Anti-inflammatory potential of 1-nitro-2-phenylethylene

Article abstract of DOI:10.3390/molecules22111977

Inflammation is a reaction of the host to infectious or sterile stimuli and has the physiological purpose of restoring tissue homeostasis. However, uncontrolled or unresolved inflammation can lead to tissue damage, giving rise to a plethora of chronic inflammatory diseases, including metabolic syndrome and autoimmunity pathologies with eventual loss of organ function. Beta-nitrostyrene and its derivatives are known to have several biological activities, including anti-edema, vasorelaxant, antiplatelet, anti-inflammatory, and anticancer. However, few studies have been carried out regarding the anti-inflammatory effects of this class of compounds. Thereby, the aim of this study was to evaluate the anti-inflammatory activity of 1-nitro-2-phenylethene (NPe) using in vitro and in vivo assays. Firstly, the potential anti-inflammatory activity of NPe was evaluated by measuring TNF-α produced by human macrophages stimulated with lipopolysaccharide (LPS). NPe at non-toxic doses opposed the inflammatory effects induced by LPS stimulation, namely production of the inflammatory cytokine TNF-α and activation of NF-κB and ERK pathways (evaluated by phosphorylation of inhibitor of kappa B-alpha [IκB-α] and extracellular signal-regulated kinase 1/2 [ERK1/2], respectively). In a well-established model of acute pleurisy, pretreatment of LPS-challenged mice with NPe reduced neutrophil accumulation in the pleural cavity. This anti-inflammatory effect was associated with reduced activation of NF-κB and ERK1/2 pathways in NPe treated mice as compared to untreated animals. Notably, NPe was as effective as dexamethasone in both, reducing neutrophil accumulation and inhibiting ERK1/2 and IκB-α phosphorylation. Taken together, the results suggest a potential anti-inflammatory activity for NPe via inhibition of ERK1/2 and NF-κB pathways on leukocytes.

Full text of DOI:10.3390/molecules22111977

molecules
Article
Anti-Inflammatory Potential of 1-Nitro-2-Phenylethylene
Michelle A. Sugimoto 1 , Márcia de Jesus Amazonas da Silva , Larissa Froede Brito ,
ID
2
1
3
4
3
Rosivaldo dos Santos Borges , Flávio Almeida Amaral , Ana Paula de Araujo Boleti ,
Maritza Echevarria Ordoñez , Jose Carlos Tavares , Lirlandia Pires Sousa and
3
5
1
2
,
ID
Emerson Silva Lima *
1
Laboratory of Inflammation Signaling, Department of Clinical Analysis, Faculty of Pharmacy,
Federal University of Minas Gerais, Belo Horizonte 31270-901, MG, Brazil;
adrianeamantea@gmail.com (M.A.S.); larissafroede@yahoo.com.br (L.F.B.); lipsousa72@gmail.com (L.P.S.)
Laboratory of Biological Activity, Faculty of Pharmaceutical Sciences, Federal University of Amazonas,
Manaus 69067-005, AM, Brazil; marciajas24@gmail.com
Nucleus of Studies and Selection of Bioactive Molecules, Institute of Health Sciences, Federal University of
Pará, Belém 66075-110, PA, Brazil; lqfmed@gmail.com (R.d.S.B.); apboleti@yahoo.com.br (A.P.d.A.B.);
echevarriamaritza8@gmail.com (M.E.O.)
Department of Physiology and Biophysics, Institute of Biological Sciences, Federal University of Minas
Gerais, Belo Horizonte 31270-901, MG, Brazil; dr.famaral@gmail.com
Laboratory of Research in Drugs, Department of Biological Sciences and Health, Federal University of
Amapá, Macapá 68903-419, AP, Brazil; jctcarvalho@gmail.com
2
3
4
5
*
Correspondence: eslima@ufam.edu.br; Tel.: +55-(092)-3305-1181
Received: 4 September 2017; Accepted: 10 November 2017; Published: 15 November 2017
Abstract: Inflammation is a reaction of the host to infectious or sterile stimuli and has the physiological
purpose of restoring tissue homeostasis. However, uncontrolled or unresolved inflammation can lead
to tissue damage, giving rise to a plethora of chronic inflammatory diseases, including metabolic
syndrome and autoimmunity pathologies with eventual loss of organ function. Beta-nitrostyrene and
its derivatives are known to have several biological activities, including anti-edema, vasorelaxant,
antiplatelet, anti-inflammatory, and anticancer. However, few studies have been carried out regarding
the anti-inflammatory effects of this class of compounds. Thereby, the aim of this study was to
evaluate the anti-inflammatory activity of 1-nitro-2-phenylethene (NPe) using in vitro and in vivo assays.
