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Effects of magnesium deficiency – More than skin deep
Navin Chandrakanth Chandrasekaran
1,2
, Christopher Weir
3
, Sumaya Alfraji
1
, Jeff Grice
2
,
Michael S Roberts
2
and Ross T Barnard
1
1
School of Chemistry and Molecular Biosciences, Australian Infectious Diseases Research Centre, The University of Queensland,
Queensland 4072, Australia;
2
School of Medicine, Translational Research Institute, The University of Queensland, Wooloongabba,
Queensland 4102, Australia;
3
Walter and Eliza Hall Institute of Medical Research and Department of Medical Biology, University of
Melbourne, Parkville, Victoria 3052, Australia
Corresponding author: Ross T Barnard. Email: rossbarnard@uq.edu.au
Abstract
Dead Sea and magnesium salt therapy are two of the oldest forms of treatment for skin disease and several other disorders,
supported by a body of largely anecdotal evidence. In this paper we review possible pathways for penetration of magnesium ions
through the epidermis to reach the circulation, in turn replenishing cellular magnesium levels. We also discuss mechanisms for
intercellular movement of magnesium ions and possible mechanisms for the interaction between magnesium ions and inflam-
matory mediators. Upon addition of magnesium ions in vitro, the expression of inflammatory mediators such as tumour necrosis
factor a (TNFa) and nuclear factor jb (NFjb) is down regulated. Dysregulation of these and other inflammatory mediators has been
linked to several inflammatory disorders, including asthma, arthritis, atherosclerosis and neuroinflammation.
Keywords: Magnesium, inflammation, skin
Experimental Biology and Medicine 2014; 239: 1280–1291. DOI: 10.1177/1535370214537745
Introduction
Dead Sea therapy is one of the oldest forms of treatment for
skin disease and some chronic inflammatory diseases like
arthritis and psoriasis.
1
Much of the research to date has
attributed the clinical effects of Dead Sea therapy to its min-
eral composition; mostly to magnesium salts.
2,3
Magnesium
salts, such as magnesium sulphate (Epsom salts), have long
been used as a spa product and as a therapeutic to manage
clinical conditions.
4
The central question addressed by this review is, ‘‘What
are the underlying mechanisms by which magnesium ions
could play a role in the regulation of inflammatory
responses in the skin and systemically?’’ Several systematic
studies have been conducted in humans, over the last two
decades, in an effort to understand the effect of magnesium
ions (Mg
2þ
) in healing skin disorders. These will be
reviewed. There has been renewed interest over the past
decade in understanding the role of magnesium salts in
clinical medicine, nutrition and physiology. This review
will discuss the known clinical effects of magnesium defi-
ciency, and both summarise and suggest molecular mech-
anisms that could mediate the inflammation induced by
magnesium deficiency. We first discuss transdermal absorp-
tion as a possible route of administration for prevention and
treatment of magnesium deficiency and for controlling
inflammation.
Transdermal absorption of magnesium
Transport of Mg
2þ
across skin is a critical precondition for
the function of topical, therapeutic compounds in treating
skin and inflammatory diseases. Transdermal absorption is
a potentially important route of transport for components
that are involved in biological processes.
5
Even though
much research has been carried out in the area of cutaneous
permeation and transdermal absorption,
5–7
mechanisms
that lead to permeation of Mg
2þ
ions through the skin are
not clearly understood and need further research.
Past studies on magnesium and other metal ion perme-
ation through human skin demonstrated that it is not read-
ily absorbed under normal physiological conditions, when
the skin is intact and healthy.
8–10
However, there is a con-
siderable body of anecdotal and research data that attributes
to magnesium a role in skin barrier and epidermal recovery
after damage.
3,11–13
In the case of compromised stratum cor-
neum (SC), the viable epidermis and nerve endings (in
atopic dermatitis [AD]) are exposed to incoming particles
and chemicals.
14,15
There is no effective barrier to restrict the
movement of magnesium ions to epidermal cells or nerve
ISSN: 1535-3702 Experimental Biology and Medicine 2014; 239: 1280–1291
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endings, thus permitting a role for Mg
2þ
in skin recovery
and modulation of the immune or nervous systems.
3,16
The permeability of the skin is modified in pathological
conditions, with both macroscopic and microscopic
lesions
17,18
that would allow penetration of magnesium
below the SC, and subsequent transport or diffusion by
mechanisms to be discussed below. Thus it is necessary to
consider both the normal skin as well as barrier compro-
mised or diseased skin.
In normal skin, the SC forms the outermost layer,
formed by continuous replacement from the newly differ-
entiated daughter cells of keratinocyte stem cells, displa-
cing outwards.
19
It functions as a physical barrier
hindering, but not completely preventing, transdermal
penetration through its cellular structure.
5
The radius of
the hydrated magnesium ion relative to the radius of the
dehydrated ion is greater compared to other ions such as
calcium, potassium and sodium.
