The mechanism of
bleomycin-induced
pulmonary fibrosis is not yet clear. Recent studies have shown that alveolar macrophages (AM) can be stimulated by
bleomycin in vitro releasing inflammatory
cytokines, suggesting that the interaction of
bleomycin with AM is an important step in the
drug-induced fibrotic process.
Bleomycin is known to bind
DNA and generate
oxygen radicals through complexation with Fe2+ and
oxygen. To provide more insight into the cellular oxidative property of
bleomycin, we have developed a fluoromicroscopic method using
2',7'-dichlorofluorescin diacetate (DCFHDA) as an oxidative fluorescence probe to study the
bleomycin-induced intracellular oxidation in rat AM and the inhibition of the oxidation by
taurine, a compound known to inhibit the
bleomycin-induced
fibrosis.
Bleomycin at 5 to 20 micrograms/ml has a moderate stimulatory effect (1.87- to 2.66-fold) on the secretion of
superoxide anion. A high concentration of
bleomycin (20 micrograms/ml), however, inhibits cell response to
zymosan-induced secretion of
superoxide anion. At 4 micrograms/ml,
bleomycin has no effect on cell membrane integrity or morphology but results in a significant increase in intracellular oxidation. This oxidative process is Fe(2+)-dependent and is accompanied by an increase in intracellular
calcium (35 nM). Both the intracellular oxidation and
calcium rise induced by internalized
bleomycin are inhibited by pretreatment of cells with varying concentrations of
taurine (25, 125, and 187.5 microM). The inhibitory effect on intracellular oxidation was found to be 36, 57, and 60%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)