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Journal ArticleDOI

Radiosynthesis and in vivo Evaluation of Carbon-11 (2S)-3-(1H-Indol-3-yl)-2-{[(4-methoxyphenyl)carbamoyl]amino}-N-{[1-(5-methoxypyridin-2-yl)cyclohexyl]methyl}propanamide: An Attempt to Visualize Brain Formyl Peptide Receptors in Mouse Models of Neuroinflammation.

01 Jul 2016-Chemistry & Biodiversity (Chem Biodivers)-Vol. 13, Iss: 7, pp 875-883

TL;DR: The very first attempt to visualize in vivo formyl peptide receptors (FPRs) in mouse brain by positron emission tomography (PET) is described and useful information is provided for the design and characterization of future potential PET radioligands for visualization of brain FPRs by PET.

AbstractHere, we describe the very first attempt to visualize in vivo formyl peptide receptors (FPRs) in mouse brain by positron emission tomography (PET). FPRs are expressed in microglial cells where they mediate chemotactic activity of β-amyloid peptide in Alzheimer disease and, thus, are involved in neuroinflammatory processes. To this purpose, we have selected (2S)-3-(1H-Indol-3-yl)-2-{[(4-methoxyphenyl)carbamoyl]amino}-N-{[1-(5-methoxypyridin-2-yl)cyclohexyl]methyl}propanamide ((S)-1), that we have previously identified as a potent non-peptidic FPR agonist. (S)-[(11) C]-1 has been prepared in high radiochemical yield. (S)-[(11) C]-1 showed very low penetration of blood-brain barrier and, thus, was unable to accumulate into the brain. In addition, (S)-[(11) C]-1 was not able to label FPRs receptors in brain slices of PS19 and APP23 mice, two animal models of Alzheimer disease. Although (S)-[(11) C]-1 was not suitable to visualize FPRs in the brain, this study provides useful information for the design and characterization of future potential PET radioligands for visualization of brain FPRs by PET.

Summary (2 min read)

Introduction

  • Neuroinflammation is a complex, dynamic, multicellular process that plays a central role in a variety of neurological diseases including neurodegenerative disorders.
  • In particular, in vivo imaging of microglia can offer a measure of the inflammatory process and a means of tracking the progression of those pathologies that trigger an immune activation in the brain and the efficacy of therapeutic treatments over time [12].
  • FPRs are expressed in several immune cells including leukocytes, monocytes/macrophages, and microglia, and are considered to play relevant roles in innate immunity and host defense mechanisms and chemotaxis [14].
  • Among FPRs, the FPRL-1, and its murine homologue FPR2, appear to be relevant to the proinflammatory aspects of AD, because FPRL-1 is a chemotactic receptor for Ab42, the 42 amino acid form of Ab, which induces monocytes migration and activation [15].
  • Conversely, non-peptidic small molecules may have some advantages because they can be suitably designed to modulate properties, such as potency, selectivity, lipophilicity, and cell permeability, that are pivotal for a potential radiotracer [23].

Lipophilicity

  • Lipophilicity indices were measured by a reversed-phase HPLC method consisting in a PerkinElmer Series 200 LC apparatus equipped with a PerkinElmer 785A UV/VIS detector set at 254 nm.
  • UV signals were monitored and obtained peaks integrated using a personal computer running PerkinElmer Turbochrom Software.
  • This mobile phase composition was chosen for the analysis due to reasonable retention times for the compounds analyzed.
  • The compounds were dissolved in MeOH and the measurements were made at a flow rate of 1 ml/min.

Serum Stability and Permeability Evaluation

  • Before embarking in the radiolabeling of (S)-1, the authors evaluated two additional features that are of importance for brain PET radiotracers.
  • First, the authors examined if (S)-1 was a P-glycoprotein (P-gp) substrate, because PET tracers that are not substrates of the P-gp efflux pump have higher chances for crossing the BBB.
  • Therefore, the authors evaluated the efflux ratio between basal-to-apical (BA) and apicalto-basal (AB) fluxes in Caco-2 cells monolayer (BA/AB) of compound (S)-1.
  • Second, the authors evaluated if (S)-1 was stable in serum for, at least, the timeframe of a PET scan.
  • (S)-1 showed the desired stability with degradation half-life (t1/2) longer than 4 h .

