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RESEARCH Open Access
Hyperglycaemia and apoptosis of microglial cells
in human septic shock
Andrea Polito
1
, Jean-Philippe Brouland
2
, Raphael Porcher
3
, Romain Sonneville
1,6
, Shidasp Siami
1
,
Robert D Stevens
4
, Céline Guidoux
1
, Virginie Maxime
1
, Geoffroy Lorin de la Grandmaison
5
, Fabrice C Chrétien
6
,
Françoise Gray
2
, Djillali Annane
1
and Tarek Sharshar
1*
Abstract
Introduction: The effect of hyperglycaemia on the brain cells of septic shock patients is unknown. The objective of
this study was to evaluate the relationship between hyperglycaemia and apoptosis in the brains of septic shock
patients.
Methods: In a prospective study of 17 patients who died from septic shock, hippocampal tissue was assessed for
neuronal ischaemia, neuronal and microglial apoptosis, neuronal Glucose Transporter (GLUT) 4, endothelial
inducible Nitric Oxide Synthase (iNOS), microglial GLUT5 expression, microglial and astrocyte activation. Blood
glucose (BG) was recorded five times a day from ICU admission to death. Hyperglycaemia was defined as a BG 200
mg/dL g/l and the area under the BG curve (AUBGC) > 2 g/l was assessed.
Results: Median BG over ICU stay was 2.2 g/l. Neuronal apoptosis was correlated with endothelial iNOS expression
(rho = 0.68, P= 0.04), while microglial apoptosis was associated with AUBGC > 2 g/l (rho = 0.70; P= 0.002).
Neuronal and microglial apoptosis correlated with each other (rho = 0.69, P= 0.006), but neither correlated with
the duration of septic shock, nor with GLUT4 and 5 expression. Neuronal apoptosis and ischaemia tended to
correlate with duration of hypotension.
Conclusions: In patients with septic shock, neuronal apoptosis is rather associated with iNOS expression and
microglial apoptosis with hyperglycaemia, possibly because GLUT5 is not downregulated. These data provide a
mechanistic basis for understanding the neuroprotective effects of glycemic control.
Introduction
Sepsis and septic shock are associated with hyperglycae-
mia and peripheral insulin resistance [1,2]. Glycemic
control strategies are commonly instituted as adjunctive
therapeutic measures in critically ill patients, although
recent studies have not consistently shown a benefit
from intensive insulin therapy [3-6]. One argument sup-
porting blood glucose control is that intensive insulin
therapy is associated with a protective effect on the per-
ipheral and central nervous system [7]. While it has
been shown that intensive insulin therapy reduces the
incidence of critical illness neuromyopathy [7,8] and
that hyperglycaemia worsens brain injury in ischemic
stroke [9-11] and head trauma [12], the effect of hyper-
glycaemia or insulin on sepsis related brain dysfunction
is not well understood. A recent in vitro study showed
that hyperglycaemia increased microglial vulnerability to
lipopolysaccharide (LPS) mediated toxicity [13], through
formation of oxidative free radicals. Interestingly, it has
also been shown that experimental sepsis induces oxida-
tivedamagesinthebrain[14].Inapreviousneuro-
pathological study, we found that septic shock is
associated with neuronal ischaemia, microglial activation
and apoptosis as well as neuronal apoptosis, which was
statistically correlated with endothelial expression of
iNOS [15]. However, the relationships between BG and
neuropathological findings have not been thoroughly
assessed. The objective of the present study was to
address this issue and also to assess whether hypergly-
caemia is associated with neuronal or microglial
* Correspondence: tarek.sharshar@rpc.aphp.fr
1
General Intensive Care Medicine, Raymond Poincaré Hospital (AP-HP),
University of Versailles Saint Quentin en Yvelines, 104 bd R. Poincaré,
Garches 92210, France
Full list of author information is available at the end of the article
Polito et al.Critical Care 2011, 15:R131
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© 2011 Polito et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons
Attribution License (http://creative commons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, pro vided the original work is properly cited.
apoptosis after adjustment to other pro-apoptotic fac-
tors. We also evaluated brain expression of Glucose
Transporter (GLUT) proteins given their role in trans-
membrane glucose transport in neurons and microglial
cells during stress conditions [16]. Assessment of the
relationships between hyperglycaemia and neuropatholo-
gical abnormalities might provide insight on the
mechanisms of sepsis associated neurological and psy-
cho-cognitive long-term consequences.