10,20
Irrespective of oral or
transdermal administration, this greater radius could ster-
ically and energetically hinder transport across cellular
membranes. A review article by Lansdown
8
reports that
magnesium in the form of hydrous polysilicate (talc) is
not readily absorbed by normal skin, however, commonly
used therapeutic formulations of magnesium utilize other
salts such as chloride, or sulphates. The absorption kin-
etics such as solubility and permeation coefficients of
chlorides and sulphates are different to those of polysili-
cates.
4,8,21,22
Moreover, Table 7 in the same review article
presents a positive score for percutaneous absorption of
magnesium ions (although the temperature conditions are
not specified). The same article cites the ability of Mg
2þ
to
bind to hair.
23
This provides the possibility of magnesium
permeation by shunt diffusion. Shunt diffusion is the
mechanism by which diffusion occurs through hair fol-
licles, pilosebaceous units and sweat glands,
5
although
these constitute a small proportion of skin surface area,
with the density dependent on the location of the skin. In
the case of bulk diffusion, water soluble molecules are
able to enter through 10 A
˚
´
pores created by protein sub-
units in the lipid of SC.
5,6,24
These could provide an
entrance for hydrated magnesium, the radius of which
is 4.76 A
˚
´
.
25,26
Subsequently, the transport of Mg
2þ
into
cells could be facilitated by transmembrane proteins
such as SLC41A1 and transient receptor potential mela-
statin 7 (TRPM7).
27,28
SLC41A2, a cell surface transmem-
brane protein with its N-terminus outside and C-terminus
inside the cell membrane, is responsible for magnesium
transport across the plasma membrane.
27
Immunohistochemistry on epidermal cells has demon-
strated a plasma membrane localization of murine
SLC41A2.
27
The N-terminus of this protein, accessible to
extracellular components, is involved in transcellular
movement of Mg
2þ
, which is in turn required for homeo-
stasis, cell growth and neuronal function.
27
Similarly, the
human SLC41A1 functions as a Mg
2þ
transporter
involved in magnesium homeostasis in epithelial cells.
27
Another important mechanism by which Mg
2þ
intracel-
lular homeostasis in humans is facilitated, is via the protein
TRPM7.
28
Knockout of TRPM7 in DT40 B cells (derived
from an avian leucosis virus induced bursal lymphoma in
a white leghorn chicken) resulted in lowered intracellular
Mg
2þ
and inhibition of cellular proliferation.
29
Under stress
(apoptotic stimuli), the TRPM7-knockdown fibroblast cell
line (3T3-M7shRNA6) was more resistant to apoptosis and
had a lower intracellular concentration of reactive oxygen
species (ROS) compared to control cells. This suggests a
role for Mg
2þ
, mediated by the magnesium transporter
TRPM7, in cell survival and regulation of cellular ROS
concentration.
29
Another factor influencing percutaneous absorption of
magnesium ions through skin, is the negative charge car-
ried on the surface of tissues.
30
Accordingly, it is likely that
the positively charged magnesium ions can be absorbed on
the negatively charged SC, enhancing the retention time
and bioavailability on the skin surface.
31
This coupled
with bulk diffusion and the factors mentioned above
could enhance magnesium ion penetration through
normal human skin.
In normal human skin, factors such as temperature and
humidity, osmolarity, dehydration and penetration enhan-
cers, could lead to enhanced percutaneous absorption of
magnesium. In certain therapies, increased temperature
conditions can also provide improved skin permeability
enabling penetration of mineral salts.
5,32,33
A study con-
ducted to measure the effect of heat on skin permeabil-
ity showed a strong dependence of permeability on
temperature. Short pulses of high temperature resulted
in increases in calcein permeability in human cadaver
skin.
34
In relation to Dead Sea therapy on normal
human skin, the high salt concentration coupled with
the hydrated state of the skin could together cause an
osmotic effect,
35
leading to increased flux of ions through
the skin due to a concentration gradient across the skin.
However, in commercially available topical magnesium
formulations it is likely that penetration enhancers
would be necessary in order to enhance passage through
the SC layer in normal skin. The role of these enhancers is
to penetrate into the skin, reversibly decrease the barrier
resistance of the SC and to create a water equilibrium
between SC and viable epidermis.
36
Control of inflammation by magnesium:
Possible mechanisms
It is well established that Mg
2þ
deficiency has a direct influ-
ence on inflammation.
37
However, the molecular mechan-
isms by which Mg
2þ
suppresses inflammation are unclear.
A possible link could be activation by Mg
2þ
of the thiamine
pyrophosphate (TPP)-dependent riboswitch, resulting in
increased synthesis of thiazole from thiazole pyrophos-
phate
38
(see Figure. 1). The TPP-dependant riboswitch is
the only known functional riboswitch mechanism in
eukaryotes and it is known that TPP binding to thiA ribos-
witch is increased by Mg
2þ
.
38,39
The adenine rich sites on
the riboswitch bind Mg
2þ
leading to structural changes
favouring TPP binding.
38
The TPP-dependant thiA ribos-
witch up-regulates thiazole synthase, an enzyme required
for catalysing the conversion of thiazole pyrophosphate to
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thiazole.
