Inducible macrophage apoptosis following sepsis is mediated by cysteine protease activation and nitric oxide release

Recent studies indicate that polymicrobial sepsis can markedly increase inducible macrophage Ao (nonnecrotic cellular suicide) and that this is associated with decreased M phi function. In vitro studies suggest that M phi Ao can be induced by IL-1 beta via interleukin-1 beta-converting enzyme (ICE, a cysteine protease), prostanoids, or reactive oxygen/nitrogen. However, the mechanism(s) underlying this process in septic M phi remains unknown. To determine this, male C3H/HeN mice were subjected to sepsis (cecal ligation and puncture, CLP) or sham-operation. Twenty-four hours thereafter, M phi were isolated from the peritoneum (PM phi) and liver (LM phi). Macrophage monolayers were treated with LPS (10 micrograms/ml) alone (Cont) or in the presence of iodoacetamide (Iodo, 5 mM), N-methylmalamide (meth, 5 mM), ibuprophen (Ibu, 40 micrograms/ml), N-methyl-L-arginine (LNMA, 0.4 mM), or superoxide dismutase (SOD, 60,000 U/ml) for 24 hr. The extent of Ao was determined using an enzyme-linked immunosorbent cell-death assay, which detects the presence of cytoplasmic oligonucleosomes measured as optical density. The results indicate that both PM phi and LM phi from septic animals exhibit increased Ao over cells from sham animals. However, only the nonspecific cysteine protease inhibitors (Iodo and meth) and the NO inhibitor LNMA blocked septic mouse M phi Ao. Furthermore, only PM phi from CLP mice treated with Iodo, but not LNMA or IBU, showed an improved capacity to release IL-6. We conclude that increased M phi Ao seen during sepsis appears to be mediated by both ICE-like cysteine protease activation and NO release but the level/mechanism of action of these inhibitors differs.