Inhibition of phospholipase A2 abrogates intracellular processing of NADPH-oxidase derived reactive oxygen species in human neutrophils

Abstract

Upon activation of human neutrophils, superoxide can be produced at two cellular sites; either in the plasma membrane, giving extracellular release of oxidants, or in intracellular organelles, resulting in oxidants being retained in the cell. The involvement of phospholipase A2 (PLA2) in phorbol myristate acetate (PMA)-induced activation of the two pools of NADPH-oxidase was investigated using a variety of PLA2 inhibitors and the oxidase activity was measured by luminol/isoluminol-amplified chemiluminescence (CL). Two of the seven inhibitors were without effect, two inhibitors inhibited both intra- and extracellular ROS production equally, and three inhibitors inhibited intracellular but not extracellular CL. Using another technique to measure ROS, PHPA oxidation, we found that intracellular ROS production was unaltered with the three last inhibitors, indicating that PLA2 is not involved in the NADPH-oxidase activity per se, but in the intracellular processing of the radicals necessary for the CL reaction to take place. The PLA2 inhibitors did not abolish the activity of myeloperoxidase (MPO), an enzyme necessary for intracellular CL to occur. Instead, we suggest that these PLA2 inhibitors block heterotypic granule fusion and prohibit the colocalization of ROS and MPO needed for intracellular CL activity.