Bacterial Lipopeptides Induce Nitric Oxide Synthase and Promote Apoptosis through Nitric Oxide-independent Pathways in Rat Macrophages (∗)

Stimulation of resident peritoneal macrophages with S-[2,3-bis(pamitoyloxy)-(2R,2S)-propyl]-N-palmytoyl-(R)-CysSerLys4 or S-[2,3-bis(pamitoyloxy)-(2R,2S)-propyl]-N-palmytoyl-(R)-CysAlaLys4, two synthetic bacterial lipopeptides, promoted the expression of the inducible form of nitric oxide synthase, exhibiting a temporal pattern of nitric oxide release that was delayed with respect to the induction elicited by bacterial lipopolysaccharide. Treatment of macrophages with genistein blocked the nitric oxide synthesis triggered by the lipopeptides or lipopolysaccharide. Simultaneous incubation with lipopolysaccharide and lipopeptide resulted in an antagonistic effect on nitric oxide synthase mRNA levels and on nitrite plus nitrate release to the medium. Triggering with bacterial lipopeptides induced macrophage programmed cell death. In macrophages activated with lipopeptide, apoptosis was observed even in the absence of nitric oxide synthesis, therefore indicating the existence of alternative pathways in the control of programmed cell death in these cells.