Evidence for DNA and Protein Binding by Styrene and Styrene Oxide

Styrene is metabolized to styrene oxide, a direct-acting mutagen and carcinogen. Styrene oxide reacts with DNA mainly at the N-7 position in guanine, but also at other sites and with other bases. Substitution occurs at both the alpha- and beta-positions of the styrene molecule. Experiments with radiolabeled styrene and styrene oxide demonstrate that both have a low level of DNA binding activity in experimental animals. 32P-Postlabeling studies have demonstrated the potential of the technique to detect styrene-DNA adducts. Styrene oxide alkylates several nucleophilic sites in proteins, particularly cysteine sulfydryl, histidine imidazole, lysine amino, aspartic, and glutamic carboxylic groups, and the N-terminal position. In experimental animals, styrene oxide treatment results in cysteine adducts in hemoglobin and albumin, valine adducts in hemoglobin, and carboxylic acid adducts in hemoglobin. The extent of alkylation is low compared with that produced by ethylene oxide. The available evidence indicates, therefore, that styrene and styrene oxide have low DNA and protein binding activities in vivo. There is preliminary evidence for the presence of DNA adducts and for adducts in hemoglobin and albumin in blood cells of styrene-exposed workers. Nevertheless, the applicability and sensitivity of DNA and protein adduct detection methods for monitoring human exposure to styrene remain to be determined.