Zinc hydroxide stimulates superoxide production by rat alveolar macrophages

Catalase catalyzes nitrotyrosine formation from sodium azide and hydrogen peroxide

Sodium azide (NaN3) is known as an inhibitor of catalase, and a nitric oxide (NO) donor in the presence of catalase and H2O2. We showed here that catalase-catalyzed oxidation of NaN3 can generate reactive nitrogen species which contribute to tyrosine nitration in the presence of H2O2. The formation of free-tyrosine nitration and protein-bound tyrosine nitration by the NaN3/catalase/H2O2 system showed a maximum level at pH 6.0. Free-tyrosine nitration induced by peroxynitrite was inhibited by ethanol and dimethylsulfoxide (DMSO), and augmented by superoxide dismutase (SOD). However, free-tyrosine nitration induced by the NaN3/catalase/H2O2 system was not affected by ethanol, DMSO and SOD. NO2- and NO donating agents did not affect free-tyrosine nitration by the NaN3/catalase/H2O2 system. The reaction of NaN3 with hydroxyl radical generating system showed free-tyrosine nitration, but no formation of nitrite and nitrate. The generation of nitrite (NO2-) and nitrate (NO3-) by the NaN3/catalase/H2O2 system was maximal at pH 5.0. These results suggested that the oxidation of NaN3 by the catalase/H2O2 system generates unknown peroxynitrite-like reactive nitrogen intermediates, which contribute to tyrosine nitration.

Histopathological changes induced by zinc hydroxide in rat lungs

Rat lungs were histologically examined at 1, 7, 14 and 28 days following a single intratracheal instillation of zinc hydroxide (1 mM). After one day of treatment, no confirmatory findings were noted. The zinc hydroxide injections were followed by an increase in proliferating cell nuclear antigen labeling indices in both alveolar macrophages and terminal bronchioles. After 7 days, the zinc hydroxide-treated lungs showed thickening of the interstitium with infiltration by alveolar macrophages, and an increase in the grade of Masson's trichrome staining (collagen fiber) in the alveolar interstitium. Thereafter, these morphological changes disappeared. The vehicle- and zinc sulfate (1 mM)-exposed lungs had no abnormalities at any time point. Formazan deposits in alveolar macrophages, formed as a result of nitro blue tetrazolium reduction, were increased in zinc hydroxide-treated lung slices, suggesting that zinc hydroxide stimulated super oxide anion generation from alveolar macrophages. These results show that zinc hydroxide can induce morphological alterations of rat lungs.

Influence of carbon particles on superoxide and hydrogen peroxide radical release during the killing of Mycobacterium bovis by alveolar macrophages

SETTING

Diagnostic bronchoscopy performed on untreated African patients with tuberculosis revealed alveolar macrophages filled with carbon particles. It was postulated that this was the result of excessive inhalation of smoke from domestic fires and the consequent phagocytosis by alveolar macrophages.

OBJECTIVE

To determine whether carbon particles influence the release of superoxide and hydrogen peroxide radicals by the alveolar macrophage during killing of Mycobacterium bovis.

DESIGN

Alveolar macrophages were recovered by bronchoalveolar lavage from adult rabbits and cultured. Experimental macrophages were exposed to M. bovis and carbon particles, controls only to M. bovis. Superoxide release was measured by the superoxide dependent cytochrome C reduction method and hydrogen peroxide release by luminol dependent chemiluminescence. Significance of differences was calculated by Student's t-test for unpaired data.

RESULTS

For superoxide and hydrogen peroxide release, results show a significant difference between the experiments and the controls. Hydrogen peroxide radicals are, however, released at a low constant average median value in the controls.

CONCLUSION

Hydrogen peroxide is not greatly involved in the killing of M. bovis by alveolar macrophages since low concentrations are released in the controls. Ingestion of large amounts of carbon particles decreases the release of superoxide and hydrogen peroxide radicals.

Effects of zinc on production of active oxygen species by rat neutrophils

The effects of zinc on the production of active oxygen species were investigated in rat neutrophils by chemiluminescence and spectrophotometric assays. The luminol-dependent chemiluminescence in unstimulated neutrophils showed a single peak. Zinc at concentrations lower than 0.1 mM augmented the intensity of chemiluminescence and showed a bimodal pattern, the first peak of which was inhibited by superoxide dismutase and catalase, while the second peak disappeared in the presence of catalase, but was unaffected by superoxide dismutase. At the same concentrations of zinc, O2- and H2O2 production increased, but secretion and activity of myeloperoxidase were not affected. Zinc at 0.1 mM enhanced the second peak of luminol-dependent chemiluminescence, and concomitantly O2- and H2O2 production of neutrophils stimulated with formyl-methionyl-leucyl-phenylalanine. Homogenized neutrophils showed a bimodal pattern on induction by zinc, the second peak of which was inhibited slightly by catalase and completely by sodium azide, but was not inhibited by superoxide dismutase. Zinc-induced O2- production was inhibited by pertussis toxin, but was not significantly inhibited by a protein kinase C inhibitor, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), or a calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7). These results suggest that zinc can augment luminol-dependent chemiluminescence by increasing O2- production through the classical signal transduction pathway, and by increasing H2O2 not via O2-.

Zinc hydroxide induced respiratory burst in rat neutrophils

The effects of zinc hydroxide on the respiratory burst and phagocytosis by rat neutrophils were examined. Zinc hydroxide induced an increase in oxygen consumption and O2- production. Electronmicroscopy showed that neutrophils engulfed zinc hydroxide particles by phagocytosis. Pertussis toxin (0.25, 0.5, 1.0 micrograms/ml) and EGTA (1, 2, 5 mM) inhibited zinc hydroxide-induced O2- production in a dose-dependent manner. The inhibitors of protein kinase C, 1-(5-isoquinolinesulfonyl)-2-methyl-piperazine and N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide inhibited zinc hydroxide-induced O2- production with IC50 values ranging between 10 microM and 25 microM. The inhibitory study using an inhibitor of myosin light chain kinase, 1-(5-iodo-naphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine, showed IC50 values ranging from 5 microM to 10 microM. These findings indicate that zinc hydroxide induces respiratory burst and phagocytosis by rat neutrophils.