Comptes Rendus Chimie

Michel Nguyen

Meijie Huang

Yan Liu

Bernard Meunier

Anne Robert

lable at ScienceDirect
C. R. Chimie 20 (2017) 987e989Contents lists avaiComptes Rendus Chimie
www.sciencedirect.comPreliminary communication / CommunicationIs iron associated with amyloid involved in the oxidative
stress of Alzheimer's disease?
Le fer en presence d'amyloïde est-il implique dans le stress oxydant de la
maladie d'Alzheimer?
Michel Nguyen a, 1, Meijie Huang a, b, 1, Yan Liu b, Bernard Meunier a, b, **, 1,
Anne Robert a, *, 1
a Laboratoire de chimie de coordination Du CNRS, 205, route de Narbonne, BP 44099, 31077 Toulouse cedex 4, France
b School of Chemical Engineering and Light Industry, Guangdong University of Technology (GDUT), Higher Education Mega Center, 100
Waihuan Xi Road, Panyu District, Guangzhou 510006, PR Chinaa r t i c l e i n f o
Article history:
Received 4 April 2017
Accepted 13 July 2017
Available online 31 October 2017
Keywords:
Alzheimer's disease
Amyloid
Copper
Iron
Oxidative stress* Corresponding author.
** Corresponding author.
E-mail addresses: michel.nguyen@lcc-toulouse.fr
1 https://www.lcc-toulouse.fr/article432.html.
https://doi.org/10.1016/j.crci.2017.07.009
1631-0748/© 2017 Académie des sciences. Publish
creativecommons.org/licenses/by-nc-nd/4.0/).a b s t r a c t
Oxidative stress induced by the failure of redox metal homeostasis plays a key role in the
neuron death, which is the characteristic of Alzheimer's disease. The Fe(III)eamyloid and
Cu(II)eamyloid complexes are often considered responsible for such an oxidative stress. In
this study, we report that, in an aqueous medium at physiological pH, copper is much more
efficient than iron to catalyze the reduction of dioxygen in the presence of Ab1-16 and of a
physiological reducing agent. This fact justifies the effort to design new efficient specific
copper chelators that should be able to regulate the homeostasis of this particular redox
metal ion in the brain of patients with Alzheimer's disease.
© 2017 Académie des sciences. Published by Elsevier Masson SAS. This is an open access
article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Mots-cles:
Alzheimer
Amyloïde
Cuivre
fer
Stress oxydantr é s u m é
Le stress oxydant, provoque par la perte de l'homeostasie demetaux a activite redox, joue un
rôle majeur dans la mort des neurones, caracteristique de la maladie d’Alzheimer. Les
complexes Fe(III)- et Cu(II)-amyloïde sont souvent consideres comme responsables de ce
stress oxydant. Les travaux decrits icimontrent que le cuivre est un catalyseur beaucoup plus
efficace que le fer pour reduire l'oxygene moleculaire en presence d'amyloïde Ab1-16 et d'un
reducteur physiologique, en milieu aqueux et a pH physiologique, justifiant ainsi l'interêt a
porter a la preparation d'un chelateur specifique du cuivre pour reguler l'homeostasie de cet
ion metallique dans le cerveau des personnes touchees par la maladie d'Alzheimer.
© 2017 Académie des sciences. Published by Elsevier Masson SAS. This is an open access
article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).(M. Nguyen), bmeunier@lcc-toulouse.fr (B. Meunier), anne.robert@lcc-toulouse.fr (A. Robert).
ed by Elsevier Masson SAS. This is an open access article under the CC BY-NC-ND license (http://
Fig. 1. Oxidation of ascorbate measured by UVevisible absorbance at
265 nm. Final concentrations are [ascorbate]¼ 100 mM, [Ab1-16]¼ 20 mM
(where present), and [FeIII] or [CuII]¼ 20 mM.
M. Nguyen et al. / C. R. Chimie 20 (2017) 987e989988The search for efficient anti-Alzheimer drugs is at the
moment the most difficult challenge in drug discovery
because all clinical trials with drug candidates failed in the
recent years [1]. These failures are due to several factors,
one of them being the lack of a really predictive animal
model. In fact, Alzheimer's disease (AD) is an aging disease
related to many epigenetic factors, rather than simple
mono- or digenic factors [2,3]. Consequently, the use of
transgenic mice as a model of human AD is questionable.
Accumulation of metal ions has been evoked as a key
parameter in the initiation of AD. A possible role for
contribution of aluminum neurotoxicity to AD has been a
