allopurinol and Leukemia--Monocytic--Acute

When differentiated into mature macrophages by the combination of all-trans retinoic acid and 1,25-dihydroxyvitamin D3, the human promonocytic cell lines U937 and THP-1 expressed inducible nitric oxide synthase (iNOS) transcripts. During their differentiation, the cells acquired the capacity to produce not only superoxide anion (O2.-) but also nitric oxide (.NO) in response to IgG (or IgE)-opsonized zymosan. The inhibitors of the iNOS pathway, aminoguanidine and NG-monomethyl-L-arginine (L-NMMA), suppressed the production of .NO and enhanced the steady-state concentration of O2.- determined. Conversely, superoxide dismutase (SOD) scavenged the O2.- released and increased the .NO-derived nitrite concentration detected. These data suggested a possible interaction between O2.- and .NO. In differentiated U937 (or THP-1) cells, IgG or IgE-opsonized zymosan induced a strong time-dependent luminol-dependent chemiluminescence (LDCL), which was abrogated by SOD and partially inhibited by aminoguanidine or L-NMMA. Since the iNOS inhibitors did not directly scavenge O2.-, LDCL determination in the presence or absence of SOD and/or iNOS inhibitors demonstrated a concomitant production of O2.- and .NO. These radicals induced the formation of a .NO-derived product(s), probably peroxynitrite (ONOO-), which was required to elicit maximal LDCL. Finally, LDCL measurement provided a convenient tool to characterize iNOS triggering and demonstrated an interaction between NADPH oxidase and iNOS products in human macrophagic cells phagocytizing opsonized-zymosan. These findings show that in activated macrophages, iNOS activity can be involved in LDCL and support the debated hypothesis of iNOS participation to the microbicidal activity of human macrophages.

Topics: Calcitriol; Cell Differentiation; Cell-Free System; Free Radical Scavengers; Guanidines; Humans; Immunoglobulin E; Immunoglobulin G; Leukemia, Monocytic, Acute; Luminescent Measurements; Luminol; Lymphoma, Large B-Cell, Diffuse; Macrophage Activation; Macrophages; Neoplastic Stem Cells; Nitrates; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; omega-N-Methylarginine; Opsonin Proteins; Phagocytosis; Superoxide Dismutase; Superoxides; Tretinoin; Tumor Cells, Cultured; Xanthine; Xanthine Oxidase; Zymosan

Nitric oxide (NO), a nitrogen-free radical, plays an important role in mediating inflammatory reaction and cytotoxicity of tissue. To determine whether NO was involved in silica-induced pulmonary tissue damage, we studied the effects of silica on nitric oxide (NO) production and inducible NO synthase (iNOS) mRNA expression by THP-1 cells, a monocyte-like cell line with properties of the pulmonary alveolar macrophage. Experimental results showed that silica elicited a marked stimulation of nitric oxide production in a time-dependent manner by THP-1 cells in vitro following the priming of these cells with the phorbol ester PMA. Both nitric oxide synthase inhibitor N-monomethyl-L-arginine (NMMA) and xanthine oxidase inhibitor allopurinol can partially suppress silica-induced NO production in PMA-primed THP-1 cells. Northern blot analysis indicated that, after 2 h of silica exposure, PMA-primed THP-1 cells began to express iNOS mRNA, which reached peak expression at 8 h. Endotoxin treatment of these cells produced a similar effect. These results indicated that silica is a potent inducer of NO production in macrophages and its ability to induce tissue damage may partially be attributed to its ability to initiate excessive production of nitric oxide from macrophages.

Topics: Allopurinol; Antimetabolites; Arginine; Cycloheximide; Dactinomycin; Enzyme Induction; Enzyme Inhibitors; Gene Expression Regulation, Leukemic; Humans; Leukemia, Monocytic, Acute; Lipopolysaccharides; Monocytes; Neoplasm Proteins; Nitric Oxide; Nitric Oxide Synthase; omega-N-Methylarginine; Protein Synthesis Inhibitors; RNA, Messenger; Silicon Dioxide; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured; Xanthine Oxidase