Asbestos-induced lung epithelial permeability: potential role
of nonoxidant pathways
Michael W.
Peterson and
Jennifer
Kirschbaum
Division of Pulmonary, Critical Care and Occupational Medicine,
Department of Medicine, University of Iowa, Iowa City, Iowa 52240
 |
ABSTRACT |
Asbestos fibers are an
important cause of lung fibrosis; however, the biological mechanisms
are incompletely understood. The lung epithelium serves an important
barrier function in the lung, and disrupting the epithelial barrier can
contribute to lung fibrosis. Lung epithelial permeability is increased
in patients with asbestosis, and asbestos fibers increase permeability
across cultured human lung epithelium. However, the mechanism of this
increased permeability is not known. Many of the biological effects of
asbestos are postulated to be due to its ability to generate oxidants,
and oxidants are known to increase epithelial permeability. However, we
previously reported that altering the iron content of asbestos
(important in oxidant generation) had no effect on its ability to
increase permeability. For that reason, we undertook these studies to
determine whether asbestos increases epithelial permeability through
nonoxidant pathways. Both extracellular
(H2O2) and intracellular (menadione) oxidants
increase paracellular permeability across human lung epithelial
monolayers. Extracellular catalase but not superoxide dismutase
prevented increased permeability after both oxidant exposures. However,
catalase offered no protection from asbestos-induced permeability. We
next depleted the cells of glutathione or catalase to determine whether
depleting normal cellular antioxidants would increase the sensitivity
to asbestos. Permeability was the same in control cells and in cells
depleted of these antioxidants. In addition to generating oxidants,
asbestos also activates signal transduction pathways. Blocking protein
kinase C activation did not prevent asbestos-induced permeability;
however, blocking tyrosine kinase with tyrophostin A25 did prevent
asbestos-induced permeability, and blocking tyrosine phosphatase with
sodium vanadate enhanced the effect of asbestos. These data demonstrate
that asbestos may increase epithelial permeability through nonoxidant
pathways that involve tyrosine kinase activation. This model offers an
important system for studying pathways involved in regulating lung
epithelial permeability.
lung fibrosis; pneumoconiosis; reactive oxygen species
 |
INTRODUCTION |
ASBESTOS FIBERS are an important cause of
pulmonary fibrosis; however, the biological basis for asbestos-induced
pulmonary fibrosis is incompletely understood. In animal models,
asbestos fibers first contact the lung epithelium at alveolar duct
bifurcations, and alveolar duct bifurcations are the first site at
which pathological changes appear (3). These data suggest that asbestos
may induce local changes in the lung epithelium that contribute to
subsequent pathological events. The lung epithelium normally provides
an important barrier between the external environment and the lung interstitium, and lung epithelial permeability is increased in patients
with asbestosis, asbestos-induced lung fibrosis (30). Increased lung
epithelial permeability can potentially contribute to lung fibrosis by
increasing fibrin deposition in the air space (4, 5), by increasing
local generation of inflammatory mediators such as fibrin degradation
products (11), and by increasing the flux of inflammatory mediators and
growth factors into the lung interstitium (12). We have previously
reported that chrysotile asbestos increases permeability across
cultured human lung epithelial monolayers (28). We undertook the
current study to investigate the pathways involved in asbestos-induced
lung epithelial permeability.
Asbestos is a collection of naturally occurring silicates that form
fibers. These fibers are composed of hydrated magnesium silicates
containing varying amounts of iron (6). In amosite and crocidolite
asbestos, iron is incorporated into the crystal structure, and iron
represents a significant proportion of the molecule (up to 27% by
weight; see Ref. 29). By contrast, chrysotile asbestos does not contain
iron in the crystal structure; however, iron is adsorbed to the crystal
surface (29). In chrysotile asbestos, iron only represents
~2-6% of the mineral by weight. Iron is potentially important
to the biological effects of asbestos because iron can catalyze the
Haber-Weiss reaction, generating the reactive oxygen species ·OH.
Many of the biological effects of asbestos are postulated to derive
from its ability to generate reactive oxygen species (18, 22).
The ability of asbestos to generate reactive oxidants is particularly
relevant to epithelial permeability because reactive oxygen species
increase both endothelial and epithelial permeability (19, 35).