matter of debate. However, there is actually no convincing
causal link between aluminum and AD initiation or pro-
gression, despite five decades of controversial studies on
this issue [4,5]. Beside zinc and copper [6], iron ions have
been suspected to be damaging since the early 1950s [7,8].
As a matter of fact, the postmortem analysis of amyloid
plaques has revealed accumulation of two redox metals
ions, namely copper and ironwith concentrations higher by
a factor of ca. 5.6 and 2.7 times, respectively, with respect to
the concentrations observed in normal brains [9]. One can
consider that disruption of metal homeostasis in the brain
of patients with AD is at the origin of the redox stress
responsible for neuron death. In fact, in the presence of
endogenous reductants, metal-loaded amyloids should
trigger the reduction of dioxygen and produce reactive
oxygen species (ROS) involved in neuron death [10e12].
Consequently, the use of metal chelators to regenerate
normal trafficking of redox metal ions has been reported in
recent articles [13e16]. Studies of such metal ligands have
been largely devoted to copper chelators [17], despite pu-
tative ironeamyloid complexes may also be involved in
ROS production (in medically focused publications, a
similar phenomenon is frequently described as involved in
inflammation processes).
To evaluate the putative role of iron associated with
amyloids in the catalytic reduction of molecular oxygen and
to compare this activity to that of coppereamyloids com-
plex, we decided to investigate the in vitro oxidation of
ascorbate by iron(III) or copper(II) in the presence or in the
absence of amyloids. In fact, oxidation of ascorbate is
considered as an indirect evaluation of Cu(II) and Fe(III)
species to reduce molecular oxygen and, therefore, to
induce catalytic reduction of dioxygen, and ROS production
[18].
The assays were carried out in saline Hepes buffer
100 mM, pH 7.4, and the ascorbate consumption was
measured by monitoring UV absorbance at 265 nm, over a
period of 30 min. Final concentrations were as follows:
[Ab1-16]¼ 20 mM (where present), [FeIII] or [CuII]¼ 20 mM,
and [ascorbate]¼ 100 mM. This [metal]/[ascorbate] ratio
allows to evidence either stoichiometric or catalytic
oxidation of ascorbate. Results are depicted in Fig. 1.
First of all, FeCl3 alone was unable to efficiently oxidize
ascorbate (only 8% after 30 min, trace a), whereas the
oxidation of ascorbate was complete in the presence of
CuCl2 (trace b) during the same interval of time. A similar
trend was observed in the presence of Ab1-16 associated
with metal ions (M/Ab1-16 molar ratio¼ 1/1): oxidation of
ascorbate was only marginal in the presence of FeCl3/Ab1-16(5%, trace c), whereas it was complete after 30 min in the
presence of CuCl2/Ab1-16 (trace d). Consistently, it has been
previously reported that Fe(NO3)3 associated with Ab1-16
was 10 times less efficient than CuCl2/Ab1-16 to oxidize
ascorbate [19]. Moreover, after 30 min of incubation of
FeCl3 or FeCl3/Ab1-16, respectively, we added 1 mol equiv of
CuCl2 (traces a and c, respectively, 30e60 min). In both
cases, the oxidation of ascorbate occurred upon addition of
CuCl2 with a similar kinetic as observed when CuCl2 was
added at t¼ 0 (traces a compared to b, and c compared to
d). When CuCl2/Ab1-16 was added at 30 min in the mixture
containing FeCl3 and ascorbate, the consumption of ascor-
batewas the same as that in the presence of Cu/Ab1-16 alone
(trace e compared to d). In addition, when FeCl3, CuCl2, and
Ab1-16 were incubated together, oxidation of ascorbate was
the same as in the presence of Cu/Ab1-16 alone (trace f
compared to d).
These results clearly evidence a much lower reductive
activation of dioxygen induced by Fe(III) associated with
ascorbate as compared to Cu(II)/ascorbate, either in the
absence or in the presence of Ab1-16, under the same con-
ditions, close to biological ones (aqueous medium pH 7.4,
presence of chloride as potential counter ion) [20]. These
results suggest that the deregulation of the homeostasis of
copper ions in AD brains and accumulation of this redox ion
in amyloids are more relevant in terms of oxidative damage
