Rapid killing of human neutrophils by the potent activator phorbol 12-myristate 13-acetate (PMA) accompanied by changes different from typical apoptosis or necrosis

To elucidate the relationship between activation of neutrophils and their subsequent death, the effect of phorbol 12-myristate 13-acetate (PMA), a potent activator of neutrophils, was examined. PMA-treated neutrophils showed morphological changes quite different from those of typical apoptosis or necrosis. After fusion of the lobate nucleus, nuclear contents of chromatin uniformly decreased in compactness and soon after the nuclear envelope was broken. Even at this stage, cytoplasmic organelles did not undergo degeneration. Membrane permeability began increasing at 3 h of incubation with PMA, subsequent to nuclear change. Conventional agarose gel electrophoresis and pulsed field gel electrophoresis of DNA from PMA-treated neutrophils revealed no DNA degradation products smaller than 300 kbp. PKC inhibitors, staurosporine and H-7, prevented cytotoxicity by PMA. Furthermore, antioxidants, thiourea, dimethylthiourea, pyrrolidinethiocarbamate, and N-acetyl-L-cysteine, but not superoxide dismutase, were also active in preventing PMA cytotoxicity, suggesting that cell suicide resulting from PMA treatment is due to oxygen radicals, especially the hydroxyl radical. A certain population of neutrophils phagocytosing opsonized zymosan also showed changes similar to those observed in PMA-treated cells.