Hydrogen peroxide release by rat alveolar macrophages: comparison with blood neutrophils

Modulation of pulmonary clearance of bacteria by antioxidants

To further delineate the mechanisms underlying murine pulmonary defenses against bacterial infection, we studied the effects of antioxidant enzymes and hydroxyl radical scavengers on pulmonary clearance processes. Intratracheal injection of catalase and superoxide dismutase resulted in prolonged intraalveolar residence of the enzymes, but caused no decrease in rates of clearance of either Staphylococcus aureus 502A or Pseudomonas aeruginosa PAO1. In contrast, dimethylsulfoxide and dimethylthiourea caused significant depression of clearance of P. aeruginosa without altering clearance of S. aureus. These results provide further differentiation between clearance processes affecting gram-negative and gram-positive bacteria and suggest that murine clearance of gram-negative organisms may be in part mediated by reactions which generate hydroxyl anion. In vivo administration of agents which inhibit hydrogen peroxide-, superoxide-, or hydroxyl anion-mediated reactions do not alter normal clearance of S. aureus.

In vitro generation of hydrogen peroxide and of superoxide anion by bovine polymorphonuclear neutrophilic granulocytes, blood monocytes, and alveolar macrophages

Studies were conducted to compare the capacity of bovine blood monocytes, polymorphonuclear granulocytes (PMNs), and alveolar macrophages (AMs) to generate hydrogen peroxide and superoxide anion. Following stimulation with opsonized zymosan, bovine PMNs respond with an immediate and vigorous liberation of both oxygen species, generating 4.7 +/- 0.3 nmol H2O2/10(6) cell and 12.3 +/- 1.8 nmol O2-/10(6) cell during the initial 15 min. This is more than twice the amount generated by AMs (1.2 nmol H2O2/10(6) cell; 2.5 and nmol O2-/10(6) cell) and blood monocytes (0.5 nmol H2O2/10(6) cell; 2.1 nmol O2-/10(6) cell) during the same period. However, AMs continue generating H2O2 and O2- at a steady rate for a longer period and consequently produce amounts equal to those of PMNs when measured over a longer time span. Also, AMs can be stimulated with nonopsonized zymosan in contrast to PMNs. However, the AM population appears to comprise at least two subpopulations, which can be clearly distinguished by their capacity for generation of reactive oxygen species, and which correlate with their tendency for adherence to a plastic surface. In contrast to what has been found in other species, the bovine phagocytes were found to lack receptors for tuftsin and formylated oligopeptides, and thus remained unresponsive to these compounds. The in vitro activity of the three cell types was found to be very dependent on culture conditions, such as cell density and an adherent versus suspended state. In addition, a comparison with macrophages and PMNs elicited into the mammary gland suggest that in vivo factors can significantly influence the in vitro activities. The mammary gland cells have lower activity than blood and alveolar cells, even though they have been "primed" by chemotactic factor(s), and this is probably caused by milk components, i.e., the microenvironment. Our observations are discussed with respect to the results obtained from different laboratories, different species, and different cell types; emphasis is placed on the problem of drawing conclusions about in vivo functions of cells from parameters assayed in vitro.

Direct measurement of hydrogen peroxide release from rat alveolar macrophages: artifactual effect of horseradish peroxidase

Investigators disagree on the amount of hydrogen peroxide (H2O2) released by resting and stimulated alveolar macrophages. The method commonly used to measure H2O2 release involves horseradish peroxidase (HRP)-catalyzed oxidation of scopoletin by H2O2. We describe an artifact in this method that may explain the seemingly inconsistent data reported by other investigators. Release of H2O2 and luminol-catalyzed chemiluminescence are stimulated in rat alveolar macrophages by type II HRP at concentrations normally used in the HRP-scopoletin method. The amount of H2O2 released depends upon the length of time the cells are preincubated at 37.5 degrees C and the time at which type II HRP is added. After stimulation with type II HRP, the cells do not release additional H2O2 upon exposure to zymosan particles. Myeloperoxidase, an alternative catalyst to type II HRP, does not stimulate H2O2 release and, therefore, can be used to measure H2O2 release from rat alveolar macrophages. Using myeloperoxidase, resting H2O2 release is negligible; after zymosan stimulation, 6.14 (+/- 0.87) X 10(-6) nmoles/cell X 10 min is released. In addition, more pure HRP preparations (types VI, VII, VIII, and IX) do not stimulate alveolar macrophages to release H2O2 and can be used to monitor zymosan-induced H2O2 release. As our data indicate that type II HRP stimulates H2O2 release from rat and guinea pig alveolar macrophages, it is not the catalyst of choice for this assay. In conclusion, our data explain the conflicting results found in the literature and indicate that rat alveolar macrophages release minimal amounts of H2O2 at rest and can be stimulated by zymosan.