However, we previously found that altering the iron content of
chrysotile asbestos had no effect on its ability to increase lung
epithelial permeability (28). Based on this observation, we postulated
that asbestos increases epithelial permeability through iron- and
oxidant-independent pathways. We undertook the current study to test
the hypothesis.
 |
MATERIALS AND METHODS |
Chemicals and reagents.
Catalase (C3155), superoxide dismutase (SOD S2515), menadione,
3-amino-1,2,4-triazole, buthionine sulfoximine (BSO), and phorbol 12,13-dibutyrate (PDBu) were all purchased from Sigma Chemical, St.
Louis, MO. All tissue culture media and supplements were purchased from
the University of Iowa Tissue Culture Facility.
[3H]mannitol (22.5 Ci/mmol) was purchased from New
England Nuclear. Tyrosphostin A25 and bisindolylmaleimide (GF 109203X)
were purchased from Calbiochem.
Asbestos.
Amosite asbestos used in these studies was kindly provided by Dr. J. G. N. Garcia, Indiana University. The chrysotile asbestos used in these
studies is a chryogenically ground Calidria asbestos previously
described (32). We have demonstrated that this chrysotile asbestos
increases cultured human lung epithelial permeability (25). Both
asbestos samples were maintained in suspension and evenly dispersed by
sonicating the sample before it was diluted and added to the cultured
cells.
Cell culture and permeability assay.
We used HBE16
cells in these studies. These cells were
obtained from a segmental human airway and immortalized using an
origin-defective SV40 (14). The cells were cultured at 37°C in 5%
CO2-95% air and in Eagle's MEM containing 10%
heat-inactivated fetal bovine serum, penicillin and streptomycin,
and 2 mM glutamine. They were passaged weekly after
brief exposure to trypsin-EDTA. For permeability experiments, the cells
were grown on collagen-coated 0.4-µm-pore Millicell HA filter inserts
(28). For mannitol permeability, we removed the medium and replaced it
with MEM containing 1 mg/ml BSA. The apical medium contained 2 µCi of
[3H]mannitol, and we measured mannitol appearance in
the basolateral medium. We calculated mannitol permeability as
previously described (28).
Antioxidant assays.
We measured both glutathione and catalase activities in the cultured
cells. For both of these assays, we collected the cells by scraping
them from the plate, centrifuged them in conical tubes, and stored them
at
70°C until use. For each of the assays, we thawed the cells and
lysed them by sonicating for 15 s at power setting 2 at 70% duty cycle
in a Tekmar sonic disrupter. For the glutathione assay, we sonicated
the cells in 10 mM HCl and diluted the sonicate to a total volume of 5 ml. Four hundred microliters of the sample were added to 400 µl of
reaction buffer I [25 ml of buffer A (15.62 g/l
Na2HPO4, 5.52 g/l
NaH2PO4, and 5.58 g/l EDTA, pH 7.2), 2 ml of
1% BSA, 23 ml of water, and 5.95 mg of 5,5'-dithio-bis-(2-nitrobenzoic
acid)] and 400 µl of reaction buffer II [25 ml buffer
B (6.8 g/l imidazole, 744 mg/ml EDTA, and 1.2 ml of 12 N HCl, pH
7.2), 1 ml of 1% BSA, 24 ml of water, 25 mg of NADPH, and 60 units of
glutathione reductase (Sigma Chemical)]. The reaction mixture was
monitored for absorbance change over 10 min at 412 nM. The change in
absorbance is used to calculate total glutathione using a standard
curve generated using known amounts of glutathione (30). For catalase
activity, we measured the disappearance of
H2O2. The sonicate was diluted to a final protein concentration of 10-20 µg/µl as determined by Bio-Rad protein assay. Sample (10-30 µl) was added to 4 ml of 50 mM
phosphate buffer, pH 7.8. Each sample was split into two samples of 2 ml. To the first sample, 1 ml of phosphate buffer was added, and to the
second sample, 1 ml of 30 mM H2O2 in phosphate
buffer was added. The two samples were monitored by absorbance at 240 nM for 3 min. Catalase activity was calculated as
|
|
where Ai is initial absorbance sample
control, Af is final absorbance sample
control, v is
volume of the sample, p is protein concentration in the sample, and
t is time (1).
Statistics.
