In vitro lung cell culture studies of particle-induced
proinflammatory responses
Paper # 541
Tyler A. Moss, John M. Veranth, William K. Nichols, Garold S. Yost
Department of Pharmacology and Toxicology, University of Utah, 112 Skaggs, 30 South
2000 East, Salt Lake City, UT 84112
ABSTRACT
Recent work with soil-derived mineral dusts and manufactured nanoparticles will be
discussed to illustrate the types of toxicological information that can be obtained from
treatment of cell cultures with low-solubility particles. Readily inhaled particulate matter
(PM), which includes the enriched PM2.5 fraction of certain soil dusts or modified
manufactured nanoparticles, was found to cause release of the proinflammatory cytokine
IL-6 or induce cell death in human lung cell cultures. There is a need to include
geological particulate matter when assessing adverse health effects of polluted air.
Extensive prior cell culture research has been done by toxicologists to understand the
affects and mechanisms of inhaled particles. Various surface-modifying treatments,
including heat and leaching, were used to identify the particle components or
characteristics that induced the cell signaling response.
INTRODUCTION
Numerous studies have reported adverse health effects correlated with increased inhaled
particulate matter, but the toxicological mechanisms by which specific types of particles
affect susceptible populations remain elusive. Pope et al.1 reported that differences in
adverse health effects associated with the mass of particulate matter (PM10) in nearby
Utah communities were due to the relative soil dust fraction. Schenker2 associated high
exposure to agricultural dust with chronic bronchitis, but epidemiology studies in
Spokane, WA found no correlation between ambient soil dust and mortality3 or hospital
visits for asthma.4
The current ambient air quality standards for PM10 and PM2.5 are based largely on
epidemiology studies that correlate particle mass in a specified size range, as measured by
community air monitoring stations, with documented public health effects such as
respiratory hospital admissions and cardiovascular deaths.5 Existing data are inadequate
to identify the pollution sources that are the most relevant to decreased human health and
there is no consensus on the biological mechanisms by which inhaled particles cause
adverse effects in sensitive populations.6
There is increasing evidence suggesting that redox-active transition metals associated
with particles can induce proinflammatory responses in lung cells.7-9, 10 , 11 Donaldson et al.
1
have concluded that ultrafine particles of low-solubility, low-toxicity materials are more
inflammogenic in the rat lung than larger particles from the same material, and they
hypothesize that the effects are related to surface area and involve oxidative stress.12
Titanium dioxide also shows increased response with ultrafine particles.13 Particleinduced tissue inflammation has been proposed as a central process connecting inhaled
particles with adverse health effects.6
Numerous approaches may be used to identify induced inflammation from particles in
sensitive populations. Epidemiology studies of humans or animals can be used, but will
not identify the biological mechanisms involved in a particulate toxic response. Human
and animal models are costly and it is uncertain which particles are potent or benign. In
vitro cell culture models such as immortalized lung cell lines BEAS-2B14-16 and A549,7, 17
normal human bronchial epithelial cells,18 macrophages, and co-cultures of macrophages
with epithelial cells19 are useful to screen substances for toxic effects, and provide an
easily-manipulated system for studying biochemical signaling mechanisms.
The approach in this paper is to assess the ability of ambient particulate matter (PM) and
manufactured nanoparticles to induce proinflammatory signaling (cytokines) in BEAS-2B
human bronchial epithelial cultured lung cells. BEAS-2B human immortalized lung cell
lines are used as an alternative to normal human bronchial epithelial cells. BEAS-2B
lung cell lines are virus transformed to produce immortalized growth. Immortalized cell
lines are cost efficient and decrease the number of variables that may be introduced using
various normal bronchial epithelial cells. Measuring particle-induced cytokines in
cultured lung cells elucidates which particles cause inflammation and may provide
information to determine individuals who may be susceptible to pulmonary problems
upon inhalation of specific sources of soil dust. Surface modifying techniques help
explain particle characteristics.
