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Bleomycin increases superoxide production in the most active alveolar macrophage subpopulation
R B Zeidler1, J W Yarbro, N S Conley
1Department of Anesthesiology, University of Missouri, School of Medicine, Columbia 65212.
Abstract:
Pig alveolar macrophages were separated into three subpopulations by density centrifugation. The most dense subpopulation of macrophages had the greatest rate of superoxide anion production of 4.4 +/- 2.6 nmol/1 x 10(6) cells/min. Bleomycin had its greatest effect on this subpopulation by increasing the rate by nearly 100% in cells stimulated with phorbol myristate acetate or phorbol dibutyrate. Bleomycin increased the maximum rate of superoxide production without changing the apparent Km of 0.012 microgram/ml. Bleomycin did not quantitatively effect phorbol dibutyrate binding to alveolar macrophages. The cells have 9.1 +/- 1.0 x 10(5) sites/cell with a KD of 16 nmol. Results indicate that bleomycin may enhance superoxide production by effecting steps distal to protein kinase C in the superoxide anion production pathway.
Insights
Bleomycin significantly enhances superoxide anion production in dense pig alveolar macrophages, particularly when stimulated. This suggests bleomycin affects pathways downstream of protein kinase C in superoxide generation.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Alveolar macrophages play a crucial role in lung defense.
- Superoxide anion production is a key function of macrophages in inflammatory responses.
- Bleomycin is an anticancer drug with known pulmonary toxicity.
Purpose of the Study:
- To investigate the effect of bleomycin on superoxide anion production in different pig alveolar macrophage subpopulations.
- To determine the specific mechanism by which bleomycin influences macrophage activity.
Main Methods:
- Separation of pig alveolar macrophages into subpopulations using density centrifugation.
- Measurement of superoxide anion production rates.
- Assessment of phorbol dibutyrate binding to macrophages.
Main Results:
- The densest macrophage subpopulation exhibited the highest basal superoxide anion production.
- Bleomycin markedly increased superoxide production in this subpopulation by nearly 100% when stimulated.
- Bleomycin enhanced the maximum rate of superoxide production without altering the Michaelis constant (Km) for the substrate.
- Bleomycin did not affect the binding of phorbol dibutyrate, indicating its action is downstream of protein kinase C activation.
Conclusions:
- Bleomycin potentiates superoxide anion production in a specific subpopulation of pig alveolar macrophages.
- The mechanism of bleomycin's action appears to involve steps distal to protein kinase C activation in the superoxide production pathway.
- These findings contribute to understanding bleomycin-induced lung injury and macrophage function.