Firstly, the potential anti-inflammatory activity of NPe was evaluated by measuring TNF-
by human macrophages stimulated with lipopolysaccharide (LPS). NPe at non-toxic doses opposed the
inflammatory effects induced by LPS stimulation, namely production of the inflammatory cytokine TNF-
and activation of NF- B and ERK pathways (evaluated by phosphorylation of inhibitor of kappa B-alpha
B- ] and extracellular signal-regulated kinase 1/2 [ERK1/2], respectively). In a well-established model
of acute pleurisy, pretreatment of LPS-challenged mice with NPe reduced neutrophil accumulation
in the pleural cavity. This anti-inflammatory effect was associated with reduced activation of NF-
and ERK1/2 pathways in NPe treated mice as compared to untreated animals. Notably, NPe was as
effective as dexamethasone in both, reducing neutrophil accumulation and inhibiting ERK1/2 and I B-
α produced
α
κ
[Iκ α
κB
κ
α
phosphorylation. Taken together, the results suggest a potential anti-inflammatory activity for NPe via
inhibition of ERK1/2 and NF-κB pathways on leukocytes.
Keywords: 1-nitro-2-phenylethylene; anti-inflammatory activity; TNF-α production
1
. Introduction
Aniba canelilla (H.B.K.) Mez [syn. Aniba elliptica A. C. Sm., Cryptocarya canelilla Kunth] (EOAC),
commonly known as “casca preciosa” (precious bark), is an aromatic plant abundant in the Amazon
region, and belongs to the Lauraceae family. In folk medicine, the decoction of bark wood is used
Molecules 2017, 22, 1977; doi:10.3390/molecules22111977
www.mdpi.com/journal/molecules

Molecules 2017, 22, 1977
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as an antispasmodic, a digestive stimulant, and a carminative [
1
–3
]. Indeed, A. canelilla bark oil
exerts cardiovascular effects, causing hypotension and bradycardia in normotensive rats [
4], as well as
presenting antioxidant properties [5].
The essential oil of A. canelilla is rich in 1-nitro-2-phenylethane (NPE, Figure 1A), the first
nitro compound isolated from plants [ ]. NPE is considered to be the odoriferous principle of leaf,
bark, and trunk wood of A. canelilla, responsible for the cinnamon scent [ ]. The content of NPE in
the plant depends on the season, been more abundant in the rainy than in the dry period [ ]. NPE has
been shown to exert antinociceptive [ ] and, vasorelaxant [10 11] effects in vivo. Furthermore, a recent
6
6,7
8
9
,
study has suggested that NPE also has anti-inflammatory activity, as demonstrated by its ability to
inhibit paw edema induced by dextran and carrageenan in rats and by croton oil in mice [12].
Figure 1. Chemical structures of (A) 1-nitro-2-phenylethane (NPE), the main component of Aniba
canelilla essencial oil; and (B) synthetic 1-nitro-2-phenylethylene (NPe).
NPE assumes different conformations due to its sp3 carbon atoms. A conformational restriction
by substitution of the alkane for the alkene moiety allows the formation of 1-nitro-2-phenylethene
(NPe, Figure 1B), also named 1-((E)-2-nitro-vinyl)-benzene or β-nitrostyrene [13]. NPe could have
increased drug potency compared to NPE, since the removal of torsional flexibility is known to reduce
the entropic penalty of binding to the target [14,15].
Inflammation is a reaction of the host to infectious or sterile tissue damage which aims to eliminate
pathogens, clear damaged host cells and restore tissue homeostasis [16
unresolved inflammation can lead to tissue damage, giving rise to a plethora of chronic inflammatory
diseases [17 18]. The acute inflammatory response can be divided into initiation and resolution
,17]. However, uncontrolled or
,
stages [19]. During the early phase of inflammation, production of inflammatory mediators promotes
leukocyte accumulation and survival in the inflammatory site, while the resolution of inflammation
depends on proper clearance of migrated leukocytes, mainly via neutrophil apoptosis and their
removal (efferocytosis) by tissue macrophages [17].