Cytokines, such as interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor-
(TNF-), are signaling molecules associated with many processes regulating cell growth,
differentiation, and death, as well as physiological responses in tissues, and recruitment of
neutrophils, macrophages and other mobile cells to specific sites.20-22 Cytokine assays are
widely used in studies of lung cell responses to particles and other pollutants.23 Much of
the recent in vitro work with environmental particles has used ELISA assays to measure
IL-624-26 IL-8,7, 27, 28 and TNF-.29-31 Cytokine induction is associated with reactive oxygen
species (ROS) formation, and there is evidence for both extracellular and intracellular
reactions leading to ROS formation.31-33
Induction of the cytokine IL-6 has been observed in BEAS-2B cells treated with diesel
exhaust particles,16 residual oil fly ash (ROFA),34 a range of ambient and combustion
particles,35 negatively charged particles,36, 37 and capsaicin-related compounds.38 Titanium
dioxide particles larger than 1 µm are inert and serve as a PM negative control,16, 39 but
mineral dust from stone quarries induces cytotoxicity and IL-6 release in A549 cells24 and
in rat lung type 2 alveolar cells.40
In vitro toxicology studies, motivated by specific biochemical signaling hypotheses, have
attempted to link specific particle sources with cellular responses. Particle modifying
2
treatments are a means to understanding particle characteristics using human cell culture
models. Physical treatments to modify particle toxicological properties include leaching
particles with the metal chelator desferrioxamine7 and applying surface-modifying
coatings.41
Various mechanisms have been proposed for particle-cell interactions.42 Mechanisms
leading to pro-inflammatory signaling include: response to particle components
dissolved in the extracellular fluid;14, 43 cell receptor recognition of materials adsorbed on
the particle surface;26 particle uptake followed by induction of an intracellular response;27,
44 and particle surface charge activation of the TRPV1 receptor.25, 35
Particle mass in the ambient air correlates with a wide range of adverse effects, but the
importance of geological dust inhalation to human health has not been resolved.
Investigating the effects of inhaled PM helps to identify endangered populations and
assist in developing programs that reduce risk. Physical modifying treatments, such as
heat and leaching, of manufactured nanoparticles serve to simulate fire and wastewater
conditions. The current studies contribute to our understanding of the biological effects
of treated particles and help elucidate the environmental health impact of air born
particles.
METHODS
PM2.5-enriched soil dusts were prepared from field samples by tumbling and aerodynamic
separation to simulate the dust generated by mechanical attrition when tires contact the
road surface, or when coarse particle bombardment generates fine dust during high wind
events. Details are described by Veranth.46
Desert Research Institute, Reno, NV, laboratory procedures were used to determine
chemical speciation measurements of samples. Elemental composition was determined
by x-ray fluorescence. Soluble ions were measured by ion chromatography or by atomic
adsorption spectroscopy. Eight carbon fractions based on desorption temperature were
determined using thermal optical reflectance method. Carbonate carbon was determined
by acid pretreatment. The accuracy of the chemical speciation measurements was
determined through the use of blanks and duplicates and the existing DRI procedures
were used to estimate measurement uncertainty using propagation of error analysis.
Particle samples were weighed, sterilized, vacuum dried, and resuspended in cell culture
media as described by Veranth.46 The thermally treated particles were prepared by heating
in loosely covered borosilicate glass tubes in air in a muffle furnace at 150, 300, or 550°C
for one hour. Leaching treatments involved suspending the particles in 5 mL of liquid
and rotating the tubes overnight at 6 RPM. The samples were centrifuged at 750 x g for
10 minutes and decanted, and the cycle was repeated three times. The leaching liquid
was LHC-9 cell culture media. The supernatant from the first 24 hr leaching was
recovered and used to measure the effects of the soluble fraction of the original particles.
Iron-silica nanoparticles were heat treated in a Thermolyne oven at 1100°C and slowly
cooled.