PET Studies

  • While these studies can offer important information on the interaction between the radiotracer and the target, they cannot predict radiotracer brain uptake or other biodistribution issues.
  • PET images were generated by averaging dynamic data at 0 – 90 min after injection of (S)-[11C]-1, and indicated minimal radioactivity in the brain (top panel in Fig. 1).
  • To this end, the authors selected the APP23 mice model, a transgenic mouse strain showing a robust formation of amyloid plaques, and the PS19 mouse model that is characterized by progressive accumulation of fibrillary tau tangles.
  • These data indicated that the occupancy of FPRs by (S)-[11C]-1 at 1 nM was very low and was not sufficient to autoradiographically label FPRs receptors in the brain.
  • High © 2016 Wiley-VHCA AG, Z€urich www.cb.wiley.com radioactivity levels were observed in the liver of control and LPS-treated rats, suggesting that (S)-1 undergoes rapid and massive hepatic clearance (Fig. 3).

Conclusions

  • In conclusion, the authors have reported here the very first attempt to visualize in vivo brain FPRs that are expressed in microglial cells where they mediate chemotactic activity of Ab peptide in AD.
  • These results could be due to possible low affinity of (S)-[11C]-1 for the target receptor in vivo, concomitant with the rapid in vivo clearance of the radioligand.
  • In addition, most of the FPRL-1 agonists reported, if not all, have been assessed solely for their ability to activate (EC50) and not for their affinity (KD or Ki) for the receptor.
  • The results presented here might suggest it is not the case.
  • This work was supported in part by Grant-in-Aid for Scientific Research on Innovative Areas (‘Brain Environment’) 23111009 (M. H.) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

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FULL PAPER
Radiosynthesis and in vivo Evaluation of Carbon-11 (2S)-3-(1H-Indol-3-yl)-2-{[(4-
methoxyphenyl)carbamoyl]amino}-N-{[1-(5-methoxypyridin-2-yl)cyclohexyl]methyl}
propanamide: An Attempt to Visualize Brain Formyl Peptide Receptors in Mouse
Models of Neuroinflammation
by Enza Lacivita*
a
), Madia Letizia Stama
a
), Jun Maeda
b
), Masayuki Fujinaga
b
), Akiko Hatori
b
), Ming-Rong Zhang
b
),
Nicola A. Colabufo
a
)
c
), Roberto Perrone
a
), Makoto Higuchi
b
), Tetsuya Suhara
b
), and Marcello Leopoldo
a
)
c
)
a
) Dipartimento di Farmacia Scienze del Farmaco, Universit
a degli Studi di Bari ‘Aldo Moro’, via Orabona, 4, IT-70125,
Bari (phone: +39-080-5442750, fax: +39-080-5442231, e-mail: enza.lacivita@uniba.it)
b
) National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology, 4-9-
1 Anagawa, Inage-ku, Chiba, Chiba 263-8555, Japan
c
) BIOFORDRUG s.r.l., Spin-off, Universit
a degli Studi di Bari ‘Aldo Moro’, via Orabona, 4, IT-70125, Bari
Here, we describe the very first attempt to visualize in vivo formyl peptide receptors (FPRs) in mouse brain by positron
emission tomography (PET). FPRs are expressed in microglial cells where they mediate chemotactic activity of b-amyloid
peptide in Alzheimer disease and, thus, are involved in neuroinflammatory processes. To this purpose, we have selected (2S)-
3-(1H-Indol-3-yl)-2-{[(4-methoxyphenyl)carbamoyl]amino}-N-{[1-(5-methoxypyridin-2-yl)cyclohexyl]methyl}propanamide ((S)-
1), that we have previously identified as a potent non-peptidic FPR agonist. (S)-[
11
C]-1 has been prepared in high
radiochemical yield. ( S)-[
11
C]-1 showed very low penetration of bloodbrain barrier and, thus, was unable to accumulate into
the brain. In addition, (S)-[
11
C]-1 was not able to label FPRs receptors in brain slices of PS19 and APP23 mice, two animal
models of Alzheimer disease. Although (S)-[
11
C]-1 was not suitable to visualize FPRs in the brain, this study provides useful
information for the design and characterization of future potential PET radioligands for visualization of brain FPRs by PET.
Keywords: Formyl peptide receptors, Neuroinflammation, PET, Radiosynthesis, Ureidopropanamide.
Introduction
Neuroinflammation is a complex, dynamic, multicellular
process that plays a central role in a variety of neurological
diseases including neurodegenerative disorders. Activation
of microglia, the innate immune system of the central ner-
vous system (CNS), represents one of the hallmarks of neu-
roinflammation [1]. In normal condition, activation of
microglia exerts a protective function, providing tissue
repair by releasing anti-inflammatory cytokines and neu-
rotrophic factors [2][3]. Upon neuronal injury or infection,
microglia becomes overactivated leading to the release of
neurotoxic and proinflammatory factors [4][5]. Recent liter-
ature evidences also indicate that microglial activation is a
phenotypically and functionally diverse process, which may
change depending on aging, stage of disease, or presence of
other inflammatory events [2][6].
Several studies indicate that neuroinflammation is an
early and continuous feature of Alzheimer disease (AD).
Amyloid-b (Ab), which is considered central to the patho-
genesis of this disease, provokes the recruitment of micro-
glia and astrocytes to the sites in close proximity to Ab
deposits. Ab is able to interact with numerous surface
receptors that are expressed by microglial cells such as
formyl peptide receptors (FPRs) [7], Toll-like receptors
[8], scavenger receptors [9], and receptors for advanced
glycation end products (RAGE) [10]. Binding of Ab to
these receptors induces proinflammatory gene expression
and subsequent production of cytokines and chemokines
[11].
Molecular imaging techniques, such as positron emis-
sion tomography (PET) and single-photon emission com-
puted tomography (SPECT), can noninvasively visualize
specific targets of the inflammation cascade through speci-
fic and sensitive probes and, as such, can be powerful
tools to track the progression of neuroinflammatory pro-
cesses including those in AD. In particular, in vivo imag-
ing of microglia can offer a measure of the inflammatory
process and a means of tracking the progression of those
pathologies that trigger an immune activation in the brain
and the efficacy of therapeutic treatments over time [12].
Over the past decade, several targets for molecular imag-
ing of neuroinflammation have been studied, including
translocator protein 18 kDa (TSPO), that is considered a
hallmark of activated microglia [13], and endothelial
adhesion molecules, that are involved in the recruitment
DOI: 10.1002/cbdv.201500281 © 2016 Wiley-VHCA AG, Z
urich
Chem. Biodiversity 2016, 13, 875 883 875

