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Antimicrobial Agents and Chemotherapy, December 2003, p. 3704-3707, Vol. 47, No. 12
0066-4804/03/$08.00+0 DOI: 10.1128/AAC.47.12.3704-3707.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
Division of Infectious Disease, Department of Internal Medicine,1 Clinical Research Institute, College of Medicine, Catholic University of Korea, Seoul, Korea2
Received 24 March 2003/ Returned for modification 30 June 2003/ Accepted 8 September 2003
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) and/or
interleukin-6 (IL-6) by PBMCs stimulated with lipopolysaccharide (LPS),
lipoteichoic acid (LTA), and heat-killed bacteria in a
concentration-dependent manner without cytotoxic effects. The addition
of moxifloxacin reduced the population of cells positive for CD-14
and TNF-
and for CD-14 and IL-6 among the LPS- or
LTA-stimulated PBMCs. By Western blot analysis, moxifloxacin
pretreatment reduced the degradation of I
B
in
LPS-stimulated PBMCs. In conclusion, moxifloxacin could interfere with
NF-
B activation by inhibiting the degradation of
I
B
and reduce the levels of production of
proinflammatory
cytokines. |
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Among numerous antibiotics, quinolones exert various immunomodulatory effects and are widely used in clinical practice, and newer quinolones with enhanced potencies against microorganisms are continuously being developed (7, 14-17).
In this study, we wanted to evaluate the effects of moxifloxacin, a synthetic methoxyfluoroquinolone with a broad antibacterial spectrum used for numerous clinical indications, on the production of some proinflammatory cytokines from peripheral blood mononuclear cells (PBMCs). The immunomodulatory effects of moxifloxacin were compared to those of another fluoroquinolone, levofloxacin, and a ß-lactam antibiotic, ceftriaxone. In addition, the pathway responsible for these changes was evaluated.
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Streptococcus pneumoniae and E. coli were also used as stimulants. They were isolated from the blood of patients in St. Mary's Hospital. E. coli was cultured in Mueller-Hinton broth (Becton Dickinson, Sparks, Md.) and S. pneumoniae was cultured in Mueller-Hinton broth with 5% lysed horse blood (Becton Dickinson, Cockeysville, Md.) at 37°C. The colonies were then harvested by centrifugation, washed twice in phosphate-buffered saline (PBS), killed by incubation at 65°C for 20 min, and stored at -70°C until use.
Isolation and stimulation of PBMCs. Blood was obtained by venipuncture from healthy volunteers. PBMCs were separated on Ficoll-Paque (Sigma) density gradients, washed twice with calcium- and magnesium-free PBS, and resuspended in RPMI 1640 with L-glutamine containing 10% fetal bovine serum and 25 mM HEPES at a density of 106 cells/ml. The cells were exposed to 100 ng of LPS per ml, 1 µg of LTA per ml, or 107 CFU of heat-killed bacteria per ml with or without antibiotic treatment. Adequate concentrations of LPS, LTA, and bacteria were finally made with RPMI 1640, and an equal volume of each stimulus was added to same volume of the PBMC preparation.
ELISA for cytokine
release.
Cells were seeded
into 24-well plates at a density of 106 cells/well and were
incubated for 6 h in the presence of LPS, LTA, and
heat-killed S. pneumoniae or E. coli with or without
antibiotics. The cell-free supernatant was collected by centrifugation
and stored at -70°C. The concentrations of tumor
necrosis factor alpha (TNF-
), and interleukin-6 (IL-6) were
assayed with enzyme-linked immunosorbent assay (ELISA) kits (BD
Pharmingen, San Diego, Calif.) according to the protocol of the
manufacturer.
Viability assay. The viabilities of PBMCs treated with moxifloxacin were evaluated by the 3-(4,5-dimethylthiazole-2-y1)-2,5-diphenyltetrazolium bromide (MTT) assay (R&D Systems, Inc., Minneapolis, Minn.). In brief, aliquots of 104 cells/well were distributed in 96-well tissue culture plates (Nunc, Rosklide, Denmark) in 0.1 ml of 10% fetal calf serum-RPMI 1640 medium and incubated at 37°C with or without moxifloxain for 24 and 48 h. After incubation, MTT solution was added to the culture medium to achieve a final concentration of 1 mg/ml. After 2 h of incubation at 37°C, detergent solution was added to solubilize the colored formazan crystal produced from MTT. The absorbance was read at 550 nm with a spectrophotometer, and the percentage of viable cells was calculated.
Flow cytometry for detection
of cytokine-producing PBMCs.
PBMCs were incubated in the absence
or presence of moxifloxacin (10 µg/ml) and stimulant (1
µg of LTA per ml or 100 ng of LPS per ml) for 6 h at
37°C in 24-well plates. After incubation, 105 cells
were harvested, washed twice with PBS, and distributed into polystyrene
round-bottom tubes for immunolabeling. Two-color staining for the
detection of cell surface markers (CD-14) and intracellular
TNF-
or IL-6 was performed by the protocol of the manufacturer
(BD Pharmingen). Flow cytometric analysis was performed on a FACScan
instrument (Becton Dickinson, San Jose, Calif.). The percentage of
double-stained cells (cells positive for CD-14 and TNF-
and
for CD-14 and IL-6) among the stimulated PBMCs was calculated and
compared by stimulus.
