MODULATION OF NONINDUCED AND PHORBOL ESTER-INDUCED GENERATION OF SUPEROXIDE ANION BY FREE LIPOSOMES AND LIPOSOMES CONTAINING DEXAMETHASONE

We tested the relative efficacy of free dexamethasone, dexamethasone c ontaining liposomes and free liposomes in preventing superoxide anion, O-2(-) generation by neutrophils. O-2(-) production by 5 x 10(5) neut rophils, whether primed or not with lipopolysaccharide, was stimulated by phorbol 12-myristate 13-acetate (PMA) to 13.4+/-1.3 nmoles after 1 5 minutes compared to 1.2+/-0.3 nmoles with nonstimulated cells. Free liposomes but not dexamethasone (dexa) decreased non-stimulated as wel l as PMA-induced O-2(-) generation. Dexa-containing phosphatidylcholin e from egg yolk: phosphatidylserine from bovine brain (PC:PS 7:3) lipo somes, unlike free dexa, diminished PMA-stimulated O-2(-) production i n a dose-dependent manner with maximal effect at 37.5 mu g/ml phosphol ipid (6.6+/-1.6 nmoles). The kinetics of cytochrome-c reduction reveal ed that decreased O-2(-) production resulted from an extended lag-time of release to almost 8 minutes with PMA induction and consequently le d to the conclusion that liposomes modified the activity of NADPH oxid ase as well as that of protein kinase C. Liposomes prepared with PC an d PS of natural origin had a greater inhibitory effect on O-2(-) gener ation by neutrophils than dipalmitoylphosphatidylcholine (DPPC) and ph osphatidylethanolamine from egg yolk (PE):PC (3:1) liposomes. When 100 mu M of Ca2+ was added to the medium, the inhibitory action of liposo mes prepared with egg yolk PC and DPPC was increased by 30 and 60% res pectively, while that of PS and PE:PC was prevented. We also verified that liposomes by themselves, even if phagocytized, did not induce O-2 (-) generation or its concentration was too low to be detected by this technique. From the clinical point of view, some formulations delayed non-induced and PMA-induced O, generation, thus adding to the anti-in flammatory effect of the glucocorticoid they transported.