40,41
Thiazole derivatives have a spectrum of anti-
inflammatory and neuroprotective activities.
42–46
Molecular mechanisms and inflammatory
pathways
Illnesses related to inflammation following a state of
chronic or acute hypomagnesaemia are well documented,
both in humans and experimental rat models.
37,47–49
However, there is a paucity of information in the literature
regarding the cascade of molecular events culminating in
inflammation during hypomagnesaemia.
Here we review known molecular mechanisms and
propose additional ones that could be responsible for
inflammation resulting from Mg
2þ
deficiency, additionally
suggesting how this might relate to inflammation loca-
lized in the skin. Firstly an examination of how the hypo-
magnesaemic state results in tumour necrosis factor a
(TNFa) and nuclear factor jb (NFjb) activation will be
considered, in view of the importance as inducers of tran-
scription of pro-inflammatory genes. These changes pave
the way for pro-inflammatory cytokine responses, fol-
lowed by alteration of macrophage and neutrophil activ-
ity, including their participation in a pro-inflammatory
positive feedback loop (see Figure 2).
Magnesium in TNFa and NFjb signalling
It has been demonstrated that hypomagnesaemia in
rodents
37
and in people with metabolic syndrome
47
result
in elevated serum concentrations of TNFa compared to
healthy counterparts (in the human studies), or controls
(in rodent studies). An elevation in TNFa and magnesium
deficiency was also observed in obese human subjects when
compared to healthy and moderately overweight individ-
uals.
50
A recent study revealed that TNFa levels declined
following in-vivo administration of MgSO
4
to human sub-
jects.
51
Additional work showed that the magnesium ion
component, not the sulphate, was responsible for the
immunomodulatory effect.
51
Other research has shown
that magnesium deficiency in mice with a knockout of the
gene encoding the TNFa receptor (TNFaR) caused less
adverse effects on bone loss than in the wild-type controls
fed the same diet.
48
These results suggest an inverse rela-
tionship between magnesium intake, TNFa concentration
and TNF actions mediated by the TNFaR. The physiological
significance of these observations becomes evident in the
context of the known pro-inflammatory actions of TNFa.
52
TNFa is a regulatory cytokine produced by various cell
types including macrophages, T-helper cells (CD4þ T
H
cells) and natural killer (NK) cells.
53
The predominant role
Figure 1 Possible influence of Mg
2þ
in thiazole synthesis in turn resulting in anti-inflammatory properties. Thiamine pyrophosphate (TPP), an activated form of
thiamine binds to thiA riboswitch in the presence of magnesium ions (Mg
2þ
). An adenine rich site in the riboswitch binds Mg
2þ
increasing the affinity of TPP binding.
13
The riboswitch undergoes structural change then expresses thiazole synthase,
13
resulting in the formation of TPP intermediate and in turn forming thiazole derivatives.
Thiazole derivatives are known to inhibit cyclooxygenase, hindering the formation of prostanoids, in turn producing anti-inflammatory effects.
17–19
The thiA riboswitch is
the only known eukaryotic riboswitch.
14
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of this cytokine is the systemic regulation of immune cells
with beneficial outcomes such as augmented recruitment of
defence mechanisms during infection, including fever
induction.
52
However, in common with all endogenous
immune mediators, balance is essential and a prolonged
high serum concentration of TNFa results in prolonged
inflammation and effective damage locally and systemic-
ally.
52
Systemic diseases such as systemic lupus erythema-
tosis and local organ diseases including psoriasis and
osteoarthritis are all associated with dysregulation
(increased concentrations) of this cytokine.
49,54,55
The biosynthesis of TNFa is increased by an array of
stimuli including hypoxia, trauma, complement compo-
nents
56
and various cytokines including interleukin 1 (IL-1),
IL-17 interferon-c (IFN-c) and granulocyte macrophage
colony-stimulating factor (GM-CSF).
52
It has been shown
in vitro, using various cell culture models (including
human and rat cell lines) that under hypomagnesaemic con-
ditions in the culture medium, the concentrations of the
aforementioned cytokines show an increase compared to
concentrations in cell lines maintained under normomagne-
saemic conditions.
57–60
The increased concentration of IL-1
and IL-17
61
can result in establishment of positive feedback
loops (which can occur locally or systemically depending
on the disease in question; see reviews referenced
62,63
for
more details beyond the scope of this review), with TNFa
facilitating the generation of IL-1 and IFN-c, in turn driving
further TNFa effects.
52,64–66
Transcription of TNFa is gov-
erned by NFjb, the inflammation-related transcriptional
factor,
67
discussed in more detail below.
