Asbestos induces apoptosis in human alveolar macrophages.
Hamilton, Raymond F., Li Li, Rashi Iyer, and Andrij Holian.
Division of Pulmonary and Critical Care Medicine, Departments of
Internal Medicine and Pharmacology, Toxicology Program, University of
Texas Medical School, Houston, Texas 77030
APStracts 3:0113L, 1996.
Asbestos refers to a group of fibrous minerals implicated in the
development of several lung diseases including fibrosis (asbestosis),
cancer, and malignant mesothelioma. Although major health risks exist
in occupationally-exposed individuals, low-level exposures of
asbestos may still contribute to health problems. The mechanism by
which asbestos causes lung disease is not clearly understood, but has
been proposed to involve the alveolar macrophage (AM). We propose
that asbestos induces apoptosis of AM resulting in the development of
an inflammatory state. In this study, we examined two forms of
asbestos, chrysotile (CHR) and crocidolite (CRO), along with a
control fiber wollastonite (WOL), to characterize their relative
cytotoxicity and ability to stimulate apoptosis in vitro. AM's were
cultured 24 hours with these particulates and examined for cell
viability (trypan blue exclusion) and apoptosis (morphology, levels
of cytosolic oligonucleosomal DNA fragments, and DNA ladder). In the
absence of a decrease in cell viability, both CHR and CRO produced
changes in cell morphology consistent with apoptosis. In addition,
levels of cytoplasmic oligonucleosomal DNA (Cell Death DetectionTM
ELISA) were significantly enhanced for CHR (3-25 [mu]g/ml) and CRO
(25-75 [mu]g/ml) in a dose dependent manner [a process that was
inhibitable by 10 [mu]M Z-Val-Ala-Asp fluoromethyl ketone, an
interleukin converting enzyme (ICE) inhibitor]. In contrast, WOL (up
to 400 [mu]g/ml) produced no significant DNA fragmentation in a 24 h
culture. Neither CHR or CRO caused DNA ladder formation in 24 h cell
cultures. However, in 48 h cell cultures both CHR and CRO exposed
cells, but not WOL, resulted in the formation of DNA ladders
characteristic of apoptosis. In summary, these results suggest that,
unlike nonfibrogenic particulates, low doses of asbestos fibers cause
apoptosis in cultured human AM which may be an early step in the
development of lung fibrosis.
Received 15 December 1995; accepted in final form 10 June 1996.
APS Manuscript Number L368-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996