Bis-basic
ethers of
fluorene and fluoren-9-substituted derivatives such as
tilorone have been reported to inhibit
silica-induced
fibrosis in rats. The potential antifibrotic potency of 2,7-bis(diethylamino)ethoxy
fluorene (F-9-H,H), fluorenone (F-9-one), fluorenoxime (F-9-oxime), and fluorenol (F-9-ol) was F-9-oxime >
F-9-one approximately F-9-H,H >> F-9-ol. Since the release of
reactive oxygen species and
growth factors from alveolar macrophages (AM) in response to
silica exposure has been linked to the development of
pulmonary fibrosis, the present study was carried out to determine the inhibitory effects of these compounds on rat AM activity in vitro. The following parameters were monitored: (1) cellular viability; (2)
zymosan-induced respiratory burst activity (
superoxide and
hydrogen peroxide release, chemiluminescence, and oxygen consumption) of AM; (3)
drug binding to AM; and (4)
lipopolysaccharide (LPS)-stimulated
interleukin-1 (IL-1) release from AM. The bis-basic
ethers, at 40 microM, did not affect cell viability when incubated with AM for 30 min, but significantly inhibited
zymosan-induced macrophage respiratory burst activity. The inhibitory effect of these agents was F-9-oxime >
F-9-one approximately F-9-H,H >> F-9-ol. Binding of these drugs to AM was time and dose dependent, and exhibited the following binding affinity: F-9-oxime >
F-9-one > F-9-H,H > F-9-ol. F-9-oxime was shown to inhibit LPS-stimulated
IL-1 release by AM in a dose-dependent manner. This inhibition of
IL-1 release by AM cannot be explained as a decrease in viability. In addition, these drugs were also shown to impair human fibroblast proliferation in response to serum stimuli without impairing cell viability. These results indicate a positive correlation between
drug binding to AM or other cell types and their inhibitory effects on cellular activities including oxygen consumption,
superoxide release,
hydrogen peroxide secretion, chemiluminescence,
IL-1 release, and proliferation. The ability of these bis-basic
ethers to modify AM and fibroblast functions in vitro suggests that further investigation of their reported antifibrotic potency in vivo is warranted.