of circulating leukocytes [12]. However, none of these
molecular targets has been fully validated as a biomarker
for the visualization of microglial activation.
The human FPR family belongs to the class A of G-pro-
tein coupled receptors and includes three subtypes, termed
FPR, FPR-like type-1 (FPRL-1), and type-2 (FPRL-2).
FPRs are expressed in several immune cells including
leukocytes, monocytes/macrophages, and microglia, and
are considered to play relevant roles in innate immunity
and host defense mechanisms and chemotaxis [14]. Among
FPRs, the FPRL-1, and its murine homologue FPR2,
appear to be relevant to the proinflammatory aspects of
AD, because FPRL-1 is a chemotactic receptor for Ab
42
,
the 42 amino acid form of Ab, which induces monocytes
migration and activation [15]. FPRL-1 also is involved in
the uptake and fibrillary aggregation of Ab
42
in mononu-
clear phagocytes by rapidly internalizing the Ab
42
-FPRL-1
complexes into cytoplasmic region [16]. FPRL-1 mediates
Ab
42
-induced senescence in neural stem/progenitor cells in
the hippocampus of APP/PS1 mice, an animal model of
AD [17]. Recently, it has been demonstrated that the
expression levels of FPRL-1 in primary microglial cells
increase after exposure to Ab and the recognition of Ab by
the FPRL-1 seems to be the starting point of the signaling
cascade inducing the inflammatory state [18]. Slowick et al.
has evidenced that APP/PS1 mice show higher expression
level of FPRs as compared to wild-type littermates. In par-
ticular, a significant increase in expression of FPR and
FPRL-1 in glial cells was observed in the cortex and hip-
pocampus through immunofluorescence and real-time PCR
analyses [19]. Therefore, FPRL1 could represent an inter-
esting target for monitoring in vivo the onset and progres-
sion of neuroinflammation in AD through molecular
imaging techniques.
To the best of our knowledge, only two studies have
been reported to date dealing with in vivo imaging of
FPRs. Locke et al. [20] have reported the radiosynthesis
and in vivo evaluation of cFLFLFK-PEG-
64
Cu, a peptide
analog of formyl peptide. The radiolabeled peptide was
able to bind to neutrophils in vitro and to accumulate
peripherally at sites of inflammation in vivo. Zhang et al.
[21] have evaluated the ability of cFLFLF-
64
Cu in the
detection of macrophages in pancreatic islets and in
the aorta in comparison with [
18
F]-fluorodesoxyglucose.
The ability of these radiotracers to penetrate and dis-
tribute into the brain was not studied. In general, the
in vivo use of peptides is hampered by short half-life due
to rapid proteolysis in plasma. Moreover, peptides cannot
cross bloodbrain barrier (BBB) unless they interact with
specific transport systems [22]. Conversely, non-peptidic
small molecules may have some advantages because they
can be suitably designed to modulate properties, such as
potency, selectivity, lipophilicity, and cell permeability,
that are pivotal for a potential radiotracer [23].
Recently, we have reported on the identification of a
series of non-peptidic agonists for FPRs with 3-(1H-indol-
3-yl)-2-[3-(4-nitrophenyl)ureido]propanamide structure
[24]. Among the studied compounds, we have focused our
attention on (S)-1 (Table) as a PET radiotracer candidate,
because (S)-1 demonstrated potent interaction with FPRs
by inducing Ca
2+
mobilization in transfected HL-60 cells
and in human neutrophils. (S)-1 was also able to potently
induce chemotaxis in human neutrophils (Table) [24].
Importantly, (S)-1 showed a MeO group amenable of easy
labeling of the molecule with
11
C. Therefore, on the basis
of such considerations, we have selected (S)-1 as a candi-
date for in vivo PET imaging of FPRs. To the best of our
knowledge, no study aimed at the visualization of FPRs in
activated microglial cells has been reported to date.
Results and Discussion
Lipophilicity
Lipophilicity is a major factor influencing passive brain
entry and can be determined in various theoretical and
Table. Chemical structure and biological properties of (S)-1
Ca
2+
Mobilization
in transfected HL-
60 cells EC
50
[lM]
a
)
Neutrophils EC
50
[lM] Log k
0
Plasma stability t
1/2
[h] BA/AB
FPR FPRL-1 Chemotaxis Ca
2+
mobilization w/o inhibitor With inhibitor
0.26 0.19 0.030 0.086 0.31 > 4 3.5 3.2
a
) Data taken from [24].
876 Chem. Biodiversity 2016, 13, 875 883
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urich