Recognition of microbial antigens plays a crucial role in host defense, and relies on the
detection of conserved molecular patterns that are essential products of microbial physiology, such as
lipopolysaccharides (LPS) of Gram-negative bacteria and peptidoglycans of Gram-positive bacteria [20].
LPS binds to toll-like receptor (TLR)-4 on the surface of macrophages, triggering the activation of signal
transduction pathways, including the well-characterized NF-
κ
B and mitogen-activated protein kinase
(
MAPK)-dependent transcription factors, which induce the expression of many of the pro-inflammatory
cytokines and immune mediators [21
involved in the transcriptional regulation of the tumor necrosis factor-
and IL-1 genes in macrophages [22]. In resting cells, NF-
–
23]. LPS-activated NF-
κ
B has been shown to be critically
(TNF- ), interleukin (IL)-6,
B dimers are sequestered to the cytoplasm
and maintained inactivated by reversible association with its inhibitor I B or unprocessed forms of
cytoplasmic p50/p105 (NF- B1) and p52/p100 (NF- B2) [24 26]. NF- B activation in response to
proinflammatory stimuli is regulated by IKK, which phosphorylates I B and promotes its proteasome
degradation and the release of NF- B for nuclear translocation and gene transcription activation [21].
α
α
κ
κ
κ
κ
–
κ
κ
κ
Activation of the MAPK/ERK pathway by LPS has also been shown to regulate the production of
pro-inflammatory cytokines, such as TNF-α, in murine macrophages [27].
In this study, we explored the potential anti-inflammatory effects of NPe, which reduced
the production of TNF-α by human macrophages stimulated with LPS, and prevented neutrophil

Molecules 2017, 22, 1977
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accumulation, in vivo, in a model of acute pleurisy. Mechanistically, our data indicate that NPe can
decrease the activation of ERK1/2 and NF- B inflammatory pathways, while further studies are
needed to fully elucidate this mechanism of action.
κ
2
. Materials and Methods
2
.1. Synthesis of NPe
NPe was synthesized in the Pharmaceutical Chemistry Laboratory at the Universidade Federal
do Pará employing the Claisen–Schmidt procedure, as previously described (Figure 2) [13,28,29].
Briefly, benzaldehyde (1) and nitromethane (2) were used as reactants (0.02 and 0.024 M, respectively)
in methanol. The product was ‘one-pot’ converted with 89–92% yield by using 0.1 M NaOH in water
◦
at 0–10 C. The precipitate was filtered out and dried under vacuum to give a solid product. NPe was
then crystallized in ethanol as a pale yellow solid. The final product was identified by FT-IR and NMR
1
13
(
H- and C-NMR) spectroscopic techniques and compared with literature data [13,30]. IR νmax 1600,
−
1 1
1
550, 1498, 1375 cm ; H-NMR (CD SOCD , 200 MHz)
.7 (d, 1H), 7.9 (d, 1H); 13C-NMR (CD SOCD , 50 MHz)
δ
7.2–7.3 (d, 2H), 7.35–7.4 (d, 2H), 7.55 (d, 1H),
3
3
7
δ 127.52, 128.84, 129.69, 136.82, 137.99, 140.96.
3
3
Figure 2. Chemical synthesis of 1-Nitro-2-phenylethylene (NPe).
2
.2. Mice and Ethics
All procedures described here had prior approval from the Ethics Committee in Animal
Experimentation of the Universidade Federal de Minas Gerais (CEUA/UFMG, Protocol number:
3/2015). Male wild-type (WT) BALB/c mice (8–10 weeks old) were obtained from the Biosciences
8
Unit of Institute of Biological Sciences (Belo Horizonte, MG, Brazil). Mice were housed under standard
conditions, and had free access to commercial chow and water.
2
.3. Drugs, Reagents and Antibodies
-Phorbol-12-myristate-13-acetate (PMA), dexamethasone, lipopolysaccharide (LPS, from Escherichia coli
serotype O:111:B4), and mouse anti- -actin (#A5316) were from Sigma Aldrich (St. Louis, MO, USA).
