Selective inhibition of leukotriene C4 synthesis and natural killer activity by ethacrynic acid

We have investigated the role of arachidonic acid (AA) metabolism in natural killer (NK) cell activity. Human nonadherent (NA) peripheral blood lymphocytes were used as effector cells against 51Cr-labeled K562 target cells. Synthesis of leukotriene C4 (LTC4) is dependent on glutathione S-transferase (GST). We have chosen to study three putative GST inhibitors, namely, ethacrynic acid (ET), caffeic acid (CA), and ferulic acid (FA), with regard to NK activity and with regard to their effect on AA metabolism. The GST inhibitors inhibited NK lysis when added directly to the NK assay. The GST inhibitors inhibited LTC4 synthesis as induced by calcium ionophore A23187 in a dose-dependent manner similar to their inhibition of NK activity. However, only ET was selective, for it had little effect on LTB4, 5-hydroxyeicosatetraenoic acid, and prostaglandin E2 synthesis. LTC4 synthesis was associated with the NK-enriched fractions obtained from discontinuous Percoll gradients. NK-specific anti-Leu-11b antibody and C treatment could abrogate NK activity and LTC4 synthesis. ET was also inhibitory when NA cells were cultured at 37 degrees C for 18 hr. In this case, LTC4 could reverse the inhibitory effect of ET. Our data suggest that LTC4 plays an important role in NK activity.