All groups were compared using one-way analysis of variance with post
hoc testing by Newman-Keuls using the Systat statistical package.
P < 0.05 is considered significant.
 |
RESULTS |
To confirm that extracellular oxidants would increase paracellular
permeability across HBE monolayers, we exposed the monolayers to
increasing concentrations of H2O2. As shown in
Fig. 1, H2O2 increased mannitol permeability (Pmann) in both a
concentration- and time-dependent pattern. Having established that
extracellular oxidants could increase Pmann, we
next asked whether extracellular antioxidants would prevent
asbestos-induced Pmann. Neither extracellular SOD
nor extracellular catalase prevented asbestos-induced permeability (Fig. 2). These results could be due to
asbestos acting through nonoxidant mechanisms to increase permeability.
However, an alternative explanation is that asbestos acts by generating
intracellular oxidants, and the extracellular antioxidant enzymes
cannot protect from intracellular oxidants. Our observation that HBE
cells internalize the asbestos particles supports this hypothesis (11).
To test this hypothesis, we exposed the cells to menadione, a vitamin K
analog that is metabolized in the mitochondria. Superoxide is generated
as a product of menadione metabolism (31). Menadione thus offers us a
model for testing intracellular oxidant production. As shown in Fig.
3, menadione did increase
Pmann across HBE monolayers, and, interestingly,
the prolonged time course was similar to the time course we saw after
adding asbestos. However, unlike asbestos, extracellular catalase
completely prevented menadione-induced permeability (Fig.
4). SOD, though, offered no protection from asbestos. These data demonstrate that extracellular antioxidants can
protect epithelial cells from intracellular oxidants and further suggest that the active oxidant species is not superoxide. Coupled with
the observation that catalase did not prevent asbestos-induced permeability, these data suggest that asbestos is acting through nonoxidant pathways.

View larger version (27K):
[in this window]
[in a new window]
|
Fig. 1.
H2O2 increases mannitol permeability across
cultured human lung epithelial (HBE) monolayers in a time- and
concentration-dependent fashion. Each bar represents 6 monolayers.
|
|

View larger version (38K):
[in this window]
[in a new window]
|
Fig. 2.
Extracellular antioxidant enzymes catalase and superoxide dismutase
(SOD) provide no protection from asbestos-induced epithelial
permeability. Monolayers were exposed to asbestos and the antioxidant
enzymes for 24 h. Each bar represents 8 monolayers.
|
|

View larger version (32K):
[in this window]
[in a new window]
|
Fig. 3.
Intracellular oxidants increase mannitol permeability across HBE
monolayers. When menadione is metabolized, superoxide is generated.
Menadione exposure results in increased epithelial permeability. Each
bar represents 6 monolayers.
|
|

View larger version (16K):
[in this window]
[in a new window]
|
Fig. 4.
Extracellular catalase but not extracellular superoxide dismutase
prevents menadione-induced permeability across HBE monolayers. These
data demonstrate that extracellular antioxidants can protect the
monolayers from intracellular oxidant exposure. However, the data
suggest that superoxide may not be the most important oxidant species.
Each bar represents 8 monolayers.
|
|
We previously reported that artificially manipulating the iron content
on the chrysotile asbestos had no effect on its ability to increase
Pmann across HBE monolayers. Because asbestos is
thought to increase oxidants through iron-dependent catalysis of the
Fenton reaction, this suggested that asbestos may be acting through
nonoxidant pathways. To further confirm this observation, we exposed
HBE monolayers to chrysotile or amosite asbestos. These two forms of
asbestos differ in their iron content. Despite the difference in iron
content, amosite and chrysotile asbestos equally increased Pmann (Fig. 5). These
data further support the conclusion that asbestos increases
Pmann through nonoxidant pathways.

View larger version (18K):
[in this window]
[in a new window]
|
Fig. 5.
