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Department of Surgery, University of Washington School of Medicine, Seattle, WA 98195
| Abstract |
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, is critical in the regulation of the acute
inflammatory response to infectious challenge. IL-8 is a potent
chemoattractant and activator of neutrophils. TNF-
, a
proinflammatory cytokine, initiates expression of endothelial cell
surface adhesion molecules and neutrophil migration. p38, a member of
the mitogen-activated protein kinases, plays an important role in
mediating intracellular signal transduction in endotoxin-induced
inflammatory responses. We examined the effects of LPS and ethanol on
p38 activation and the corresponding IL-8 and TNF-
production in
human mononuclear cells. LPS-induced IL-8 and TNF-
production was
inhibited in a similar pattern by pretreatment with either EtOH or
SB202190 (1 µM), a specific inhibitor of p38 kinase. Western blot
analysis, using a dual phospho-specific p38 mitogen-activated protein
kinase Ab, demonstrated that EtOH pretreatment inhibited LPS-induced
p38 activation. These results demonstrate that alcohol suppresses the
normal host immune inflammatory response to LPS. This dysregulation
appears to be mediated in part via inhibition of p38 activation.
Inhibition of IL-8 and TNF-
production by acute EtOH intoxication
may inhibit inflammatory focused neutrophil migration and activation
and may be a mechanism explaining the increased risk of trauma- and
burn-related infections. | Introduction |
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LPS, the outer component of the Gram-negative bacterial cell wall, is a
powerful activator of host mononuclear cells and prompts the synthesis
and release of multiple cytokines (11). The production of these
cytokines, particularly IL-8 and TNF-
, is central in the regulation
of the acute inflammatory response to bacterial challenge (1, 2, 3, 4, 5, 6, 7, 8). IL-8
or neutrophil-activating peptide is a potent chemoattractant (12, 13, 14, 15)
as well as a crucial activator of neutrophils for an optimal immune
response to bacterial foci (16, 17, 18). TNF-
, a proinflammatory
cytokine critical to the initiation of multiple components of the host
immuno-inflammatory response, stimulates the endothelial cell to
express cell surface adhesion molecules and initiates neutrophil
migration to foci of inflammation or tissue injury (19).
Several in vivo studies have demonstrated that acute alcohol
intoxication inhibits neutrophil chemotaxis and suppresses the
responses to various inflammatory stimuli. However, the mechanism of
this action remains ill defined (20, 21, 22, 23). Inhibition of neutrophil
recruitment and migration may explain the observed increase in
infection rate in trauma and burn victims with acute alcohol
intoxication (24, 25). LPS-induced activation of specific signal
transduction pathways, such as p38 MAPK, may be critical in the
appropriate cytokine production and inflammatory cell responses to
infection. In the current study we examined the effect of ethanol
(EtOH) on LPS-induced p38 activation in the human mononuclear cells
(HMO) and the corresponding effect on IL-8 and TNF-
production.
| Materials and Methods |
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Human blood from healthy adult volunteers was drawn into polypropylene syringes containing sodium citrate. HMO were isolated from the buffy coat layer of a Ficoll-Paque (Pharmacia, Piscataway, NJ) density centrifugation gradient. The cells were washed with normal saline and resuspended in RPMI 1640 (BioWhittaker, Walkersville, MD) with 100 µg/ml of gentamicin and 10% heat-inactivated adult bovine serum. HMO at 1 x 106 cells/ml were placed in round-bottom, 12- x 75-mm polypropylene tubes and treated with or without Escherichia coli 0111:B4 LPS (Sigma, St. Louis, MO). Some cells were pretreated with either SB202190 (Calbiochem, La Jolla, CA) or absolute ethanol (McCormick Distilling, Weston, MO) at varying doses for 1 h. Ethanol doses were expressed as a percentage (weight/volume), similar to legal statutes, and values were confirmed by the Harborview Medical Center Toxicology Laboratory (Seattle, WA). After 24 h of LPS treatment, cell supernatants were harvested and frozen at -70°C for later cytokine analysis. Cell viability was confirmed by trypan blue exclusion.
IL-8, TNF-
, and IL-6 determinations
IL-8, TNF-
, and IL-6 were quantitated by Titerzyme enzyme
immunoassay kits from PerSeptive Biosystems (Framingham, MA), which are
based on coated well, sandwich enzyme immunoassays.
Northern blots
HMO were placed in 50-ml polypropylene tubes at 15 x 106 cells/tube. After 8 h of LPS stimulation, total cellular RNA was extracted using the Ultraspec RNA isolation system (Biotex Laboratories, Houston, TX). Fifteen micrograms of RNA were electrophoresed in a denaturing 1.25% agarose-formaldehyde gel and transferred to a Hybond-N nylon membrane (Amersham, Arlington Heights, IL). IL-8 mRNA was determined by hybridizing the membrane overnight at 42°C in hybridization buffer (5x SSPE, 50% formamide, 1% SDS, and 0.1 g/ml polyethylene glycol) containing an IL-8 cDNA probe. The IL-8 probe is a 40-mer oligonucleotide (Oncogene, Cambridge, MA) end labeled with [32P]ATP (New England Nuclear, Boston, MA). The membrane was then autoradiographed using an intensifying screen with exposure of Kodak XAR-5 film (Eastman Kodak, Rochester, NY) for 45 days. To assure equal loading, the membrane was stripped and rehybridized with [32P]ATP-labeled 28S ribosomal RNA cDNA probe. The autoradiograms were analyzed by densitometry using the NIH Image program.
