Iron and multiple sclerosis

Abstract

Iron is essential for normal cellular functioning of the central nervous system. Abnormalities in iron metabolism may lead to neuronal death and abnormal iron deposition in the brain. Several studies have suggested a link between brain iron deposition in normal aging and chronic neurologic diseases, including multiple sclerosis (MS). In MS, it is still not clear whether iron deposition is an epiphenomenon or a mediator of disease processes. In this review, the role of iron in the pathophysiology of MS will be summarized. In addition, the importance of conventional and advanced magnetic resonance imaging techniques in the characterization of brain iron deposition in MS will be reviewed. Although there is currently not enough evidence to support clinical use of iron chelation in MS, an overview of studies of iron chelation or antioxidant therapies will be also provided.

Full text

Review
Iron and multiple sclerosis
James M. Stankiewicz, Mohit Neema, Antonia Ceccarelli
*
Department of Neurology, Brigham and Women’s Hospital, Harvard Medical School, Partners Multiple Sclerosis Center, Brookline, MA, USA
article info
Article history:
Received 20 November 2013
Received in revised form 28 February 2014
Accepted 14 March 2014
Available online 15 May 2014
Keywords:
Iron
Multiple sclerosis
Brain
Chelation
Antioxidant
abstract
Iron is essential for normal cellular functioning of the central nervous system. Abnormalities in iron
metabolism may lead to neuronal death and abnormal iron deposition in the brain. Several studies
have suggested a link between brain iron deposition in normal aging and chronic neurologic diseases,
including multiple sclerosis (MS). In MS, it is still not clear whether iron deposition is an epiphe-
nomenon or a mediator of disease processes. In this review, the role of iron in the pathophysiology of
MS will be summarized. In addition, the importance of conventional and advanced magnetic reso-
nance imaging techniques in the characterization of brain iron deposition in MS will be reviewed.
Although there is currently not enough evidence to support clinical use of iron chelation in MS, an
overview of studies of iron chelation or antioxidant therapies will be also provided.
Ó2014 Elsevier Inc. All rights reserved.
1. Introduction
Iron is critical for normal brain functioning. However, aberrant
iron metabolism and abnormal iron deposition in the brain are
associated with many neurologic disorders including multiple
sclerosis (MS) (Stankiewicz and Brass, 2009). Several possible
causes of abnormal iron deposition in MS have been postulated
including blood-brain barrier dysfunction, decreased iron clearance
because of axonal dysfunction and inflammation, or dysregulation
of iron transport proteins because of inflammation (Stankiewicz
et al., 2007). Abnormal iron homeostasis may contribute to the
neurodegeneration seen in MS.
Magnetic resonance imaging (MRI) studies have shown that
excessive iron accumulates in the gray matter (GM) of MS patients,
mainly in the basal ganglia. Recently, the use of advanced MRI
techniques and ultraehigh-field MRI has aided characterization of
iron deposits in both the GM and white matter (WM) of patients
with MS. However, further MRI optimization will enhance our
understanding of iron’s role in MS pathophysiology. Combined
histopathologic MRI studies have begun to elucidate the role of iron
deposition in MS pathology. More investigation in MS is required to
clarify whether either chelation or antioxidant treatments repre-
sent a viable therapeutic alternative.
In this article, we will provide an overview of research related
to the normal iron homeostasis and role of iron in the pathophys-
iology of MS. Recent data from key original reports regarding the
role of conventional and advanced MRI techniques in the assess-
ment of iron deposition in MS will be explored. We will also focus
on the most relevant therapeutic intervention studies with respect
to both animal and human models that have added to the current
understanding of iron toxicity in MS.
2. Iron metabolism
The maintenance of proper iron concentrations in the body is
vital to optimal functioning. Iron is involved in many crucial
processes including myelin production, oxygen transport, glucose
metabolism, synthesis of neurotransmitters, and DNA replication
(Pinero and Connor, 2000). It is, therefore, unsurprising that iron
deficiency at birth can impair normal cognitive development. Iron
deficiency later in life may lead to cognitive impairment, attentional
problems, or restless leg syndrome (Beard, 2003). Conversely, too
much iron can also cause neurologic disease. Neuroferritinopathy, a
disorder of movement characterized by extrapyramidal symptoms,
is thought to be because of a mutation in ferritin light chain gene 1
resulting in ferritin and iron accumulation in the brain (Mancuso
et al., 2005).