Amosite and chrysotile asbestos differ in the amount of iron they
contain; however, they increase permeability across HBE monolayers to a
similar degree. Each bar represents 6 monolayers.
|
|
We next asked whether we could accentuate the effect of asbestos by
depleting the cells of their normal antioxidant defenses. We first
depleted the cells of glutathione using BSO. As shown in Table
1, we could reduce cellular glutathione by
90% using BSO. However, asbestos caused no more permeability increase
in cells depleted of glutathione than it did in native cells (Fig. 6). We next asked whether depleting
cellular catalase would increase the effect of asbestos. We used
3-amino-1,2,4-triazole (ATZ) to deplete the cellular catalase. ATZ
decreased cell catalase by 60% in the presence of either
H2O2 or asbestos (Table
2). Depleting cell catalase similarly had
no effect on asbestos-induced permeability (Fig.
7). These data further support the
conclusion that asbestos increases lung paracellular permeability
through nonoxidant pathways.

View larger version (31K):
[in this window]
[in a new window]
|
Fig. 6.
Depleting cellular glutathione did not increase asbestos-induced
permeability across HBE monolayers. Buthionine sulfoximine (BSO)
exposure resulted in a 90% reduction in cellular glutathione. Each bar
represents 6 monolayers.
|
|

View larger version (34K):
[in this window]
[in a new window]
|
Fig. 7.
Depleting cellular catalase did not increase asbestos-induced
permeability across HBE monolayers. Aminotriazole (ATZ) exposure with
asbestos resulted in a 60% reduction in cellular catalase activity.
Each bar represents 6 monolayers.
|
|
Having determined that asbestos increases paracellular permeability
through nonoxidant pathways, we next asked whether asbestos acts
through second messengers. Asbestos is known to increase protein kinase
C (PKC) activity in cultured hamster lung epithelial cells, and PKC
activation increases paracellular permeability across cultured
epithelial monolayers (25, 36). To test the hypothesis that asbestos
acts through PKC, we blocked PKC activation using GF 109203X (23, 43).
Blocking PKC had no effect on asbestos-induced permeability (Fig.
8). As previously reported, however, GF
109203X did prevent increased permeability after PKC activation with
PDBu. We next investigated the role of tyrosine kinase in
asbestos-induced permeability by inhibiting tyrosine kinase using
tyrophostin A25 (7). As shown in Fig.
9A,
tyrophostin A25 completely prevented asbestos-induced permeability at
24 h and significantly blocked asbestos-induced permeability after 48 h
of asbestos exposure. In addition, blocking tyrosine phosphatase with
sodium vanadate enhanced the effect of asbestos on mannitol
permeability (Fig. 9B).

View larger version (33K):
[in this window]
[in a new window]
|
Fig. 8.
Blocking protein kinase C activity with GF 109203X did not prevent
asbestos-induced permeability across HBE monolayers. GF 109203X had no
effect itself on permeability over 24 h but did block phorbol
12,13-dibutyrate (PDBu)-induced permeability. Each bar represents 6 monolayers.
|
|

View larger version (33K):
[in this window]
[in a new window]

View larger version (28K):
[in this window]
[in a new window]
|
Fig. 9.
A: blocking tyrosine kinase with tyrophostin A25 completely
prevented asbestos-induced permeability across HBE monolayers after
either 24 or 48 h of exposure. Tyrophostin A25 itself had no effect on
permeability. Each bar represents 6 monolayers. NS, not significant.
B: blocking tyrosine phosphatase with 100 µM sodium vanadate
enhanced the effect of asbestos on mannitol permeability. Epithelial
monolayers were incubated with sodium vanadate for 5 h before asbestos
was added. Sodium vanadate was maintained at 100 µM throughout the
experiment. Each bar represents 6 monolayers.
|
|
 |
DISCUSSION |
Human epidemiological studies and animal studies provide strong support
linking asbestos exposure and fibrotic lung disease. However, the
biological basis for asbestos-induced lung fibrosis is incompletely
understood. Recent investigation into the pathophysiology of
interstitial lung disease suggests that the lung epithelium occupies a
central role in subsequent lung fibrosis (4, 5). Interstitial lung
disease is difficult to study because most cases are idiopathic.