experimental ways [25]. For this purpose, we assessed the
retention factor of (S)-1, log k
0
as lipophilicity index,
using a reversed-phase HPLC method (Table) [26]. We
determined also the retention factor of PD-176252, a
bombesin antagonist that is structurally related to (S)-1
and that is known to be active in vivo in various behav-
ioral tests after i.p. administration in the rat and guinea
pig [27], suggesting that it is able to accumulate into the
brain. The log k
0
for (S)-1 and PD-176252 were 0.31 and
0.43, respectively, indicating that the two compounds have
similar lipophilic properties and, thus, it is likely that (S)-1
is able to enter into the brain.
Serum Stability and Permeability Evaluation
Before embarking in the radiolabeling of (S)-1, we evalu-
ated two additional features that are of importance for
brain PET radiotracers. First, we examined if (S)-1 was a
P-glycoprotein (P-gp) substrate, because PET tracers that
are not substrates of the P-gp efflux pump have higher
chances for crossing the BBB. Therefore, we evaluated
the efflux ratio between basal-to-apical (BA) and apical-
to-basal (AB) fluxes in Caco-2 cells monolayer (BA/AB)
of compound (S)-1. Generally, a cutoff value of 3 is used
to distinguish P-gp substrate from nonsubstrate [28]. The
efflux ratio was evaluated in the presence or in the
absence of a P-gp inhibitor in order to assess the magni-
tude of the interaction with P-gp interaction. (S)-1
showed an efflux ratio of 3.5 and 3.2 in the absence or in
the presence of a P-gp inhibitor, respectively (Table).
These data indicated that (S)-1 can cross biological mem-
branes and has very weak interaction with P-gp. Second,
we evaluated if (S)-1 was stable in serum for, at least, the
timeframe of a PET scan. (S)-1 showed the desired stabil-
ity with degradation half-life (t
1/2
) longer than 4 h
(Table).
Radiochemistry
As stated above, we selected (S)-1 as a candidate for the
preparation of a PET radiotracer, because it presents a
MeO group that can be easily radiolabeled with a posi-
tron emitter
11
C. We chose to prepare the desmethyl
derivative (S)-5, which bears the OH group on the pheny-
lureidic moiety of the molecule, because of its chemical
accessibility.
The desmethyl precursor for
11
C-radiolabeling (S)-5
was easily prepared as shown in Scheme 1.(S)-Boc-tryp-
tophan was activated with N,N
0
-carbonyldiimidazole and
condensed with the amine 2, prepared as previously
reported [29], to give the Boc-protected derivative (S)-3.
Subsequently, the latter compound was deprotected with
trifluoroacetic acid to give the amine (S)-4, which was
condensed with 4-aminophenol in the presence of N,N
0
-
carbonyldiimidazole to give the ureido derivative (S)-5 in
good yield.
The radiosynthesis of (S)-[
11
C]-1 was successfully per-
formed in high yield using a home-made automated syn-
thesis system [30]. (S)-[
11
C]-1 was prepared by reacting
the precursor (S)-5 with [
11
C]-MeI. [
11
C]-MeI was pre-
pared by reducing cyclotron-produced [
11
C]-CO
2
with
LiAlH
4
, followed by iodination with 57% HI. After distil-
lation and drying, [
11
C]-MeI was transferred into a DMF
solution of (S)-5 and NaOH. The [
11
C]-methylation
Scheme 1
(S)-Boc-tryptophan activated with N,N
0
-carbonyldiimidazole. b) Trifluoroacetic acid. c) 4-Aminophenol, N,N
0
-carbonyldiimidazole. d)[
11
C]MeI.
Chem. Biodiversity 2016, 13, 875 883 877
© 2016 Wiley-VHCA AG, Z
urich www.cb.wiley.com

