DT-diaphorase protects against menadione-induced oxidative stress

To study the role of DT-diaphorase in menadione-mediated cytotoxicity, mena dione-resistant cells were selected from P19 cells by stepwise increasing c oncentrations of menadione from 10 to 60, 120 or 300 mu M without mutagenic pretreatment. Three isolated clones, K60, K120 and K300, were maintained i n media containing 60, 120 or 300 mu M menadione, respectively. The resista nce of these cells to menadione, in order, was: K300 > K120 > K60 > P19 cel ls. K300 cells were the most resistant. Acquisition of resistance was assoc iated with elevation in DT-diaphorase activity. Pretreatment of the resista nt cells with 30 mu M dicumarol at 37 degrees C for 30 min sensitized the r esistant cells to menadione. When the resistant cells were maintained in th e absence of menadione for 28 days, the resistance of K60 and K120 cells wa s lost. The lower degree of resistance was accompanied by a decrease in DT- diaphorase activity in the revertant cells. However, the resistance and the activity of DT-diaphorase in K300 cells were quite stable in the same peri od. These results support strongly that DT-diaphorase protects against mena dione-induced oxidative stress. (C) 1999 Published by Elsevier Science Irel and Ltd. All rights reserved.