Inhibition of lipopolysaccharide-induced inducible nitric oxide synthase expression by a novel compound, mercaptopyrazine, through suppression of nuclear factor-kappaB binding to DNA

Article abstract of DOI:10.1016/j.bcp.2004.05.005

Macrophage cells in response to cytokines and endotoxins produced a large amount of nitric oxide (NO) by expression of inducible nitric oxide synthase (iNOS), resulting in acute or chronic inflammatory disorders including septic hypotension and atherosclerosis. In the present study, we investigated the effect and the mechanism of mercaptopyrazine (MP) in the induction of iNOS and NO production as a culminating factor for several inflammatory disorders. Pretreatment of MP alleviated the mortality of endotoxemic mice receiving a lethal bolus of lipopolysaccharide (LPS), which was associated with the reduced levels of serum nitrite/nitrate and IL-1β. In RAW264.7 mouse macrophage cells, MP (300 μM) inhibited both protein and mRNA levels of iNOS stimulated by LPS/interferon-γ (IFNγ) up to 50%. The nuclear factor-kappa B (NF-κB)-driven transactivation was also suppressed by MP to the same degree. Treatment of MP reduced the binding of NF-κB to the oligonucleotides containing NF-κB consensus sequence, while it did not affect the translocation of NF-κB to nuclear. Suppression of NF-κB activity by MP was completely reversed by a reducing agent, dithiothreitol, implying that MP might oxidize the sulfhydryl group(s) of DNA binding domain of NF-κB. In conclusion, MP would be one of interesting candidates or chemical moieties of iNOS expression inhibitor via specific suppression of NF-κB binding to DNA, and be useful as a chemopreventive agent or a therapeutic against iNOS-associated inflammatory diseases.

Full text of DOI:10.1016/j.bcp.2004.05.005

Biochemical Pharmacology 68 (2004) 719–728
Inhibition of lipopolysaccharide-induced inducible nitric oxide
synthase expression by a novel compound, mercaptopyrazine,
through suppression of nuclear factor-kappaB binding to DNA
a
Sunny Lim , Keon Wook Kang , Soo-Young Park , Seok-In Kim , Yon Sik Choi ,
b
c
d
a
e
a
f
Nak-Doo Kim , Ki-Up Lee , Hong-Kyu Lee , Youngmi Kim Pak
a,*
a
Asan Institute for Life Sciences, University of Ulsan, Seoul 138-736, Republic of Korea
b
College of Pharmacy, Chosun University, Gwangju 501-759, Republic of Korea
Division of Metabolic Diseases, Department of Biomedical Sciences, National Institute of Health, Seoul 122-701, Republic of Korea
c
d
AnyGen, K-JIST, Gwangju 500-712, Republic of Korea
College of Pharmacy, Seoul National University, Seoul 151-742, Republic of Korea
e
f
School of Medicine, Seoul National University, Seoul 151-742, Republic of Korea
Received 19 November 2003; accepted 6 May 2004
Abstract
Macrophage cells in response to cytokines and endotoxins produced a large amount of nitric oxide (NO) by expression of inducible
nitric oxide synthase (iNOS), resulting in acute or chronic inflammatory disorders including septic hypotension and atherosclerosis. In the
present study, we investigated the effect and the mechanism of mercaptopyrazine (MP) in the induction of iNOS and NO production as a
culminating factor for several inflammatory disorders. Pretreatment of MP alleviated the mortality of endotoxemic mice receiving a lethal
bolus of lipopolysaccharide (LPS), which was associated with the reduced levels of serum nitrite/nitrate and IL-1b. In RAW264.7 mouse
macrophage cells, MP (300 mM) inhibited both protein and mRNA levels of iNOS stimulated by LPS/interferon-g (IFNg) up to 50%. The
nuclear factor-kappa B (NF-kB)-driven transactivation was also suppressed by MP to the same degree. Treatment of MP reduced the
binding of NF-kB to the oligonucleotides containing NF-kB consensus sequence, while it did not affect the translocation of NF-kB to
nuclear. Suppression of NF-kB activity by MP was completely reversed by a reducing agent, dithiothreitol, implying that MP might
oxidize the sulfhydryl group(s) of DNA binding domain of NF-kB. In conclusion, MP would be one of interesting candidates or chemical
moieties of iNOS expression inhibitor via specific suppression of NF-kB binding to DNA, and be useful as a chemopreventive agent or a
therapeutic against iNOS-associated inflammatory diseases.
#
2004 Elsevier Inc. All rights reserved.
Keywords: Mercaptopyrazine; iNOS inhibitor; LPS; NF-kB activation; DNA binding; Inflammation
Nitric oxide (NO), a radical produced from L-arginine
via NO synthase (NOS), plays a dual role as both a
beneficial and a detrimental molecule in the process of
inflammation. NO produced by constitutive NOS (cNOS)
is critical in maintaining cellular function, whereas NO
produced by inducible NOS (iNOS) is an important med-
iator of acute or chronic inflammation [1,2]. The iNOS-
mediated high output production of NO contributes to the
killing of virally infected cells, tumor cells, and some
pathogens partly because it inactivates their mitochondrial
respiratory chain enzymes. If the inflammation becomes
chronic, then even healthy host cells also may be killed by
NO, contributing to inflammatory pathologies [3].
The iNOS expression is induced by the activated NF-kB
since iNOS gene contains functional nuclear factor-kB
(NF-kB) binding sites in its promoter [4,5]. The transcrip-
tion factor NF-kB is activated by a variety of stimuli
and regulates diverse gene expressions and biological
responses. The stimuli include bacterial endotoxin, lipo-
polysaccharide (LPS), ionizing radiation, and carcinogens
Abbreviations: 2-AP, 2-allylthiopyrazine; MP, 2-mercaptopyrazine;
0
DTBP, 2,2 -dithiobispyrazine; LPS, lipopolysaccharide; NF-kB, nuclear
factor-kB; NO, nitric oxide; NOx, nitrite/nitrate; iNOS, inducible nitric
oxide synthase; IL-1b, interleukin-1b; TNF-a, tumor necrosis factor-a;
PDTC, pyrolidine dithiocarbamate; PPAR-g, peroxisome proliferator
activated receptor-g; PPRE, PPAR responsive element; DTT, dithiothreitol
*
Corresponding author. Tel.: þ82 2 3010 4191; fax: þ82 2 3010 4182.