proceeded efficiently in 5 min at 70°. Semipreparative
RP-HPLC purification of the mixture gave (S)-[
11
C]-1 in
15 3(n = 5) radiochemical yield (decay-corrected)
based on [
11
C]-CO
2
. Starting from 12.2 to 18.5 GBq of
[
11
C]-CO
2
, 0.73 1.41 GBq of (S)-[
11
C]-1 were produced
(31 min of synthesis time from the end of bombardment
(EOB)).
The identity of (S)-[
11
C]-1 was confirmed by coinjec-
tion with unlabeled (S)-1 on analytical RP-HPLC. In the
final product solutions, the radiochemical purity was
higher than 99% at EOS. No significant peak correspond-
ing to unreacted (S)-5 was observed in the final product.
Moreover, the radioligand did not show radiolysis at
room temperature after 180 min from formulation,
showing adequate radiochemical stability within the time-
frame of one PET scan. The analytical results were in
compliance with our in-house quality control/assurance
specifications for radiopharmaceuticals.
PET Studies
Fol low ing a heuristic approach, we decided to evaluate
the ability of (S )-[
11
C]-1 to acc umulate in mouse brain
bypassing in vitro autoradiography studies. While these
studie s can offer important in formati on on the interac-
tion bet ween the radiotracer and the target, they cannot
predict radiotracer brain uptake or other biodistribution
issues. In vivo dynamic P ET scans of normal rat brains
were conducted immediately after bolus intravenous
injection of the radioligand. PET images were generated
by averaging dynamic data at 0 90 min after injection
of (S)-[
11
C]-1, and indicated minimal radioactivity in the
brain (top panel in Fig. 1). Timeradioactivity curve for
the whole brain also demonstrated an initial spike cor-
responding to radioactivity in cerebral vessels, followed
by very low retention of radioactivity in the b rain (bot-
tom panel in Fig. 1).Thesedataindicatedthat
(S)-[
11
C]-1 was not able to accumulate into the brain
and, therefore, it is not suitable for imaging of FPRL-1
in living brain. The lack of brain uptake was quite
unexpected based on the permeability study in Caco-2
cell monolayer.
Subsequently, we tested the ability of (S)-[
11
C]-1 to
label FPRs in mouse brain in autoradiography studies. To
this end, we selected the APP23 mice model, a transgenic
mouse strain showing a robust formation of amyloid pla-
ques, and the PS19 mouse model that is characterized by
progressive accumulation of fibrillary tau tangles. Both
animal models are characterized by abundant accumula-
tion of activated microglia in tight association with tau
and amyloid deposits that can be visualized through an
in vitro autoradiography or an in vivo PET with suitable
radioligands [31 33]. The brain tissue slices from aged
PS19 and APP23 mice and from their wild-type litter-
mates were incubated for 1 h with (S)-[
11
C]-1 solution at
1n
M concentration (2 mCi/l). Total binding (TB) and
nonspecific binding (NSB) of (S)-[
11
C]-1 were assessed by
challenging the radioligand in the absence or in the pres-
ence of 10 l
M of fMLF. No specific radioligand binding
was observed in the sections from any of the mouse
strains, despite massive gliosis in PS19 and APP23 mouse
brains (Fig. 2). These data indicated that the occupancy
of FPRs by (S)-[
11
C]-1 at 1 nM was very low and was not
sufficient to autoradiographically label FPRs receptors in
the brain.
In parallel, we evaluated the ability of (S)-[
11
C]-1 to
label FPRs in peripheral inflammation. To this end, pneu-
monia was induced in rats by administration of
lipopolysaccharide (LPS). LPS is a bacterial endotoxin
that is used to stimulate the immune system through acti-
vation of macrophage-like cells in peripheral tissues.
Moreover, it has been reported that LPS is able to upreg-
ulate expression of FPRs in both peripheral tissues and
microglial cells [34]. According to established experimen-
tal procedures [35], the animals were administered intra-
tracheally with LPS (1.25 mg, 1 d before the scan) to
induce the inflammatory response. Pulmonary radioactiv-
ity retention in the LPS-treated rats was very low and
Fig. 1. (top) Sagittal PET images showing distribution of radioacticity
in the rat brain and surrounding tissues after intravenous administra-
tion of (S)-[
11
C]-1. PET data were generated by summation of dynamic
data at 0 90 min after radioligand injection, and were merged onto
the MRI anatomical template. (bottom) Time-radioactivity curve in
the whole brain of a rat after intravenous administration of (S)-[
11
C]-1.
878 Chem. Biodiversity 2016, 13, 875 883
www.cb.wiley.com © 2016 Wiley-VHCA AG, Z
urich