Stimulation by oxygen radicals of prostaglandin production by rat renal glomeruli

Polymorphonuclear leukocytes secreting oxygen radicals are found in the glomerular capillaries at an early stage of experimental acute glomerulonephritis. The aim of this work was to study the effects of these radicals on prostaglandin (PG) production by the glomeruli. Glomeruli were isolated from rat renal cortex and incubated in the presence of a biochemical system capable of generating oxygen radicals (addition to 100 microM xanthine of increasing concentrations of xanthine oxidase). Synthesis of PGE2, PGF2alpha, 6 keto PGF1alpha, and TXB2 estimated using specific radioimmunoassays was twofold greater in the presence of oxygen radicals. This effect was inhibited by catalase, slightly stimulated by superoxide dismutase, unaffected by hydroxyl radical scavengers, thus suggesting that hydrogen peroxide was the by-product responsible. This was confirmed by the stimulatory effect of hydrogen peroxide itself (1 to 100 microM) on PG synthesis. The effect of mepacrine, an inhibitor of phospholipase activity, on PG production was more marked in the presence of hydrogen peroxide and the stimulation of PG synthesis by hydrogen peroxide or oxygen radicals was progressively inhibited in the presence of arachidonic acid. Moreover, oxygen radicals stimulated the release of 14C-arachidonic acid previously incorporated in isolated glomeruli. This demonstrates that the increase in PG synthesis in response to oxygen radicals is due to activation of glomerular phospholipase by these radicals. This effect that is likely to occur at an early stage of experimental glomerulonephritis could play a role in the mechanism of the inflammatory process.

The contribution of hydrogen peroxide resistance to virulence of Mycobacterium tuberculosis during the first six days after intravenous infection of normal and BCG-vaccinated guinea-pigs

The course of infection with Mycobacterium tuberculosis strains H37Rv, H37Ra and their isoniazid-resistant, hydrogen peroxide-susceptible mutants in guinea-pig spleen and lung were assessed by measuring changes in number of viable bacteria during the first and second 3-day intervals after i.v. infection of normal and BCG-vaccinated animals. Vaccination had no effect on bacterial survival in the first 3 days of infection. The peroxide-susceptible mutants were killed or inhibited more than their parent strains; in normal animals this enhanced susceptibility was expressed equally during the first and second 3-day intervals while in vaccinated animals the effect was greater in the second 3-day interval. The results suggest that hydrogen peroxide is generated in significant amounts in the environment of tubercle bacilli lodged in normal tissues and in enhanced amounts when acquired immunity becomes expressed after a few days' lodgement in the tissues of vaccinated animals. Thus hydrogen peroxide resistance may contribute to virulence by protecting against both normal resident and immunologically activated macrophages.

Transmembrane potential changes associated with superoxide release from human granulocytes

Treatment of human granulocytes with concanavalin A, phorbol myristate acetate (PMA), N-formyl-methionyl-leucyl-phenylalanine (FMLP), and A23187 (a calcium ionophore) stimulates the release of superoxide anion and the generation of chemiluminescence. The fluorescent probe, Di-S-C3(5), has been used to monitor shifts in membrane potential in response to these stimulants which precede the secretion of superoxide. Concanavalin A, PMA, and FMLP induce a biphasic shift in transmembrane potential (Em), i.e., a rapid depolarization followed by a prolonged hyperpolarization. This depolarization is dependent on both external sodium and calcium while the hyperpolarization is inhibited by ouabain which blocks the electrogenic Na-K pump. In contrast, A23187 induces a rapid and prolonged depolarization. This monophasic shift in Em is dependent on external calcium. These results suggest that depolarization acts as a signal to initiate events associated with the "respiratory burst" of these phagocytes.

Production of hydroxyl radical by human alveolar macrophages

Stimulated human alveolar macrophages were demonstrated to oxidize B-methyl proprionaldehyde (methional) or 2-keto-4-thiomethylbutyric acid to ethylene (C2H4). Agents which are believed to scavenge the hydroxyl radical (.OH), sodium benzoate, and mannitol, as well as scavengers of superoxide anion (O2-) or hydrogen peroxide, decreased C2H4 production, implicaing .OH as the oxidizing radical. Differences in C2H4 rpoduction, as well as oxygen uptake and O2- release between human alveolar macrophages and polymorphonuclear leukocytes, were also documented.