Because of the known relationship between asbestos and lung fibrosis,
asbestos provides us with an important experimental model for studying
early events in lung fibrosis. Inhaled asbestos fibers preferentially
deposit at bifurcations in the alveolar ducts, and the alveolar duct
bifurcations are the anatomic areas where changes are first seen in
animal inhalation models (3). We have previously shown that asbestos
increases paracellular permeability across cultured human lung
epithelial monolayers (28). Plasma proteins, including fibrinogen, will
cross the altered lung epithelium and form fibrin in the distal airways (16). Gross and colleagues (13) have shown that the lung epithelium expresses significant amounts of urokinase-type plasminogen activator (uPA) that activates plasmin and leads to increased fibrin degradation. We have also shown that asbestos increases uPA expression by lung epithelial cells and that the fibrin degradation products cross asbestos-exposed epithelial monolayers more readily (11). Finally, fibrin degradation products are biologically active
compounds that act as chemoattractants for polymorphonuclear
neutrophils, inactivate surfactant, and increase cytokine production
(20, 26). These observations have led us to propose the hypothetical pathway shown in Fig. 10 as one arm
through which asbestos exposure can lead to lung fibrosis. Altered lung
epithelial permeability is central in both initiating and perpetuating
this pathophysiological sequence.

View larger version (28K):
[in this window]
[in a new window]
|
Fig. 10.
Diagrammatic representation of the hypothesis by which
altered lung epithelial permeability can contribute to lung fibrosis.
Increased lung epithelial permeability is central to initiating and
perpetuating the loss of distal lung units in this model. uPA,
urokinase-type plasminogen activator; FDP, fibrin degradation
product.
|
|
Both human studies and animal studies confirm that asbestos exposure
increases lung epithelial permeability. With
99mTc-diethylenetriaminepentaacetate as a marker, patients
with asbestosis have increased lung epithelial permeability (8, 30).
Similarly, in animals exposed to asbestos, the airways contain
increased protein, consistent with increased epithelial permeability
(24).
Having established that asbestos increases lung epithelial permeability
in our model, we designed the current study to ask whether asbestos
increases epithelial permeability through oxidant-dependent mechanisms.
Many of the biological effects of asbestos are thought to be due to its
ability to induce or amplify oxidant injury, and extracellular oxidants
increase paracellular permeability across both Madin-Darby canine
kidney monolayers and rat type II epithelial monolayers (19, 35).
Four experimental observations support the hypothesis that
asbestos contributes to lung injury through oxidant mechanisms. First,
asbestos generates ·OH when it is incubated with
H2O2, and the iron chelator deferoxamine blocks
·OH production (33, 34). Second, ·OH is produced in the lungs
of animals exposed to asbestos (28). Third, the antioxidant enzyme SOD
is increased in the lungs of animals exposed to asbestos (16, 17).
These observations, however, do not provide evidence directly linking
oxidant production to biological events. A fourth study does suggest a
more causal link. In a rapid animal model of asbestosis, antioxidants
partially prevented lung fibrosis (24). Even in this model, however,
protection was incomplete, and, interestingly, catalase did not prevent
increased bronchoalveolar lavage protein, a marker of lung
permeability. These data demonstrate that asbestos generates oxidants
in the lung; however, they do not causally link increased lung
permeability with oxidant generation. Furthermore, some of the
biological effects of asbestos occur independent of oxidants. In mouse
macrophages, vitamin E blocked asbestos-induced lipid peroxidation but
did not prevent asbestos toxicity (10).
Asbestos can increase oxidant stress in the lung in two ways: by
amplifying oxidant injury by catalyzing ·OH production from H2O2 or by increasing oxidant production from
inflammatory cells. Both of these mechanisms can explain the
experimental observations using electron spin resonance (ESR) and the
experimental findings in whole animals (16, 17, 19, 28, 33-35).
They do not, however, explain increased permeability in our cultured
cell system. Unlike the studies using ESR, we did not
provide an exogenous source of H2O2, and
inflammatory cells were not present in our system. These data, together
with the observation that altering iron content had no effect on
asbestos-induced permeability (28), suggest that asbestos increases
epithelial permeability through nonoxidant mechanisms.