Normally, elimination of iron from the body is fairly consistent
and occurs from either bleeding or shedding of cells from the skin
or gut. Consequently, iron concentration in the body is regulated by
control of iron intake from food (Fig. 1).
*Corresponding author at: Department of Neurology, Brigham and Women’s
Hospital, Harvard Medical School, Partners Multiple Sclerosis Center, 1 Brookline
Place, Brookline, MA 02445, USA. Tel.: þ1 6177326118; fax: þ1 6177326540.
E-mail address: antonia@bwh.harvard.edu (A. Ceccarelli).
Contents lists available at ScienceDirect
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0197-4580/$ esee front matter Ó2014 Elsevier Inc. All rights reserved.
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Neurobiology of Aging 35 (2014) S51eS58

3. Iron trafficking in the body
3.1. Entry through the gut
Iron is absorbed via the gut, most often in the duodenum
through the crypts of Lieberkühn. For iron to enter the blood-
stream, it must pass through the gut cells. On the intestinal
luminal side, mechanisms involving ferrireductase duodenal
cytochrome b activity and divalent metal transporter 1 (DMT1) are
involved in entry into the enterocyte (De Domenico et al., 2008).
Export from the basolateral side of the enterocyte involves fer-
roportin and hephaestin. Hepcidin and hemochromatosis protein
2 are thought to interact to determine how much iron is admitted
to the bloodstream via a feedback loop (Pantopoulos et al., 2012).
In the bloodstream, iron circulates in the blood bound to trans-
ferrin (Tf) (Fig. 2).
3.2. Cellular iron transport and homeostasis
Transferrin receptor (TfR) and Tf mediate cellular uptake. Tf
and TfR have a high binding affinity for one another. These binding
complexes are taken up by cells via clathrin-coated pits. After
acidification in the endosome, iron is released from Tf and is
exported into the cytoplasm by DMT1 (De Domenico et al., 2008).
Dissociated Tf and TfR are exported back to the cell surface, and Tf
reenters the bloodstream (Dautry-Varsat et al., 1983). Regulation
of cellular iron levels are achieved through feedback loops
involving iron-response proteins and iron-response elements that
are involved in translation of ferritin, TfR, and other regularly
proteins. Further details can be found in an excellent review by
Rouault (2006a).
4. Iron trafficking and distribution in the brain
4.1. Brain iron transit
Iron intake in the brain is also rigorously regulated and interacts
withothermetalssuchascopper(Skjørringe et al., 2012). It can enter
the brain through the blood-brain barrier and blood-cerebrospinal
fluid barrier, which exists between the blood and the choroid
plexus (Skjørringe et al., 2012). Most commonly, iron-bound Tf in the
blood is captured by TfR found on brain endothelial cells, and this
complex is then endocytosed. Once iron has crossed into the central
nervous system, it is released from Tf into the interstitium (Benarroch,
2009). Brain iron homeostasis is tightly regulated, and this balance is
achieved in a similar way to peripheral control of intracellular iron
(Rouault and Cooperman, 2006b). Currently, the mechanisms for iron
egress from the brain are poorly understood. Brain iron is likely
reabsorbed back into the bloodstream via the cerebrospinal fluid
through the subarachnoid space (Benarroch, 2009)(Fig. 3).