Materials and methods
Patients
We investigated consecutive patients who died from
septic shock while receiving treatment in the ICU at
Raymond Poincaré University Hospital, Garches, France
[15]. Exclusion criteria were: age younger than 18 years;
pregnancy; evidence of an underlying degenerative neu-
rological disease determined clinically or on post-mor-
tem examination, or any concomitant disease other than
infection that might have accounted for shock and
death. We obtained informed consent from the patient’s
closest relatives. The protocol was approved by the
Comité Consultatif de Protection des Personnes se Prê-
tantàlaRechercheBiomédicaledeSaintGermainen
Laye, France.
Data collection
Demographic characteristics, pre-existing risk factors for
vascular disease, and severity of illness using simplified
acute physiology score II (SAPS II) [17] and sequential
organ failure assessment (SOFA) [17,18] score were rou-
tinely recorded. Vital signs were recorded continuously,
enabling calculation of duration of shock and cumula-
tive time passed with a mean blood pressure of less
than 60 mmHg. Standard laboratory tests and relevant
microbiological data were recorded daily. All arterial
and capillary BG levels measured between admission
and death were collected. Hyperglycaemia and hypogly-
caemia were considered when BG levels were above 2 g/
l and 0.4 g/l, respectively [5,6,19]. Then, we assessed the
highest and lowest BG, highest variation (Δmax) in one
dayinBG,meanBG,areaundertheBGcurve
(AUBGC), and AUBGC above 2 g/l (that is, hyperglycae-
mia). The AUBGC cut-off of 2 g/L was chosen because
it reflected a compromise between the duration of
hyperglycaemia and the value of blood glucose. This
cut-off also allows to account for the irregular times
intervals between sample collection. We also assessed
the percentage of follow-up time in hypoglycaemia and
in hyperglycaemia, as well as the proportion of patients
who were treated with insulin and who developed hypo-
glycaemia and hyperglycaemia. We defined prolonged
hyperglycaemia as BG values higher than 2 g/l more
than 50% of follow-up time (with linear interpolation
between two consecutive blood samplings). During the
study period (from 1997 to 2001), no specific protocol
for the management of hyperglycaemia had been
implemented.
Brain sampling
Brain samples were collected within 12 h of death.
Gross examination of the brain was done after four to
six weeks of formalin-fixation on coronal sections of the
cerebral hemispheres and horizontal sections of the
brain stem and cerebellum. Macroscopic changes were
noted, and we selected the hippocampus for microscopic
examination, after paraffin embedding. We decided to
evaluate changes in the hippocampus as it is highly vul-
nerable to metabolic insults, hypoxemia and ischaemia
[20,21]. Sections were stained with haematoxylin and
eosin and Bodian silver impregnation combined with
Luxol fast blue.
Ischaemia, gliosis and apoptosis
Histological analysis was performed by one observer
(FG) who was blinded to glycemic levels. As previously
described [15,22], neurons were described as ischaemic
when they presented with shrunken eosinophilic cyto-
plasm and pyknotic nuclei. Glial reaction (that is, glio-
sis) was identified as rod-shaped microglial cells and
astrocytes with clear nuclei. Astrocyte and microglial
activation was assessed by evaluating immunohisto-
chemical expression of glial fibrillary acidic protein
(GFAP, Dako, Glostrup, Denmark) and MHC class II
antigens (HLA-DR) (Dako), CD68 (Dako). Axonal
damage was assessed using immunohistochemistry for
Amyloid Precursor ProteinA4(beta-APP)(MAB348,
Chemicon, Lyon, France). Tissue expression of GLUT1
(a3536, Dako), GLUT3 (ab41525, Abcam, Cambridge,
UK), GLUT4 (ab65976, Abcam) and GLUT5 (ab36057,
Abcam), were also assessed as well as that of tumor
necrosis factor a(TNFa) (Genzyme, Dako) and induci-
ble NO synthase [23]. We previously found that sepsis-
associated expression of TNFaand iNOS involve glial
and endothelial cells, respectively [15]. Apoptosis was
identified using a caspase 3 monoclonal antibody
(Dako), and by in-situ end labelling (ISEL) [24] with
use of ApopTag kit (Oncor, Gaithersburg, MD, USA).