E-mail address: ymkimpak@amc.seoul.kr (Y.K. Pak).
0006-2952/$ – see front matter # 2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.bcp.2004.05.005

720
S. Lim et al. / Biochemical Pharmacology 68 (2004) 719–728
that are often associated with inflammatory diseases or
tumorigenesis. Recent observations support that NF-kB
activation also may be important in pathogenesis of
chronic diseases such as atherosclerosis [6] and diabetes
(A)
SH
(B)
N
N
S
S
N
N
N
N
Fig. 1. Chemical structures of (A) 2-mercaptopyrazine (pyrazine-2-thiol)
0
[
7]. That is, an activated NF-kB was found in athero-
and (B) 2,2 -dithiobispyrazine.
sclerotic lesion [8] and several types of cells from diabetic
animal models [9]. Moreover, the activated NF-kB induces
transcription of inflammatory cytokines such as tumor
necrosis factor (TNF)-a and interleukin-1b [10,11] as well
as iNOS. The cytokines secreted from macrophages, bind
to their receptors on macrophage itself (autocrine) or on
other cells (paracrine) to further activate NF-kB in the
cells, consequently aggravating the diseases. It is interest-
ing to note that the elevated level of TNF-a was also
reported to associate with the development of insulin
resistance, possibly with diabetes [12].
Persistent and excessive NO production by iNOS relaxes
the vascular smooth muscle and decreases its responsive-
ness to vasoconstrictive agents such as norepinephrine,
resulting in septic hypotension [13]. Since the deleterious
production of NO is resulted from the induction of the
iNOS gene, the most effective way to repress NO produc-
tion would be the suppression of iNOS gene expression.
For treatment of septic shock, however, only competitive
1. Materials and methods
0
1.1. Synthesis of 2-mercaptopyrazine and 2,2 -
dithiobispyrazine (DTBP)
To a solution of sodium ethoxide, prepared from sodium
(6.9 g, 0.3 mol) and ethanol (150 ml), N,N-dimethylforma-
mide (150 ml) was added. After removing the ethanol by
distillation, the residual solution was saturated with hydro-
gen sulfide. The deep green solution was heated with 2-
chloropyrazine (17.25 g, 150 mmol) at 100 8C for 3 h, and
solvent was then removed under reduced pressure. The
residue was dissolved in water, then acidified with acetic
acid to give yellow precipitates, which were extracted with
2N NaOH (75 ml). After filtration, acidification of the
solution gave MP (15 g, 88%), m.p. 209–214 8C. A solu-
tion of iodine (1.3 g) in potassium iodide (2.5 g) and water
(10 ml) was added drop-wise to a solution of 2-mercapto-
pyrazine (0.55 g) in 2N NaOH (5 ml). After refrigeration,
the crystalline precipitate (0.3 g) was filtered off and
identified as DTBP by its proton NMR spectra and
m.p. 106–108 8C.
G
inhibitors for L-arginine, a substrate of NOS, such as L-N -
monomethyl arginine (L-NMMA) [14], nitro-L-arginine
G
methyl ester (L-NAME) [15], and N -nitro-L-arginine (L-
NLA) [16], are available. These inhibitors act non-selec-
tively on all forms of NOS including beneficial endothelial
constitutive NOS (ecNOS), which may result in increased
organ damage and mortality. Therefore, a selective inhibi-
tion of iNOS transcription via NF-kB inactivation would be
more desirable to treat the patients with septicemia. More-
over, a weak and chronic suppression of NF-kB would also
be beneficial to prevent the chronic disease development, if
we understand the chronic diseases like atherosclerosis as
inflammatory disease in the respect that the inflammatory
environment increases the production of NO by iNOS in
human atherosclerotic lesion in macrophages and foam
cells, contributing to vascular injury [17,18].
1.2. Animal treatment and sample preparation
Animal studies were conducted in accordance with the
institutional guidelines for care and use of laboratory
animals. Male ICR mice at 6 weeks of age (25–30 g) were
supplied from DaiHan Experimental Animal Center and
maintained under 12-h light/12-h dark cycles in an air-
conditioned room with commercially available rat chow
(Purina, Korea) and water available ad libitum. LPS
(20 mg/kg, Escherichia coli, serotype 0127B8, Sigma
Co.) was intra-peritoneally injected, as dissolved in sterile
saline (10 ml/kg body weight). MP was orally adminis-
tered as a suspension of olive oil (100 or 200 mg/kg body
weight/day) for 3 days prior to LPS injection. Control mice
received olive oil as a vehicle. Blood was collected from
retroorbital sinuses of mice at the indicated time point after
LPS injection. Animals were sacrificed under light
anesthesia with diethyl ether and left lung was isolated
and homogenized for the detection of iNOS.
We previously reported that the mortality of mice
receiving a lethal dose of LPS was decreased by 2-
(
allylthio)pyrazine (2-AP), an experimental chemopreven-
tive compound and an analog of diallyl sulfide [13]. As an
effort to screen new therapeutic agents against septic shock
or chronic inflammatory disorder caused by iNOS induc-
tion, we investigated analogs of diallyl sulfide as an
inhibitor of iNOS induction. We report here that 2-mer-
captopyrazine (MP; Fig. 1), which is a synthetic precursor
and one of metabolites of 2-AP, inhibits LPS-induced
iNOS expression in mice and macrophages. Furthermore,
MP interfered the NF-kB binding to iNOS promoter
through –SH blockage of NF-kB, but had no effect on
the nuclear translocation of NF-kB. To our knowledge, it is
the first time to identify a NF-kB inhibitor, which blocks
the step of DNA binding specifically.