4.2. Normal cellular and structural distribution of iron in the brain
Starting at low levels at birth, brain iron concentration increases
rapidly over the first 2 decades of life and then rises more slowly
thereafter (Hallgren and Sourander, 1958). Oligodendrocytes and
astrocytes acquire solely noneTf-bound iron, whereas neurons
have both TfRs and DMT1 (Moos et al., 2007). Although monocytes
and macrophages contain iron to promote free radicals as part of
respiratory burst activity, brain microglia rarely contain iron. Iron
can also be stored in the central nervous system bound not only to
stable ferritin but also to more reactive substances like neuro-
melanin and hemosiderin. In the normal brain, the highest
Fig. 1. Dietary iron (1e2 mg per day) is absorbed by cells of the duodenum before being exported into plas ma where it binds to transferrin (Tf). Tf-bound iron is delivered to
tissues and cel ls (primarily to reticuloc ytes) where it is incorporated in hemoglobin. Old erythrocytes (red blood cells) are phagocytosed by macrophages, which degrade
hemoglobin and recycle iron back into plasma (2 0e30 mg per day) where it again binds Tf. If iron is absorbed or released into the plasma at a higher level than the iron-binding
capacity of Tf , then the excess noneTf-bound iron is deposited in paren chymal tissues (such as the liver). Reprinted from De Domenico et al. (20 08) with permission from the
publisher.
J.M. Stankiewicz et al. / Neurobiology of Aging 35 (2014) S51eS58S52

concentrations of iron are found in the globus pallidus, caudate
nucleus, putamen, dentate nucleus, red nucleus, and substantia
nigra (Aoki et al., 1989).
5. Imaging brain iron deposition in multiple sclerosis
MRI is a powerful tool to detect and quantify brain iron
deposition in vivo. Among all the brain’s essential metals, brain
iron concentrations are normally high enough to affect the MRI
signal (Stankiewicz et al., 2007). Iron can be found as heme iron,
such as in hemoglobin, or non-heme iron. Unlike heme iron,
failure to achieve homeostasis of non-heme iron metabolism has
been associated with neurodegeneration (Madsen and Gitlin,
2007). Although MRI is not able to accurately differentiate
between heme iron and non-heme iron in vivo, it is suggested
that ferritin and hemosiderin are the only types of non-heme iron
responsible for MRI signal changes (Haacke et al., 2005; Schenck
and Zimmermann, 2004). Other non-heme iron forms, such as
the free liable iron pool or Tf-bound iron, do not seem to influence
the MRI signal because of their low concentration (Haacke et al.,
2005; Schenck and Zimmermann, 2004). Brain iron accumula-
tion shortens the longitudinal (T1) and transverse (T2) relaxation
times of the mobile protons in the brain resulting in signal loss or
hypointensity on T2-weighted images (T2 hypointensity) and
hyperintensity on T1-weighted images (T1 hyperintensity).
Building on these principles, several pulse sequences and quan-
titative MRI techniques have been developed and employed in
detection and quantification of iron in the brain. The use of high-
field (3 T) and ultraehigh-field (>3 T) MRI has further facilitated
the detection of brain iron in both GM and WM. In the following
Fig. 2. Ferric iron, Fe(III), in the diet is converted toferrous iron, Fe(II),bya ferroreductase duodenal cytochrome b that is located on the apical surface of enterocytes of the duodenal
mucosa. Fe(II) is then transported into enterocytes through the divalent metal transporter (DMT1). Fe(II) in enterocytes can be incorporated into the cytosolic iron-storage molecule
ferritin or can be transported across the basolateral surface of enterocytes into the plasma by ferroportin. Fe(II) is subsequently converted to Fe(III) by a membrane-associated
ferroxidase, hephaestin. Reprinted from De Domenico et al. (2008) with permission from the publisher.
J.M. Stankiewicz et al. / Neurobiology of Aging 35 (2014) S51eS58 S53

sections, the role of iron in the pathophysiology of MS and its link
to neuroinflammation, neurodegeneration, and clinical status is
described.
5.1. GM iron deposition
A common finding in patients with MS on spin-echo
T2-weighted clinical MRI scans is diffuse hypointensity of the
cortical and deep GM areas (e.g., the red nucleus, thalamus, dentate
nucleus, lentiform nucleus, caudate, and rolandic cortex) versus
age-matched normal controls (Fig. 4).
