Sodium metabisulfite as a contact allergen--an example of a rare chemical mechanism for protein modification.

BACKGROUND

Skin-sensitizing chemicals that cause allergic contact dermatitis do so by reacting with self-proteins such that the modified structure becomes antigenic. The reaction chemistry involved is well characterized, but there are exceptions, such as the occasional allergen sodium metabisulfite.

OBJECTIVES

To identify the potential in cutaneo reaction chemistry of sodium metabisulfite.

METHODS

The established protein reaction chemistry associated with aqueous sulfite chemistry was explored in the context of the protein modification stage in allergic contact dermatitis.

RESULTS

A probable mechanism for the in cutaneo modification of proteins by sodium metabisulfite involves the sulfite di-anion, acting as a nucleophile towards electrophilic centres in proteins, which is a rare mechanism, as most known skin-sensitizing chemicals behave as electrophiles.

CONCLUSIONS

Sodium metabisulfite is an unusual but not infrequent contact allergen whose chemistry suggests a previously unrecognized protein modification mechanism involving nucleophilic attack by sulfite di-anions on target electrophilic centres in skin proteins. The chemical properties required for sensitization by nucleophilic attack on skin proteins are quite restrictive, so the domain of nucleophilic sensitizers is expected to be small. Thiourea derivatives are among the sensitizers likely to act by this mechanism.