Figure 2 General summarized pathway of inflammation following hypomagnesaemia. Evidence suggests that hypomagnesaemic conditions can exacerbate trauma
and hypoxia (leading to increased oxidative damage to cells and tissues from free radicals,
112,113
and stimulates the production of interleukin 1 (IL-1), IL-17, interferon c
(IFN-c) and granulocyte macrophage colony-stimulating factor (GM-CSF). The presence of these soluble proteins allows for the stimulation of various immune cells to
produce tumour necrosis factor a (TNFa) and its reciprocal receptor (for cell surface presentation) following the nuclear translocation of nuclear factor jb (NFjb) acting
as a transcription factor. The secretion of TNFa from cells (after TNFa converting enzyme (TACE) converts tm TNFa to its soluble form) allows for autocrine and paracrine
effects that upon TNFa binding facilitates amplification of inflammatory responses such as transcription, translation and secretion of more TNFa, IL-1, IL6 and IFN-c.A
positive feedback loop is established and the latter two cytokines cause inflammation. Normally prostaglandins, IL-10 and corticosteroids have an inhibitory effect on
TNFa transcription; however this is promoted by Mg
2þ
and may therefore be disrupted in hypomagnesaemic conditions.
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Negative feedback loops also operate, these are known
to regulate TNFa levels by inhibition of transcription of
TNFa mRNA.
52
This negative feedback arises when TNFa
stimulates the production of molecules that inhibits TNFa
transcription including prostaglandins, IL-10 and cortico-
steroids. Mg
2þ
is also known to promote prostaglandin
synthesis, and so it can be speculated that in the hypomag-
nesaemic individual, the negative feedback loop is dis-
rupted, with less feedback control over elevated TNF-a
levels.
52,64,68–70
It remains to be determined what levels of
magnesium deficiency tip the balance towards uncontrolled
positive feedback in humans, resulting in clinically observ-
able effects. Nor is it known how prolonged such effects
would be. There is a paucity of data regarding the effects
of Mg
2þ
on IL-10 or corticosteroid levels, hence the inter-
action between Mg
2þ
and the endocrine system is ripe for
investigation.
After translation, TNFa exists in a cell-surface bound
precursor form, termed transmembrane TNFa (tmTNFa).
This intermediate is converted to a soluble cytokine via
TNFa-converting enzyme.
71,72
Both tmTNFa and sTNFa
are biologically active and capable of binding to their recep-
tors, TNFR1 and TNFR2, triggering different downstream
signalling events, which result in outcomes such as apop-
tosis, necroptosis, transcriptional factor AP-1 activation, or
NFjb activation and translocation to the nucleus.
73
Once
binding has occurred between TNFa and its receptor
(either TNFR1 or 2), a conformational change occurs in
the latter, followed by the interaction between the intracel-
lular domains of TNFR and other proteins including
TRAF2, cIAP1 and cIAP2, forming a complex. This complex
formation leads to the activation of the IJB kinase (IKK)
complex. The IKB complex consists of two kinase subunits,
which phosphorylate the NFjb inhibitor protein IJBa, tag-
ging it for the ubiquitin-proteosome pathway of degrad-
ation. This allows NFjb to freely translocate to the
nucleus where it coordinates the transcription of genes
such as cIAP1/2 and TRAF2, which are important in the
regulation of NFjb and apoptotic pathways.
74,75
Interplay and importance of Ca
2þ
and Mg
2þ
signalling
NFjb activity is regulated by various secondary messengers
including intracellular calcium ions ðCa
2þ
i
. In rats fed a
Mg
2þ
deficient diet, where plasma Mg
2þ
fell to 60% of con-
trol levels, a rise in Ca
2þ
levels was observed.
76
This rise in
Ca
2þ
i
secondary to a decrease in Mg
2þ
is seen in a variety of
systems including human patient studies, rodent models
and cell culture (including immune cells), all of which are
mentioned in the 2010 review by Rayssiguier et al.
77
The
increased Ca
2þ
i
can induce formation of reactive oxygen
intermediates following an oxidative burst from cells such
as neutrophils,
78
which in turn cause phosphorylation of
IJB (through an as yet unknown mechanism), which will
release the active form of NFjb for nuclear translocation.
The critical role of Ca
2þ
in the NFjb pathway is sup-
ported by the observation that Ca
2þ
chelators prevent the
induction of NFjb activity in vivo in murine models.
79
Other research has shown that when Mg
2þ
deficient rats
were fed a Ca
2þ
deficient diet, the inflammatory effect
was greatly reduced (as measured by reduced inflamma-
tion scores, prevention of leucocytosis and reduced spleno-
megaly) when compared to other hypomagnesaemic rats.
80
Once the active NFjb crosses the nucleus it up-regulates the
transcription of TNFa.
81,82
It should be mentioned, how-
ever, that the evidence for NFjb-mediated TNFa expression
is mostly limited to murine models, and studies relating to
humans are limited.
83,84
However, in 2010 one study uti-
lized mouse bone marrow-derived dendritic cells to dem-
onstrate NFjb-mediated positive expression of the TNFa
gene.
81
Additionally it would be of interest to study
whether a high Ca
2þ
, low Mg
2þ
state up-regulates NFjb
activity and TNFa expression permitting TNFa synergism
with STAT6 to switch B cells to IgE production.
