Inhibition of rifampin of elastase and lysozyme secretion in mouse peritoneal macrophages

Loading with oxidised low density lipoprotein alters endocytic and secretory activities of murine macrophages

Lipid-loaded macrophages were produced in vitro by incubation with acetylated or copper-oxidized LDL. In order to establish whether cellular membrane traffic is generally perturbed by such loading, we assessed endocytosis of fluid; cell surface binding, internalisation and degradation of a soluble ligand and of a particulate preparation; and exocytosis of lysosmal enzymes. Fluid-phase pinocytosis of sucrose was unaffected by either form of loading. Binding, uptake and degradation of soluble (mannosylated-BSA) and particulate (zymosan) ligands by these lipid-loaded and by non-loaded cells were compared. Loading with oxidized LDL decreased the processing of both ligands, while loading with acetylated LDL had little effect. Loading with oxidized LDL (Ox-LDL) also decreased zymosan binding at 4 degrees C; and the internalisation and degradation of ligands in Ox-LDL loaded and non-loaded cells reflected the extent of surface binding. Changes in binding and uptake of mannosylated-BSA and zymosan were not due to changes in viability or cell number. Zymosan stimulated release of lysosomal beta-N-acetyl-D-glucosaminidase from the cells. Loading with Ox- but not Ac-LDL decreased beta-N-acetyl-D-glucosaminidase secretion. After incubation with zymosan, intracellular levels of the enzyme were increased in the Ox-LDL loaded cells. Zymosan uptake and beta-N-acetyl-D-glucosaminidase secretion were correlated, but enzyme activity per culture rose more in the absence than in the presence of zymosan. We conclude that membrane traffic is perturbed in model foam cells, particularly those loaded with Ox-LDL.

Inhibition of some spontaneous secretory processes in macrophages and fibroblasts by ammonium chloride

Ammonium chloride inhibits the spontaneous secretion of lysozyme by mouse macrophages and the murine macrophage-like cell line P388D1 and the spontaneous secretion of lysosomal enzymes by P388D1 cells, normal human fibroblasts and the hypersecretory mucolipidosis II (I-cell) fibroblasts. NH4Cl can also inhibit protein synthesis, but this is shown to occur mainly at higher concentrations, or after longer periods of exposure, than are needed for the inhibition of the spontaneous secretory processes. It is confirmed that this amine can also interfere with the continuous endocytosis of fluid in the murine cell types. The nature of the inhibitions is discussed.