3
BEAS-2B human bronchial epithelial cells were used as cell culture models. Cells were
maintained and passaged as described by Veranth.46 Figure 1 describes the cell culture
model. Cells were seeded in 24 or 48-well polystyrene plates (Costar, Fisher Scientific)
at a concentration of about 30,000 cells/cm2. After two days new cell culture media was
applied. The cell culture media containing particle samples was applied to the cells on
the fourth day. On the fifth day the cell culture media was harvested for cytokine assays
and viable cell count was measured. Experiments used triplicate wells for each treatment
level, and allocated 6 or 9 wells per culture plate as controls. Positive controls were
included to monitor changes in the cell response.
Figure 1. Cell culture procedure.
Cell viability and concentration of IL-6 was assessed by using the Dojindo assay and
R&D kits as described by Veranth.46
RESULTS
Cell culture can be used to screen a wide range of materials for the ability to induce
proinflammatory signaling in lung cells. Figure 2 shows the cytotoxicity and
proinflammatory signaling from twenty-six different soils and two positive controls (LPS
and V80). The particle soils were taken from various places in New Mexico, Texas, and
Utah. Each source of enriched soil dust for PM2.5 was applied at a concentration of
4
80µg/cm2. The cytotoxicity was measured as percent viability compared to control. IL-6
induction was measured as fold over control. The viability of cells was not directly
correlated with induction of IL-6 for most soil samples. For example the soil dust JE
seemed to be a potent inducer of IL-6 (30x), but did not appear to be toxic (80% viable
compared to control). Whereas the soil dust 2SB appears to be both a potent inducer of
IL-6 (25x) and toxic (40% viable compared to control). There seemed to be about ten
soils that produced a proinflammatory response less than ten fold over control. Nine soils
that produced a response between ten and twenty-fold over control and six soils that
produced a response greater than twenty-fold over control. Ten soil samples produced
significant cytotoxicity (below 60% viable compared to control). The diverse responses
from the different non-soluble materials support the hypothesis that cell culture models
may be used to identify the particle components or characteristics that induce the cell
signaling response.
5
Figure 2. Proinflammatory and cytotoxic response of BEAS-2B cells exposed to different
particles. Figure 2A is IL-6 production (fold over control). Figure 2B is cell viability
(viable cells over control). Cell culture is a means to identify potent and benign particles
for further study. x  SD, N = 6
Figure 2A
90
IL-6 Fold over Control
80
70
60
50
40
30
20
10
JE
V8
0
M
N
C
on
tro
l
LP
S
C
FA
AC
TR
SR
R
PH
P
PE
SR
M
D
V
2S
A
W
F
U
N
W
TR
M
SR
R
40
W R
M T
14
1
PH
R
D
D
8m
i
W
W M
F0
1
2S
B
0
PM2.5 Soil Dusts (80µg/cm
2
)
Figure 2B
1.2
Viable Cells/Control
1
0.8
0.6
0.4
0.2
JE
V8
0
M
N
C
on
tro
l
LP
S
C
FA
AC
TR
SR
R
PH
P
PE
SR
M
D
V
2S
A
W
F
U
N
W
TR
M
SR
R
40
W R
M T
14
1
PH
R
D
D
8m
i
W
W M
F0
1
2S
B
0
PM2.5 Soil Dusts (80µg/cm
2
)
The particle characteristics or components that cause cell death and IL-6 release are
robust, but can be altered by physical treatments. Figure 3 shows the effect of the thermal
and leaching treatments of three diverse particle samples: DD, WM, and R4. Heating of
the particles had no effect on cytotoxicity, but three-day aqueous washing did reduce the
cytotoxicity of the particles. However, the effect of leaching was likely a combination of
mechanical loss of particles during washing and partial dissolution. Separation of the
6
samples into an LHC-9-leached solid and a supernatant containing the components that
dissolve in media showed that cytotoxicity was associated with the solid phase.