85
This is
important to establish the role of IgE in atopic and inflam-
matory conditions such as AD.
85
The antagonism between Mg
2þ
and Ca
2þ
, and competi-
tion for binding sites on receptors, enables Mg
2þ
to over-
come the toxic effects produced by excessive Ca
2þ
concentrations in cells of the immune system that are
located in the brain (human microglial cells in tissue cul-
ture).
86
In the case of neuroinflammation, in vitro experi-
mentation has shown that an influx of Ca
2þ
into microglia
(brain resident macrophages) and THP-1 cells activates
their associated purinergic receptors and subsequently
inflammation.
87
Mg
2þ
is effective in ameliorating the neuro-
toxic effect produced by over-activation of human micro-
glial cells that occurs as a result of elevated levels of
inflammatory cytokines in the cells such as TNF-a, IL-6
and nitrite ions.
86,88
These agents are released as a result
of intracellular inflammatory pathway activation, via P38
MAPK and NFjb.
86
Pro-inflammatory cytokine responses and
resident microflora
In addition to stimulating TNFa transcription, NFjb acti-
vates the transcription of IL-6 and IFN-c after binding to
the cognate promoter regions.
81,89,90
These potent pro-
inflammatory cytokines have been shown to be present in
high levels during periods of Mg
2þ
deficiency.
91–93
Additionally, in one study of septic shock using ex vivo
human whole-blood, it was shown that following addition
of Mg
2þ
, the baseline level of TNFa and IL-6 production
fell.
94
This observation provides further evidence of the
inverse relationship between these inflammatory mediators
and magnesium concentration.
94
However, the concentra-
tion of Mg
2þ
was well above physiologically relevant
levels.
94
More research in other conditions, using a similar
experimental set up is needed to further elucidate links
between Mg
2þ
levels in human blood and pro-inflamma-
tory cytokine production. Further, a more recent study,
using THP-1 cells isolated from human neonatal cord
blood, found that treatment with Mg
2þ
(at levels known
to be clinically effective in vivo) reduced the production of
IL-1b, TNF-a and IL-8 cytokines and IL-6 in cord blood
monocytes.
95
IL-6 exerts effects on a variety of cells including T and B
lymphocytes, hepatocytes, hematopoietic progenitor cells
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and fibroblasts, with consequent systemic effects such as
acute phase reactant protein production, immunoglobulin
synthesis and naive CD4þ T cell differentiation into Th17
cells. IL-17 secreted from Th17 cells is responsible for auto-
immune tissue injury.
96
In relation to skin pathology, it has
been shown that the epidermis from psoriatic skin produces
high levels of IL-6 in addition to over-expression of TNFR,
due in turn to the higher levels of IFN-c.
97
Many of the
characteristic phenotypic features of keratinocytes from
psoriatic skin, including growth activation and ICAM-1
up-regulation, are a result of the actions of IL-6, TNFa
and IFN-c.
97,98
The histological features of psoriasis such
as the presence and accumulation of inflammatory cells
(including polymorphonuclear leukocytes) and epidermal
hyperplasia have been attributed to elevated TNFa activ-
ity.
99,100
Given the aforementioned studies
97
indicating a
role for magnesium in modulating the production of pro-
inflammatory cytokines such as IL-6 and TNFa, there may
be a role for magnesium-containing compounds in the treat-
ment of psoriasis. However, whether such treatment would
be effective in either acute or chronic cases, differing levels
of severity, or what the most effective dose and route of
administration would be (i.e. topical or oral) remain to
be shown.
Another interesting finding is that mice fed on a Mg
2þ
deficient diet for four days showed higher levels of IL-6 and
TNFa mRNA in the liver and intestine, a drop in the
levels of the mRNA of zonula occludens-1, occludin and
proglucagon in the ileum (three factors controlling gut bar-
rier integrity and function) and possessed reduced gut
bifidobacteria levels when compared to controls.
101
Bifidobacterium strains have been shown to repress inflam-
mation in a variety of situations including studies of ulcera-
tive colitis and skin inflammation (i.e. acne).
102–104
With
respect to skin inflammation, Bifidobacterium strains
appear to facilitate reduction in substance P, a molecule
that increases TNFa expression. One study in human
female volunteers demonstrated a reduction in sensitive
skin and heightened resistance to physical and chemical
insults to the skin (in contrast to a negative control cream)
following topical application of B. longum spp. products.
Additionally, in the same paper, the authors report a statis-
tically significant reduction in markers of inflammation
(including oedema, mast cell degranulation and TNFa
release) following the application of a B. longum preparation
on ex-vivo human skin explants.
104
However, in the above mentioned
101
mouse study, the
animals on a Mg
2þ
-deficient diet for 21 days demonstrated
a potentially compensatory increase in caecal Bifidobacteria
levels, restoration of intestinal barrier function and a
waning of inflammation when compared to control mice.
