Inhibitory effects of negatively charged liposomes on nitric oxide production from macrophages stimulated by LPS.

The effects of liposomes on nitric oxide (NO) productions induced by lipopolysaccharide were investigated using thioglycollate-induced mouse peritoneal macrophages. Negatively charged liposomes composed of phosphatidic acid (PA-liposomes) and phosphatidylserine (PS-liposomes) showed inhibitory effect on NO production in a dose dependent manner, but not in liposomes composed of phosphatidylcholine (PC-liposomes). Pretreatment of macrophages with liposomes was required in order to observe the inhibitory effect on NO production. NO production induced by IFN-gamma was also inhibited by negatively charged liposomes. To clarify the mechanism of inhibitory effect of liposomes, immune blotting was performed using anti mouse inducible nitric oxide synthase (iNOS) antibody. An immunoreactive band at 130 kDa was observed in the extract of control and PC-liposome- treated macrophages, whereas a faint or no band was observed in PS- and PA-liposome-treated ones. These finding revealed that the inhibition of NO production by negatively charged liposomes could be a result in the inhibition of iNOS induction, but not enzyme activity.