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Departments of
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Experimental Internal Medicine, and
Infectious Diseases, Tropical Medicine, and AIDS, Academic Medical Center, Amsterdam, The Netherlands
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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, 
, 
, and 
. Together with c-Jun amino-terminal kinase
and p42/44 MAPK, p38 MAPK forms the MAPK family. MAPK are activated by
phosphorylation of the Thr and Tyr in a Thr-X-Tyr motif by dual
specificity MAPK kinases (MKK). A striking feature of p38 MAPK is its
activation by a variety of inflammatory stimuli including cytokines and
LPS (1, 2, 3), suggesting a role in inflammation. Insight
into p38 MAPK action in inflammation has been gained by use of
SB203580, a piridinyl imidazole derivative and a potent and specific
inhibitor of p38 MAPK (4, 5). SB203580 binds to the ATP
binding site, thus preventing phosphorylation of downstream targets
including MAPK-activated protein kinase-2 and activating transcription
factor-2 (ATF-2), though not preventing phosphorylation of p38 MAPK by
its upstream activators, MKK3 and MKK6 (6). Although the
exact function of p38 MAPK in inflammation remains ambiguous, studies
using SB203580 have suggested involvement of this kinase in
phospholipase A2 activation (7), ischemia induced
apoptosis (8), NO synthase induction (9) and
attenuating Drosophila antimicrobial peptide gene expression
following exposure to LPS (10).
The most marked effect of p38 MAPK inhibition is the altered control of
cytokine release. p38 MAPK activation seems to be a prerequisite for
production of several cytokines in vitro. For example IL-1 and TNF-
production in monocytes (1), IL-8 production in
polymorphonuclear cells (11), and IL-6 production in L929
fibrosarcoma cells (12) have been shown to be dependent on
functional p38 MAPK activity. Baldassare et al. (13)
reported an effect of SB203580 on the LPS-dependent induction of IL-1
but not TNF- in macrophage cell lines. Strikingly, in
SB203580-treated mast cells, enhanced TNF- production was reported
(14). In peritoneal macrophages from
MKK3-/- mice, which show diminished p38 MAPK
activation, no difference was seen in TNF- levels upon stimulation
with LPS, although production of IL-12 was impaired (15).
Together, these findings highlight the uncertainty with respect to the
role of p38 MAPK in cytokine production in general and emphasize the
need for in vivo assessment of the usefulness of p38 MAPK inhibition as
an anti-cytokine anti-inflammatory strategy.
The above mentioned considerations prompted us to investigate the role
of p38 MAPK in several cell types important for cytokine production and
in murine models of disease. To this end we investigated the effect of
p38 MAPK inhibition in L929 fibrosarcoma cells and 4-4 murine
macrophages as well as in freshly obtained, nontransformed, peritoneal
macrophages and whole blood. In addition, we tested the effect of p38
MAPK inhibition on cytokine production in three well-established murine
models of disease: an endotoxemia model and a pneumococcal pneumonia
model that are representative for acute inflammatory disease, and a
chronic inflammatory tuberculosis model. Using the endotoxemia model we
were able to establish p38 MAPK activation in vivo and the efficacy of
our strategy for inhibiting p38 MAPK (daily i.p. injection with
SB203580). Our results show a dual role for p38 MAPK. Whereas
inhibition of p38 MAPK results in decreased levels of cytokines in L929
cells and whole blood, 4-4 macrophages and freshly obtained peritoneal
macrophages show enhanced cytokine production when p38 MAPK enzymatic
activity is impaired. This dichotomy in the effect of p38 MAPK
inhibition on cytokine production is also reflected in in vivo
experiments: in both the pneumococcal pneumonia and tuberculosis model
we observed increased TNF- levels when mice were subjected to p38
MAPK inhibition, but this was not observed in endotoxin-challenged
mice. Furthermore, in these experiments, we observed that in vivo p38
MAPK inhibition correlated with enhanced bacterial outgrowth. Hence,
these data indicate a critical role for p38 MAPK in bacterial
clearance, but also show that the effect of p38 MAPK inhibition on
cytokine production maybe cell type specific.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Murine macrophages (4-4 clone, which we previously showed to be
a suitable model for studying macrophage function ex vivo, as these
cells are phenotypically and functionally not different from primary
isolated mature macrophages (16, 17)), whole blood
obtained from healthy volunteers and freshly obtained murine peritoneal
macrophages were cultured in RPMI 1640 supplemented with 10% FCS, 2 mM
L-glutamine, and antibiotic-antimyotic. To isolate fresh
murine macrophages, the peritoneal cavity was lavaged with RPMI 1640.