T2 hypointensity in GM has been shown to be associated with
brain atrophy, disability progression, and cognitive impairment
in patients with MS (Bakshi et al., 2000, 2001, 2002; Bermel
et al., 2005; Brass et al., 2006a, 2006b; Ceccarelli et al., 2009,
2010, 2011; Drayer et al., 1987a, 1987b; Neema et al., 2007,
2009, 2012; Tjoa et al., 2005; Zhang et al., 2007, 2010). T2
hypointensity, as a sign of excessive GM iron deposition, has
been shown to be present in all MS subtypes (Bakshi et al., 2000,
2001, 2002; Bermel et al., 2005; Brass et al., 2006a, 2006b;
Ceccarelli et al., 2009, 2010, 2011; Drayer et al., 1987a, 1987b;
Neema et al., 2007, 2009; Tjoa et al., 2005; Zhang et al., 2007,
2010). Although iron has emerged as a surrogate marker for
neurodegeneration in MS, it still remains unclear whether iron
deposition is simply an epiphenomenon resulting from brain
tissue degeneration or if it directly contributes to brain damage
in MS.
Recent T2 intensity studies involving early and milder forms
of MS (Ceccarelli et al., 2009, 2010, 2011) have begun to bridge
gaps in knowledge regarding the role of iron deposition in the
pathophysiology of the disease. In patients with clinically
isolated syndrome (CIS), lower T2 intensity in the caudate nu-
cleus was found compared with healthy controls (Ceccarelli et al.,
2010). In patients with established MS, T2 hypointensity best
predicted disability progression over time and was a better
marker of disability than other measures such as whole brain
atrophy and T2-lesion volume (Neema et al., 2009). In contrast,
in CIS patients, T2 hypointensity of deep GM was not associated
with subsequent evolution to clinically definite MS (Ceccarelli
et al., 2010). Further evidence that iron could accumulate early
in the disease course has been provided by studies in pediatric
MS patients (Ceccarelli et al., 2011). Like CIS, selective T2 hypo-
intensity was found in the caudate nucleus of pediatric MS
patients with a sparing of other deep GM structures (Ceccarelli
et al., 2011). Furthermore, despite their favorable clinical course
and the lower overall brain tissue damage, similar T2 intensity
was found in benign MS patients compared with secondary
progressive MS patients (Ceccarelli et al., 2009). Taken together,
Fig. 3. Overview of iron homeostasis in the central nervous system. The transferrin receptor 1 (TfR1) in the luminal membrane of brain endothelial cells binds ferric iron (Fe
3þ
)e
loaded Tf and internalizes this complex in endosomes, where Fe
3þ
is reduced to ferrous iron (Fe
2þ
). Ferrous iron may be transported to the cytosol by the endosomal divalent metal
transporter 1 (DMT1) and then exported into the extracellular fluid by action of ferroportin. An alternative hypothesis (not shown) is that the Tf-TfR1 receptor complex may be
transported from the luminal to the abluminal surface followed by iron release. Ceruloplasmin, expressed in astrocyte end-foot processes, oxidizes newly released Fe
2þ
to Fe
3þ
,
which binds to Tf. Tf is the main source of iron for neurons. Fe
2þ
may also bind to adenosine triphosphate (ATP) or citrate released from astrocytes and be transported in the form of
nonetransferrin-bound iron (NTBI), which is the source of iron to oligodendrocytes and astrocytes. Oligodendrocytes synthesize Tf, which may have a role in intracellular iron
transport along their processes. In the cytosol, the storage protein ferritin sequesters and reduces levels of free iron. Mitoferrin (not shown) transports iron into the mitochondria,
where the chaperone frataxin facilitates the biosynthesis of iron-sulfur (Fe/S) clusters. Reprinted from Benarroch (2009) with permission from the publisher.
J.M. Stankiewicz et al. / Neurobiology of Aging 35 (2014) S51eS58S54

these findings suggest that brain iron accumulation occurs early
in the disease course and increases with disease duration. Few
studies have looked at the effect of treatment on brain T2 signal
change (Bermel et al., 2005; Pawate et al., 2012). A recent
longitudinal year long pilot study of natalizumab treatment of
MS patients (Pawate et al., 2012) showed a treatment effect on
limiting progression of T2 hypointensity in GM, suggesting that
impeding the inflammatory cascade could lead to decreased iron
deposition in the brain.
