Inhibition of some polymorphonuclear leukocyte functions by ethacrynic acid

The compromise of macrophage functions by hyperoxia is attenuated by ethacrynic acid via inhibition of NF-κB-mediated release of high-mobility group box-1

The prolonged exposure to hyperoxia can compromise macrophage functions and contribute to the development of ventilator-associated pneumonia. High levels of extracellular high-mobility group box-1 (HMGB1) in the airways of mice exposed to hyperoxia can directly cause macrophage dysfunction. Hence, inhibition of the release of nuclear HMGB1 into the extracellular milieu may help to maintain macrophage functions under hyperoxic conditions. The present study investigates whether ethacrynic acid (EA) affects hyperoxia-induced HMGB1 release from macrophages and improves their functions. Macrophage-like RAW 264.7 cells and bone marrow-derived macrophages were exposed to different concentrations of EA for 24 hours in the presence of 95% O2. EA significantly decreased the accumulation of extracellular HMGB1 in cultured media. Importantly, the phagocytic activity and migration capability of macrophages were significantly enhanced in EA-treated cells. Interestingly, hyperoxia-induced NF-κB activation was also inhibited in these cells. To determine whether NF-κB plays a role in hyperoxia-induced HMGB1 release, BAY 11-7082, an inhibitor of NF-κB activation, was used. Similar to EA, BAY 11-7082 significantly inhibited the accumulation of extracellular HMGB1 and improved hyperoxia-compromised macrophage migration and phagocytic activity. Furthermore, 24-hour hyperoxic exposure of macrophages caused hyperacetylation of HMGB1 and its subsequent cytoplasmic translocation and release, which were inhibited by EA and BAY 11-7082. Together, these results suggest that EA enhances hyperoxia-compromised macrophage functions by inhibiting HMGB1 hyperacetylation and its release from macrophages, possibly through attenuation of the NF-κB activation. Therefore, the activation of NF-κB could be one of the underlying mechanisms that mediate hyperoxia-compromised macrophage functions.

Felodipine-induced inhibition of polymorphonuclear leukocyte functions

Felodipine inhibits fMet-Leu-Phe or ionophore A23187-induced exocytosis in rabbit peritoneal polymorphonuclear leukocytes (PMNs), in the concentration range 1-50 microM. Activation of the metabolic burst, and migration of PMNs towards fMet-Leu-Phe are equally inhibited by felodipine in the same concentration range. The effect is not due to blocking of calcium channels in the plasma membrane, because the degree of inhibition remains the same when Ca2+ is omitted from the medium. Felodipine interferes with ionophore A23187-induced association of 45Ca with the PMN but this interference occurs at lower concentrations than the inhibition of exocytosis. Hypotonic hemolysis of erythrocytes is inhibited by felodipine; maximal protection against hemolysis occurs at a concentration of 50 microM felodipine. It is suggested that at least a part of the inhibiting effect on PMN functions might be due to an anesthetic-like membrane effect of felodipine.

Protamine sulfate-induced enzyme secretion from rabbit neutrophils

Protamine sulfate induces enzyme secretion from rabbit neutrophils. Enzyme secretion is mainly due to exocytosis but, depending on the experimental conditions, a small amount of cytolysis may occur. As compared with stimulation of neutrophil functions by other activators, protamine sulfate-induced enzyme release by exocytosis is a relatively slow process and is not accompanied by a marked activation of the metabolic burst. For optimal exocytosis, extracellular Ca2+ is required, but there is still some enzyme release in its absence, and other metal ions (Sr2+, Ba2+, Mg2+) can partly mimic the effect of Ca2+. Positive charges on protamine are of primary importance because the polyanion heparin completely inhibits protamine sulfate-induced enzyme release. Protamine linked to agarose beads is able to induce enzyme release; thus the induction of exocytosis is due to an interaction of the positive charges on protamine with the plasma membrane. Sialic acid residues on the membrane, however, seem not to play an important role in this process.

Toxicity of organotin compounds for polymorphonuclear leukocytes: the effect on phagocytosis and exocytosis

Phagocytosis and concomitant release of enzymes by rabbit polymorphonuclear leukocytes (PMNs) are inhibited by micromolar concentrations of triphenyltin and tributyltin; inhibition by triethyltin occurs at higher concentrations. Chemotactic peptide-induced exocytosis is inhibited at the same concentrations as phagocytosis. Tributyltin causes cell lysis at slightly higher concentrations as required for inhibition of phagocytosis and exocytosis. The organotin compounds have little effect on ATP level in PMNs, which makes an effect on metabolic energy providing processes unlikely. The increase of Ca2+-permeability of the plasma membrane, induced by chemotactic peptide, is inhibited by the organotin compounds. Inhibition of exocytosis by triphenyltin can be counteracted by a number of sulfhydryl compounds. The results suggest that the organotin compounds interfere with PMN function in an early phase of cell activation, where all functions have a common pathway, and where vulnerable sulfhydryl groups play a pivotal role.

The mouse ear edema: a quantitatively evaluable assay for tumor promoting compounds and for inhibitors of tumor promotion

The induction of edema in the mouse ear has been established as a reliable in vivo assay for tumor promoting compounds and for inhibitors of tumor promotion. Apparently all skin tumor promoting compounds induce an edema, and all inhibitors of a tumor promoter-induced edema are most likely inhibitors of skin tumor promotion. No exception to this rule has been found as yet. Besides the application of this assay in the screening of compounds, the assay allows comparison of various compounds (e.g. complete and incomplete tumor promoters) with respect to their kinetics and dosage response in the induction of edema.