Cells were placed in culture flasks and, 2 h after isolation,
nonadherent cells were removed. L929 fibrosarcoma cells were cultured
in DMEM supplemented with 10% FCS, 2 mM L-glutamine, and
antibiotic-antimyotic. Cultures were routinely checked for
Mycoplasma infection. DMEM, FCS, and antibiotic-antimyotic
were obtained from Life Technologies (Grand Island, NY) and RPMI 1640
was obtained from Bio-Whittaker Europe (Verviers, Belgium). SB203580
(4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)imidazole)
was obtained from Alexis Biochemicals (Leiden, The Netherlands).
SB203580 stock solution, dissolved in DMSO at 20 mM, was stored at
-20°C. In cell culture, SB203580 was used at 1–10 µM; the DMSO
concentration was never higher than 0.05%. Cells were incubated with
SB203580 for 1.5 h before stimulation. Stimulation was performed
with either LPS (Escherichia coli 0111:B4; Sigma, St. Louis,
MO; various concentrations), heat-killed Streptococcus
pneumoniae (HKSP; 2 x 107
bacteria/ml), human rTNF- (rhTNF-; Knoll, Ludwigshaven, Germany;
50 ng/ml), or lipoteichoic acid from S. aureus (Sigma; 250
ng/ml) for 8 or 16 h. Supernatants were collected and stored at
-20°C for later cytokine sampling with ELISA. All phosphospecific
Abs were obtained from New England Biolabs (Beverly, MA),
HRP-conjugated goat-anti-rabbit Ig was obtained from Dako
(Glostrup, Denmark). Lumilight+ substrate and the
Lumi-imager were obtained from Boehringer Mannheim (Mannheim,
Germany).
Murine models of disease
The animals used were 8-wk-old female BALB/c mice (Harlan Nederland, Horst, The Netherlands). All animal experiments were approved by the Institutional Animal Care and Use Committee of the Academic Medical Center. Experimental groups consisted of eight mice. For in vivo experiments, mice were subjected to 1 µM SB203580 per kilogram body weight (b.w.) by i.p. injection in 1 ml sterile saline or 1 µl solvent control (DMSO) in 1 ml sterile saline for controls. One and one-half hours before inducing disease SB203580 was administered, then given once daily, for up to 2 wk if appropriate. No apparent toxicity was observed.