Western blot
analysis of I
B.
PBMCs were exposed to 100 ng of LPS
per ml with or without pretreatment with 10 µg of moxifloxacin
per ml for 1 h. Nuclear extracts were harvested from the
stimulated cells by the method described by Ichiyama et al.
(5). The protein
concentrations were determined with Bio-Rad (Hercules, Calif.) protein
concentration reagents. Samples containing 30 µg of protein
were separated by electrophoresis on a 10% polyacrylamide gel
and were then transferred to a polyvinylidene difluoride membrane.
After the membranes were washed three times in TBST (10 mM Tris-Cl
[pH 8.0], 0.05% 150 mM NaCl, Tween 20), they were
incubated overnight in a 1:1,000 dilution of rabbit polyclonal
anti-I
B
antibodies (Cell Signaling Technology Inc.,
Beverly, Mass.) in TBST containing 5% skim milk at 4°C.
After the membranes were washed in TBST, they were incubated in a
1:2,000 dilution of horseradish peroxidase-conjugated anti-rabbit
immunoglobulin G (Santa Cruz Biotechnology, Santa Cruz, Calif.) for
2 h at room temperature. Chemiluminescent detection was
performed with enhanced chemiluminescence (ECL) reagents (Amersham
Pharmacia Biotech, Piscataway, N.J.) after the membranes were washed in
TBST. Autoradiography of the membranes was performed with Hyperfilm-ECL
(Amersham Pharmacia
Biotech).
Statistical analysis. All experiments were repeated at least three times. Statistical analysis was performed by analysis of variance by Tukey's method or the Scheffe test. A P value of <0.05 was judged to be statistically significant.
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and IL-6 release from
PBMCs in a concentration-dependent manner without
cytotoxicity.
To determine
the effects of antibiotics on cytokine production, LPS, LTA, or
bacteria were added to PBMCs with or without antibiotics. None of the
antibiotics used in the experiments led to the production of cytokines
by the PBMCs without stimulation. LPS, LTA, and bacteria induced
TNF-
and IL-6 production by the PBMCs.
Addition of
moxifloxacin, levofloxacin, or ceftriaxone to LPS-stimulated PBMCs
decreased the level of production of TNF-
, and among these
agents, moxifloxacin showed the greatest inhibitory effect.
Moxifloxacin also decreased the levels of production of TNF-
by LTA- and heat-killed E. coli-stimulated PBMCs, but
levofloxacin and ceftriaxone did not affect the levels of production of
TNF-
by these cells. The level of TNF-
production by
heat-killed S. pneumoniae-stimulated PBMCs did not show any
significant change with the addition of antibiotics (Table
1).
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View this table: [in a new window] |
TABLE 1. Effect
of moxifloxacin on production of TNF- by
PBMCsa
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and IL-6 in a
dose-dependent fashion (Fig.
1). Moxifloxacin was not toxic for the cultured PBMCs at any concentration
used, as determined by the MTT assay (Fig.
2). Levofloxacin and ceftriaxone also did not show any significant toxicity
to the PBMCs (data not
shown). |
View this table: [in a new window] |
TABLE 2. Effect
of moxifloxacin on production of IL-6 by PBMCsa
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![]() View larger version (23K): [in a new window] |
FIG. 1. Concentration-dependent
effect of moxifloxacin (Moxi) on the production of TNF-
(A) and IL-6 (B). Data are expressed as the level of
production of TNF- or IL-6 in the presence of moxifloxacin as
a percentage of the level of production of TNF- or IL-6 by
PBMCs stimulated with only LPS or LTA
(100%).
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![]() View larger version (34K): [in a new window] |
FIG. 2. Cytotoxic
effect of moxifloxacin (Moxi) assessed by MTT assay. Data are expressed
as the mean ± standard error of the mean absorbance for
quadruplicate measurements. O.D. (550 nm), optical density at 550
nm.
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from
49.72% ± 2.19% to 37.85% ±
0.96% (P < 0.05) among the LPS-stimulated PBMCs
and from 34.50% ± 3.84% to 22.24%
± 1.04% among the LTA-stimulated PBMCs (P
< 0.05). Moxifloxacin treatment also reduced the proportion of
cells positive for both CD-14 and IL-6 from 55.66% ±
1.64% to 42.38% ± 2.09% (P
< 0.05) among the LPS-stimulated PBMCs and from 38.22%
± 1.04% to 26.11% ± 0.68% among
the LTA-stimulated PBMCs (P <
0.05) in quadruplicate
experiments.
Moxifloxacin inhibits
I
B
degradation.
We hypothesized that
moxifloxacin's modulatory effect might be associated with the
nuclear factor
B (NF-
B) signaling pathway and
performed a Western blot analysis to assess the level of
I
B
degradation. Although moxifloxacin pretreatment
initially (5 min) enhanced the level of I
B
degradation by LPS challenge, I
B
degradation started
to be inhibited by moxifloxacin pretreatment 10 min after LPS
challenge. After 15 min, the density of I
B
expression
was nearly similar to that of control cells (Fig.