equivalent to control levels (Fig. 3). These data indicated
that (S)-[
11
C]-1 was not able to label FPRs in this animal
model. post mortem Examinations of LPS-treated animals
proved profound infiltration of neutrophils in the lungs of
LPS-treated rats. Therefore, it is possible that in vivo (S)-
[
11
C]-1 has low affinity for FPRs. However, high
Fig. 2. In vitro autoradiographic labeling of coronal mouse brain slices with (S)-[
11
C]-1. Brain samples were derived from PS19 and APP23 trans-
genics and their wild-type littermates. The images demonstrate radioligand binding without blockade (total binding, TB) and with 10 l
M fFML
(nonspecific binding, NSB).
Fig. 3. Horizontal (top) and sagittal (bottom) PET images showing distribution of radioactivity in the lungs and liver at 20 90 min after intra-
venous administration of (S)-[
11
C]-1 in normal control rat (right) and rat with LPS-induced lung inflammation (left).
Chem. Biodiversity 2016, 13, 875 883 879
© 2016 Wiley-VHCA AG, Z
urich www.cb.wiley.com

Citations
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Journal ArticleDOI
TL;DR: A new series of ureidopropanamide derivatives were designed with the goal of converting functional activity from agonism into antagonism and to develop new FPR2 antagonists, and showed that they decreased the production of reactive oxygen species in mouse microglial N9 cells after stimulation with lipopolysaccharide.
Abstract: Formyl peptide receptor-2 (FPR2) is a G protein-coupled receptor belonging to the N-formyl peptide receptor (FPR) family that plays critical roles in peripheral and brain inflammatory responses. FPR2 has been proposed as a target for the development of drugs that could facilitate the resolution of chronic inflammatory reactions by enhancing endogenous anti-inflammation systems. Starting from the structure of the FPR2 agonists (R)- and (S)-4 and 2, we designed a new series of ureidopropanamide derivatives with the goal of converting functional activity from agonism to antagonism and to develop new FPR2 antagonists. Although none of the compounds behaved as antagonist, some of the compounds were able to induce receptor desensitization, thus functionally behaving as antagonists. Evaluation of these compounds in an in vitro model of neuroinflammation showed that they reduced reactive oxygen species (ROS) production in mouse microglial N9 cells after stimulation with lipopolysaccharide (LPS). These FPR2 ligands may protect cells from damage due to inflammation-associated oxidative stress.