Pneumococcal pneumonia was induced as described (18). Briefly S. pneumoniae serotype 3 was obtained from American Type Culture Collection (ATCC 6303; Manassas, VA). Pneumococci were grown for 6 h to midlogarithmic phase at 37°C in 5% CO2 using Todd-Hewittt broth (Difco, Detroit, MI), harvested by centrifugation at 1500 x g for 15 min, and washed twice in sterile isotonic saline. Bacteria were then suspended in sterile isotonic saline at 2 x 106 CFU/ml, as determined by plating serial 10-fold dilutions onto sheep-agar plates. Mice were lightly anesthetized by inhalation of isoflurane (Abott, Queensborough, Kent, U.K.). During this short anesthesia, intranasal inoculation was conducted by placing 50 µl suspension on the nares. At 24 h after inoculation, mice were anesthetized with Hyponorm (Jansen Pharmaceutica, Beerse, Belgium) and midazolam (Roche, Meidrecht, The Netherlands) and blood and whole lungs or bronchoalveolar lavage (BAL) fluid were obtained. Blood was collected from the vena cava inferior. Whole lungs were harvested and homogenized in 5 volumes of sterile isotonic saline with a tissue homogenizer that was carefully cleaned and disinfected with 70% alcohol after each homogenization. Serial 10-fold dilutions in sterile isotonic saline were made of these homogenates, and 50-µl volumes were plated onto sheep-blood agar plates and incubated at 37°C and 5% CO2. CFU were counted after 16 h. Homogenates of lungs were diluted 1:1 with lysis buffer (150 mM NaCl, 15 mM Tris, 1 mM MgCl, 1 mM CaCl2, 1% Triton X-100, and protease inhibitors) for 30 min at 4°C. Homogenates were then spun at 1500 x g at 4°C for 15 min, to remove cell debris, after which the supernatants were stored at -20°C until cytokine measurements. For BAL the trachea was exposed trough a midline incision and cannulated with a sterile 22-gauge Abbocath-T catheter (Abott, Sligo, Ireland). BAL was performed by instilling two 0.5 ml aliquots of sterile isotonic saline. Lavage fluid (0.8 ml) was retrieved per mouse and spun at 750 x g for 5 min at 4°C, and supernatants were frozen at -20°C until measurements were performed.
For induction of murine tuberculosis, M. tuberculosis (H37Rv laboratory strain) was grown in liquid Dubos medium containing 0.01% Tween 80 for 4 days. A replicate culture was incubated at 37°C and stirred gently, harvested at mid-log phase and stored at -70°C. Before the experiments, a vial was thawed and washed twice with sterile saline to clear the mycobacteria of medium. Mice were lightly anesthetized by inhalation of isoflurane. During this short anesthesia, intranasal inoculation was conducted by placing 105 viable M. tuberculosis organisms in 50 µl saline on the nares. The inoculum was plated immediately after inoculation to check on viable counts. At 2 wk after inoculation, mice were anesthetized with Hyponorm and midazolam and whole lungs were obtained. Lungs were handled as described previously, except for serial 10-fold plating which was performed on Middlebrook 7H11 plates containing oleic acid, albumin, dexrose, and catalase enrichment (Difco, Braunschweig, Germany) and CFU counting which was performed 3 wk after plating.
Endotoxemia was induced by injecting 150 µg of LPS i.p., 1.5 h after injection with SB203580 or DMSO control. Animals were sacrificed 0, 15, 30, 60, or 90 min after LPS injection. Blood was removed through cardiac puncture and spun at 7000 x g; supernatants were collected and stored at -20°C for later cytokine determination. Spleens were removed and snap frozen in liquid NO2, then stored at -80°C until further processing.
Western blot analysis
Spleens were thawed at 4°C and passed through a 40-µm
strainer, which was then rinsed with ice-cold PBS. Cells were spun down
and resuspended in ice-cold cell lysis buffer (20 mM Tris (pH 7.5), 150
Mm NaCl, 1 mM EDTA, 1 mM EGTA, 1% Triton X-100, 2.5 mM sodium
pyrophosphate, 1 mM -glycerolphosphate, 1 mM
Na3VO4 1 µg/ml leupeptin
and 1 mM Pefabloc). Samples were sonicated four times for 5 s on
ice and spun at 7000 x g for 10 min at 4°C. Protein
concentration in the clear supernatant was determined according to
Bradford, the supernatant was then stored at -80°C. Approximately 37
µg splenic cell lysate was mixed with 4x SDS-sample buffer, and the
mixture was boiled for 5 min followed by brief centrifugation. Samples
were loaded on 10% SDS-polyacrylamide gels and transferred to
polyvinylidene difluoride membranes (Millipore, Bedford, MA). To check
for equal loading of protein in each lane, Coomassie brilliant blue
staining of the membrane was performed. Subsequently, membranes were
blocked in 2% nonfat dry milk in PBS supplemented with 0.1% Tween 20
and washed in 0.2% nonfat dry milk in PBS supplemented with 0.1%
Tween20. The extent of p38 MAPK activation was determined using Abs
against phosphorylated
(Thr180/Tyr182) p38 MAPK,
used in a 1:1000 dilution overnight. After three washes for 10 min
secondary Ab incubation was performed for 1 h with HRP-conjugated
goat-anti-rabbit Ig in a 1:2000 dilution. After enhanced
chemoluminescence using Lumilight+ substrate, Ab
binding was visualized using a Lumi-imager. The membranes were then
stripped with strip buffer (62.5 mM Tris-HCl (pH 6.8), 2% SDS, and 100
mM 2-ME) and reprobed with Ab for p38 MAPK (New England Biolabs) by a
similar procedure.