Although T2 intensity studies have provided important clues
regarding iron accumulation in the brain of MS patients, the
effects of various other confounding factors, such as water con-
tent, make the T2 intensity method a nonspecific indicator for
estimating iron levels (Neema et al., 2007). Because of their
increased sensitivity to iron-related susceptibility changes, new
advanced quantitative MRI techniques, and related postprocessing
analysis, combined with the use of high-field and ultraehigh-field
strength MRI, are currently being employed to further define the
role of iron in MS (Bagnato et al., 2013; Ge et al., 2007; Habib et al.,
2012; Hagemeier et al., 2012a, 2013a, 2013b; Hammond et al.,
2008; Khalil et al., 2009, 2011a, 2011b; Lebel et al., 2012; Pitt
et al., 2010; Ropele et al., 2011; Rumzan et al., 2013; Walsh
et al., 2014; Zivadinov et al., 2012). To date, most of these MRI
studies have significantly improved the detection of abnormal
iron deposition in cortical and deep GM and confirmed its clinical
relevance in MS (Bagnato et al., 2013; Ge et al., 2007; Habib et al.,
2012; Hagemeier et al., 2012a, 2013a, 2013b; Hammond et al.,
2008; Khalil et al., 2009, 2011a, 2011b; Lebel et al., 2012; Pitt
et al., 2010; Ropele et al., 2011; Rumzan et al., 2013; Walsh
et al., 2014; Zivadinov et al., 2012). Interestingly, using 7-T MRI
and quantitative magnetic susceptibility mapping (Al-Radaideh
et al., 2013), iron deposition in several deep GM areas, including
the caudate, putamen, pallidus, and pulvinar nucleus, has been
shown in CIS patients, further supporting and extending previous
findings (Ceccarelli et al., 2010). Recently, a study using
susceptibility-weighted filtered phase imaging found that GM
iron-related changes may precede GM atrophy in CIS patients
suggesting that abnormal iron deposition may be an early surro-
gate of the disease (Hagemeier et al., 2012a).
Although the measures of GM iron deposition hold promise as
clinically relevant biomarkers, more work is necessary before these
techniques find use in clinical practice to inform care for individual
patients.
5.2. WM iron deposition
Pathologic studies have shown that iron accumulation in the
WM is mainly present at the level of MS lesions (Craelius et al.,
1982; Hametner et al., 2013) and near the veins (Adams, 1988).
However, MRI detection of iron deposition in the WM is still
challenging because of the confounding effect on the MRI signals
of edema, inflammation, gliosis, and myelin content (Langkammer
et al., 2010; Neema et al., 2007; Walsh et al., 2013; Yao et al.,
2012). The application of multimodal approach of advanced
iron-sensitive MRI techniques, such as phase imaging, R2*, and
ultraehigh-field scanners, has enhanced the current understand-
ing of WM iron deposition in MS. In particular, with the use of
phase imaging, it is possible to visualize phase hypointense WM
lesions that are likely high in iron content and often missed by
conventional MRI sequences (Eissa et al., 2009; Haacke et al.,
2009; Hagemeier et al., 2012b; Hammond et al., 2008). Various
phase hypointense WM MS lesion patterns have also been iden-
tified such as nodular, ring, and scattered shapes, suggesting that
iron deposition could be inside or at the edge of phase WM le-
sions in MS (Eissa et al., 2009; Haacke et al., 2009; Hagemeier
et al., 2012b). Such phase WM lesions have also been observed
even at the earliest clinical stages of MS (Hagemeier et al., 2012b).
Although the interplay between various cellular structures is
thought to be responsible for the diverse hypointense patterns in
the WM lesions (Bagnato et al., 2011; Bian et al., 2013; Mehta
et al., 2013), the mechanisms behind these have yet to be eluci-
dated. In addition, a reliable MRI method to characterize the
presence of iron in WM is currently unavailable (Walsh et al.,
2013; Yao et al., 2012). Future combined histopathologic-
multimodal MRI studies will shed light on the mechanisms un-
derlying iron-related MRI changes seen in WM, which in turn may
provide insights into understanding the link between WM dam-
age and clinical status.
Fig. 4. T2 hypointensity in multiple sclerosis (MS): T2-weighted fast spin-echo axial magnetic resonance imaging scans obtained at 1.5 Tof a healthy control (A) in the fifth decade
and an age-matched patient with relapsing-remitting MS (B). In the patient with MS, note bilateral hypointensity of various deep gray matter areas, including the thalamus,
lentiform nucleus, and caudate compared with the healthy control. This T2 hypointensity most likely represents pathologic iron deposition. The patient also has brain atrophy.