3). These findings suggest that moxifloxacin could interrupt NF-
B
activation by inhibiting I
B
degradation.
![]() View larger version (21K): [in a new window] |
FIG. 3. Representative
Western blot analysis of I B expression. PBMCs were
pretreated with 10 µg of moxifloxacin per ml and then
challenged with LPS (10 ng/ml). Lanes: C, controls; L, LPS-stimulated
PBMCs; M, moxifloxacin-pretreated, LPS-stimulated
PBMCs.
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and IL-6 by LPS-
and heat-killed bacterium-stimulated PBMCs in a concentration-dependent
manner. The inhibitory effect of moxifloxacin on the production of IL-6
was greater than that of ceftriaxone. These results were similar to
those reported by Purswani et al.
(16), who assessed the
inhibitory effect of trovafloxacin on the production of cytokines and
who compared the effects of trovafloxacin to those of ceftriaxone and
ciprofloxacin. Purswani et al.
(16) showed that
trovafloxacin and ciprofloxacin clearly had different effects on
TNF-
and IL-6 production, but we could not find any consistent
differences between the effects of moxifloxacin and levofloxacin.
Moxifloxacin showed more inhibitory activity than levofloxacin only
when it was added to heat-killed E. coli-stimulated PBMCs. The
differences in the immunomodulating effects among the quinolones and
the meaning of these differences are still hard to
understand.
Although we confirmed these inhibitory effects with
lower concentrations of moxifloxacin, we used the highest
concentrations of antibiotics to maximize the differences in some
experiments, and the moxifloxacin concentrations in tissues and cells
commonly exceeded the peak levels achievable in serum (2.5
to 5.0 µg/ml)
(11). Moxifloxacin
inhibited cytokine production by CD-14-positive cells such as
monocytes, a well-known source of the cytokine response to stimuli,
such as bacteria (1,
21,
23). This inhibitory
effect was not associated with cellular toxicity. The MTT assay did not
show any significant difference in the responses of control and
moxifloxacin-treated PBMCs at any concentration tested (Fig.
2). This means that
moxifloxacin could directly interfere with the production of cytokines
from the stimulated PBMCs, as Araujo et al.
(1) have reported. They
explained that the moxifloxacin-induced inhibition was a result of the
direct interaction with LPS, its receptor, and/or its stimulatory
pathway. We wanted to explain this by focusing on the NF-
B
signaling pathway.
NF-
B is a ubiquitous and important
transcription factor for genes that encode proinflammatory cytokines,
such as IL-1, IL-6, IL-8, and TNF-
. The prototype of
NF-
B is a heterodimer consisting of p50 and p65 bound by
members of the I
B family, including I
B
, in
the cytoplasm. NF-
B activation requires degradation of the
I
B protein. Phosphorylation of I
B
by drugs,
cytokines, bacterial products, and viruses rapidly leads to I
B
degradation and the translocation of NF-
B to the nucleus.
Activation of NF-
B results in the binding of specific promoter
elements and the expression of mRNAs for proinflammatory cytokine genes
(2,
12,
13).
As shown in
Fig. 3, at 5 min after LPS
challenge, PBMCs pretreated with 10 µg of moxifloxacin per ml
showed more degradation of I
B
than PBMCs not treated
with moxifloxacin. However, the levels of expression of
I
B
by moxifloxacin-pretreated LPS-stimulated PBMCs
started to increase and were similar to those of control cells after 15
min. These findings could be the explanation for the decreased levels
of TNF-
and IL-6 production by stimulated PBMCs achieved with
moxifloxacin treatment. Ichiyama et al.
(5) reported that
clarithromycin inhibited NF-
B activation in pulmonary
epithelial cells, but this inhibition was not linked to the
preservation of I
B
degradation. Macrolides and
quinolones might inhibit NF-
B activation by different
pathways, but we could not hypothesize what this pathway is because the
result could be affected by certain characteristics of the stimuli
(such as characteristics related to the bacterium itself or to some
bacterial component) and the target cells. Recently, Hoffmann et al.
(4) have made an
interesting suggestion concerning a negative-feedback loop within the
NF-
B and I
B
signaling
pathway.
Although an assay to evaluate the alteration of the
dynamics of I
B
and a direct assay for NF-
B
were not performed in this study, we can assume from the results of
Western blot analysis that moxifloxacin inhibits the degradation of
I
B
and exerts inhibitory effects on the production of
proinflammatory cytokines. Further studies on the alteration of
NF-
B and I
B
by repeated exposure to
quinolones and the effect on the production of anti-inflammatory
cytokines and chemokines will be helpful to extend our knowledge about
immunomodulating antibiotics.
In conclusion, moxifloxacin has an
inhibitory effect on the production of TNF-
and IL-6 from
human PBMCs stimulated with bacteria and bacterial components by
inhibiting the degradation of
I
B
.
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278:818-819.
B. Immunol. Today
19:80-88.[CrossRef][Medline]
B transcription factors. J. Antimicrob.
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49:745-755.
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