Physical treatments also affected the particle factors controlling the IL-6 response. Figure
3 shows thermal treatment at 150, 300, and 550 °C to DD, WM and R4. Thermal
treatment at 150 °C for 1 h had no significant effect on the IL-6 response. Heating to 300
and 550 °C attenuated the IL-6 release. Heating to 550 °C is used to prebake quartz
filters for trace organic analysis, and is sufficient to oxidize most organic materials, but
550 °C treatment surprisingly did not reduce the IL-6 response to the control level for
DD. The three-day leaching treatment attenuated the IL-6 release, but did not reduce it to
control level. The IL-6 release response was predominantly associated with the solid
phase for all three soil dusts. The LHC-9 supernatant caused a small, but statistically
significant, IL-6 response for R4.
7
Figure 3. Cytotoxicity (A) and IL-6 (B) response of BEAS-2B cells exposed to untreated
and physically modified particles of soil dust. Identifications: WT, wild-type unmodified
particles, 150, 300, 550°C, oxidizing thermal treatment at indicated temperature for one
hour; LHC-S, supernatant from initial leaching in cell culture media; LHC-P, particles
recovered after three cycles of leaching in cell culture media. * designates statistically
different from untreated particles, # designates not statistically different from media-only
control, p<0.05. x  SD, N = 6
Figure 3A
Viable Cells / Control
1.2
*
*
*
1.0
*
0.8
0.6
0.4
0.2
0.0
WT
150
DD - Desert Dust
300
550
WM - West Mesa
LHC-P
LHC-S
R4 - Range 40
Figure 3B
IL-6 Fold over Control
10
8
6
*
4
*
*
*
#
2
*
* * #
#
* * *
# #
0
WT
150
DD - Desert Dust
300
550
WM - West Mesa
LHC-P
LHC-S
R4 - Range 40
8
Figure 4 presents the heating of iron-silica nanoparticle mixtures to flame temperatures.
Concentrations of 10, 30, and 90µg/cm2 were used to treat BEAS-2B cells. Thermal
treatment increased the toxicity of iron-silica particles suggesting that chemical reactions
or mineral transformations are creating a more toxic species. When a carbon source was
added toxicity of iron-silica particles appeared to decrease. The thermal treatment of
iron-silica particles caused slight increases in IL-6 production by these lung cells at the 10
and 30µg/cm2 doses.
9
Figure 4. BEAS-2B cells exposed to untreated and physically modified iron-silica
nanoparticles. Particles were modified by heat (HT) and heat with a carbon source
(HT+C). Particles exposed to heat induce IL-6 (A) and are more toxic (B). x  SD, N = 2
IL6 Fold over Control
Figure 4A
10
8
6
4
2
0
SiFe
10 ug/cm^2
SiFe+HT
30 µg/cm^2
SiFe+HT+C
90 µg/cm^2
Viable Cells/ Control
Figure 4B
1.5
1
0.5
0
SiFe
10 ug/cm^2

SiFe+HT
30 µg/cm^2
SiFe+HT+C
90 µg/cm^2
DISCUSSION
Cell culture models can be used to derive information on particle components or
characteristics that cause toxicological responses. Exposure to different sources of well
characterized particles using human lung cell cultures provides a way to study
biochemical mechanisms and to select particles for animal exposure studies.
New insights have been gained from the physical treatment experiments, but the specific
components or characteristics of the soil-derived particles that cause the IL-6 release
remain elusive. Many papers have been published reporting in vitro cytokine induction in
response to particles. The novel contributions of this paper are that a significant range of
responses, from benign to highly inflammatory and cytotoxic, is caused by particles that
are representative of fugitive dust from unpaved roads, and that physical treatments can
be used to modify soil-derived PM2.5 particles and manufactured nanoparticles as a means
of testing toxicology hypotheses related to potential active components or particle
characteristics.