Our current study provides strong evidence further supporting this
hypothesis. First, we found that extracellular catalase but not SOD
protects HBE monolayers from both extracellular and intracellular
oxidants (menadione). The finding that catalase but not SOD protects
from menadione suggests that the important oxidant species is not
superoxide because superoxide is initially produced after menadione
exposure. Superoxide is further metabolized to
H2O2, ·OH, and H2O. This
suggests that the important oxidant in altering epithelial permeability
is either H2O2 or ·OH. Unlike menadione,
extracellular catalase provided no protection from asbestos-induced
permeability, consistent with asbestos acting through a nonoxidant
mechanism. Furthermore, depleting the cells of either catalase or
glutathione, steps that should increase sensitivity to oxidant injury,
had no effect on asbestos-induced permeability. We did, however, find
evidence for oxidant generation in asbestos-exposed cells because ATZ
only depletes catalase in an oxidant-containing environment. In our
experiments, ATZ had no effect on catalase in control cells but
depleted catalase from cells exposed to asbestos.
In addition to inducing and amplifying oxidant production, asbestos is
also reported to activate signal transduction pathways in cells.
Asbestos is reported to activate phospholipase C and PKC in airway
epithelial cells, and a related mineral, silica, activates tyrosine
kinase in macrophages (15, 27). Both of these pathways are potentially
important in epithelial permeability. Several investigators have
reported that activating PKC increases epithelial permeability, and,
recently, the PKC inhibitor GF 109203X was reported to block this
permeability without inducing any injury itself (23). Our studies
demonstrate that asbestos does not act through PKC because GF X109203
had no effect on asbestos-induced permeability. The role of tyrosine
kinase in epithelial permeability is less firmly established. However,
increasing tyrosine phosphorylation of the adherence junction protein
-catenin alters epithelial cell shape and opens gaps between cells
(2). Our studies with tyrophostin A25 and sodium vanadate suggest a
role for asbestos-induced tyrosine kinase activation without
specifically identifying the target protein(s).
These data suggest that asbestos has nonoxidant biological effects.
This is important for at least three reasons. First, it may not be
adequate to screen mineral fibers for their ability to generate
oxidants in an attempt to develop "safe" mineral fibers. Second,
altering asbestos or other mineral fibers to decrease their
oxidant-generating capacity may not completely prevent disease after
exposure. Finally, increasing lung antioxidant mechanisms may not
prevent mineral fiber-induced lung disease. However, using asbestos as
a model, we can further our understanding of the early pathways
involved in lung fibrosis and study the cellular pathways regulating
lung epithelial permeability.
 |
ACKNOWLEDGEMENTS |
This work was supported by a developmental grant from the National
Institute of Environmental Health Sciences and by the American Lung
Association. M. W. Peterson is a Career Investigator of the American
Lung Association.
 |
FOOTNOTES |
Address for reprint requests: M. W. Peterson, C33H GH, Univ. of Iowa,
Iowa City, IA 52240.
Received 23 September 1996; accepted in final form 16 April 1998.
 |
REFERENCES |
1.
Beers, R. F., Jr.,
and
I. W. Sizer.
A spectrophotometric method for measuring the breakdown of hydrogen peroxide by catalase.
J. Biol. Chem.
195:
133-140,
1952[Free Full Text].
2.
Behrens, J.,
L. Vakaet,
R. Friis,
E. Winterhager,
F. Van Roy,
M. M. Mareel,
and
W. Birchmeier.
Loss of epithelial differentiation and gain of invasiveness correlates with tyrosine phosphorylation of the E-cadherin/
-catenin complex in cells transformed with a temperature-sensitive v-SRC gene.
J. Cell Biol.
120:
757-766,
1993[Abstract].
3.
Brody, A. R.,
L. H. Hill,
and
D. B. Warheit.
Induction of early alveolar injury by inhaled asbestos and silica.
Federation Proc.
44:
2596-2601,
1985[Medline].
4.
Burkhardt, A.
Alveolitis and collapse in the pathogenesis of pulmonary fibrosis.
Am. Rev. Respir. Dis.
140:
513-524,
1989[Medline].
5.
Crouch, E.
Pathobiology of pulmonary fibrosis.
Am. J. Physiol.
259 (Lung Cell. Mol. Physiol. 3):
L159-L184,
1990[Abstract/Free Full Text].
6.
Esmen, N. A.,
and
S. Erdal.
Human occupational and nonoccupational exposure to fibers.
Environ. Health Perspect.
88:
277-286,
1990[Medline].
7.
Gazit, A.,
P. Yaish,
C. Gilon,
and
A. Levitzki.
Tyrophostins 1. Synthesis and biological activity of protein kinase inhibitors.
J. Med. Chem.
32:
2344-2352,
1989[Medline].
