Formation of RNA adducts resulting from metabolic activation of spice ingredient safrole mediated by P450 enzymes and sulfotransferases.

Safrole (SFL) is an IARC class 2B carcinogen. To better understand the mechanism involved in SFL toxicity, we explored the potential interactions between SFL metabolites and RNA. Three guanosine adducts (G1-G3), two adenosine adducts (A1-A2), and two cytosine adducts (C1-C2) were detected by LC-MS/MS in mouse liver S9 incubations, cultured mouse primary hepatocytes, and liver tissues of mice after exposure to SFL. These adducts were chemically synthesized, and one of the guanosine adducts was structurally characterized by H-NMR. Studies in vitro and in vivo showed that SFL was oxidized by cytochrome P450 enzymes to the corresponding 1'-hydroxyl metabolite which was further metabolized by sulfotransferases to form allylic sulfate esters. The formed reactive intermediate(s) subsequently reacted with bases of RNA, leading to RNA adduction, which could play a partial role in the toxicities of SFL through the alteration of RNA biochemical properties and interruption of RNA functions.