Formation of hepatic DNA adducts by methyleugenol in mouse models: Drastic decrease by Sult1a1 knockout and strong increase by transgenic human SULT1A1/2

Methyleugenol—a natural constituent of herbs and spices—is hepatocarcinogenic in rodent models. It can form DNA adducts after side-chain hydroxylation and sulfation. We previously demonstrated that human sulfotransferases (SULTs) 1A1 and 1A2 as well as mouse Sult1a1, expressed in Salmonella target strains, are able to activate 1′-hydroxymethyleugenol (1′-OH-ME) and 3′-hydroxymethylisoeugenol (3′-OH-MIE) to mutagens. Now we investigated the role of these enzymes in the formation of hepatic DNA adducts by methyleugenol in the mouse in vivo. We used FVB/N mice [wild-type (wt)] and genetically modified strains in this background: Sult1a1 knockout (ko), transgenic for human SULT1A1/2 (tg) and the combination of both modifications (ko-tg). Methyleugenol (50mg/kg body mass) formed 23, 735, 3770 and 4500 N 2-(trans-methylisoeugenol-3′-yl)-2′-deoxyguanosine adducts per 108 2′-deoxyribonucleosides (dN) in ko, wt, ko-tg and tg mice, respectively. The corresponding values for an equimolar dose of 1′-OH-ME were 12, 1490, 12 400 and 13 300 per 108 dN. Similar relative levels were observed for the minor adduct, N 6-(trans-methylisoeugenol-3′-yl)-2′-deoxyadenosine. Thus, the adduct formation by both compounds was nearly completely dependent on the presence of SULT1A enzymes, with human SULT1A1/2 producing stronger effects than mouse Sult1a1. Moreover, a dose of 0.05mg/kg methyleugenol (one-fourth of the estimated average daily exposure of humans) was sufficient to form detectable adducts in humanized (ko-tg) mice. Although 3′-OH-MIE was equally mutagenic to 1′-OH-ME in Salmonella strains expressing human SULT1A1 or 1A2, it only formed 0.14% of hepatic adducts in ko-tg mice compared with an equimolar dose of 1′-OH-ME, suggesting an important role of detoxifying pathways for this isomer in vivo.