Intensity of neuronal ischaemia, gliosis, glial activation
and apoptosis were graded between 0 and 3, as
described elsewhere [15]. Expression of neuronal beta-
APP, glial TNFa, endothelial iNOS, neuronal GLUT 1,
GLUT3, GLUT4 and microglial GLUT5 expression
were also graded from 0 to 3 [15]. Because immunos-
taining of GLUT3 was not satisfactory and that of
GLUT1 immunostainings did not vary among patients,
we did not assess their statistical correlation with
blood glucose level.
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Statistical analyses
Quantitative and qualitative variables were expressed as
median (interquartile range, IQR) and percentage,
respectively. Association between continuous variables
was assessed by non parametric Spearman correlation
coefficient. Adjustment was performed by multiple lin-
ear models based on ranks, in accordance to the use of
non-parametric rank correlation coefficients. Continuous
and categorical variables were compared between groups
of patients by Wilcoxon rank-sum test and Fisher’s
exact test, respectively. Values of P<0.05wereconsid-
ered as indicating statistical significance. All statistical
analyses were performed using R 2.6.2 statistical soft-
ware (The R Foundation for Statistical Computing,
Vienna, Austria).
Results
From 1997 to 2001, 17 patients who died from septic
shock were included. Patient characteristics are pre-
sented in Table 1. Septic shock had a median duration
of four days and was mainly secondary to pneumonia or
cellulitis. Four patients had pre-existing diabetes melli-
tus. Median BG over ICU stay was 2.17 g/l. Episodes of
hyperglycaemia were observed in all patients and hypo-
glycaemia occurred in five (29%) patients. Nine (53%)
patients developed prolonged hyperglycaemia and six
(35%) were treated with insulin (with mean BG level of
2.7 g/L (1.9 to 3.0)). Macroscopic findings were ischae-
mia (n = 12), haemorrhage (n = 9) and disseminated
abcesses (n = 3). Oedema was observed in only one
patient.
In contrast to HLA-DR, expression of microglial CD68
tended to be correlated with AUBGC > 2 g/l (rho =
0.44, P= 0.08). Intensity of neuronal and microglial
apoptosis was correlated with AUBGC > 2 g/l (rho =
0.53; P= 0.03 and rho = 0.70; P= 0.002) (Table 2, Fig-
ure 1). Intensity of neuronal beta-APP expression corre-
lated with AUBGC > 2 g/l (rho = 0.61; P= 0.03) (Figure
2). Endothelial iNOS expression was correlated with
intensity of neuronal apoptosis (rho = 0.68, P= 0.005)
but not with that of microglial apoptosis (rho = 0.34, P
= 0.17). The intensities of neuronal and microglial apop-
tosis were correlated (rho = 0.56, P=0.02).Immunos-
taining of GLUT3 was not satisfactory. GLUT1 rather
stained endothelial cells than neurons and its expression
did not vary among patients. Neuronal GLUT4 (Figure
3) and microglial GLUT5 expression (Figure 4) did not
correlate with prolonged hyperglycaemia nor with neu-
ronal or microglial apoptosis (Table 3). Expressions of
endothelial iNOS and microglial GLUT5 were inversely
correlated (rho = -0.54; P= 0.03). Neuronal and micro-
glial apoptosis were not correlated with SAPS-II at
admission, highest SOFA score, duration of septic
