Protease inhibitors protect macrophages from lipopolysaccharide-induced cytotoxicity: possible role for NF-kappaB.

Recent studies suggest lipopolysaccharide (LPS) mediated cell death as underlying mechanism of hyporesponsiveness and dysfunction of macrophages in the late phase of septic shock. In the present study LPS (0.001 - 30 microg/ml) caused a concentration-dependent toxicity in the macrophage cell line (J774.1A) within 24 h. The toxicity induced by LPS (1 microg/ml) was completely inhibited by the serine protease inhibitors, N-alpha-tosyl-L-phenylalanine chloromethyl ketone (TPCK) and N-alpha-tosyl-L-lysine chloromethyl ketone (TLCK) as measured by the mitochondrial-dependent oxidation of 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromid (MTT) to formazan. These inhibitors antagonize the activation of nuclear transcription factor-kappaB (NF-kappaB) indirectly by inhibiting I kappaB alpha-protease. SN50, a direct inhibitor of NF-kappaB translocation into the nucleus also protected macrophages from LPS-mediated toxicity. We conclude from these data that the early phase signal transduction pathway leading to LPS-mediated cytotoxicity in macrophages involves the activation of NF-kappaB. Thus, I kappaB alpha-protease inhibitors might serve as therapeutical agents to maintain macrophage viability during sepsis and to prevent sepsis-induced immune dysfunction.