Reprinted from Neema et al. (2012) with permission from the publisher.
J.M. Stankiewicz et al. / Neurobiology of Aging 35 (2014) S51eS58 S55

6. Iron toxicity
Bound iron is considered “safe,”but free iron is more likely to
exchange electrons with nearby molecules and produce free radi-
cals. Normal metabolic processes in the mitochondria form
hydrogen peroxide as the result of molecular reduction of oxygen.
Hydrogen peroxide alone is not particularly toxic, but in the pres-
ence of free iron (Fe2þ), a free radical (∙OH) is formed when free
iron donates an electron to hydrogen peroxide via the Fenton
reaction. This free radical can interact with oxygen and other
molecules in the brain to form more free radicals propagating a
deleterious positive feedback loop. Hydroxyl radicals can attack
proteins, deoxynucleic acids, and lipid membranes. This process can
disrupt cellular integrity and function eventually leading to cell
apoptosis (Halliwell, 2006). Oxidative stress has been implicated in
the pathogenesis of MS, potentially contributing to both demye-
lination and axonal damage (Gilgun-Sherki et al., 2004).
7. Protection from iron-mediated damage
7.1. Endogenous protection
Experimental work suggests that the body has natural processes
in place to stem potentially damaging free-radical formation. Both
glutathione and vitamin E have been implicated as protective.
Glutathione in a reduced state interacts with hydrogen peroxide
and other organic peroxides to yield an oxidized form of gluta-
thione, water, and alcohol. Removal of hydrogen peroxide leaves
less potential for interaction with free iron and less subsequent
production of hydroxyl radicals. Cells able to survive potentially to
toxic iron show increased glutathione production (Aguirre et al.,
2006). A form of vitamin E (alpha-tocopherol) can act as an anti-
oxidant by donating a proton to reactive oxygen species, thus
making them more stable and less reactive (Crichton et al., 2002).
Experimental work finds that cerebellar granule cell cultures and
hippocampal neurons treated with iron in the presence of either
alpha-tocopherol or an analogue were better preserved (de Jesus
Ferreira et al., 2005; Van der Worp et al., 1999).
7.2. Exogenous protection
Because iron may contribute to the pathogenesis of MS, human
and animal investigations have been performed to ascertain
whether binding iron (chelation) or reducing iron associated free-
radical damage (antioxidants) might represent viable treatment
strategies.
7.2.1. Chelation
Iron chelators may attenuate free-radical toxicity by binding
circulating free iron and preventing this iron from participating in
redox reactions. Iron chelation therapy has been tried in the
experimental autoimmune model of MS with some success. A study
conducted in experimental autoimmune encephalomyelitis (EAE)
induced by spinal cord homogenates showed a response to des-
ferrioxamine (Bowern et al., 1984). Two other studies investigated
desferrioxamine in a myelin basic protein-induced EAE model.
Willenborg et al. (1988) found no response if the desferrioxamine
was administered in a preclinical phase, whereas Pedchenko and
LeVine (1999) found that if the desferrioxamine was administered
later, during a time of clinical symptoms, it effectively attenuates
the disease. The short half-life of desferrioxamine, potential critical
window for effect, or other free-radical scavenging effects outside
iron binding might account for the discrepant studies. Pedchenko
and Levine (1999) also reported that dexrazoxane, another iron
chelator similar to desferrioxamine but with a longer half-life also
attenuated the course of EAE, but its effect was less robust than that
seen with desferrioxamine. Also, rats given dexrazoxane in
conjunction with mitoxantrone experienced more improvement on
clinical indices than rats treated solely with mitoxantrone
(Weilbach et al., 2004).