1.3. Cell culture and transfections
The macrophage cell line RAW264.7 (ATCC No. TIB-
71) was cultured in Dulbecco’s modified Eagle’s media
(DMEM) supplemented with 10% fetal bovine serum
(FBS), 100 mg/ml penicillin and 100 mg/ml streptomycin,

S. Lim et al. / Biochemical Pharmacology 68 (2004) 719–728
721
5
in 5% CO at 37 8C. RAW264.7 cells (2 Â 10 cells/well)
polyclonal antibody (Transduction Lab). Equivalent load-
ing of protein was verified by anti-b-actin monoclonal
antibody (Sigma Co.). In order to analyze the translocation
of NF-kB, nuclei from the treated cells were isolated as
described [21]. The nuclear proteins (20 mg) were sub-
jected onto 10% SDS–PAGE and Western blot analysis was
performed using antibodies against either p65 or p50
subunit of NF-kB (Transduction Lab, Lexington, KY)
[22]. HRP-conjugated goat anti-rabbit IgG or alkaline
phosphatase-conjugated goat anti-rabbit IgG (Bio-Rad)
was used as a secondary antibody and the nitrocellulose
paper was developed using enhanced chemiluminescence
system (ECL, Amersham Pharmacia Biotech).
2
in 6-well plate were pretreated with either MP or pyrolidine
dithiocarbamate (PDTC) for 2 h at the indicated final
concentrations (up to 500 mM) prior to the stimulation
with LPS (100 ng/ml, E. coli, serotype 0127B8, Sigma
Co.) and IFNg (100 U/ml, recombinant murine, GIBCO-
BRL) for 24 h. The cells were harvested with lysis buffer
10 mM HEPES, pH 7.9, 10 mM KCl, 2 mM MgCl2,
.5 mM dithiothreitol, 1 mM phenylmethylsulfonyl fluor-
ide, 5 mg/ml aprotinin, 5 mg/ml pepstatin A, 5 mg/ml leu-
peptin, and 1% Triton X-100) for western analysis. To
measure nitrite/nitrate contents in conditioned media, the
(
0
4
cells (10 cells/well) were cultured in 96-well plate as
described above except using phenol red-free MEM.
For transfections, RAW264.7 cells were grown in 6-well
plates with DMEM supplemented with 10% FBS and
transfected for 5 h with either pNF-kB-luc (1 mg) or
piNOS-luc (1 mg) together with pcDNA3.1-LacZ (Invitro-
gen) by calcium phosphate co-precipitation method
[19,20]. To inhibit the lysosomal degradation of the
DNA constructs, the cells were transfected in the presence
of 50 mM chloroquine in complete media and shocked with
1.6. Reverse transcriptase-polymerase chain reaction
(RT-PCR)
Total RNA from cell monolayers was isolated using
guanidinium isothiocyanate and phenol [20]. Total cDNA
synthesized from 2 mg of total RNA was amplified for 30
cycles at 94 8C for 30 s, 54 8C for 30 s, and 72 8C for
0
2 min. The oligonucleotide primer set (5 -ATG TCC GAA
0
0
1
0% DMSO in DMEM for 5 min after the transfection.
GCA AAC ATC AC-3 and 5 -TAA TGT CCA GGA AGT
0
Then, the cells were washed twice with PBS and incubated
in DMEM with 10% FBS for 16 h. Treatment of either MP
or PDTC was followed at the indicated concentrations for
AGG TG-3 ) was used for amplification of a 450 bp
fragment of mouse iNOS. The reaction products from
the PCR were examined by 1% agarose gel electrophoresis.
Band intensities were quantified by densitometer and
normalized by comparison to the RT-PCR product of
glyceraldehyde-3-phosphate dehydrogenase mRNA [20].
2
(
h before the stimulation with LPS (100 ng/ml) plus IFNg
100 U/ml). In some experiments, cells were treated with
dithiothreitol (DTT, 100 mM) for 2 h prior to MP treat-
ment. Luciferase activity was measured from the harvested
cells using Luciferase Assay Kit (Promega, Madison, WI)
and luminometer (Berthold, German). The transfection
efficiencies were normalized by the b-galactosidase activ-
ity. All data are the mean Æ S.D. of three independent
measurements of duplicate.
1.7. Enzyme-linked immunosorbent assay (ELISA)
The IL-1b level in the serum of mice was measured by
ELISA Kit (Endogen) for murine IL-1b using rabbit anti-
mouse IL-1b antibody and a biotinylated secondary anti-
body according to the manufacturer’s instruction.
1
.4. Plasmids
1.8. Electrophoretic mobility shift assays (EMSA)
The À973/þ82 fragment of murine iNOS promoter from
piNOS973-CAT [5] was subcloned into BamHI/HindIII
sites of pGL2-basic luciferase vector (Promega Co.). The
cloned promoter was sequenced to ensure the fidelity of the
resulting constructs. The pNF-kB-luc was the luciferase
reporter construct containing three upstream NF-kB bind-
ing elements as previously described [19,20].
EMSA was performed using the end-labeled NF-kB
probe of double-stranded synthetic oligonucleotides con-
0
taining NF-kB motif of iNOS promoter (À92 to À65nt, 5 -
0
tcgaCCA ACT GGG GAC TCT CCC TTT GGG AAC A-3
0
and 5 -tcgaTG TTC CCA AAG GGA GAG TCC CCA
0
GTC CCC AGT TGG-3 ) and nuclear extract isolated from
5
the cells (2 Â 10 ) as described [21]. Briefly, the nuclear
1
.5. Western blot analysis
extracts without DTT were prepared from LPS/IFNg-sti-
mulated RAW264.7 cells and treated with MP (0–500 mM)
for 30 min at room temperature. The end-labeled annealed
Lung homogenates from the mice were prepared in
.1 M Tris acetate buffer (pH 7.4) containing 0.1 M potas-
4
0
oligonucleotides (50 ng, 5 Â 10 dpm) were incubated for
sium chloride and 1 mM EDTA by centrifugation at 10,000
 g for 10 min and the supernatants were collected and
stored at À70 8C until use. Cell lysate proteins (25 mg) or
lung homogenates (100 mg) were analyzed by 8% sodium
dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–
PAGE) and Western blot using rabbit anti-murine iNOS
30 min at 4 8C with the nuclear extracts (10 mg) in the
binding buffer (10 mM Tris–HCl, pH 7.8, 1 mM EDTA,
100 mM KCl, 5 mM MgCl , 1 mg/ml poly dI.dC) in the
2
absence of DTT. The oligonucleotide–protein complexes
were separated onto 6% polyacrylamide gel. One hundred-
fold excess amount of the cold annealed oligonucleotides

722
S. Lim et al. / Biochemical Pharmacology 68 (2004) 719–728
were added in binding reaction to prove if the shifted bands
binds specifically to NF-kB oligonucleotides. For antibody
supershift/inhibition assays, 5 mg of rabbit anti-p65 poly-
clonal antibodies (Santa Cruz Co.) were incubated with the
protein extract on ice for 30 min prior to binding reaction.