In vitro p38 MAPK assay
This assay was performed using the p38 MAPK assay kit purchased
from New England Biolabs. Splenic cell lysates were prepared as
described previously for immunoblotting. A once-diluted slurry of
agarose hydrazide-bound Abs to phosphorylated
(Thr180/Tyr182) p38 MAPK
(40 µl) was used to selectively immunoprecipitate active p38 MAPK
from 
100 µg splenic cell lysate (in 200 µl cell lysis buffer) by
gently shaking overnight at 4°C. The immunoprecipitate was washed
twice with 500 µl of ice cold cell lysis buffer and twice with 500
µl of ice cold kinase buffer (25 mM Tris (pH 7.5), 5 mM
-glycerolphosphate, 2 mM DTT, 0.1 mM
Na3VO4, 10 mM
MgCl2) at 4°C. The kinase reactions were
conducted in the presence of 200 µM ATP and 2 µg ATF-2 fusion
protein at 30°C for 30 min. After the reaction had been terminated by
the addition of 3x SDS-sample buffer, the mixture was boiled for 5 min
followed by brief centrifugation. ATF-2 phosphorylation was selectively
measured by Western immunoblotting as described previously using
specific Abs against phosphorylated (Thr71)
ATF-2.
Cytokine determination
Cytokines were measured by using commercially available ELISAs
as follow according to the manufacturers recommendations: murine
TNF- (Genzyme, Cambridge, MA), IL-6 (PharMingen, San Diego, CA), and
human TNF- (Central Laboratory of the Netherlands Red Cross Blood
Transfusion Service, Amsterdam, The Netherlands).
Statistical analysis
Data were statistically analyzed by the Student’s t test unless otherwise mentioned. All data are given as the mean ± SEM.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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A large variety of inflammatory stimuli activate p38 MAPK and a
role for p38 MAPK in the regulation of cytokine production has been
suggested. The nature of this role is unclear. Most authors report
reduced cytokine production upon p38 MAPK inhibition (e.g., Lee et al.,
Ref. 1), but enhanced cytokine release has also been
reported (e.g., Zhang et al., Ref. 14). Therefore, we
investigated the influence of the p38 MAPK inhibitor SB203580 on
TNF--induced IL-6 production in L929 fibrosarcoma cells and on
LPS- or HKSP-stimulated TNF- and IL-6 production by 4-4 macrophages.