Rabbit anti-phospho-ERK1/2 and mouse anti-phospho-I B- were purchased from Cell Signaling
4α
β
κ
α
Technology (Beverly, MA, USA). Secondary anti-mouse (Sc-2005) and anti-rabbit (#7074) peroxidase-conjugate
antibodies were purchased from Santa Cruz Biotechnology (Santa Cruz, CA, USA) and Cell Signaling
Technology, respectively.
2
.4. Cell Culture and In Vitro Assays
The human monocyte-like cell line THP-1 and the murine macrophage-like cell line J774A.1 were
obtained from the American Type Culture Collection (ATCC, Rockville, MD, USA). THP-1 cells were
cultured in RPMI 1640 medium (Cultilab, São Paulo, Brazil), supplemented with 10% heat-inactivated fetal
bovine serum (FBS, Cultilab, São Paulo, Brazil) and antibiotics (100
µg/mL streptomycin and 100 U/mL
penicillin, both from Sigma-Aldrich). J774A.1 cells were cultured in DMEM (Cultilab, São Paulo, Brazil
)
◦
under the same conditions. Cell cultures were maintained at 37 C and 5% CO . To evaluate the effect of
2
NPe on viability of murine macrophages, J774A.1 cells were seeded (50,000 cells per well) in 96-well cell
culture plates (BD Biosciences, Franklin Lakes, NJ, USA). Twenty-four hours later, when a confluent cell
monolayer was observed, media and non-adherent cells were removed from the wells and the adherent
cells were treated with NPe at concentrations from 1 to 20 µg/mL for 24 h. To evaluate the cell viability of

Molecules 2017, 22, 1977
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human macrophages treated with NPe, THP-1 monocytes were seeded (50,000 cells per well) in 96-well
cell culture plates (BD Biosciences, Franklin Lakes, NJ, USA), differentiated into macrophages using PMA
2
0 ng/mL (Sigma Aldrich, St. Louis, MO, USA), and serum-deprived with FBS 0.5% for 16 h. Subsequently,
cells were either left untreated, or treated with NPe at different concentrations (1, 5, 10 and 20 µg/mL) for
, and thereafter with LPS (100 ng/mL) for a further 4 h. LPS was added to the wells without removing
2
h
the supernatant, which means that NPe was present during the entire time of stimulation with LPS.
Crystallized NPe was dissolved in dimethyl sulfoxide (DMSO) and diluted in medium supplemented with
0.5% FBS for all assays. The concentration of DMSO ranged from 0.002 to 0.04%. Cell viability was evaluated
by the MTT method [31]. Viability of murine and human macrophages was tested using untreated cells and
LPS-treated cells as reference, respectively. Cell viability higher than 90% was considered nontoxic for both
cell lines. The potential anti-inflammatory activity of NPe was evaluated by measuring the cytokine TNF-
α
produced by LPS-stimulated THP-1 macrophages. For this, the supernatant was collected, and TNF-
α
was measured using the cytokine-specific sandwich quantitative enzyme-linked immune-sorbent assay
ELISA) according to the manufacturer’s instructions (TNF-α duo set, R&D Systems).
(
2
.5. LPS-Induced Pleurisy Model
To further confirm the anti-inflammatory properties of NPe, we evaluated its effect in an
established model of pleurisy induced by LPS [32–34]. For this purpose, mice were pretreated with an
injection of NPe (0.9 mg/kg, i.p.), dexamethasone (2 mg/kg, i.p.), or vehicle, comprising 2% DMSO in
phosphate-buffered saline (PBS). After 1 h, mice were challenged with an intrapleural (i.pl.) injection
of LPS (250 ng/cavity) from Escherichia coli serotype (O:111:B4) purchased from Sigma Chemicals
(St. Louis, MO, USA) or PBS. Cells were recovered from the pleural cavity 7 h after LPS injection
by washing with PBS containing EDTA (1 mM). Total cell counts were performed on cells harvested
from the pleural cavity in a Neubauer chamber using Turk’s stain. Differential counts were performed
on cytocentrifuge preparations (Shandon III) after staining with May-Grunwald-Giemsa and using
standard morphological criteria to identify cell types [32
–34]. The results are shown as the number of
cells per cavity. Cell extracts were prepared for western blot analysis as previously described [32
–34].