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Journal ArticleDOI
01 Aug 2017
TL;DR: The review summarizes the developments of various radiolabeled ligands for PET imaging of neuroinflammation, based on detection of isotope labeled tracers, which emit positrons.
Abstract: Non-invasive molecular imaging techniques can enhance diagnosis of neurological diseases to achieve their successful treatment. Positron emission tomography (PET) imaging can identify activated microglia and provide detailed functional information based on molecular biology. This imaging modality is based on detection of isotope labeled tracers, which emit positrons. The review summarizes the developments of various radiolabeled ligands for PET imaging of neuroinflammation.

1 citations


Journal ArticleDOI
Abstract: Formyl peptide receptors (FPRs) are a group of G protein-coupled cell surface receptors that play important roles in host defense and inflammation. Owing to the ubiquitous expression of FPRs throughout different cell types and since they interact with structurally diverse chemotactic agonists, they have a dual function in inflammatory processes, depending on binding with different ligands so that accelerate or inhibit key intracellular kinase-based regulatory pathways. Neuroinflammation is closely associated with the pathogenesis of neurodegenerative diseases, neurogenic tumors and cerebrovascular diseases. From recent studies, it is clear that FPRs are important biomarkers for neurological diseases as they regulate inflammatory responses by monitoring glial activation, accelerating neural differentiation, regulating angiogenesis, and controlling blood brain barrier (BBB) permeability, thereby affecting neurological disease progression. Given the complex mechanisms of neurological diseases and the difficulty of healing, we are eager to find new and effective therapeutic targets. Here, we review recent research about various mechanisms of the effects generated after FPR binding to different ligands, role of FPRs in neuroinflammation as well as the development and prognosis of neurological diseases. We summarize that the FPR family has dual inflammatory functional properties in central nervous system. Emphasizing that FPR2 acts as a key molecule that mediates the active resolution of inflammation, which binds with corresponding receptors to reduce the expression and activation of pro-inflammatory composition, govern the transport of immune cells to inflammatory tissues, and restore the integrity of the BBB. Concurrently, FPR1 is essentially related to angiogenesis, cell proliferation and neurogenesis. Thus, treatment with FPRs-modulation may be effective for neurological diseases.

References
More filters

Journal ArticleDOI
TL;DR: This review focuses on several key observations that illustrate the multi-faceted activities of microglia in the normal and pathologic brain.
Abstract: Microglial cells constitute the resident macrophage population of the CNS. Recent in vivo studies have shown that microglia carry out active tissue scanning, which challenges the traditional notion of 'resting' microglia in the normal brain. Transformation of microglia to reactive states in response to pathology has been known for decades as microglial activation, but seems to be more diverse and dynamic than ever anticipated—in both transcriptional and nontranscriptional features and functional consequences. This may help to explain why engagement of microglia can be either neuroprotective or neurotoxic, resulting in containment or aggravation of disease progression. Moreover, little is known about the heterogeneity of microglial responses in different pathologic contexts that results from regional adaptations or from the progression of a disease. In this review, we focus on several key observations that illustrate the multi-faceted activities of microglia in the normal and pathologic brain.

2,925 citations


Journal ArticleDOI
TL;DR: A wealth of data now demonstrate that the microglia have very diverse effector functions, in line with macrophage populations in other organs, and the term activatedmicroglia needs to be qualified to reflect the distinct and very different states of activation-associated effector function in different disease states.
Abstract: Microglia, the macrophages of the central nervous system parenchyma, have in the normal healthy brain a distinct phenotype induced by molecules expressed on or secreted by adjacent neurons and astrocytes, and this phenotype is maintained in part by virtue of the blood-brain barrier's exclusion of serum components. Microglia are continually active, their processes palpating and surveying their local microenvironment. The microglia rapidly change their phenotype in response to any disturbance of nervous system homeostasis and are commonly referred to as activated on the basis of the changes in their morphology or expression of cell surface antigens. A wealth of data now demonstrate that the microglia have very diverse effector functions, in line with macrophage populations in other organs. The term activated microglia needs to be qualified to reflect the distinct and very different states of activation-associated effector functions in different disease states. Manipulating the effector functions of microglia has the potential to modify the outcome of diverse neurological diseases.