The dried gel was analyzed by exposure to X-OMAT AR
film (Kodak, Rochester) at À70 8C.
survival rate of MP pretreated mice (200 mg/kg) was
80% while that of untreated mice was less than 10%. It
is possible that MP is a potential chemical moiety that may
regulate immune responses in animal. It is interesting to
note that the MP-treated mice without LPS injection do not
show any signs of toxicity. Instead, we observed protective
effects of MP at 10 mg/kg on chemical-induced hepato-
toxicity, suggesting a possible use of MP as a chemopre-
ventive small chemical (data not shown).
1
.9. Nitrite/nitrate determination
RAW264.7 cells were grown on 96-well plates in phenol
2.2. MP inhibits the LPS-induced increase of serum NO
and iNOS protein expression in mice
red-free MEM and the nitrite/nitrate (NOx) contents of the
conditioned media were analyzed by NO analyzer (Antek).
In the case of serum sample, 1 ml of serum was used for the
analysis.
We assessed the effect of MP on the production of NO in
serum of mice treated with LPS. A single dose of LPS
treatment (20 mg/kg, i.p.) increased nitrite/nitrate (NOx)
production over the basal level from 6 h (400 mM) and
peaked at 24 h (1200 mM). Pretreatment of MP (200 mg/
kg/3 days, p.o.) reduced the serum NOx concentration
below 400 mM even at 24 h (Fig. 3A). Inhibition of
LPS-induced NOx production by MP was achieved in a
dose-dependent manner. IC50 of MP was approximately
1
.10. Statistical analysis
Student’s t test was used to determine the statistical
differences between various experimental and control
groups. P value <0.05 was considered as significant.
100 mg/kg (Fig. 3B). These results suggest that the
2
. Results
mechanistic basis for the protective effect of MP against
LPS toxicity results from the inhibition of the LPS-induced
NO production. To test whether MP affects the transcrip-
tion of iNOS gene, we further determined the expression
level of iNOS protein in lung homogenates of the mice
using Western blot analysis. Lung homogenates were
chosen for iNOS protein analysis since lung had been
suggested as a major organ for iNOS production resulting
in LPS-induced septic hypotension. Fig. 3C showed that a
single dose of LPS (20 mg/kg, i.p.) strongly increased
iNOS protein levels at 6 h and 12 h, and returned to control
level at 24 h (Fig. 3C). Treatment of mice with MP
(200 mg/kg for 3 days) blocked the LPS-induced iNOS
protein expression approximately 50% at both 6 h and 12 h
post LPS stimulation (Fig. 3D).
2.1. Pretreatment of MP alleviates the LPS-induced
mortality
We studied whether MP contains the in vivo protective
effects against systemic inflammatory toxicity by LPS.
ICR mice that were pretreated with MP for 3 days (100
and 200 mg/kg/day, p.o.) were exposed to lethal doses of
LPS (55 mg/kg). Cumulative proportions of mice surviving
after lethal dose of LPS are shown in Fig. 2. MP pretreat-
ment of mice prior to LPS injection elevated the survival
rate by 70–80% from 40% in LPS alone when examined at
2
4 h after LPS injection. At 72 h after LPS injection,
LPS (55 mg/kg, i.v.)
2.3. MP inhibits IL-1b secretion into serum
+
+
MP 100 (mg/kg, p.o.)
MP 200 (mg/kg, p.o.)
100
IL-1b is one of principal mediators of the responses to
80
LPS and is involved in the inflammatory process [11,23]. To
determine whether IL-1b plays a role in inhibitory effects of
MP on the LPS-induced responses, the concentrations of
plasma IL-1b of mice were assessed using ELISA. As
shown in Fig. 4, the elevation of plasma IL-1b up to
6
0
40
20
463 pg/ml of plasma at 2 h after LPS treatment was pre-
vented by the three consecutive treatments of MP (200 mg/
kg, p.o. per day) in a concentration-dependent manner.
0
0
12
24
36
48
60
72
Time after LPS injection (h)
2.4. MP inhibits the NO production by suppression of
iNOS expression in macrophages
Fig. 2. MP protects the increase in mortality induced by LPS. MP (100 or
00 mg/kg) was orally administered for 3 days prior to LPS injection. LPS
2
was intravenously injected at the dose of 55 mg/kg. (*) LPS-treated
group; (*) LPS-treated þ MP (100 mg/kg) group; (!) LPS-treated þ MP
Since macrophages are the major cells that produce NO
by iNOS, the mouse macrophage cell RAW264.7 was
(
200 mg/kg) group, n ¼ 10.

S. Lim et al. / Biochemical Pharmacology 68 (2004) 719–728
723
Fig. 3. MP inhibits the increase in serum NOx and lung iNOS expression in mice treated with LPS. MP (200 mg/kg) was orally administered for 3 days prior
to i.p. injection of LPS (20 mg/kg). Serum NOx level was determined using NO analyzer with or without treatment of MP. (A) Time-dependent effects of MP
on the level of serum NOx ((*) LPS-treated group; (*) LPS-treated þ MP group) and (B) dose-dependent effects of MP on the level of serum NOx. The
iNOS expression was monitored by Western blot analysis using anti-mouse iNOS antibody. (C) Time-dependent changes in the expression of iNOS protein in
lung homogenate of LPS-treated mice. (D) Effect of MP on pulmonary iNOS protein levels in LPS-treated mice. Time denotes the time after LPS injection.
The graph shows the result of densitometric scanning of immunoblot. Values are mean Æ S.E.M. Asterisk denote values are significantly different from the
ꢀ
ꢀꢀ
LPS-treated group, P < 0.05 and P < 0.01, n ¼ 3.
introduced for further study. When RAW264.7 cells were
pretreated with MP (100 mM) for 2 h prior to LPS þ IFNg
stimulation, the NO content in the conditioned media was
decreased as expected to the same level with PDTC
2.5. MP inhibits the NF-kB-driven transcriptional
activity
The iNOS promoter contains two NF-kB binding sites,
which mainly regulate the transcription of iNOS mRNA
[5]. To study if MP blocks iNOS expression via suppres-
sion of NF-kB activity, the effects of MP were determined
on the luciferase activity of the pNF-kB-luc-transfected
RAW264.7 cells. This NFkB-luc reporter vector contains
three copies of NF-kB-binding sites in E-selectin promoter
and utilized for determining the NF-kB-driven transactiva-
tion [19]. MP inhibits the NF-kB transcriptional activity in
a dose-dependent manner from 10 to 300 mM (Fig. 6A).