2
.6. Western Blot Analysis
THP-1 cells and inflammatory cells harvested from the pleural cavity were washed with PBS
and whole-cell extracts were prepared as previously described [32 34]. Protein concentrations
were quantified with the Bradford assay reagent from Bio-Rad (Bio-Rad, Redmond, WA, USA).
Equal amounts of protein (50 g) from each group were loaded and separated by electrophoresis
–
µ
on denaturing 10% polyacrylamide-SDS gels and electrotransferred to nitrocellulose membranes.
Membranes were blocked for 1 h at room temperature with PBS containing 5% (w/v) nonfat dry
milk and 0.1% Tween-20. Afterwards, the membranes were washed three times with PBS containing
◦
0
.1% Tween-20 and then incubated overnight at 4 C with specific primary antibody (anti-ERK1/2,
anti-phospho-ERK1/2, anti-phospho-I
BSA and 0.1% Tween-20. For normalization of the bands, the same membranes were incubated for
h at room temperature with anti- -actin using a dilution of 1:1000 in PBS containing 5% (w/v)
κB-alpha) using a dilution of 1:1000 in PBS containing 5% (w/v)
2
β
BSA and 0.1% Tween-20. After washing, membranes were incubated with appropriated horseradish
peroxidase-conjugated secondary antibody (1:3000). Immunoreactive bands were visualized using
the ECL detection system, as described by the manufacturer (GE Healthcare, Piscataway, NJ, USA).
The values of phosphorylated levels of ERK1/2 and IkB-α were quantified by using a densitometric
analysis software (ImageJ, Image Processing and Analysis in Java; NIH, Bethesda, MD, USA). Changes
in protein levels were estimated, and the results were expressed in arbitrary units—AU normalized to
the values of β-actin in the same sample.

Molecules 2017, 22, 1977
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2
.7. Statistical Analysis
Results are presented as the mean
±
SEM. Data were analyzed by one-way ANOVA, and differences
between groups were assessed using the Student-Newman-Keuls post-hoc test, except where otherwise
indicated. A p value < 0.05 was considered significant. Calculations were performed using the prism 5.0
software program for Windows (GraphPad software, San Diego, CA, USA).
3
. Results
3
.1. Definition of Toxic and Non-Toxic Doses of NPe on Murine and Human Macrophages
Initially, we aimed to define the viability of both murine and human cells exposed to NPe in order to
define non-toxic doses. Murine macrophage-like cell line J774A.1 was exposed to NPe at four different
concentrations (1, 5, 10 and 20 g/mL) for 24 h. We observed cell viability below 40% when murine
macrophages were treated with NPe at concentrations higher or equal to 5 g/mL. NPe was non-toxic
at the lower concentration (1 g/mL), showing cell viability similar to the control (Figure 3A). After this
µ
µ
µ
initial assay, we used the same concentrations in human macrophages, using conditions that would
better simulate those used in the following functional assays. To investigate cell viability of human
macrophages, differentiated THP-1 macrophages were exposed to the different NPe concentrations
(
1, 5, 10 and 20 µg/mL) for 6 h in inflammatory conditions (under LPS stimuli). We observed cell viability
below 70% when cells were treated with NPe at 10 or 20 g/mL. As observed for the murine macrophages,
NPe was non-toxic at the two lower concentrations (1 and 5 g/mL), showing cell viability similar to the
µ
µ
control group (Figure 3B) and, for this reason, these concentrations were used in the following assays using
human macrophages.
Figure 3. Cell viability of murine and human macrophage cell lines treated with NPe. (
macrophage-like cells were transferred to a 96-well plate at a density of 50,000 cells per well. After 24 h
the cells were either left untreated, or treated with NPe at concentrations from 1 to 20 g/mL for 24 h;
) Human monocytic cell line THP-1 was transferred to a 96-well plate at a density of 50,000 cells per well,
differentiated into macrophages and serum-deprived with FBS 0.5% for 16 h. Subsequently, cells were either
left untreated, or treated with NPe at different concentrations (1, 5, 10 and 20 g/mL) for 2 h, and thereafter
with LPS (100 ng/mL) for a further 4 h. Cell viability was evaluated by the MTT method using untreated cells
as a reference for viability. Data are shown as the mean SEM of three wells in each group. Experiments
were performed at least 3 times with similar results. *** p < 0.001 when compared to the control group.