In agreement with Beyaert et al. (12), cells pretreated
with SB203580 showed reduced IL-6 production upon stimulation with
TNF- (p = 0.01; Fig. 1
A). In contrast,
SB203580-pretreated 4-4 macrophages stimulated with HKSP showed
enhanced IL-6 production (p < 0.05; Fig. 1B). 4-4 macrophages pretreated with SB203580 showed
enhanced TNF- production upon stimulation with LPS as compared with
vehicle-treated cells (p < 0.05 when pooled
experiments are tested with the Wilcoxon test; a representative
experiment is shown in Fig. 1C). and also HKSP induced
enhanced TNF- production upon p38 MAPK inhibition in these cells
(p < 0.01; Fig. 1D). Subsequently
we decided to investigate the effects of p38 MAPK inhibition on
cytokine release in nontransformed cells. LPS-stimulated whole blood
showed inhibition of TNF- production by SB203580 (10 µM SB203580,
p < 0.01; 1 µM SB203580, p < 0.01;
Fig. 2A) but peritoneal
macrophages exhibited increased TNF- levels upon p38 MAPK inhibition
(10 µM SB203580, p < 0.01; 1 µM SB203580,
p < 0.05; Fig. 2B). To further exclude the
possibility that the differences in effect of p38 MAPK inhibition on
cytokine production may be condition dependent rather than a cell
type-specific effect, we stimulated 4-4 macrophages with rhTNF- and
lipoteichoic acid from S. aureus, and peritoneal macrophages
with HKSP. The results are summarized in Table I and all show increased cytokine release
upon p38 MAPK inhibition in macrophages. Apparently p38 MAPK has
distinct functions in the regulation of cytokine release in different
cell types, macrophages responding to p38 MAPK inhibition with
increased cytokine production but other cell types showing diminished
release.
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The contrasting effect of p38 MAPK inhibition on cytokine
production in different cell types prompted us to investigate the
relevance of this phenomenon in in vivo models of disease. The ability
of SB203580 to inhibit p38 MAPK enzymatic activity in vitro is well
established (4) but its potency in vivo is less clear. To
test the capacity of SB203580 to inhibit p38 MAPK in vivo, we used a
murine endotoxemia model. As shown in Fig. 3, LPS-dependent p38 MAPK phosphorylation
and enzymatic activity was detectable in spleen cells obtained from
mice treated with solvent control. However, in SB203580-treated mice,
almost no enzymatic activity of the kinase was detected although
phosphorylation of the enzyme was much more pronounced, demonstrating
that the inhibitor interfered with kinase activity itself but did not
inhibit the signal transduction cascade leading to the phosphorylation
of Thr180/Tyr182, further
supporting the specificity of this compound. However, despite the
inhibition of p38 MAPK, no significant differences in the LPS-induced
TNF- production was measured in the plasma (Fig. 4A). These results are, to our
knowledge, the first demonstration of p38 MAPK activation in an in vivo
model of disease, but do not support a role for p38 MAPK in the
regulation of endotoxemia-induced cytokine release.
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levels in murine models of
pneumococcal pneumonia and tuberculosis
To further investigate the role of p38 MAPK in in vivo models of
disease we tested SB203580 in murine pneumococcal pneumonia and
tuberculosis. Induction of both diseases was associated with a marked
increase in TNF- levels in lung homogenates or BAL fluid, in
parallel with a rise in the numbers of CFU in lung homogenates. TNF-
levels were enhanced in the SB203580-treated group compared to controls
in both lung homogenates (p < 0.01) and BAL
fluid (p < 0.05) from mice with pneumococcal
pneumonia (Fig. 4
, B and C) and the lung
homogenates from mice with tuberculosis (p =
0.01; Fig. 4D). In both the pneumococcal pneumonia model and
the tuberculosis model the numbers of CFU in the SB203580-treated group
were significantly higher (pneumococcal pneumonia, p <
0.01; tuberculosis, p < 0.05; Fig. 5). We conclude that the stimulation of
cytokine release observed in p38 MAPK-inhibited macrophages in vitro is
also reflected in increased cytokine production in vivo and is
accompanied by severely reduced bacterial clearance, suggesting that
p38 MAPK directed anti-cytokine strategy in infectious disease is
not advisable.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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-stimulated
L929 fibrosarcoma cells and in LPS-challenged whole blood p38 MAPK
activity is required for cytokine production. Strikingly, however, we
observed that inhibition of p38 MAPK stimulated cytokine production in
a macrophage cell line as well as in nontransformed peritoneal
macrophages. Hence we suggest that p38 MAPK acts in a cell-specific
fashion, its inhibition increasing cytokine release in macrophages,
while such inhibition reduces cytokine release in other cell types.