(100 mM), a known NF-kB inhibitor (Fig. 5A). Treatment
of MP also leads to a significant decrease of both iNOS
protein (Fig. 5B) and mRNA levels (Fig. 5C) in a dose-
dependent manner. At a concentration of 300 mM, MP
decreased the expression of iNOS protein up to 95% and
IC50 was approximately 100 mM. The mRNA level of LPS/
IFNg-stimulated iNOS was suppressed 26 and 44% by MP
at concentrations of 100 and 300 mM, respectively. Simi-
larly, PDTC decreased the iNOS mRNA levels by 20–40%.
(A)
(B)
7
6
5
4
3
2
1
00
00
00
00
00
00
00
0
1
1
1
40
20
00
8
0
0
0
0
*
6
*
**
4
2
0
MP
LPS
0
0
50 100 200 (mg/kg, p.o.)
+ 20 mg/kg,i.p.
0
6
12
18
24
Time after LPS injection (h)
-
Fig. 4. Dose-dependent decrease of LPS-induced serum IL-1b by MP. (A) Time-course of serum IL-1b level in LPS-treated mice. (B) Dose-dependent effect
of MP on LPS-induced serum IL-1b increase in LPS-treated mice. MP was orally administered for 3 days prior to LPS injection (20 mg/kg, i.p.). Blood
ꢀ
was collected 2 h after LPS treatment. Values are mean Æ S.E.M. Asterisk denote values are significantly different from LPS-treated group, P < 0.05 and
ꢀꢀꢀ
P < 0.001, n ¼ 5–6.

724
S. Lim et al. / Biochemical Pharmacology 68 (2004) 719–728
5
Fig. 5. MP inhibits the production of NO by iNOS. RAW264.7 cells (2 Â 10 cells/well) in 6-well plate were pretreated with either MP or PDTC at the
indicated final concentrations for 2 h. In the absence or presence of 24 h incubation with LPS (100 ng/ml) þ IFNg (100 ng/ml), (A) the nitrite contents in the
conditioned media were determined using NO analyzer and (B) the expression of iNOS protein in total cell extracts (25 mg) was analyzed by western blot. (C)
After 4 h of incubation instead of 24 h with LPS þ IFNg, total RNA was isolated to assess the level of iNOS mRNA by RT-PCR and 1% agarose gel. M
denotes molecular weight marker. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was utilized for the normalization of data. Band intensities of the
agarose gel were quantified with a densitometer. All data are mean Æ S.D. of three independent measurements of duplicates. Asterisk denote values are
ꢀ
ꢀꢀ
significantly different from the LPS þ IFNg-treated control. P < 0.05; P < 0.01.
Fig. 6. MP suppresses the activation of NF-kB via inhibition of DNA binding. (A) RAW264.7 cells were transfected with a reporter gene kB-luc and
LacZ expression vector. The transfected cells were treated with MP or PDTC as indicated for 2 h, stimulated with LPS þ IFNg for 24 h and harvested for
luciferase assay. Normalized luciferase expressions (n ¼ 6) were calculated relative to the LacZ expressions and the results were expressed as percent
control over the value obtained with the LPS þ IFNg. (B) RAW264.7 cells were pretreated with MP as (A), and nuclei were prepared. Nuclear proteins
(
20 mg) were separated onto 10% SDS–PAGE and analyzed by Western blot using p65 or p50 antibodies. Protein expression of iNOS and b-actin in total
cell lysates (25 mg) were analyzed by Western blot for comparison. (C) The nuclear extracts were prepared from LPS-stimulated RAW264.7 cells and
treated with MP for 30 min at room temperature as indicated. The MP-treated nuclear extracts were subjected onto the NF-kB EMSA assay in the absence
of DTT as described in Section 2. NF-kB binding activities to DNA were decreased as MP increased. The shifted bands were abolished by incubating with
100-fold excess amount of cold probes. The p65 antibody supershifted the NF-kB complex. (D) The inhibition mode of iNOS or kB-dependent
expression by MP is schematically presented.

S. Lim et al. / Biochemical Pharmacology 68 (2004) 719–728
725
The NF-kB-dependent transactivation could be blocked
by ligands for peroxisome proliferator activated receptor-g
NF-kB binding site of the promoter. To test whether MP
interferes with binding activity of NF-kB protein to the
NF-kB binding sites, electrophoretic mobility shift analy-
sis of isolated nuclear extract was performed. As shown in
Fig. 6C, the MP treatment inhibited the binding of NF-kB
protein to the oligonucleotides containing the NF-kB
consensus sequence of iNOS promoter in a dose-dependent
manner.
(PPAR-g) [20]. We tested if MP might be a PPAR-g ligand
using the PPAR responsive element (PPRE)-driven trans-
activation assay in RAW264.7 cells [19]. MP did not
activate the PPRE-dependent luciferase activity implying
that MP was not a PPAR-g ligand (data not shown).
2
.6. MP does not inhibit the nuclear translocation
of NF-kB protein
2.8. MP may interact with sulfhydryl groups of NF-kB
subunits to suppress its activity
Most known NF-kB inhibitors, including PDTC, prevent
NF-kB activation by a mechanism that involves inhibition
of I-kB degradation followed by IKK-induced phosphor-
ylation [24–26]. Since we also hypothesized that MP might
block the NF-kB translocation into nuclei in the similar
manner of PDTC, the content of p65 and p50 subunit of
NF-kB in the nuclei were quantified by western analysis.
Surprisingly, the protein levels of p65 and p50 in nuclei
were not altered in spite of MP treatments at the same
concentrations that suppress the transactivation of NF-kB
and iNOS expression (Fig. 6B). In cytosol, p65 and p50
proteins were not detected at all after the treatment (data
not shown). This result showed that MP did not affect the
translocation of NF-kB into the nucleus as well as I-kB
degradation, which was distinct from PDTC or other NF-
kB inhibitors.
