Protein kinase C inhibitors suppress LPS-induced TNF production in alveolar macrophages and in whole blood: The role of encapsulation into liposomes

Abstract

Tumor necrosis factor (TNF) is a pivotal mediator of endotoxin shock, but the regulation of lipopolysaccharide (LPS)-induced TNF production in different populations of mononuclear cells has not been fully clarified. Protein kinase C (PKC) is thought to play a central role in signal transduction in response to inflammatory stimuli. We studied the effect of two PKC inhibitors, staurosporine (STP) and sphingosine (SPG), on TNF production in rat alveolar macrophages (AM) and in whole blood (BM) incubated with 0.25–25 000 ng/ml of LPS. We also assessed the role of STP encapsulation into pH-sensitive and pH-insensitive liposomes composed of cholesterolhemisuccinat/dioleoylphosphatidyl ethanolamine and cholesterolhemisuccinat/distearylphosphatidyl choline, respectively. LPS induced a dose-dependent TNF response that was 2.5–4.5-times higher in AM than in BM with the same amount of monocytes. SPG and STP significantly reduced TNF in both cultures by 40–96%. Encapsulation of STP into pH-sensitive, but not pH-insensitive liposomes, significantly increased the effectiveness of TNF suppression. We conclude that the LPS-induced TNF production by AM and BM is strongly dependent on PKC activation. However, AM were less sensitive to PKC inhibition than BM.