As p38 MAPK has been suggested to be a suitable target for in vivo
anti-cytokine therapy in a number of inflammatory diseases, the
possible cell type-specific effects of p38 MAPK inhibition make it
important to assess the action of p38 MAPK inhibition on cytokine
production during pathophysiology in vivo. Interestingly, p38 MAPK
inhibition had no effect on plasma TNF- levels of LPS-challenged
mice. This observation may be explained in two ways: either different
TNF- production from different cell types cancel each other out,
or p38 MAPK contributes less to the generation of TNF- levels,
induced by in vivo LPS challenge, than hitherto assumed. In both the
murine pneumococcal pneumonia model and the tuberculosis model, higher
levels of TNF- were found in lung homogenates or BAL fluid from
SB203580-treated mice. Macrophages are likely to play a role in
cytokine production both in pneumococcal pneumonia as well as in
tuberculosis (19, 20), although other cell types are
obviously involved as well. Thus, the enhanced TNF- levels observed
in these pneumonia models, after p38 MAPK inhibition, may be an in vivo
reflection of the increased cytokine production we encountered in p38
MAPK-inhibited macrophages in vitro. However, it should be stressed
that our measurements cannot discriminate between different cell-types.
Thus it is possible that at the concentrations used, p38 MAPK in
macrophages is not really inhibited in vivo. Hence the final proof of
the notion that the enhanced cytokine levels observed in p38
MAPK-inhibited animals reflect cell type-specific effects of this
inhibition, as opposed to a dose-response-specific effect for different
cells under different conditions, awaits experiments in which p38 MAPK
is cell type-specific knocked out. Until then, other possibilities
should be kept in mind. For instance, the increase in cytokine
production in SB203580-treated mice may have resulted from the observed
increased bacterial burden in the p38 MAPK-inhibited group.
The reduced bacterial clearance and increased cytokine production encountered in p38 MAPK-inhibited mice strongly argue against a function of p38 MAPK inhibitors in therapeutic anti-cytokine strategy in infectious disease or in individuals at risk for infectious disease. As the main proposed beneficiaries of anti-p38 MAPK therapy are patients with autoimmune disease who typically are treated with immune-suppressive drugs; this is an important consideration.
Although stimulation of p38 MAPK is assumed to be a general response to inflammatory stimuli in vivo, actual activation of this kinase in a disease model had not yet been shown. To assess the role of p38 MAPK we used a murine model for endotoxemia since acute i.p. application of LPS should produce a rapid and synchronized activation of p38 MAPK. Indeed, we were able to demonstrate, using the endotoxemia model, in vivo activation of p38 MAPK. This was evident from both its enhanced phosphorylation state as well as by increased kinase activity when assayed by an in vitro kinase assay. Furthermore, the latter assay showed the efficacy of i.p.-administrated SB203580 to inhibit in vivo p38 MAPK activity. These experiments also provided further proof as to the specificity of the inhibitor; we observed enhanced levels of p38 MAPK phosphorylation in SB203580-treated animals, demonstrating that the inhibitor does not interfere with an upstream activator of this kinase. This SB203580-induced enhanced p38 MAPK phosphorylation may reflect the action of a p38 MAPK-dependent feedback mechanism, regulating the phosphorylation state of this kinase. If such a feedback mechanism involves the deactivation of p38 MAPK upstream activators, which may regulate other targets apart from p38 MAPK, inhibition of p38 MAPK enzymatic activity would result in sustained stimulation of such other targets. In turn, such target may mediate the enhanced cytokine release observed in our study. If this hypothesis is confirmed, this would imply that p38 MAPK inhibitors would be relatively ineffective for reducing cytokine release (at least in macrophages) but in contrast, inhibitors of its upstream activators would be suitable targets for anti-cytokine therapy.