This is in contrast to mice on the same diet for four days
only; in the latter case decreased levels of Bifidobacteria, and
an increase in IL-6, TNFa and other markers of pathology
were present. Drawing generalizable conclusions from this
study is difficult given that it was a mouse-model study
(not human) and measurements of bacteria and relevant
mRNA levels were not continued after 21 days. If there
was adaptation, were there any other long-term adverse
effects on physiology? In the future it will also be important
to work out the complex relationship between the gut bac-
teria and cytokine responses; is it bidirectional or unidirec-
tional? What feedback loops exist? Moreover, the regulation
is unlikely to be the same for all cytokines. These are all
questions that need to be investigated.
Changes in macrophages and neutrophils
In rodent studies, a state of hypomagnesaemia has been
associated with the activation of macrophages and neutro-
phils.
105,106
It has been suggested that this is due to the
increase in circulating pro-inflammatory mediators, includ-
ing substance P, IL-6, TNFa and IFN-c; however, given that
macrophages and neutrophils are amongst the cells that
produce these cytokines, it remains difficult to say whether
the aforementioned cells are activated by these substances
or if they are activated directly by the low levels of Mg
2þ
.
107
Malpuech-Bruge
`
re and colleagues suggest that it is due to
the latter, a drop in circulating Mg
2þ
concentration, which
would lead to a significant increase in Ca
2þ
levels,
37,108
in
turn stimulating cellular proliferation. Whilst macrophages
are also able to be activated independently of Ca
2þ
i
(for
example, via the lipopolysaccharide pathway), the Ca
2þ
-
dependent activation pathway results in a more rapid
expression of IL-6.
108
Aside from enhanced protein expression of IL-6 and
TNFa, activated macrophages also demonstrate increased
expression of IL-1 proteins in Mg
2þ
-deficient rats when
compared to a control group. In the same study it was
postulated that this contributed to cardiac lesions (IL-1 pro-
motes expression of endothelin from heart endothelial cells
which causes vasospasm).
106
Additionally, IL-1 is antagon-
istic to endothelial proliferation, suggesting another mech-
anism behind the lesions seen.
109
Furthermore, in the skin,
IL-1 is implicated in wound repair and skin pathology, with
IL-1 receptor (IL-1R) knockout mice demonstrating reduced
cutaneous and deep tissue fibrosis and scarring and restor-
ation of skin architecture.
110
Neutrophils are capable of releasing superoxide anions
via their NADPH oxidase system and can contribute to
tissue damage during Mg
2þ
deficiency, as demonstrated
in a study which also demonstrated phagocytic activity of
neutrophils in rats on a magnesium deficient diet.
105
The
study also showed that the free radical production from
neutrophils is inhibited when high Mg
2þ
levels are present
in the extracellular space.
105
Mg
2þ
was also found to inhibit
superoxide in cultured human neutrophils.
110
The latter
experiment also revealed synergistic inhibition of super-
oxides with the addition of zinc ions to the magnesium
solutions.
110
Neutrophil migration to the skin, a process
that promotes keratinocyte apoptosis is TNFa dependant.
These phenomena are key features of hyper-proliferative
skin diseases such as psoriasis.
111
Clinical implications of magnesium deficiency
Magnesium is a micronutrient required for normal growth
and development. Numerous clinical disorders have been
associated with magnesium deficiency. Inflammation is a
primary reaction brought about by magnesium deficiency,
Chandrasekaran et al. Mg
+2
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creating oxidative stress and subsequent immune stress.
The clinical disorders could be a consequence of this
stress response.
91,112,113
Magnesium ions bind to macromol-
ecules and cell membranes. Mg
2þ
is known to affect cellular
functions, including the transport of potassium and Ca
2þ
,
modulation of signal transduction, cell proliferation and
energy metabolism.
114
Early stages of Mg
2þ
deficiency can
be characterized by a wide range of symptoms such as
anorexia, vomiting, weakness, paraesthesia, muscular
cramps, irritability and impaired cognitive functioning
reflected by a decreased attention span. Mg
2þ
deficiency
is related to poor dietary Mg
2þ
intake, often as a result of
lifestyle changes, leading to the aforementioned health dis-
orders.
114–116
Mg
2þ
deficiency triggers inflammatory
responses, including abnormal calcium homeostasis, acti-
vation of N-methyl-
D-aspartate (NMDA) receptors, release
of neurotransmitters, membrane oxidation and activation of
NFjb (see previous section, ‘Magnesium in TNFa and
NFjb signalling’).
76,91
Some of the important inflamma-
tion-related clinical disorders, known to be caused by or
exacerbated by, magnesium deficiency, are outlined below.
The pathogenesis of asthma, a chronic inflammatory dis-
order involves activation of NFjb and, expression of pro-
inflammatory cytokines, chemokines and inflammatory
mediators (IFN-c and ROS).
117
In this pathological condi-
tion, NFjb activation leads to dysregulation of cytokines
and infiltration of inflammatory cells such as mononuclear
cells and fibroblasts in the lung.
117,118
Indeed, increased
NFjb activity has been observed in the airways of asthmatic
patients.
