Distinct modes of cell death induced by different reactive oxygen species: amino acyl chloramines mediate hypochlorous acid-induced apoptosis.

Oxidants derived from inflammatory phagocytes compose a key element of the host immune defense system and can kill mammalian cells by one of several different mechanisms. In this report, we compare mechanisms of cell death induced in human B lymphoma cells by the inflammatory oxidants superoxide, H(2)O(2), and HOCl. The results indicate that the mode of cell death induced depends on the nature of the oxidant involved and the medium in which the cells are treated. When human Burkitt's lymphoma cells are exposed to superoxide anion, generated as a flux from xanthine and xanthine oxidase, the cells die by a non-apoptotic mechanism (pyknosis/necrosis) identical to that seen when cells are treated with a bolus of reagent H(2)O(2). Addition of superoxide dismutase has no effect, whereas catalase is completely protective, indicating that exogenously generated superoxide kills cells entirely through its dismutation into H(2)O(2). In contrast, cells treated in culture media with reagent HOCl die largely by apoptosis. HOCl-induced apoptosis is mediated by aminoacyl chloramines generated in the culture media and can be mimicked by treatment of cells with taurine chloramine or with long lived chloramines generated from modified Lys or Arg. The results suggest that in a physiological milieu in which O(2)(-) and H(2)O(2) are the main oxidants being formed, the principal form of cell death may be necrotic, and under inflammatory conditions in which HOCl is generated, apoptotic cell death may predominate.