1,513 citations


Journal ArticleDOI
TL;DR: These mice resemble major features of AD pathology and suggest a central role of A beta in the pathogenesis of the disease.
Abstract: Mutations in the amyloid precursor protein (APP) gene cause early-onset familial Alzheimer disease (AD) by affecting the formation of the amyloid β (Aβ) peptide, the major constituent of AD plaques. We expressed human APP751 containing these mutations in the brains of transgenic mice. Two transgenic mouse lines develop pathological features reminiscent of AD. The degree of pathology depends on expression levels and specific mutations. A 2-fold overexpression of human APP with the Swedish double mutation at positions 670/671 combined with the V717I mutation causes Aβ deposition in neocortex and hippocampus of 18-month-old transgenic mice. The deposits are mostly of the diffuse type; however, some congophilic plaques can be detected. In mice with 7-fold overexpression of human APP harboring the Swedish mutation alone, typical plaques appear at 6 months, which increase with age and are Congo Red-positive at first detection. These congophilic plaques are accompanied by neuritic changes and dystrophic cholinergic fibers. Furthermore, inflammatory processes indicated by a massive glial reaction are apparent. Most notably, plaques are immunoreactive for hyperphosphorylated tau, reminiscent of early tau pathology. The immunoreactivity is exclusively found in congophilic senile plaques of both lines. In the higher expressing line, elevated tau phosphorylation can be demonstrated biochemically in 6-month-old animals and increases with age. These mice resemble major features of AD pathology and suggest a central role of Aβ in the pathogenesis of the disease.

1,427 citations


Journal ArticleDOI
01 Feb 2007-Neuron
Abstract: Filamentous tau inclusions are hallmarks of Alzheimer's disease (AD) and related tauopathies, but earlier pathologies may herald disease onset. To investigate this, we studied wild-type and P301S mutant human tau transgenic (Tg) mice. Filamentous tau lesions developed in P301S Tg mice at 6 months of age, and progressively accumulated in association with striking neuron loss as well as hippocampal and entorhinal cortical atrophy by 9-12 months of age. Remarkably, hippocampal synapse loss and impaired synaptic function were detected in 3 month old P301S Tg mice before fibrillary tau tangles emerged. Prominent microglial activation also preceded tangle formation. Importantly, immunosuppression of young P301S Tg mice with FK506 attenuated tau pathology and increased lifespan, thereby linking neuroinflammation to early progression of tauopathies. Thus, hippocampal synaptic pathology and microgliosis may be the earliest manifestations of neurodegenerative tauopathies, and abrogation of tau-induced microglial activation could retard progression of these disorders.

1,244 citations


Journal ArticleDOI
TL;DR: An in vivo method for use with positron emission tomography (PET) that results in a quantitative characterization of neuroleptic binding sites using radiolabeled spiperone, the first direct evidence that PET can be used to characterize quantitatively, locally and in vivo, drug binding sites in brain.
Abstract: We propose an in vivo method for use with positron emission tomography (PET) that results in a quantitative characterization of neuroleptic binding sites using radiolabeled spiperone. The data are analyzed using a mathematical model that describes transport, nonspecific binding, and specific binding in the brain. The model demonstrates that the receptor quantities Bmax (i.e., the number of binding sites) and KD-1 (i.e., the binding affinity) are not separably ascertainable with tracer methodology in human subjects. We have, therefore, introduced a new term, the binding potential, equivalent to the product BmaxKD-1, which reflects the capacity of a given tissue, or region of a tissue, for ligand-binding site interaction. The procedure for obtaining these measurements is illustrated with data from sequential PET scans of baboons after intravenous injection of carrier-added (18F)spiperone. From these data we estimate the brain tissue nonspecific binding of spiperone to be in the range of 94.2 to 95.3%, and the regional brain spiperone permeability (measured as the permeability-surface area product) to be in the range of 0.025 to 0.036 cm3/(s X ml). The binding potential of the striatum ranged from 17.4 to 21.6; these in vivo estimates compare favorably to in vitro values in the literature. To ourmore » knowledge this represents the first direct evidence that PET can be used to characterize quantitatively, locally and in vivo, drug binding sites in brain. The ability to make such measurements with PET should permit the detailed investigation of diseases thought to result from disorders of receptor function.« less

931 citations


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Q1. What are the contributions mentioned in the paper "Full paper radiosynthesis and in vivo evaluation of carbon-11 (2s)-3-(1h-indol-3-yl)-2-{[(4- methoxyphenyl)carbamoyl]amino}-n-{[1-(5-methoxypyridin-2-yl)cyclohexyl]methyl} propanamide: an attempt to visualize brain formyl peptide receptors in mouse models of neuroinflammation" ?

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