shock, or with serum sodium (especially hyponatremia),
lowest systolic arterial pressure, PaO
2
and SaO
2
.Inten-
sity of neuronal apoptosis and ischaemia tended to be
Table 1 Patients’characteristics
Whole population
(n = 17)
Women (%) 6 (35)
Age (years) 68 (53 to 72)
Cerebrovascular risk factors (%) 11 (65)
Diabetes (%) 4 (24)
Medical admission 11 (65)
Site of infection
Lung only (%) 9 (53)
Abdominoperitoneal only (%) 0
Urinary tract only (%) 0
Cellulitis only (%) 5 (29)
> 1 site 5 (18)
Unknown 0
Positive culture at any site (%)
Gram-positive only (%) 4 (24)
Gram-negative only (%) 6 (35)
Fungus only (%) 0
Mixed (%) 7 (411)
Positive blood culture (%) 4 (24)
SAPS-II at admission 43 (30 to 58)
Highest OSF score during ICU stay 4 (4 to 5)
Duration of septic shock (days) 4 (2 to 10)
Cumulative time spent with MAP < 60 mm Hg (h) 11 (4 to 25)
Lowest SAP (mm Hg) 57 (33 to 66)
Lowest PaO
2
(kPa) 8.1 (6.1 to 9.0)
Lowest SaO
2
(%) 85 (73 to 90)
Highest blood sodium level (mmol/L) 139 (135 to 149)
Lowest blood sodium level (mmol/L) 132 (128 to 137)
Blood glucose level
Lowest BG (gr/l) 0.6 (0.3 to 1.1)
Highest BG (gr/l) 3.5 (3.3 to 5.4)
Δmax BG (gr/l) 3.4 (2.1 to 4.8)
Mean BG (gr/l) 2.2 (1.4 to 2.8)
Patients with hypoglycaemia (%) 5 (29)
Patients with hyperglycaemia (%) 15 (88)
Patients with prolonged hyperglycaemia (%) 9 (53)
Patients treated with insulin (%) 6 (35)
Neuronal apoptosis 1.0 (1.0 to 2.0)
Microglial apoptosis 1.0 (1.0 to 1.5)
GFAP expression 2.0 (2.0 to 3.0)
HLA-DR expression 1.0 (1.0 to 2.0)
CD68 expression 1.0 (0.5 to 1.5)
Glial TNF-aexpression 1.0 (0 to 1.0)
iNOS expression 1.0 (1.0 to 1.0)
Neuronal GLUT4 1.5 (1.0 to 2.0)
Microglial GLUT5 1.0 (0.5 to 1.0)
CD68 1.5 (1.0 to 2.0)
Beta-APP 1.0 (1.0 to 1.5)
Beta APP, beta-amyloid precursor protein; BG, blood glucose; CD68, Cluster of
Differentiation; GFAP, Glial Fibrillary Acid Protein; GLUT, glucose transporter;
HLA-DR, Major Histocompatibility Complex Class II cell surface receptor; ICU,
intensive care unit; iNOS, inducible Nitric Oxide Synthase; MAP, mean arterial
pressure; OSF, organ systemic failure; PaO
2
, partial pressure of oxygen in
arterial blood; SAP, systolic arterial pressure; SAPS-II, simplified acute
physiology score; SaO
2
, saturation of oxygen in arterial blood; TNFa, tumor
necrosis factor alpha.
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correlated with cumulative time of hypotension (rho =
0.45, P= 0.06 and rho = 0.38, P= 0.11).
Discussion
In patients dying of septic shock, hyperglycaemia was
associated with microglial apoptosis while neuronal
apoptosis was preferentially associated with endothelial
iNOS expression. We also found that hyperglycaemia
tended to be correlated with CD68 expression, which is
a marker of microglial activation. The postulated rela-
tionship between hyperglycaemia and microglial cell
apoptosis was supported by its absence of statistical cor-
relation with hypotension, hypoxemia or hypernatremia,
while it is known that hippocampus is highly vulnerable
to these factors. We also found that neuronal GLUT4
and microglial GLUT5 expressions were not correlated
with blood glucose level, suggesting impaired
downregulation.