created on neurons than the loading of iron ions on
amyloids.
However, an indirect role of iron ions in AD cannot be
ruled out, because the metabolism of iron is linked to
proteins involved in AD. As an example, like the copper-
M. Nguyen et al. / C. R. Chimie 20 (2017) 987e989 989carrier ceruloplasmin, the Amyloid Precursor Protein (APP)
protein interacts with ferroportin, oxidizes Fe(II), and loads
Fe(III) into transferrin, thus taking part in iron regulation
[21].
In conclusion, the reported data indicate that the
reductive activation of coppereamyloid complexes by a
biological reductant is much more critical in terms of
oxidative damage than that of the ironeamyloid com-
plexes. Consequently, these results support the necessity to
design specific copper chelators as potential drug candi-
dates for the treatment of the early stages of AD, to avoid
the continuous destruction of neurons by an oxidative
stress created by the reductive activation of coppereamy-
loid complexes.
Acknowledgments
This work was supported by the CNRS and partially by
GDUT (M.H., Y.L., and B.M.).
References
[1] J.L. Cummings, M. Travis, K. Zhong, Alzheimers Res. Ther. 6 (2014)
37e43.
[2] Lancet 376 (2010), 658e658.
[3] J. Ceccom, F. Cosledan, H. Halley, B. Frances, J.-M. Lassalle,
B. Meunier, PLoS One 7 (2012) e43105, 7 pages.
[4] J. Savory, M.M. Herman, O. Ghribi, J. Alzheimers Dis. 10 (2006)
135e144.
[5] L.E. Scott, C. Orvig, Chem. Rev. 109 (2009) 4885e4910.
[6] H. Tamano, A. Takeda, Metallomics 7 (2015) 1205e1212.
[7] L. Goodman, J. Nerv. Ment. Dis. 117 (1953) 97e130.
[8] J.M.G. van Bergen, X. Li, J. Hua, S.J. Schreiner, S.C. Steininger,
F.C. Quevenco, M. Wyss, A.F. Gietl, V. Treyer, S.E. Leh, F. Buck,
R.M. Nitsch, K.P. Pruessmann, P.C.M. van Zijl, C. Hock, P.G. Unschuld,
Sci. Rep. 6 (2016) 35514.[9] M.A. Lovell, J.D. Robertson, W.J. Teesdale, J.L. Campbell,
W.R. Markesbery, J. Neurol. Sci. 158 (1998) 47e52.
[10] M.L. Schlief, A.M. Craig, J.D. Gitlin, J. Neurosci. 25 (2005) 239e246.
[11] L. Guilloreau, S. Combalbert, A. Sournia-Saquet, H. Mazarguil,
P. Faller, ChemBioChem 8 (2007) 1317e1325.
[12] D. Jiang, L. Men, J. Wang, Y. Zhang, S. Chickenyen, Y. Wang, F. Zhou,
Biochemistry 46 (2007) 9270e9282.
[13] K.J. Barnham, A.I. Bush, Chem. Soc. Rev. 43 (2014) 6727e6749.
[14] M.A. Telpoukhovskaia, C. Orvig, Chem. Soc. Rev. 42 (2013)
1836e1846.
[15] L.R. Perez, K.J. Franz, Dalton Trans. 39 (2010) 2177e2187.
[16] A. Robert, Y. Liu, M. Nguyen, B. Meunier, Acc. Chem. Res. 48 (2015)
1332e1339.
[17] M. Nguyen, C. Bijani, N. Martins, B. Meunier, A. Robert, Chem. Eur. J.
21 (2015) 17085e17090.
[18] G.R. Buettner, B.A. Jurkiewitz, Free Rad. Biol. Med. 14 (1993) 49e55.
[19] N. Nakamura, N. Shishido, A. Nunomura, M.A. Smith, G. Perry,
Y. Hayashi, K. Nakayama, T. Hayashi, Biochemistry 46 (2007)
12737e12743.
[20] Reactivity of Fe(III) species, namely reduction to Fe(II) and ROS
production, is expected to depend on the solubility of the iron
species involved. Fe3þ salts are very insoluble in aqueous media
and the ability of iron to bind Ab1-16 under these conditions has
not been established. So, the formation of insoluble and, conse-
quently, poorly reactive iron oxides/hydroxides may account for
the lack of redox reactivity of iron in the presence or absence of
Ab1-16. In several reports dealing with iron reactivity in the
presence of Ab1-16, authors used iron(III) complexes as “soluble
forms” of iron(III): FeIII-citrate [X. Huang et al. Biochemistry 38
(1999) 7609e7616) or FeIII(NTA)2 (NTA stands for nitriloacetic
acid), D. Jiang et al. Biochemistry 48 (2009) 7939e7947]. With the
latter one, the authors evidenced the formation of a ternary
complex Ab1-16eFeIII/II-NTA that was able to reduce dioxygen.
However, we used FeCl3 because Cl is the most concentrated
anion in biological fluids (115e130 mM in the cerebrospinal fluid),
but not nitrate, citrate, or NTA, and we compared it to CuCl2.
[21] J.A. Duce, A. Tsatsanis, M.A. Cater, S.A. James, E. Robb, K. Wikhe,
S.L. Leong, K. Perez, T. Johanssen, M.A. Greenough, H.H. Cho,
D. Galatis, R.D. Moir, C.L. Masters, C. McLean, R.E. Tanzi, R. Cappai,
K.J. Barnham, G.D. Ciccotosto, J.T. Rogers, A.I. Bush, Cell 142 (2010)
857e867.


