Vol. 27, Issue 6, 667-673, June 1999

Molecular Basis for Hepatic Detoxifying Enzyme Induction by 2-(Allylthio)pyrazine in Rats in Comparison with Oltipraz: Effects on Prooxidant Production and DNA Degradation

Sang Geon Kim, Min Kyung Cho, Sung Hee Choi, Hye Jung Kim, Mi Kyong Kwak, and Nak Doo Kim

College of Pharmacy, Seoul National University (S.G.K., M.K.K., N.D.K.), Seoul, Korea; and College of Pharmacy, Duksung Women's University (S.G.K., M.K.C., S.H.C., H.J.K.)

The expression of hepatic microsomal epoxide hydrolase (mEH) and glutathione S-transferases (GSTs) by 2-(allylthio)pyrazine (2-AP), an experimental chemopreventive agent, was investigated in rats. Northern blot analysis revealed 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 exposed 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 oxygens produced from the agents could be reduced by cysteine. Gel shift analysis revealed that nuclear factor-B, which is associated with the altered cellular redox state, was not activated by the agents. Effects of these agents on the breakage of x-174 DNA were compared in vitro. 2-AP effectively reduced the conversion of supercoiled DNA to the open circular form induced by benzenetriol and prevented benzenetriol- and iron-catalyzed degradation of DNA, whereas Olt failed to prevent strand breakage of DNA. These results provided 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-B 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 effect of 2-AP in vitro differed from that of Olt.