Western blots
HMO were placed in 50-ml polypropylene tubes at 10 x 106 cells/tube. After 15 min of LPS stimulation, total cellular protein was extracted by lysing the cells in 1 ml of lysis buffer (20 mM Tris, 137 mM NaCl, 2 mM EDTA, 10% glycerol, 1% Triton X-100, 1 µM sodium orthovanadate, 100 µM DTT, 200 µM PMSF, 10 µg/ml leupeptin, and 0.15 U/ml aprotinin) at 4°C. Protein concentration was determined by the bicinchoninic acid protein assay (Pierce, Rockford, IL). Twenty micrograms of protein was electrophoresed in a 10% SDS-PAGE gel and transferred to a Hybond-ECL nitrocellulose membrane (Amersham, Arlington Heights, IL). The membrane was blocked for 1 h at room temperature with 5% milk, then incubated with a phospho-specific p38 MAPK (Thr180/Tyr182) Ab (New England Biolabs, Beverly, MA) or a phospho-specific ERK1/ERK2 (Thr202/Tyr204) MAPK Ab (New England Biolabs) overnight at 4°C. These phospho-specific MAPK Abs detect p38 or ERK only when activated by dual phosphorylation. The membrane was then incubated with an HRP-conjugated secondary Ab for 1 h at room temperature. The blot was developed using the SuperSignal chemiluminescent substrate (Pierce) and was exposed to Kodak XAR-5 film; densitometry by the NIH Image program was used to quantitate the OD.
Statistical analysis
Values were expressed as the mean ± SD. Data were analyzed by ANOVA, with post-hoc testing by Fishers least significant difference test. A p value of <0.05 was considered significant.
| Results |
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We studied the LPS-induced p38 activation in HMO using a dual
phospho-specific Ab that binds only to the activated p38. LPS
activation of p38 peaked at 30 min and returned to baseline in 2 h
(data not shown). Western blot analysis demonstrated that LPS,
throughout the dose range of 10 pg/ml to 100 ng/ml, activated p38 in a
linear fashion with respect to the log doses of LPS (Fig. 1
). Western blot analysis using
phospho-specific ERK Ab demonstrated no significant ERK activation in
response to the same dose range of LPS (data not shown).
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LPS stimulated HMO to produce up to 40 ng/ml of IL-8 compared with
12 ng/ml in controls (Fig. 3
). However,
IL-8 production, in contrast to p38 activation, which was linear with
respect to log doses of LPS, reached an early plateau at the threshold
LPS dose of 1 ng/ml. Increasing the LPS dose above 1 ng/ml did not
significantly increase IL-8 production. IL-8 production was inhibited
by SB202190 (1 µM) pretreatment, a specific p38 inhibitor, but this
inhibitory effect was less efficient with increasing LPS dose beyond
the threshold. Similar to the SB202190 inhibition, alcohol inhibited
IL-8 production by HMO. This inhibition was also less efficient beyond
the LPS dose of 1 ng/ml. Similar results were obtained using SB203580
(1 µM) pretreatment (data not shown).
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production by HMO
LPS also stimulated TNF-
production by HMO (Fig. 6
A). TNF production reached
statistical significance at LPS doses higher than 1 ng/ml. Throughout
the LPS dose range, SB202190 pretreatment inhibited TNF production by
6070%. Similar to SB202190, 0.8% EtOH pretreatment inhibited
TNF-
production by 70%. TNF production induced by 100 ng/ml of LPS
was inhibited by EtOH pretreatment in a dose-related manner (Fig. 6
B).
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LPS also caused increased production of IL-6 by HMO. IL-6
production by HMO in response to LPS was not inhibited by alcohol (Fig. 7
). These data demonstrate that
inhibition of IL-8 and TNF-
by EtOH does not appear to be due to a
global inhibition of cytokine production or diffuse nonspecific
toxicity.
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| Discussion |
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In addition, we studied the pattern of IL-8 production by HMO and compared it to that of p38 activation. LPS induced p38 phosphorylation and activation in a dose-related manner. p38 activation occurred at low doses of LPS (<100 pg/ml) and resulted in a significant amount of IL-8 production. At lower levels of p38 activation (LPS dose <1 ng/ml), IL-8 production was attenuated with 1 µM SB202190 pretreatment, approaching control levels. However, IL-8 production, in contrast to p38 activation, which was linear with respect to log doses of LPS, reached a plateau at an LPS dose of 1 ng/ml. Increasing p38 activation with doses of LPS above 1 ng/ml did not translate into more IL-8 production. The increased levels of p38 activation, however, rendered the HMO resistant to the inhibitory effect of SB202190 pretreatment. The inability to effectively inhibit IL-8 production when the p38 level of activation was beyond the maximal response may explain the inconsistencies demonstrated between effective in vitro control of inflammatory mediators under controlled stimulatory conditions and the lack of response in clinically relevant in vivo models, where activation has exceeded the capacity of inhibitors to down-regulate the HMO and inflammatory responses.
