Effect of sodium azide on hydrogen peroxide production by zymosan-activated human neutrophils

Inhibitory and enhancing effects of piroxicam on whole blood chemiluminescence

The effects of piroxicam on the production of reactive oxygen species by stimulated phagocytes was studied in whole blood by a chemiluminescence (CL) technique in relation to maximum activity, localization and kinetics of radical generation. We found that piroxicam dose-dependently inhibited total (intra- and extracellular) zymosan-stimulated luminol CL (LCL) at a high stimulant concentration (p = 0.0001). Piroxicam additionally decreased cytochalasin B-reduced LCL, which shows that the effect of the drug should be sought in the extracellular component of the response. Piroxicam inhibited the first phase of extracellular LCL in a dose-dependent manner (p = 0.0001) and revealed itself as an enhancing agent of CL in later time intervals after the start of respiratory burst, in a model system containing horseradish peroxidase (HRP) and sodium azide. It enhanced LCL of a cell-free system, i.e. influenced the CL due to HRP-catalysed decomposition of hydrogen peroxide. It also dose-dependently inhibited the early extracellular superoxide production, evaluated by lucigenin CL (p = 0.022). Piroxicam inhibited the total fMLP-stimulated LCL by 70% approximately and, only by about 30%, the first phase of fMLP-stimulated extracellular LCL, which presupposes an effect on myeloperoxidase-catalysed formation of hypochloric acid. Piroxicam slightly increased the intracellular LCL by phagocytes (p = 0.02), an effect that is probably connected with its ability to induce the release of secondary messengers in signal transduction. In conclusion, the anti-inflammatory effect of piroxicam is probably related to the inhibition of the extracellular generation of superoxide and hypochloric acid in the early stages of phagocyte activation.

Interaction between neutrophil-derived elastase and reactive oxygen species in cartilage degradation

The role of proteases and reactive oxygen species (ROS) in polymorphonuclear neutrophil (PMN) induced cartilage degradation in vitro were studied. ONO-5046, a novel synthetic elastase inhibitor, significantly and dose dependently protected cartilage from degradation induced by PMNs stimulated with phorbol myristate acetate (PMA), opsonized zymosan, N-formyl-methionyl-leucyl-phenylalanine plus cytochalasin-B, or A-23187. The degradation by PMA-stimulated PMNs was unaffected by protease inhibitors which lack anti-elastase activity. However, the hydrogen peroxide (H2O2) reducing agent catalase afforded significant protection. Measurement of elastase activity following PMN activation by PMA showed that antioxidants which reduce H2O2 and/or hypochlorous acid decreased elastase activity. Thus, it is suggested that an indirect interaction between ROS and elastase activity may exist in PMN induced cartilage degradation. Furthermore, the possible implication of an endogenous elastase inhibitor(s) is discussed.

A peroxidase-independent method for the quantitation of extracellular hydrogen peroxide generated by activated phagocytes in vitro

A peroxidase-independent method for the determination of phagocyte-derived hydrogen peroxide in vitro is described. The method is based on the catalase-inhibitable oxidation of added cysteine. Human blood neutrophils (1 x 10(6)/ml) were coincubated with the myeloperoxidase (MPO) inhibitor, sodium azide (10 micrograms/ml), for 30 min at 37 degrees C followed by addition of phorbol 12-myristate 13-acetate (PMA, 10 ng/ml), a potent activator of membrane-associated oxidative metabolism. After incubation at 37 degrees C the cells were removed and the supernatants aliquoted and incubated with and without catalase (500 U/ml) for 10 min at room temperature followed by addition of cysteine (50 microM). Thereafter the catalase-inhibitable, H2O2-mediated oxidation of added cysteine was assayed spectrophotometrically following the addition of the thiol-reactive agent 5,5'-dithiobis-(2-nitrobenzoic acid), and the H2O2 concentration determined using a standard curve constructed from difference data based on the oxidation of cysteine by H2O2 (0-200 nmol). The average amount of H2O2 produced by 10(6) PMA-activated neutrophils was 47 +/- 7 nmol/30 min. This sensitive assay procedure is likely to be particularly useful for investigating the effects of pharmacological agents and anti-oxidant nutrients on H2O2 production by activated phagocytes, since these agents are generally unsuited for use in peroxidase-based assays.

Hypochlorous acid potentiates hydrogen peroxide-mediated DNA-strand breaks in human mononuclear leucocytes

In this study the formation of DNA single-strand breaks in MNL in close proximity to activated phagocytes, or in contact with added H2O2 and/or HOCl, were evaluated. Neutrophils activated by phorbol myristate acetate (PMA), induced DNA-strand breaks in neighboring lymphocytes which increased after 1-2 h incubation in a repair medium. These DNA-strand breaks could be prevented by the addition of catalase or substitution of the neutrophils with cells from a patient with chronic granulomatous disease. Inclusion of the myeloperoxidase (MPO) inhibitor, sodium azide (NaN3), to the system was associated with less damage after 1-2 h incubation and a faster repair rate. Exposure of MNL to added reagent H2O2 (12-100 microM) was also accompanied by DNA damage. Addition of reagent HOCl (3-25 microM) did not induce any DNA-strand breaks. However, when combined with H2O2 (12.5 microM), HOCl increased H2O2-mediated DNA damage and compromised the repair process. Interactions between the phagocyte-derived reactive oxidants H2O2 and HOCl are probably involved in the etiology of inflammation-related cancer.