118
In acute asthma, the therapeutic effect of mag-
nesium is well established.
12
Studies in acute asthma have
shown that intravenous and inhaled magnesium sulphate
(MgSO
4
) improved lung function and reduced hospitaliza-
tion frequency, particularly in patients with the lowest
levels of forced expired volume.
116
In chronic asthma
patients with persistent airflow limitation short-term treat-
ment with magnesium inhalations had no statistically sig-
nificant, direct bronchodilating effect, however, clinical
observations suggested heterogeneity in the response, prob-
ably related to treatment intensity, and supported further
exploration of magnesium administration in those
patients.
116
A characteristic property of Mg
2þ
is its antagonism of
Ca
2þ
(see prior section ‘Interplay and importance of Ca
2þ
and Mg
2þ
signalling’). It competes with Ca
2þ
for entry
into cells through voltage-gated channels and receptors
and inhibits Ca
2þ
i
release from the sarcoplasmic
reticulum.
119,120
The synovial fluid from patients with rheumatoid arth-
ritis contains elevated levels of TNFa (an activator of NFjb),
which is important in the pathogenesis.
118,121
Mg
2þ
defi-
ciency can lead to lipid peroxidation and membrane oxida-
tion, which in turn activates the NFjb pathway.
91,122
Activation of inflammatory responses due to Mg
2þ
defi-
ciency causes chronic inflammation leading to different
types of arthritis, depending on the site of NFjb activation.
Studies in humans indicate that low Mg
2þ
intake and
blood plasma concentration are linked with enhanced risk
of atherosclerotic disease.
123
Atherosclerosis is currently
classified as an inflammatory disease, having interactions
between modified lipoproteins, macrophages, T lympho-
cytes and the components of arterial walls,
91
leading to
the development of atherosclerotic lesions. Experimental
results suggest regression of such lesions and suppression
of atherogenesis in low-density lipid receptor deficient mice
fed with Mg
2þ
supplement.
124,125
Infusion of Mg
2þ
at supra-
physiological concentrations causes vasodilation of coron-
ary arteries and systemic vasculature, antiarrhythmic
effects and platelet inhibition.
126
Studies also show dietary
administration of Mg
2þ
attenuates atherosclerotic lesions
by lowering serum cholesterols and triglycerides in choles-
terol fed animals.
91
On the basis of these studies, it appears
that Mg
2þ
concentration regulates lipid metabolism and
reduces atherosclerosis in animal models.
91
Even though the immune system and, in particular, the
inflammatory response operates systemically, the inter-rela-
tionship between inflammation occurring in the nervous
system and systemic inflammation needs to be better
understood. It is widely accepted that several neurological
disorders are characterised by an inflammatory compo-
nent.
127,128
There are several drugs undergoing test that
are posited to act by reducing neurodegeneration, at least
in part through inhibition of the inflammatory response of
glial cells.
129
However, these drugs exert their effect
throughout the body, resulting in global immunosuppres-
sion.
130
It would be ideal for such drugs to specifically
target the glial cells and control inflammation in the brain
without producing systemic immunosuppression.
129,131
Studies conducted in mice using the compound 4,6-diphe-
nyl-3-(4-(pyrimidin-2-yl)piperazin-1-yl) pyridazine
(MW01-5-188WH), aimed at selective suppression of neu-
roinflammation, has yielded some positive outcomes with-
out producing extra-neural inflammation.
129
Mg
2þ
administration could potentially be an effective
treatment of neurodegenerative diseases via its antagonism
of Ca
2þ
channels. This selectively suppresses neuroinflam-
mation.
86,91
If treatment for neurodegenerative diseases
involved administration of Mg
2þ
locally to the brain, it
could conceivably avoid the generalised stress on the
immune system that is caused by non-targeted anti-inflam-
matory drugs. Experiments conducted on rat ischaemic and
excitotoxic brain injury models shows the activity of Mg
2þ
as a neuroprotective agent.
114,132,133
This is achieved by
Mg
2þ
blockade of NMDA receptors and enhancement of
regional cerebral blood flow to ischaemic areas of the
brain. Mg
2þ
also inhibits entry of Ca
2þ
into cells through
voltage-operated and receptor-operated channels.
114,126
The nervous and immune systems interact bi-direction-
ally. Mg
2þ
deficiency is known to induce a systemic stress
response by activating neuroendocrine pathways, modify-
ing production and activity of neuromediators such as
acetylcholine, catecholamines and substance P. These have
well established roles in the progression of both local and
systemic inflammatory responses.
134
Administration of
Mg
2þ
has been shown to block Ca
2þ
traffic through cell
surface channels, acting as a broad inhibitor of neuroinflam-
mation.
86,135
Elevated systemic levels of Mg
2þ
have been
shown to reduce damaging consequences of Ca
2þ
induced
neuroinflammation in Parkinson’s disease and Alzheimer’s
disease.