Is iron associated with amyloid involved in the oxidative stress of Alzheimer's disease?

Doina Georgescu

Ana-Maria Brezoiu

Raul-Augustin Mitran

Daniela Berger

Cristian Matei

Bogdan Negreanu-Pirjol

Mesostructured silica–titania composites for improved oxytetracycline delivery systems

Laura I. Rossi

Claudio O. Kinen

Rita Hoyos de Rossi

Important role of native <strong>β</strong>-cyclodextrin in the stabilization of transition metal salts

Hanane Messiad

Tarek Yousfi

Rayenne Djemil

Habiba Amira-Guebailia

Modeling of the inclusive complexation of natural drug <i>trans</i> 3,5,3′,4′-tetrahydroxystilbene with β-cyclodextrin

Marta Michalska-Domańska

Jerzy Bystrzycki

Bartłomiej Jankiewicz

Zbigniew Bojar

Effect of the grain diameter of Ni-based catalysts on their catalytic properties in the thermocatalytic decomposition of methanol

Reza Teimuri-Mofrad

Farzaneh Mirzaei

Hassan Abbasi

Kazem D. Safa

Synthesis of new binuclear ferrocenyl compounds by hydrosilylation reactions

Karen L. Mulfort

Interrogation of cobaloxime-based supramolecular photocatalyst architectures

Mallory Kato

Quan Lam

Meghana Bhandarkar

Tam Banh

Jeremiah Heredia

Andrew U

Lionel Cheruzel

Selective C–H bond functionalization with light-driven P450 biocatalysts

Kalliopi Ladomenou

Vasilis Nikolaou

Georgios Charalambidis

Asterios Charisiadis

Athanassios G. Coutsolelos

Porphyrin–BODIPY-based hybrid model compounds for artificial photosynthetic reaction centers

Masoumeh Orojloo

Saeid Amani

Naked-eye detection of cyanide ions in aqueous media based on an azo-azomethine chemosensor

Not a member yet

Is iron associated with amyloid involved in the oxidative stress of Alzheimer's disease?

Mesostructured silica–titania composites for improved oxytetracycline delivery systems

Important role of native <strong>β</strong>-cyclodextrin in the stabilization of transition metal salts

Modeling of the inclusive complexation of natural drug <i>trans</i> 3,5,3′,4′-tetrahydroxystilbene with β-cyclodextrin

Effect of the grain diameter of Ni-based catalysts on their catalytic properties in the thermocatalytic decomposition of methanol

Synthesis of new binuclear ferrocenyl compounds by hydrosilylation reactions

Interrogation of cobaloxime-based supramolecular photocatalyst architectures

Selective C–H bond functionalization with light-driven P450 biocatalysts

Porphyrin–BODIPY-based hybrid model compounds for artificial photosynthetic reaction centers

Naked-eye detection of cyanide ions in aqueous media based on an azo-azomethine chemosensor

2,199

3,559