resonance (NMR) analyses. It elicited positive reactions in guinea pigs sensitized to Sudan I. It was also shown to be allergenic. The results suggest that para-hydroxylation of the phenyl group of Sudan I may play an important rôle in its allergenicity.