A) J774A.1
,
µ
(B
µ
±

Molecules 2017, 22, 1977
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3
.2. Pre-Treatment of THP-1 Differentiated Macrophages with Non-Toxic Doses of NPe Has
Anti-Inflammatory Effects
Next, we assessed the anti-TNF-
α
activity of NPe over THP-1 macrophages stimulated with LPS
(
Figure 4A). Pre-treatment of cells with NPe 2 h before stimulation with LPS significantly reduced the
production of TNF- at the two tested concentrations. The reduction in TNF- production by NPe
was concentration-dependent, with complete prevention of cytokine production observed for NPe at
µg/mL. In line with these observations, NPe attenuated the activation of ERK pathway induced by
LPS, whereas total ERK levels did not change (Figure 4B). Once again, the effect of NPe in preventing
cell activation by LPS was -dependent. Hence, the increased phosphorylation of I B- induced by LPS
was reduced by NPe at 1 g/mL and almost abolished by NPe at a higher concentration (5 g/mL).
α
α
5
κ
α
µ
µ
In sum, NPe at non-toxic doses opposed the inflammatory effects induced by LPS stimulation, namely,
production of the inflammatory cytokine TNF-α and activation of NF-κB and ERK pathways.
3
.3. Pre-Treatment of LPS-Inflamed Mice with NPe Reduces Neutrophil Accumulation and
Inflammatory Markers
Next, we evaluated whether NPe could operate in vivo to prevent neutrophil accumulation
induced by LPS. Therefore, we treated mice with an intraperitonial (i.p.) injection of NPe, followed
by an intrapleural (i.pl.) inflammatory challenge with 250 ng of LPS. Dexamethasone was used
as a positive control. As expected, i.pl. injection of LPS induced an influx of leukocytes into the
pleural cavity of mice (Figure 5A). Differential cell counts revealed that cells migrated into the
cavity were mainly neutrophils (Figure 5B), with no significant increase in number of mononuclear
cells (Figure 5C). The analysis of pleural cellularity showed that pre-treatment with NPe decreased
neutrophil accumulation in the pleural cavity 7 h after LPS injection when compared to untreated
mice (Figure 5B). Remarkably, equimolar doses of NPe and dexamethasone, had similar effectiveness
in reducing neutrophil accumulation in the pleural cavity of LPS-challenged mice. As previously
demonstrated [32
,33], LPS injection markedly induced activation of pro-inflammatory pathways in
pleural cells, as observed by the increased phosphorylated forms of ERK1/2 and I
κ
B-α, proteins
associated with neutrophil survival and consequent accumulation. In this study, we observed that
NPe prevented the activation of both pathways, as demonstrated by the return of phospho-ERK
and phospho-I
κ
B-
α
levels to basal levels, as compared to the unchallenged group. Again, NPe was
B pathways (Figure 5D,E). Overall,
as effective as dexamethasone in inhibiting ERK1/2 and NF-
κ
NPe acted in a similar manner to dexamethasone to reduce neutrophil accumulation and prevent
activation of neutrophil pro-survival pathways in response to LPS.

Molecules 2017, 22, 1977
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Figure 4. Effect of NPe on LPS-stimulated THP-1 cells assayed at the non-toxic doses. Human promonocytoid
cell line THP-1 was transferred to a 96-well plate at a density of 50,000 cells per well, differentiated into
macrophages and serum-deprived with FBS 0.5% for 16 h. Subsequently, cells were either left untreated,
or treated with NPe at different concentrations (1 and 5
100 ng/mL) for a further 4 h. ( ) TNF- release was measured in the supernatant. Data are shown as the
mean SEM of three wells in each group. Experiments were performed at least 3 times with similar results.
** p < 0.001 when compared to the control group. p < 0.05 and
untreated cells challenged with LPS. The statistical difference between the 2 doses of NPe used is indicated in
the graph; ( ) Phosphorylated I B- and ERK1/2, as well the total form of ERK, were assessed by western
µg/mL) for 2 h, and thereafter with or without LPS
(
A
α
±
#
###
*
p < 0.001 when compared treated to
B
κ α
blot analysis. Blots were normalized with
using pooled cells from at least four wells; (
β
-actin and are representative of three independent experiments
C,
D
) Densitometry data for phosphorylated ERK1/2 and I B- are
κ α
#
#
represented graphically. * p < 0.05, **p < 0.01, and *** p < 0.001 when compared to the control group. p < 0.01
###
and
p < 0.001 when compared cells challenged with LPS treated or not with NPe. All experiments were
performed at least 3 times (n = 3 in each group) with similar results.

