Molecular basis for hepatic detoxifying enzyme induction by 2-(allylthio)pyrazine in rats in comparison with oltipraz: Effects on prooxidant production and DNA degradation

The expression of hepatic microsomal epoxide hydrolase (mEH) and glutathion e S-transferases (GSTs) by 2-(allylthio)pyrazine (2-AP), an experimental ch emopreventive agent, was investigated in rats. Northern blot analysis revea led that 2-AP caused increases in mEH, rGSTA2/3/5, and rGSTM1/2 mRNA levels , mEH and rGSTA2 proteins were also induced, Molecular basis of the enzyme induction by 2-AP was studied in comparison with oltipraz (Olt). Rats expos ed to buthionine sulfoximine, a GSH-depleting agent, before treatment with either 2-AP or Olt exhibited greater increases in the mRNA levels than the individual treatment. Conversely, increases of the mRNAs were prevented by cysteine treatment, indicating that metabolic intermediates or reactive oxy gens produced from the agents could be reduced by cysteine, Gel shift analy sis revealed that nuclear factor-KS, which is associated with the cellular redox state, was not activated by the agents. Effects of these agents on th e breakage of phi x-174 DNA were compared in vitro. 2-AP effectively reduce d the conversion of supercoiled DNA to the open circular form induced by be nzenetriol and prevented benzenetriol- and iron-catalyzed degradation of DN A, whereas Olt failed to prevent strand breakage of DNA. These results prov ided evidence that: 1) 2-AP was effective in elevating the hepatic mEH and GST gene expression in rats, which might be mediated with the production of reactive oxygen species; 2) nuclear factor-KB activation was not involved in the induction of the detoxifying enzymes by either 2-AP or Olt in spite of their production of reactive oxygens in vivo; and 3) the antioxidant eff ect of 2-AP in vitro differed from that of Olt.