8.
Gellert, A. R.,
J. A. Langford,
R. J. D. Winter,
S. Uthayakumar,
G. Sinha,
and
R. M. Rudd.
Asbestosis: assessment by bronchoalveolar lavage and measurement of pulmonary epithelial permeability.
Thorax
40:
508-514,
1985[Abstract].
9.
Ghio, A. J.,
T. P. Kennedy,
A. R. Whorton,
A. L. Crumbliss,
G. E. Hatch,
and
J. R. Hoidal.
Role of surface complexed iron in oxidant generation and lung inflammation induced by silicates.
Am. J. Physiol.
263 (Lung Cell. Mol. Physiol. 7):
L511-L518,
1992[Abstract/Free Full Text].
10.
Goodglick, L. A.,
L. A. Pietras,
and
A. B. Kane.
Evaluation of the causal relationship between crocidolite asbestos-induced lipid peroxidation and toxicity to macrophages.
Am. Rev. Respir. Dis.
139:
1265-1273,
1989[Medline].
11.
Gross, T. J.,
S. M. Cobb,
and
M. W. Peterson.
Asbestos exposure increases human bronchial epithelial cell fibrinolytic activity.
Am. J. Physiol.
264 (Lung Cell Mol. Physiol. 8):
L276-L283,
1993[Abstract/Free Full Text].
12.
Gross, T. J.,
S. M. Cobb,
and
M. W. Peterson.
Asbestos exposure increases paracellular transport of fibrin degradation products across human airway epithelium.
Am. J. Physiol.
266 (Lung Cell. Mol. Physiol. 10):
L287-L295,
1994[Abstract/Free Full Text].
13.
Gross, T. J.,
R. H. Simon,
and
R. G. Sitrin.
Expression of urokinase-type plasminogen activator by rat pulmonary alveolar epithelial cells.
Am. J. Respir. Cell Mol. Biol.
5:
449-456,
1990.
14.
Gruenert, D. C.,
W. E. Finkbeiner,
and
J. H. Widdicombe.
Culture and transformation of human airway epithelial cells.
Am. J. Physiol.
268 (Lung Cell. Mol. Physiol. 12):
L347-L360,
1995[Abstract/Free Full Text].
15.
Holian, A., K. Kelley, and R. F. Hamilton, Jr. Mechanisms
associated with human alveolar macrophage stimulation by particulates.
Environ. Health Perspect. 102, Suppl. 10: 69-74,
1994.
16.
Idell, S.,
K. K. James,
E. G. Levin,
B. S. Schwartz,
N. Manchanda,
R. J. Maunder,
T. R. Martin,
J. McLarty,
and
D. S. Fair.
Local abnormalities in coagulation and fibrinolytic pathways predispose to alveolar fibrin deposition in the adult respiratory distress syndrome (Abstract).
J. Clin. Invest.
84:
695,
1989[Medline].
17.
Janssen, Y. M. W.,
J. P. Marsh,
M. P. Absher,
D. Hemenway,
P. M. Vacek,
K. O. Leslie,
P. J. A. Borm,
and
B. T. Mossman.
Expression of antioxidant enzymes in rat lungs after inhalation of asbestos or silica.
J. Biol. Chem.
267:
10625-10630,
1992[Abstract/Free Full Text].
18.
Kamp, D. W.,
P. Graceffa,
W. A. Pryor,
and
S. A. Weitzman.
The role of free radicals in asbestos-induced diseases.
Free Radic. Biol. Med.
12:
293-315,
1992[Medline].
19.
Kim, K.-J.,
and
D.-J. Suh.
Asymetric effects of H2O2 on alveolar epithelial barrier properties.
Am. J. Physiol.
264 (Lung Cell Mol. Physiol. 8):
L308-L315,
1993[Abstract/Free Full Text].
20.
Leavell, K. L.,
M. W. Peterson,
and
T. J. Gross.
The role of fibrin degradation products in neutrophil recruitment to the lung.
Am. J. Respir. Cell Mol. Biol.
14:
53-60,
1996[Abstract].
21.
Lowry, O. H.,
N. J. Rosebrough,
A. L. Farr,
and
R. J. Randall.
Protein measurement with the Folin phenol reagent.