Molecules 2017, 22, 1977
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Figure 5. Effect of pre-treatment of mice with NPe on LPS-induced pleurisy. Mice received an injection
of equimolar dose of NPe (0.9 mg/kg, i.p.), dexamethasone (2 mg/kg, i.p.), or vehicle (2% DMSO/PBS).
After 1 h, mice were challenged with LPS (250 ng/cavity, i.pl.). Cells from pleural cavity were processed for
total (
per cavity, and is shown as mean
when compared with unchallenged mice (that did not receive LPS injection). Statistical differences between
LPS-injected mice treated or not with NPe are indicated in the graph; ( ) Inflammatory markers were
analyzed for the whole extract of cells harvested from the pleural cavity. Blots were normalized with
-actin and are representative of three independent experiments using pooled cells from at least four mice;
A
) and differential (
B
,
C
) cell counts. The pleural cellularity was expressed as number of leukocytes
±
SEM of at least four mice in each group. * p < 0.05 and *** p < 0.001
D
β
(
E
) Densitometry data for phosphorylated ERK1/2 and I
κ
B-
α
are represented graphically. ** p < 0.01 when
#
#
###
compared with mice that did not receive LPS injection.
LPS-injected mice treated or not with NPe.
p < 0.01 and
p < 0.001 when comparing
4
. Discussion
Inflammation occurs as a result of recognition of foreign bodies or self-antigens by patrolling cells
present in tissues, followed by increased vascular permeability, leukocyte recruitment and release of
pro-inflammatory mediators [16 17] . Recognition of microbial products, such as LPS from membrane
of Gram-negative bacteria, by toll-like receptors and other pattern-recognition receptors, initiates the
production of pro-inflammatory cytokines including TNF- , IL-1 and IL-6, as well as a number of
,
α
chemokines. Although an efficient inflammatory response is crucial for host defense, uncontrolled
inflammation leads to chronic or autoimmune diseases [18]. Since deregulated inflammation is usually
associated with excessive cytokine production, inhibiting cytokine action or production represent
important pharmacological strategies for resolving acute inflammation. In addition to the reduction
of chemokine and cytokine gradients, the termination of inflammation, the so-called resolution of
inflammation, depends on down-regulation of survival pathways, apoptosis of granulocytes and their

Molecules 2017, 22, 1977
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effective removal by macrophages [17]. In this study, we explored the anti-inflammatory effects of NPe
and the underlying mechanisms both in vitro and in vivo.
NPe and its derivatives have been found to exert various biological effects, including
anti-edema [35], vasorelaxant [13], antiplatelet [36
activities [39 40]. Despite the several therapeutic actions described for NPe derivatives, they are
also recognized to reduce cell viability [37 40 41]. In many cases, apoptosis, a programmed cell
death, was identified as the mechanism of cell death induced by NPe and its derivatives [40 42].
,37] , anti-inflammatory [35,38], and anticancer
,
,
,
–
Apoptosis-inducing cytotoxic activity associated with caspase-3 activation was also identified for
hybrid analogs of NPe, nitrovinylstilbene and flavanone scaffolds in breast cancer cells [41]. Neutrophil
apoptosis is essential for the termination of inflammation [17], and the pro-apoptotic effect of NPe
could be advantageous in inflammatory contexts. On the other hand, monocytes and macrophages
are crucial for the resolution of inflammation and should be preserved from cell death. With this in
mind, we initially assessed the non-toxic concentrations of NPe on monocytes and macrophages.
Here, we identified that NPe did not alter cell viability of murine and human macrophages in
concentrations lower than or equal to 1 µg/mL and 5 µg/mL, respectively.
The anti-inflammatory potential of nitroderivatives has been previously demonstrated [35
For instance, the derivative 3,4-methylenedioxy- -nitrostyrene exhibited inhibitory effects on ATPase
and decreased inflammasome activation [38]. This -nitrostyrene derivative also exhibited suppressed
1-integrin activation resulting in suppression of breast cancer cell adhesion and migration [39].