Only 1 human trial using desferrioxamine has been conducted in
a small group of secondary progressive MS patients (Lynch et al.,
2000). Nine patients received up to 8 courses of desferrioxamine,
and although the drug was well tolerated, little effect was seen on
disability. Specifically, a single patient improved, 3 patients were
unchanged, and 5 patients worsened. These disappointing results
call into question whether treatment with desferrioxamine (or iron
chelation more generally) could be an effective treatment strategy
for MS. It is worth noting, however, that this trial was small and that
the enrolled patients had more advanced disease. Patients with
higher disability typically have been refractory to treatment in MS
drug trials.
It is clear that iron deposition occurs in MS and that iron
chelation can work in the EAE model. It remains to be seen, how-
ever, whether chelation therapy can be a successful treatment
strategy in MS.
7.2.2. Antioxidants
Antioxidants might help counteract iron’s role in disease by
protecting the body from oxidative stresses. A study of MS plaques
revealed decreased levels of antioxidants and increased free-radical
activity (Langemann et al., 1992). MS patients also exhibit increased
levels of oxidative stress markers compared with normal controls,
with correlation seen between disability and higher levels of
oxidative stress markers (Oliveira et al., 2012).
Many antioxidants have been suggested to be neuroprotective
through reduction of free-radical formation including vitamin A,
vitamin C, vitamin E, coenzyme Q10, green tea extract, nitric oxide,
selegiline (monoamine oxidase inhibitor with antioxidant proper-
ties), and Ginkgo biloba.
A full accounting of antioxidants that have been successful in
attenuating the EAE model of MS is outside the scope of this review,
but many have succeeded. Commonly recognized antioxidants that
work on an EAE model include vitamin A (Massacesi et al., 1987),
vitamin C (Spitsin et al., 2002), lipoic acid (Marracci et al., 2002),
resveratrol (Shindler et al., 2010), blueberries (Xin et al., 2012),
green tea (Aktas et al., 2004), and curcumin (Xie et al., 2009).
Although these antioxidants can show an effect in animals, it is not
always clear that this effect is because of reduction of free radicals.
For example, experimental work with green tea extract demon-
strates that this compound affects T cells (Wang et al., 2012). It is
also worth noting that some antioxidants such as idebenone have
failed to provide a beneficial effect in the EAE model (Fiebiger et al.,
2013).
Few human trials of antioxidants have been performed. Perhaps,
the most visible drug with potential antioxidant effect in the MS
space is the recently Food and Drug Administrationeapproved
dimethyl fumarate. Although argument remains about how the
drug is having its treatment effect on MS, experiments suggest that
the drug works on a free-radical scavenging pathway (Nrf2) and has
antioxidant effects (Linker et al., 2011). Another drug, inosine, has
been trialed in 2 separate MS cohorts. This precursor drug is
metabolized to the antioxidant uric acid. Although successful in an
EAE model, inosine has shown mixed results in relapsing-remitting
MS patients. Gonsette et al. (2010) did not show a benefit from the
drug. Markowitz et al. (2009) found that MS patients with higher
serum urate levels did benefit from inosine compared with their
pretreatment state. Renal calculi were seen in both the Gonsette
(3.8%) and Markowitz (25%) trials. Double-blind placebo-controlled
studies with increased enrollment and longer observation periods
J.M. Stankiewicz et al. / Neurobiology of Aging 35 (2014) S51eS58S56

are needed before conclusions about long-term efficacy and safety
of antioxidants can be made.
8. Conclusions
We have reviewed the physiology of iron metabolism and the
role of abnormal brain iron deposition in MS. We have seen that
although iron is vital for normal neuronal processes, abnormal iron
accumulation may cause neurodegeneration through lipid peroxi-
dation and cell death in the brain. Human MRI studies reported an
association between abnormal brain iron deposition and clinical
dysfunction in MS patients. It remains to be elucidated whether
iron deposition is a marker or mediator of the destructive cascade in
MS. Future studies incorporating newer pulse sequences, multi-
modal MRI in conjunction with histopathologic assessments, and
novel postprocessing techniques should shed light on mechanisms
responsible for abnormal iron deposition and on its role in the
pathogenesis of MS. Animal models of MS have shown a neuro-
protective effect by either iron chelation or antioxidants; however,
in MS patients, the effectiveness of these pharmacologic modifi-
cation is still debatable and requires further investigation.
Disclosure statement
None of the authors have a conflicts of interest.
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