In order to determine if the sulfhydryl functional group of
MP reacted with the cysteine residues in DNA-binding
domains of p65 or p50 of NF-kB subunits [27,28], RAW
264.7 cells were treated with 100 mM DTT for 2 h prior to
the treatment of MP (100 mM for 2 h) and then exposed to
LPS. DTT did not alter the NF-kB-driven transactivation of
NF-kB-luc by LPS; instead it reversed the action of MP
(data not shown). To confirm if the effect of MP and/or DTT
on NF-kB would be reproduced in iNOS promoter-luc
system, we constructed iNOS promoter region from
À973 to þ82 into pGL2-basic luciferase reporter and
performed transient transfection followed by luciferase
assay as similarly as pNF-kB-luc experiments. As expected,
DTT pretreatment also reversed the MP-mediated suppres-
sion of iNOS promoter activity (Fig. 7A). It is very possible
that DTT treatment maintains the reduced status of NF-kB
subunits as an active form. Then MP might oxidize the
sulfhydryl group of NF-kB by formation of disulfide bond
with MP. To check if the –SH group of MP is a reactive site
for NF-kB inactivation, we synthesized DTBP (Fig. 1B), a
MP analogue of which two pyrazine moieties from two MPs
were connected via disulfide bond. DTBP did not inhibit the
2
.7. MP prevents the binding of NF-kB to DNA
Although the most common mechanism of NF-kB
inactivation is the blockade of nuclear translocation of
NF-kB, MP did not inhibit this step. Then, it would be
possible for MP to reduce the DNA binding affinity onto
Fig. 7. MP suppresses the iNOS promoter- and NF-kB-driven transactivation via modification of –SH group of NF-kB subunits. RAW264.7 cells were
transfected with a reporter gene (A) iNOS-promoter-luc (piNOS-luc), (B) pNF-kB-luc) together with LacZ expression vector. The transfected cells were
treated with MP or DTBP for 2 h as indicated, stimulated with LPS þ IFNg for 24 h, and harvested for luciferase assay. DTT (100 mM) was pretreated for 2 h
prior to MP treatment. Normalized luciferase expressions (n ¼ 6) were calculated relative to the LacZ expressions and the results were expressed as percent
control over the value obtained with the LPS þ IFNg.

726
S. Lim et al. / Biochemical Pharmacology 68 (2004) 719–728
NF-kB-driven transactivation by LPS at 50 mM concentra-
tion (Fig 7B). This concentration of DTBP is equivalent to
glutathiones (GSH/GSSG ratio) or peroxiredoxins to
change DNA binding. We have to investigate further by
monitoring the direct interaction between MP and NF-kB.
There are several ways to inhibit the NF-kB-dependent
gene transcription. One of them is to inhibit the signaling
pathways leading to I-kB degradation. The oxygen radical
scavenger PDTC blocks the release of I-kB from NF-kB.
Requirement of zinc ion for PDTC-induced NF-kB inac-
tivation implies that zinc may be an important regulator for
NF-kB activity [34]. In our study, however, MP inhibited
NF-kB activity even under serum-free condition, suggest-
ing that zinc ion is not required for DNA binding activity.
Anti-inflammatory drugs like salicylates inhibited I-kBa
phosphorylation and degradation [35] and glucocorticoid
dexamethasone increased the expression of I-kBa, fol-
lowed by repressing the nuclear NF-kB p65 level [36].
Recently, Kitazawa et al. [37] reported that a cystine
derivative, N,N’-diacetyl-L-cystine demethylester pre-
vented the activated NF-kB from binding DNA, without
influencing the I-kB degradation. This cystine derivative
enhanced the intracellular GSSG sufficiently enough to
shift the redox balance to the oxidized state. But DTBP in
our study did not suppress the NF-kB binding to DNA
although its structure is similar to the cystine derivative in
the aspect that two MP molecules are connected via
disulfide bond. Thus, the inhibitory mechanism of MP
may be different from the cystine derivative. On the other
hand, avicins, a family of triterpenoid saponins were
reported to inhibit the activation of NF-kB by blocking
both its localization and DNA binding ability [38]. Like
MP, the treatment of DTT reversed the avicin-induced NF-
kB activation. Since avicin does not contain sulfhydryl in
its structure, two ester groups of avicin were suggested to
react with cysteine of NF-kB.
Excessive proinflammatory cytokine and NO production
by activated macrophages play a critical role in septic
hypotension and other chronic inflammatory diseases such
as atherosclerosis and neurodegenerative disorders. Rosse-
let et al. [39] reported that selective iNOS inhibition is
better than norepinephrine in the treatment of endotoxic
shock in rats. Cho et al. [40] showed that N-acetyl-O-
methyldopamine, a neuroprotectant for neurodegenerative
diseases, down-regulates the genes involved in macroglial
activation including TNF-a, IL-1b, and iNOS. These
reports support an idea that repression of the proinflam-
matory cytokines and iNOS gene expression in macro-
phages or macrophage-like cells may provide new
therapeutic or chemopreventive strategies for chronic
degenerative diseases or endotoxin-induced septic shock.
One of the major challenges of chemoprevention is the
development of new effective drugs that have little or no
effect on normal cells and tissues. From our in vivo study,
we demonstrated the pretreatment of MP significantly
reduced the LPS-induced mortality in mice. The present
result provides a possibility for MP to develop as a new
therapeutic or chemopreventive agent against chronic and
1
00 mM MP because 100 mM MP can be produced from
reduction of 50 mM DTBP. It should be noted that DS-MS
was toxic to the cells at higher than 50 mM. It was con-
cluded that MP inhibited the LPS-induced expression of
iNOS and/or NF-kB activation in macrophages by suppres-
sion of NF-kB binding to DNA (Fig. 6D). MP might
achieve the suppression via modification of the –SH groups
of NF-kB subunits.
3
. Discussion
In this study we demonstrated that MP, a chemically
synthesized sulfhydryl group-containing small molecule,
inhibited the NO production by suppression of iNOS
protein expression in vivo and in vitro. MP blocked the
iNOS transcription by interfering with NF-kB binding to
the iNOS promoter DNA in a dose-dependent manner. MP
did not affect the signaling pathway to the nuclear trans-
location of NF-kB, which was distinct from other known
inhibitors.