10
Geological dusts have often been assumed to be a benign or inert component of ambient
air pollution. However this study strongly supports the hypothesis that the solid-phase
PM2.5 component of certain soil dusts is responsible for both proinflammatory and
cytotoxic responses in lung epithelial cells exposed to particles in vitro. Thus, studies of
the health effects associated with the complex mixtures in ambient air pollution need to
include assessment of the fine particles of geological origin.
Similar methods will be used in a recently initiated study of the toxic effects of
manufactured nanoparticles. Commercially manufactured nano-scale particles will be
characterized using physical assays and cell culture assays that are motivated by the
hypothesis that transition metals in particles induce lung inflammation through a cytokine
signaling mechanism involving reactive oxygen species (ROS). Materials will be tested
in the as-manufactured condition and after being subjected to surface-modifying
treatments simulating fire and wastewater conditions. The future research focus of these
studies will be on nanomaterials that: 1) contain transition metals, 2) produced and
commercially distributed in powder or liquid suspension form, and 3) have identifiable
uses in manufacturing, coatings, or consumer products.
ACKNOWLEDGEMENTS
This work was supported by NIEHS K25 ES011281, Southwest Center for
Environmental Research and Policy EH-03-03 the US EPA Science To Achieve Results
(STAR) research program, and National Heart Lung and Blood Institute HL069813
(GSY).
REFERENCES
1. Pope, A.C.; Hill, R.W.; Villegas, G.M., Environ. Health Perspect., 1999, 107, 567573.
2. Schenker, M., Environ. Health Perspect., 2000, 108, 661-664.
3. Schwartz, J.; Norris, G.; Larson, T., et al., Environ. Health Perspect., 1999, 107, 339342.
4. Claiborn, C.S.; Larson, T.; Sheppard, L., Environ. Health Perspect., 2002, 110, 547552.
5. EPA, Air Quality Criteria for Particulate Matter, United States Environmental
Protection Agency, EPA/600/P-95-001 aF thru cF, 1996.
6. HEI, Understanding the Health Effects of Components of the Particulate Matter Mix:
Progress and Next Steps, Health Effects Institute, HEI Perspectives, April 2002, 2002.
7. Smith, K.R.; Veranth, J.M.; Hu, A.A., et al., Chem. Res. Toxicol., 2000, 13, 118-125.
8. Aust, A.E.; Ball, J.C.; Hu, A., et al., Particle characteristics responsible for effects on
human lung epithelial cells, Health Effects Institute, Research Report 110, 2002.
11
9. Devlin, R.B.; Ghio, A.J.; Costa, D.L., "Responses of Inflammatory Cells," in ParticleLung Interactions, Marcel Dekker: New York, 2000 pp. 437-472.
10. Rice, T.M.; Clarke, R.W.; Godleski, J.J., et al., Toxicol. Appl. Pharmacol., 2001, 177,
46-53.
11. Zelikoff, J.T.; Schermerhorn, K.R.; Fang, K., et al., Environ. Health Perspect., 2002,
110 Suppl 5, 871-875.
12. Donaldson, K.; Brown, D.; Coulter, A., et al., J. Aerosol. Med., 2002, 15, 213-220.
13. Churg, A.; Gilks, B.; Dai, J., Am. J. Physiol, 1999, 277, L975-L982.
14. Frampton, M.W.; Ghio, A.J.; Samet, J.M., et al., Am. J. Physiol. Lung Cell Mol.
Physiol., 1999, 21, L960-L967.
15. Ghio, A.J.; Stonehurner, J.; Dailey, L.A., et al., Inhalation Toxicol., 1999, 11, 37-49.
16. Steerenberg, P.A.; Zonnenberg, J.A.; Dormans, J.A., et al., Exp. Lung Res., 1998, 24,
85-100.
17. Seagrave, J.C.; Nikula, K.J., Inhalation Toxicol., 2000, 12 Suppl 4, 247-260.
18. Carter, J.D.; Ghio, A.J.; Samet, J.M., et al., Toxicol. Appl. Pharmacol., 1997, 146,
180-188.