Our results contradict a previous report in which a small number of
mice was challenged with LPS and inhibition of TNF- production was
noted, although no actual inhibition of p38 MAPK activity was shown in
this study (21). However, this effect of SB203580 was only
observed in mice at concentrations in excess of 34 µM/kg b.w.,
whereas in the present study we have demonstrated complete inhibition
of p38 MAPK enzymatic activity in vivo at a SB203580 concentration of 1
µM/kg b.w. As SB203580 has been reported to inhibit other kinases at
concentration in excess of 10 µM (22) it is possible
that inhibition of these kinases may explain the discrepancy between
this earlier report and our study.
The most puzzling finding in the present study is the apparent
cell-specific effect of p38 MAPK inhibition on cytokine release,
enhancing cytokine production in peritoneal macrophages and a
macrophage cell line but inhibiting this production in other cell types
and whole blood. Recently it was reported that p38 MAPK inhibits
TNF--induced inhibitory protein that dissociates with NF-
B
phosphorylation and degradation (23, 24) and thus p38 MAPK
may negatively regulate the NF-B pathway, of which the involvement
in cytokine production is undisputed. Thus the effects of p38 MAPK
inhibition on cytokine release may result from negative signaling of
p38 MAPK toward the NF-B pathway. We are currently exploring this
possibility.
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Acknowledgments |
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Footnotes |
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2 Abbreviations used in this paper: MAPK, mitogen-activated protein kinase; MKK, MAPK kinases; ATF-2, activating transcription factor-2; HKSP, heat-killed Streptococcus pneumoniae; rhTNF, human rTNF-; BAL, bronchoalveolar lavage; b.w., body weight.
Received for publication May 15, 2000. Accepted for publication October 9, 2000.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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mitogen-activated protein kinase, a developmentally regulated protein kinase that is activated by stress and proinflammatory cytokines. J. Biol. Chem. 274:7095.-induced phosphorylation and activation of cytosolic phospholipase A2 are abrogated by an inhibitor of the p38 mitogen-activated protein kinase cascade in human neutrophils. Biochem. J. 319:17.
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Y. Takanami-Ohnishi, S. Amano, S. Kimura, S. Asada, A. Utani, M. Maruyama, H. Osada, H. Tsunoda, Y. Irukayama-Tomobe, K. Goto, et al. Essential Role of p38 Mitogen-activated Protein Kinase in Contact Hypersensitivity J. Biol. Chem., September 27, 2002; 277(40): 37896 - 37903. [Abstract] [Full Text] [PDF]
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J. Arcaroli, K.-Y. Yang, H.-K. Yum, J. Kupfner, T. M. Pitts, J. S. Park, D. Strassheim, and E. Abraham Effects of catecholamines on kinase activation in lung neutrophils after hemorrhage or endotoxemia J. Leukoc. Biol., September 1, 2002; 72(3): 571 - 579. [Abstract] [Full Text] [PDF]
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M. D. Lehner, F. Schwoebel, A. Kotlyarov, M. Leist, M. Gaestel, and T. Hartung Mitogen-Activated Protein Kinase-Activated Protein Kinase 2-Deficient Mice Show Increased Susceptibility to Listeria monocytogenes Infection J. Immunol., May 1, 2002; 168(9): 4667 - 4673. [Abstract] [Full Text] [PDF]
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J. Branger, B. van den Blink, S. Weijer, J. Madwed, C. L. Bos, A. Gupta, C.-L. Yong, S. H. Polmar, D. P. Olszyna, C. E. Hack, et al. Anti-Inflammatory Effects of a p38 Mitogen-Activated Protein Kinase Inhibitor During Human Endotoxemia J. Immunol., April 15, 2002; 168(8): 4070 - 4077. [Abstract] [Full Text] [PDF]
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E. Carballo, H. Cao, W. S. Lai, E. A. Kennington, D. Campbell, and P. J. Blackshear Decreased Sensitivity of Tristetraprolin-deficient Cells to p38 Inhibitors Suggests the Involvement of Tristetraprolin in the p38 Signaling Pathway J. Biol. Chem., November 2, 2001; 276(45): 42580 - 42587. [Abstract] [Full Text] [PDF]
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