Inhibitory Effect of Acetylshikonin on the Activation of NADPH Oxidase in Polymorphonuclear Leukocytes in Both Whole Cell and Cell-Free Systems

Abstract

The effects of acetylshikonin (AS) on the activation of NADPH oxidase (EC 1.6.99.6) in guinea pig polymorphonuclear leukocytes (PMNs) in both whole cell and cell-free activation systems were investigated. When PMNs were treated with AS before exposure to phorbol myristate acetate (PMA), superoxide (O^-₂) generation in these cells was significantly reduced, but after exposure of PMNs to PMA, inhibition of O^-₂ generation by AS did not occur. Thiol compounds completely abolished the inhibitory effect of AS on the O^-₂ generating activity of PMNs. In the cell-free system, AS inhibited the activation of NADPH oxidase induced by myristate in a combination of cytosol and membrane fractions obtained from intact PMNs, but did not inhibit the activity of NADPH oxidase already induced. These results suggest that AS inhibits the generation of NADPH oxidase complex in the activation of respiratory burst of PMNs, but does not directly inhibit the activity of NADPH oxidase already generated.