,38].
β
β
β
It is known that integrin-mediated cell adhesion and migration are not only important for cancer
metastasis, but also for leukocyte recruitment during inflammation [43]. Thus, the suppression of
β
1-integrin activation by
as an anti-inflammatory. NPe derivatives have also been demonstrated to inhibit the TNF
signaling pathway in MCF-7 human breast cancer cells [44]. Furthermore, several nitroderivatives,
including NPe itself, reduced edema and myotoxic activity provoked by PLA purified from snake
β
-nitrostyrenes could also interfere with leukocyte migration, thus acting
α
/NFκB
2
venom [35]. In this study, we found that, in non-toxic concentrations, NPe inhibited TNF-
by LPS-stimulated THP-1 human macrophages, and reduced the levels of phosphorylated ERK and
B- . These results indicate the potential anti-inflammatory properties of NPe, since it significantly
reduced macrophage activation by LPS. Future studies might investigate whether the altered levels
of TNF- protein, observed in this study, are a consequence of transcriptional regulation of TNF-
α release
I
κ α
α
α
gene expression. Changes in gene expression by NPe are likely to be observed, as suggested by
the decreased levels of phospho-ERK in treated macrophages, a MAPK involved in gene expression
of pro-inflammatory cytokines. In order to provide complementary observations, future studies
will also need to address the effect of NPe on other pro-inflammatory cytokines (e.g., IL-1β and
IL-6), as well as other important pro-inflammatory mediators (e.g., prostaglandins and nitric oxide)
and pro-inflammatory pathways in macrophages, such as cyclooxygenase-2, the main enzyme in
the arachidonic acid cascade responsible for eicosanoid production [45]. The regulation of ERK1/2
phosphorylation being associated to the reduced protein expression of TNF-α by NPe suggests that
this nitroderivative regulates the downstream transcription factor AP-1, which must be confirmed in
future. Indeed, we cannot exclude that NPe can also have an inhibitory effect on other MAPKs, such as
JNK and p38, in addition to the observed effect on ERK1/2 phosphorylation. This study also opens
new avenues of research for better understanding the effect of NPe on interferon regulatory factor
(IRF)-signaling, another important signaling pathway in macrophages.
Equally important was to expand these in vitro analyses by investigating the efficacy of NPe on
acute inflammation in a murine model of pleurisy induced by LPS. In this study, we observed that
NPe was as effective as an equimolar dose of dexamethasone in reducing neutrophil accumulation
in the pleural cavity after LPS challenge. Indeed, we noticed that the levels of phospho-ERK and
phospho-I
of NF- B and ERK1/2 pathways may contribute at least in part, to the anti-inflammatory actions
observed for NPe in this study.
κB-α were decreased after exposure to NPe. These observations indicate that the inhibition
κ

Molecules 2017, 22, 1977
10 of 12
In summary, NPe showed anti-inflammatory properties both in vitro and in vivo
.
In vitro, it
prevented macrophage activation, as indicated by the abolished production of pro-inflammatory
cytokine and reduced activation of the NF- B and ERK pathways. In an experimental model of
acute inflammation, pre-treatment with NPe was as effective as dexamethasone in reducing neutrophil
accumulation and preventing the activation of NF- B and ERK1/2 pathways. These results indicate the
κ
κ
potential anti-inflammatory properties of NPe by interfering with leukocyte migration and activation
of pro-inflammatory pathways.
Acknowledgments: The authors thank FAPEMIG, FAPEAM, CAPES and CNPq for financial support.
Author Contributions: M.A.S, M.d.J.A.d.S, L.F.B. carried out experiments. R.d.S.B., A.P.d.A.B., M.E.O. and J.C.T.
contributed reagents/materials/analysis tools. F.A.A. contributed to the experiments in vivo. M.A.S, M.d.J.A.d.S,
L.P.S. and E.S.L. conceived and designed the experiments. M.A.S, L.P.S. and E.S.L. wrote the manuscript.
Conflicts of Interest: The authors declare no conflicts of interest.
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Sample Availability: Samples of the compound NPe are available from the authors.
©
2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).