These results are consistent with several experimental
studies. Discrepancy between microglial CD68 and
HLA-DR immunostaining has been previously observed
Table 2 Association of the area under the BG curve
above 2 g/l with clinical characteristics and
neuropathological findings
Spearman r(95%CI) P
SAPS-II at admission 0.34 (-0.17 to 0.71) 0.18
Knauss -0.21 (-0.63 to 0.30) 0.43
McCabe 0.05 (-0.44 to 0.52) 0.85
Neuropathological findings
Neuronal ischaemia 0.05 (-0.43 to 0.53) 0.82
Gliosis 0.15 (-0.36 to 0.59) 0.57
GFAP expression 0.11 (-0.39 to 0.56) 0.67
HLA-DR expression 0.06 (-0.43 to 0.53) 0.81
CD68 expression 0.44 (-0.05 to 0.76) 0.08
Beta-APP expression 0.61 (0.06 to 0.88) 0.03
Neuronal apoptosis 0.53 (0.07 to 0.81) 0.028
Microglial apoptosis 0.70 (0.33 to 0.88) 0.002
Glial TNFaexpression -0.04 (-0.51 to 0.45) 0.86
Endothelial iNOS expression 0.04 (-0.45 to 0.51) 0.87
Each neuropathological finding was score from 0 to 3 (see methods). beta-
APP, beta-amyloid precursor protein; CD68, Cluster of Differentiation; GFAP,
glial fibrillary acidic protein; HLA-DR, Major Histocompatibility Complex Class II
cell surface receptor; iNOS, inducible Nitric Oxide Synthase; TNFa, tumor
necrosis factor alpha.
Figure 1 Neuronal and microglial apoptosis in cerebral
amygdale. Case 7359, Cerebral amygdala. The back arrows show
two apoptotic neurons with darkly stained nucleus. The red arrow
shows an apoptotic microglial cell with a dark nucleus. The
cytoplasm of the apoptotic cells is also stained corresponding to
disintegration of nuclear chromatin into apoptotic bodies. (ISEL
×800).
Figure 2 Axonal damage in the hippocampal white matter.
Cortico-subcortical junction in the hippocampus. Black arrows show
axonal swellings in the white matter. These represent the
accumulation of the precursor of the beta-amyloid protein due to
alteration of the axonal flow. (APP imunostaining ABC/peroxidase/
DAB x25).
Figure 3 Hippocampal expression of GLUT4. Hippocampal
interneurons in CA1 and CA4 exhibit a homogeneous cytoplasmic
staining (arrow) with GLUT4 antibody (ABC/peroxidase/DAB, x40).
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[25] and was ascribed to the fact that CD68 is a better
marker of activated microglia. Nitric oxide has been
extensively documented as pro-apoptotic factor, notably
in experimental sepsis [26-28]. In experimental models
of cerebral trauma or ischaemia, hyperglycaemia has
been linked to neuronal and glial cell injury through
various mechanisms including mitochondrial dysfunc-
tion, oxidative stress, inflammation and excitotoxicity
[29]. Although the similar mechanisms have been impli-
cated in sepsis associated encephalopathy, the potential
contribution of hyperglycaemia had not been elucidated.