The promoter of iNOS contains two consensus
sequences for the binding of NF-kB, which mediates
LPS-inducibility [4]. The heterodimer of p65/p50 has been
reported as a responsible NF-kB complex for LPS-induced
iNOS expression. When the activated NF-kB binds to NF-
kB-responsive elements on promoters of target genes in
nuclei, –SH functional group in DNA binding domains of
p50 or p65 seemed to be in reduced state. Accumulating
reports support that the cellular redox status can modify the
function of NF-kB [29,30]. Oxidative, nitrosative, and –SH
modifying agents such as iodoacetamide or N-ethylmalei-
mide can inhibit the DNA binding activity of NF-kB.
Pineda-Molina et al. [31] actually reported that S-glu-
tathionylation or sulfenic acid formation of cysteine resi-
due 62 of the NF-kB p50 subunit inhibited the DNA
binding using MALDI-TOF mass spectroscopy. The
report strongly suggests that modification of –SH groups
of NF-kB subunits may be a powerful tool for interfering
NF-kB.
Several similar situations like NF-kB were also reported
recently. Cysteine sulfinic acid formation in active site of
peroxiredoxin by oxidation totally blocked its peroxidase
activity [32]. Oxidation of a cysteine residue in phospho-
tyrosine phosphatase 1B (PTP1B) active site could irre-
versibly inactivate the enzyme activity [33]. The reduced
and oxidized states of cysteines on the active (or binding)
site of the proteins may provide an important cyclic
(
–
possibly reversible) modification/regulation strategy to
SH containing proteins. By this reason, NF-kB could
act as a sensor for redox status in cells. Although MP might
affect the interaction of –SH of NF-kB subunit with DNA,
it is not clear if MP directly modifies the –SH of NF-kB
subunits, or if it alters the intracellular redox indicator like

S. Lim et al. / Biochemical Pharmacology 68 (2004) 719–728
727
[
16] Shindoh C, Wu D, Ohuchi Y, Kurosawa H, Kikuchi Y, Hida W, et al.
Effects of L-NAME and L-arginine on diaphragm contraction in a
septic animal model. Comp Biochem Physiol A Mol Integr Physiol
acute inflammatory disorders in which iNOS induction
involves in their pathogenesis.
1
998;119:219–24.
[
17] Depre C, Havaux X, Renkin J, Vanoverschelde JL, Wijns W. Expres-
sion of inducible nitric oxide synthase in human coronary athero-
sclerotic plaque. Cardiovasc Res 1999;41:465–72.
Acknowledgments
This study was supported by grants of FPR02A6-24-110
of 21C Frontier Functional Proteomics Project From Kor-
ean Ministry of Science & Technology, and in part by 01-
PJ1-PG3-20500-0147 and 02-PJ1-PG1-CH04-0001, Good
Health 21 from MOWH, Korea.
[18] Behr D, Rupin A, Fabiani JN, Verbeuren TJ. Distribution and pre-
valence of inducible nitric oxide synthase in atherosclerotic vessels of
long-term cholesterol-fed rabbits. Atherosclerosis 1999;142:335–44.
[
19] Han CY, Park SY, Pak YK. Role of endocytosis in the transactivation
of nuclear factor-kappaB by oxidized low-density lipoprotein. Bio-
chem J 2000;350(Pt 3):829–37.
[
20] Kim YS, Han CY, Kim SW, Kim JH, Lee SK, Jung DJ, et al. The
orphan nuclear receptor small heterodimer partner as a novel cor-
egulator of nuclear factor-kappa b in oxidized low density lipoprotein-
treated macrophage cell line RAW 264.7. J Biol Chem 2001;276:
33736–40.
References
[
[
[
[
1] Michel T, Feron O. Nitric oxide synthases: which, where, how, and
why? J Clin Invest 1997;100:2146–52.
[21] Dignam JD, Lebovitz RM, Roeder RG. Accurate transcription initia-
tion by RNA polymerase II in a soluble extract from isolated mam-
malian nuclei. Nucleic Acids Res 1983;11:1475–89.
2] Mayer B, Hemmens B. Biosynthesis and action of nitric oxide in
mammalian cells. Trends Biochem Sci 1997;22:477–81.
3] Brown GC. Cell biology. NO says yes to mitochondria. Science
[22] Peng HB, Libby P, Liao JK. Induction and stabilization of I kappa B
alpha by nitric oxide mediates inhibition of NF-kappa B. J Biol Chem
1995;270:14214–9.
2003;299:838–9.
4] Xie QW, Whisnant R, Nathan C. Promoter of the mouse gene encoding
calcium-independent nitric oxide synthase confers inducibility by
interferon gamma and bacterial lipopolysaccharide. J Exp Med
[23] Parmentier M, Hirani N, Rahman I, Donaldson K, MacNee W,
Antonicelli F. Regulation of lipopolysaccharide-mediated interleu-
kin-1beta release by N-acetylcysteine in THP-1 cells. Eur Respir J
2000;16:933–9.
1993;177:1779–84.
[
[
[
5] KimYM, LeeBS, YiKY, PaikSG.UpstreamNF-kappaBsiteisrequired
forthemaximalexpressionofmouseinduciblenitricoxidesynthasegene
in interferon-gamma plus lipopolysaccharide-induced RAW 264.7
macrophages. Biochem Biophys Res Commun 1997;236:655–60.
6] Schackelford RE, Misra UK, Florine-Casteel K, Thai SF, Pizzo SV,
Adams DO. Oxidized low density lipoprotein suppresses activation of
NF kappa B in macrophages via a pertussis toxin-sensitive signaling
mechanism. J Biol Chem 1995;270:3475–8.
[24] Liu SF, Ye X, Malik AB. Inhibition of NF-kappaB activation by
pyrrolidine dithiocarbamate prevents in vivo expression of proinflam-
matory genes. Circulation 1999;100:1330–7.
[25] Schreck R, Meier B, Mannel DN, Droge W, Baeuerle PA. Dithiocar-
bamates as potent inhibitors of nuclear factor kappa B activation in
intact cells. J Exp Med 1992;175:1181–94.