J. Biol. Chem.
193:
265-275,
1951[Free Full Text].
22.
Lund, L. G.,
and
A. E. Aust.
Iron-catalyzed reactions may be responsible for the biochemical and biological effects of asbestos.
Biofactors
3:
83-89,
1991[Medline].
23.
Marano, C. W.,
K. V. Laughlin,
L. M. Russo,
and
J. M. Mullin.
The protein kinase C inhibitor, bisindolylmaleimide, inhibits the TPA-induced but not the TNF-induced increase in LLC-PK1 transepithelial permeability.
Biochem. Biophys. Res. Commun.
209:
669-676,
1995[Medline].
24.
Mossman, B. T.,
J. P. Marsh,
and
A. Sesko.
Inhibition of lung injury, inflammation, and interstitial fibrosis by polyethylene-glycol-conjugated catalase in a rapid inhalational model of asbestosis.
Am. Rev. Respir. Dis.
141:
1266-1271,
1989.
25.
Mullin, J. M.,
and
T. G. O'Brien.
Effects of tumor promoters on LLC-PK1 renal epithelial tight junctions and transepithelial fluxes.
Am. J. Physiol.
251 (Cell Physiol. 20):
C597-C602,
1986[Abstract/Free Full Text].
26.
O'Brodovich, H.,
J. Weitz,
and
F. Possmayer.
Effect of fibrinogen degradation products and lung ground substance on surfactant function.
Biol. Neonate
57:
325-333,
1990[Medline].
27.
Perderiset, M.,
J. P. Marsh,
and
B. T. Mossman.
Activation of protein kinase C by crocidolite asbestos in hamster tracheal epithelial cells.
Carcinogenesis
12:
1499-1502,
1991[Abstract].
28.
Peterson, M. W.,
M. E. Walter,
and
T. J. Gross.
Asbestos directly increases lung epithelial permeability.
Am. J. Physiol.
265 (Lung Cell. Mol. Physiol. 9):
L308-L317,
1993[Abstract/Free Full Text].
29.
Pooley, F. D.
Mineralogy of asbestos: the physical and chemical properties of the dusts they form.
Semin. Oncol.
8:
243-249,
1981[Medline].
30.
Rinderknecht, J.,
L. Shapiro,
M. Krauthammer,
G. Taplin,
K. Wasserman,
J. M. Eszler,
and
R. M. Effros.
Accelerated clearance of small solutes from the lungs in interstitial lung disease.
Am. Rev. Respir. Dis.
121:
105-117,
1980[Medline].
31.
Thor, H.,
M. T. Smith,
P. Hartzell,
G. Bellomo,
S. A. Jewell,
and
S. Orrenius.
The metabolism of menadione (2-methyl-1,4-naphthoquinone) by isolated hepatocytes.
J. Biol. Chem.
257:
12419-12425,
1982[Abstract/Free Full Text].
32.
Thorne, P. S.,
E. N. Lightfoot,
and
R. M. Albrecht.
Physicochemical characterization of cryogenically ground, size separated, fibrogenic particles.
Environ. Res.
36:
89-110,
1985[Medline].
33.
Weitzman, S. A.,
J. F. Chester,
and
P. Graceffa.
Binding of deferoxamine to asbestos fibers in vitro and in vivo.
Carcinogenesis
9:
1643-1645,
1988[Abstract].
34.
Weitzman, S. A.,
and
P. Graceffa.
Asbestos catalyzes hydroxyl and superoxide radical generation from hydrogen peroxide.
Arch. Biochem. Biophys.
228:
373-376,
1984[Medline].
35.
Welsh, M. J.,
D. M. Shasby,
and
R. M. Husted.
Oxidants increase paracellular permeability in a cultured epithelial cell line.
J. Clin. Invest.
76:
1155-1168,
1985[Medline].
36.
Winter, M.,
J. S. Wilson,
K. Bedell,
and
D. M. Shasby.
The conductance of cultured epithelial cell monolayers: oxidants, adenosine triphosphate, and phorbol dibutyrate.
Am. J. Respir. Cell Mol. Biol.
2:
355-363,
1990[Medline].
Am J Physiol Lung Cell Mol Physiol 275(2):L262-L268
0002-9513/98 $5.00
Copyright © 1998 the American Physiological Society