19. Tao, F.; Kobzik, L., Am. J. Respir. Cell Mol. Biol., 2002, 26, 499-505.
20. Kelley, J., Am Rev Respir Dis, 1990, 141, 765-788.
21. Nelson, S.; Martin, T.R., Cytokines in pulmonary disease: infection and
inflammation, Marcel Dekker: New York, 2000.
22. Thèze, J., The Cytokine Network and Immune Functions, Oxford University Press:
New York, 1999.
23. Mills, P.R.; Davies, R.J.; Devalia, J.L., Am. J. Respir. Crit. Care Med., 1999, 160,
S38-S43.
24. Hetland, R.B.; Refsnes, M.; Myran, T., et al., J. Toxicol. Environ. Medicine, 2000, 60,
47-65.
25. Veronesi, B.; Wei, G.; Zeng, J.-Q., et al., NeuroToxicology, 2003, 24, 463-473.
26. Becker, S.; Soukup, J.M.; Sioutas, C., et al., Exp. Lung Res., 2003, 29, 29-44.
27. Stringer, B.; A, I.; Kobzik, L., Exp Lung Res, 1996, 22, 495-508.
12
28. Koyama, S.; Sato, E.; Nomura, H., et al., Am. J. Physiol. Lung Mol. Physiol., 2000,
278, L658-L666.
29. Driscoll, K.E., Toxicol. Lett., 2000, 112-113, 177-183.
30. Smirnov, I.M.; Bailey, K.; Flowers, C.H., et al., Am. J. Physiol., 1999, 277, L257263.
31. Brown, D.M.; Donaldson, K.; Borm, P.J., et al., Am. J. Physiol. Lung Cell Mol.
Physiol., 2003, 10, 1152.
32. Wilson, M.R.; Lightbody, J.H.; Donaldson, K., et al., Toxicol. Appl. Pharmacol.,
2002, 184, 172-179.
33. Prahalad, A.K.; Inmom, J.; Dailey, L.A., et al., Chem. Res. Toxicol., 2001, 14, 879887.
34. Veronesi, B.; Oortgiesen, M.; Carter, J.D., et al., Toxicol. Appl. Pharmacol., 1999,
154, 106-115.
35. Veronesi, B.; de Haar, C.; Roy, J., et al., Inhalation Toxicol., 2002, 14, 159-183.
36. Agopyan, N.; Li, L.; Yu, S., et al., Toxicol. Appl. Pharmacol., 2003, 186, 63-76.
37. Veronesi, B.; de Haar, C.; Lee, L., et al., Toxicol. Appl. Pharmacol., 2002, 178, 144154.
38. Reilly, C.A.; Taylor, J.L.; Lanza, D.L., et al., Toxicological Sciences, 2003, 73, 170181.
39. van Maanen, J.M.; Borm, P.J.; Knaapen, A., et al., Inhalation Toxicol., 1999, 11,
1123-1141.
40. Becher, R.; Hetland, R.B.; Refsnes, M., et al., Inhalation Toxicol., 2001, 13, 789-805.
41. Schins, R.P.F., Chem. Res. Toxicol., 2002, 15, 1166-173.
42. Gehr, P.; Heyder, J., Particle- Lung Interactions, Marcel Dekker: New York, 2000.
43. Dreher, K.L.; Jaskot, R.H.; Lehmann, J.R., et al., J. Toxicol. Environ. Health, 1997,
50, 285-305.
44. Churg, A., "Particle Uptake by Epithelial Cells," in Particle-Lung Interactions,
Marcel Dekker: New York, 2000.
45. Labban, R.; Veranth, J.M.; Chow, J.C., et al., Water, Air, and Soil Pollution, 2004,
157, 13-21.
13
46. Veranth, J.M.; Reilly, C.A.; Veranth, M.M., et al., Toxicological Sciences, 2004, 82,
88-96.
14