[26] Gao Y, Lecker S, Post MJ, Hietaranta AJ, Li J, Volk R, et al. Inhibition
of ubiquitin-proteasome pathway-mediated I kappa B alpha degrada-
tion by a naturally occurring antibacterial peptide. J Clin Invest
2000;106:439–48.
7] Cardozo AK, Heimberg H, Heremans Y, Leeman R, Kutlu B, Kru-
hoffer M, et al. A comprehensive analysis of cytokine-induced and
nuclear factor-kappa B-dependent genes in primary rat pancreatic
beta-cells. J Biol Chem 2001;276:48879–86.
[27] Chen FE, Huang DB, Chen YQ, Ghosh G. Crystal structure of p50/p65
heterodimer of transcription factor NF-kappaB bound to DNA. Nature
1998;391:410–3.
[
[
8] Brand K, Page S, Rogler G, Bartsch A, Brandl R, Knuechel R, et al.
Activated transcription factor nuclear factor-kappa B is present in the
atherosclerotic lesion. J Clin Invest 1996;97:1715–22.
[28] Kumar S, Rabson AB, Gelinas C. The RxxRxRxxC motif conserved in
all Rel/kappa B proteins is essential for the DNA-binding activity and
redox regulation of the v-Rel oncoprotein. Mol Cell Biol 1992;12:
3094–106.
9] Bierhaus A, Schiekofer S, Schwaninger M, Andrassy M, Humpert PM,
Chen J, et al. Diabetes-associated sustained activation of the tran-
scription factor nuclear factor-kappaB. Diabetes 2001;50:2792–808.
[
10] Swantek JL, Christerson L, Cobb MH. Lipopolysaccharide-induced
tumor necrosis factor-alpha promoter activity is inhibitor of nuclear
factor-kappaB kinase-dependent. J Biol Chem 1999;274:11667–71.
11] Cogswell JP, Godlevski MM, Wisely GB, Clay WC, Leesnitzer LM,
Ways JP, et al. NF-kappa B regulates IL-1 beta transcription through a
consensus NF-kappa B binding site and a nonconsensus CRE-like site.
J Immunol 1994;153:712–23.
[29] Andus T, Bauer J, Gerok W. Effects of cytokines on the liver.
Hepatology 1991;13:364–75.
[30] Li N, Karin M. Is NF-kappaB the sensor of oxidative stress? FASEB J
1999;13:1137–43.
[
[31] Pineda-Molina E, Klatt P, Vazquez J, Marina A, Garcia dL, Perez-Sala
D, et al. Glutathionylation of the p50 subunit of NF-kappaB: a
mechanism for redox-induced inhibition of DNA binding. Biochem-
istry 2001;40:14134–42.
[12] Peraldi P, Spiegelman BM. Studies of the mechanism of inhibition of
insulin signaling by tumor necrosis factor-alpha. J Endocrinol
[32] Woo HA, Chae HZ, Hwang SC, Yang KS, Kang SW, Kim K, et al.
Reversing the inactivation of peroxiredoxins caused by cysteine
sulfinic acid formation. Science 2003;300:653–6.
1997;155:219–20.
[
13] Kim ND, Kang KW, Kim SG, Schini-Kerth VB. Inhibition of in-
ducible nitric oxide synthase expression and stimulation of the en-
dothelial formation of nitric oxide most likely accounts for the
protective effect of 2-(allylthio)pyrazine in a murine model of en-
dotoxemia. Biochem Biophys Res Commun 1997;239:310–5.
14] Cotter G, Kaluski E, Blatt A, Milovanov O, Moshkovitz Y, Zaidenstein
R, et al. L-NMMA (a nitric oxide synthase inhibitor) is effective in the
treatment of cardiogenic shock. Circulation 2000;101:1358–61.
15] Weisz A, Cicatiello L, Esumi H. Regulation of the mouse inducible-
type nitric oxide synthase gene promoter by interferon-gamma. Bio-
chem J 1996;316(Pt 1):209–15.
[33] Salmeen A, Andersen JN, Myers MP, Meng TC, Hinks JA, Tonks NK,
et al. Redox regulation of protein tyrosine phosphatase 1B involves a
sulphenyl-amide intermediate. Nature 2003;423:769–73.
[34] Kim CH, Kim JH, Hsu CY, Ahn YS. Zinc is required in pyrrolidine
dithiocarbamate inhibition of NF-kappaB activation. FEBS Lett 1999;
449:28–32.
[
[
[35] Schwenger P, Alpert D, Skolnik EY, Vilcek J. Activation of p38
mitogen-activated protein kinase by sodium salicylate leads to inhibi-
tion of tumor necrosis factor-induced IkappaB alpha phosphorylation
and degradation. Mol Cell Biol 1998;18:78–84.

728
S. Lim et al. / Biochemical Pharmacology 68 (2004) 719–728
[
36] De Vera ME, Taylor BS, Wang Q, Shapiro RA, Billiar TR, Geller DA.
Dexamethasone suppresses iNOS gene expression by upregulating I-
kappa B alpha and inhibiting NF-kappa B. Am J Physiol 1997;273:
G1290–6.
and ability to bind DNA. Proc Natl Acad Sci USA 2001;98:
11557–62.
[39] Rosselet A, FeihlF, MarkertM, GnaegiA, PerretC, Liaudet L. Selective
iNOS inhibition is superior to norepinephrine in the treatment of rat
endotoxic shock. Am J Respir Crit Care Med 1998;157:162–70.
[40] Cho S, Kim Y, Cruz MO, Park EM, Chu CK, Song GY, et al.
Repression of proinflammatory cytokine and inducible nitric oxide
synthase (NOS2) gene expression in activated microglia by N-acetyl-
O-methyldopamine: protein kinase A-dependent mechanism. Glia
2001;33:324–33.
[
37] Kitazawa M, Nakano T, Chuujou H, Shiojiri E, Iwasaki K, Sakamoto
K. Intracellular redox regulation by a cystine derivative suppresses
UV-induced NF-kappa B activation. FEBS Lett 2002;526:106–10.
38] Haridas V, Arntzen CJ, Gutterman JU. Avicins, a family of triterpenoid
saponins from Acacia victoriae (Bentham), inhibit activation of
nuclear factor-kappaB by inhibiting both its nuclear localization
[