It was recently shown that high glucose and LPS syner-
gistically induce microglial apoptosis by enhancing for-
mation of oxidative free radicals [13]. Interestingly, the
statistical correlation between neuronal and microglial
apoptosis suggest that they are interdependent phenom-
enon. It is established that neuronal function and survi-
val is intimately linked to both astroglial and microglial
cells [30]. Therefore, one may speculate that hypergly-
caemia induces microglial death that, synergistically with
endothelial iNOS, induces neuronal apoptosis, suggest-
ing a mechanistic sequence to account for sepsis asso-
ciated brain dysfunction. This model takes into account
the inflammatory [23] and metabolic (hyperglycaemia)
pathways that are a major pathophysiological process
and disturbance of septic shock, respectively. The
correlation between hyperglycaemia and axonal beta-
APP expression is consistent with that reported in
experimental brain ischaemia [31]. It suggests also
another scenario in which hyperglycaemia would first
induce axonal injury, then secondary degeneration of
microglia [31]. Interestingly, this finding proposes a new
pathophysiological mechanism for the long-term cogni-
tive decline in septic patients [32].
Thepresentstudyisthefirsttodescribetheneuro-
pathological consequences of hyperglycaemia in patients
who had died from septic shock. However, our study
has several limitations. First, one may argue that apopto-
sis was rather a post-mortem phenomenon. Although
this possibility cannot be ruled out, we have previously
shown that cell death did not correlate with time to
brain sampling [15]. Second, since BG levels were not
assessed continuously, it is likely that discrete hypogly-
caemic or hyperglycaemic events were not detected.
However, the rate of BG assessment was not different
between patients with and without hyperglycaemia or
prolonged hyperglycaemia. Third, it has been shown
that the capillary test does not provide an accurate mea-
surement of BG, notably overestimating it [33]. How-
ever, despite this flaw, capillary meter is used both in
clinical trials and in routine for titrating insulin therapy.
It has to be noted that microglial apoptosis was also
correlated with median BG. Fourth, we have limited our
investigation to the hippocampus as it is highly sensitive
to hemodynamic, hypoxic or metabolic insults but also
involved in ICU associated delirium pathophysiology
[34,35]. The impact of neuronal and microglial apoptosis
on hippocampal function cannot be obviously inferred
from these simple neuropathological observations. It
would be of interest to determine experimentally if
hyperglycaemia is associated with alterations in hippo-
campal electrophysiological function and with cognitive
impairments mediated by hippocampal structures. It has
been reported that high glucose level is associated with
occurrence of delirium in ICU patients [36]. Conversely,
it has been shown that infusion of glucose is a memory
enhancer in septic rats, suggesting that glucose tight
control, or at least hypoglicaemia, may affect hippocam-
pal functions [37].
While we have demonstrated an association between
hyperglycaemia and cell death in the brains of septic
shock patients, these data do not allow us to make any
Figure 4 Hippocampal expression of GLUT5.Inhippocampal
interneurons (CA1 and CA4), microglial cells are strongly stained
(arrows) whereas neurons are not labelled with GLUT5 antibody
(ABC/peroxidase/DAB, x25).
Table 3 Association of neuronal GLUT4 and microglial GLUT5 expression with glycaemia and cell apoptosis
Spearman r(95% CI) Neuronal GLUT4 expression PMicroglial GLUT5 expression P
Area under the BG curve > 2 g/l -0.006 (-0.49 to 0.48) 0.98 0.03 (-0.46 to 0.50) 0.91
Neuronal apoptosis -0.29 (-0.68 to 0.22) 0.25 -0.40 (-0.74 to 0.10) 0.11
Microglial apoptosis -0.002(-0.48 to 0.48) 0.99 -0.25 (-0.65 to 0.26) 0.33
Each neuropathological finding was score from 0 to 3 (see methods). BG, blood glucose; GLUT, glucose transporter.
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definitive conclusions on hyperglycaemia as a causative
mechanism for cell death. Indeed, statistical correlations
between ante-mortem variables and post-mortem find-
ings do not prove a causal relationship. Demonstration
ofsuchalinkwouldrequireamoredetailedinvestiga-
tion of how glucose levels affect microglial cellular and
molecular function and the demonstration that glycemic
control reduces microglial apoptosis. Only experimental
studies could reasonably address these issues. Indeed,
post-mortem examination does not yield insight into the
proximal processes that precede apoptosis in humans.