86
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AD is a skin disease that is a result of interactions
between skin, nervous system and immune cells. Nerve
growth factor (NGF) is a neurotrophin, mainly produced
in the basal keratinocytes and are present in elevated
levels in plasma of AD patients.
136
In normal skin, less
expression of NGF was found.
137,138
These NGFs are
known to be involved in the extension of C-fibres and pro-
mote increased density of nerve endings. In AD this results
in exposure of a high density of unprotected nerves to exter-
nal conditions, leading to the itch and scratch cycle that
characterizes the disease.
14,139
Semaphorin3A (Sema3A) is
another factor involved in the development of AD. It is an
axon guidance molecule that inhibits outgrowth of sensory
neurons. It does so by binding to plexin–A1-4 and its co-
receptor neuropilin-1 (NRP-1), subduing the effects caused
by NGFs.
140,141
Sema3A acts by suppressing nerve exten-
sion, and inhibition of histamine release from mast cells
(existing treatments for AD rely on blocking the histamine
receptors (H1-R) with anti-histamines or topical steroids).
Further, Sem3A also binds to NRP-1.
142
NRP-1 is known to
activate the NFjb pathway and to initiate keratinocyte
proliferation.
143
One study has shown that increased calcium ion concen-
tration (0.45–0.75 mmol/L) in normal human epidermal
keratinocytes augments the expression of Sema3A.
144
While calcium and magnesium have antagonist effects at
the cellular level, it is possible that the skin barrier recovery
after treatment with Dead Sea minerals (comprising cal-
cium and magnesium salts) is due to the combined role of
calcium in upregulating Sema3A, and the prevention by m
magnesium of mast cell degranulation through other mech-
anisms (potentially via effects on TNFa or STAT-6
145,146
).
However, a direct role for magnesium ions in regulation
of Sema3A and NGFs remains to be established, and is an
important area for further investigation, given the role of
these factors in AD.
In relation to skin disease, a clinical study was conducted
on 30 AD candidates, in which subjects were tested over six
weeks for transepidermal water loss (TEWL), skin hydra-
tion, skin redness and skin roughness.
3
Upon treating one
of their arms with a 5% Dead Sea salt solution at 38–42
C
and the other arm with tap water (38–42
C) as control, an
improvement in TEWL, with reduction in AD symptoms in
the Dead Sea salt treated group was shown.
3
Further work
is needed, to confirm these studies and to measure the intra-
cellular and molecular correlates of the structural changes
in the skin.
Conclusion
Absorption of Mg
2þ
ions across the normal SC could occur
under conditions of elevated temperature or changed
hydration conditions (for example high salt concentrations).
Absorption of magnesium will take place in cases of skin
pathology or injury, where there is physical disruption of
the SC. Subsequently, transmembrane proteins, such as
SLC41A2 could assist intercellular transport of magnesium
ions, leading to further penetration through the organ sys-
tems.
27
The action of magnesium ion as an anti-inflamma-
tory agent could be via several pathways, such as activation
of the TPP-dependant riboswitch.
38
Magnesium deficiency
results in activation of TNFa and NFjb, which can further
facilitate pro-inflammatory cytokines.
76,106
It would also be
of interest to study the effect of Mg
2þ
on the synergism
between TNF-a and STAT6, a mediator of IgE receptor
mediated mast cell responses in late phase allergic
responses and AD.
145,146
Experimental data from humans
and mice suggest an inverse relationship between magne-
sium intake and TNFa concentration, in addition to several
other markers of inflammation.
147–149
The hypomagnes-
aemic condition increases the influx of calcium into cells,
resulting in elevated NFjb activity.
150,151
Evidence for acti-
vation of neutrophils and macrophages by calcium ions in
mice has also been found.
150
Collectively, the inflammatory
responses triggered by magnesium deficiency can result in
clinical disorders. The interaction between Mg
2þ
and
inflammatory mediators is ripe for investigation. For exam-
ple, there is a paucity of data relating to the effects of Mg
2þ
on IL-10 or corticosteroid concentrations. More research is
needed to further elucidate links between Mg
2þ
levels in
human blood and pro-inflammatory cytokines. The effect
of treatment with magnesium containing compounds in
acute or chronic diseases with differing levels of severity,
and the most effective doses and routes of administration in
these cases, remain to be systematically determined.
Although a role of magnesium deficiency in neurodegen-
erative disease is established, and may be mediated by
interaction of magnesium ions with glial cells,
134
the inter-
relationship between inflammation in the nervous system
and systemic inflammation needs to be better understood.
Thus, there exist plausible mechanisms by which several
metabolic and inflammatory conditions might potentially
be alleviated through magnesium administration, either
systemically or locally. These mechanisms are ripe for fur-
ther investigation.
Author contributions: All authors participated in the writ-
ing, review and editing of this manuscript. NCC and CW
contributed equally to the writing of this manuscript.
ACKNOWLEDGMENTS
This work was funded by grants from the University of
Queensland, The National Health and Medical Research coun-
cil of Australia, and Cancer Council Queensland.
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(Received February 9, 2014, Accepted April 14, 2014)
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