In contrast, significant TNF-
production by HMO occurred only at
higher doses of LPS (1 ng/ml and higher). Although the rate of increase
in TNF-
production decreased at higher LPS doses, there was no
plateau, up to 1 µg/ml of LPS (data for LPS dose >100 ng/ml not
shown). The 1-µM SB202190 pretreatment continued to effectively
and proportionately inhibit TNF-
production.
Similar to SB202190, EtOH pretreatment inhibited both IL-8 and TNF-
production by HMO. This inhibition was dose dependent and, in the case
of IL-8, was significant at 0.1% EtOH. This observation has potential
clinical significance, as approximately 30% of seriously injured
patients have blood alcohol levels higher than 0.2% (25). This effect
is not a global toxicity, since cells remained viable and able to
exclude trypan blue over 24 h, IL-6 production by HMO was not
inhibited by EtOH, and the inhibition of IL-8 production could be
overcome by increasing the LPS dose.
Both EtOH and SB202190 inhibited the LPS-induced increase in IL-8 mRNA
levels using Northern blot analysis. Nair et al. demonstrated a
decrease in TNF-
mRNA with alcohol treatment using RT-PCR in HMO
(31). To our knowledge this is the first report of inhibition of
IL-8 production by alcohol pretreatment, and in the case of TNF-
our
results agree with the literature (31, 32).
EtOH may inhibit LPS-induced IL-8 and TNF-
production via the p38
pathway. p38 MAPK plays a regulatory role in IL-8 and TNF-
production (33, 34). The pattern of EtOH inhibition of IL-8 and TNF-
production is very similar to that of SB202190, a p38 MAPK inhibitor.
Furthermore, Western blot analysis using the dual phospho-specific p38
Ab demonstrated inhibition of LPS-induced p38 activation by EtOH
pretreatment in a dose-related manner.
The mechanism of inhibition of p38 MAPK activation by alcohol is not clear. One possible mechanism may involve phospholipase D. EtOH serves as a false substrate, replacing water, in the phospholipase D-catalyzed hydrolytic cleavage of choline from phosphatidylcholine (35, 36, 37), thus producing phosphatidylethanol instead of phosphatidic acid, an important second messenger in the inflammatory response (38). Further studies are needed to investigate this potential mechanism.
In the clinical arena, acute intoxication suppresses the inflammatory response in normal subjects by inhibiting granulocyte migration (20, 21, 22, 23). The inhibition of neutrophil migration in vivo has been demonstrated in both human and animal models. This has been implicated as a major cause of the increased risk of infection following trauma and burns (24, 25). Spagnuolo and MacGregor (22) demonstrated that acute alcohol intoxication suppresses granulocyte migration to inflammatory sites in man. To further define the mechanism of this anti-inflammatory action, granulocytes were subjected to an in vitro neutrophil migration assay. These studies demonstrated no inhibition of neutrophil chemotaxis in cells exposed to alcohol, concluding that the inhibition of neutrophil chemotaxis does not appear to be a direct effect on neutrophils.
Our studies suggest that acute ethanol intoxication may impair
neutrophil chemotaxis by inhibiting IL-8 and TNF-
production at the
inflammatory sites in response to stimuli such as LPS. IL-8 is a potent
neutrophil chemoattractant and causes a rapid and prolonged neutrophil
recruitment and accumulation at the site of injection (12, 13, 14, 15, 16, 17, 18). TNF-
also plays a key role in the neutrophil inflammatory response;
specifically, TNF-
produced by monocytes/macrophages at the site of
inflammation activates endothelial cells to express cell surface
adhesion molecules that modulate rolling, adherence, and migration of
neutrophils (19). Therefore, inhibition of IL-8 and TNF-
production
may explain the block of neutrophil recruitment and migration to
areas of acute inflammation.
In summary, we have demonstrated that LPS-induces p38 activation in
HMO, which plays a key role in IL-8 and TNF-
production. Alcohol
inhibits LPS-induced p38 activation. This correlates with inhibition of
IL-8 and TNF-
production by HMO. This inhibition of IL-8 and TNF-
production may be a mechanism explaining the inhibition of neutrophil
chemotaxis by alcohol intoxication in vivo.
| Footnotes |
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2 Address correspondence and reprint requests to Dr. Saman Arbabi, Department of Surgery, University of Washington, 1959 NE Pacific Street, Box 356410, Seattle, WA 98195. E-mail address: ![]()
3 Abbreviations used in this paper: MAPK, mitogen-activated protein kinase; ERK, extracellularly regulated kinase; EtOH, ethanol; HMO, human mononuclear cells. ![]()
Received for publication January 28, 1999. Accepted for publication April 6, 1999.
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