This may explain that hyperglycaemia tended to be cor-
related with microglial activation (reflected by CD68
expression), which is prior to apoptosis. Assessment of
neuropathological effect of BG control would require
brain sampling in patients who had died from septic
shock and who had or not been treated with insulin
therapy: a task not so easily achievable. Our neuropatho-
logical samples were obtained before the widespread
implementation of glycemic control with intensive insu-
lin therapy in many critical care units. This is illustrated
by the fact that insulin was administered in a small pro-
portion of patients and was not targeted to normogly-
caemia. These observations prevented us from assessing
the neuropathological effect of insulin. Moreover, antici-
pating a neurological benefit from insulin therapy is pre-
mature. First of all, even if microglial cells play a major
role in host defence of the brain, and are involved in
neuroinflammatory and neurodegenerative processes,
their implication in sepsis related brain dysfunction is
not demonstrated [38]. It is unknown whether micro-
glial apoptosis is an adaptive, negligible or deleterious
phenomenon. Unlike the situation in neurons, interpre-
tation of positive ISEL staining in glial and microglial
cells is not straightforward. As ISEL is not absolutely
specific for double-stranded DNA breaks and can also
detect single-stranded breaks as observed in cell multi-
plication [39], positive staining may also reflect cell pro-
liferation. On the other hand, Petito and Roberts [40]
suggested that apoptotic death of reactive astrocytes
might be a physiological mechanism whereby the brain
removesanexcessnumberofastrocytesthathavepro-
liferated after certain types of brain injury. This can also
apply for microglia [41]. Second, cerebral glucose meta-
bolism is highly complex and its disturbances in sepsis
insufficiently elucidated. Therefore, neuronal sensitivity
to hypoglycaemia and hyperglycaemia might be deeply
changed in sepsis, making the effect of insulin on neuro-
nal metabolism unpredictable. We have found that neu-
ronal GLUT4 and microglial GLUT5 expression were
neither correlated with blood glucose levels or cell apop-
tosis. This does not rule out that glucose transporters
are involved in cell death process. For instance, it has
been experimentally shown that GLUT5 is implicated in
hyperglycaemia-related microglial cell death [13].
Furthermore, one may have expected that glucose trans-
porter expression would have been inversely proportion-
ate to blood glucose level [40,42,43]. Therefore, it is
conceivable that its absence of downregulation might
have increased intracellular glucose concentration and,
thereby, its toxicity. We acknowledge that absence of
correlation between microglial apoptosis and GLUT
expression does not rule out an alteration of GLUT
functioning, which in future studies could be indirectly
evaluated by measuring intracellular glucose load and
protein glycation. Additionally, it is biologically plausible
that hypoglycaemia potentially is far more harmful for
the brain than hyperglycaemia. It will be worthwhile to
assess the neuropathological correlates of hypoglycaemia
in patients who had died from septic shock. This would
require a greater proportion of patients who had devel-
oped hypoglycaemia than that observed in the present
study. It is interesting to note that iNOS has been
shown to decrease cerebral GLUT1 expression [44].
One may argue that the slight GLUT1 immunostaining
of neurons reflects a downregulation. Although expres-
sion of GLUT3 could not have been assessed for techni-
cal reasons, it has to be noted that alteration of GLUT3
cannot account for the relationship between hypergly-
caemia and apoptosis microglial cells as it is not
expressed by these cells.
The present study suggests a similar effect on micro-
glial GLUT5 expression. Other mechanisms could be
involved, especially perivascular edema that can compro-
mise substrate and oxygen delivery. Although we have
not specifically assessed this mechanism, it is established
that the BBB is altered in experimental sepsis but also
in septic shock patients [45].
Despite these limitations, our study suggests that
hyperglycaemia may contribute to the complex web of
abnormal signalling, which causes sepsis associated
brain dysfunction. Future studies should investigate the
mechanisms of hyperglycaemia related microglial apop-
tosis, particularly the impaired downregulation of
GLUT, and assess the neuropathological as well as neu-
rological effects of BG control by insulin therapy.
Conclusions
It appears likely that hemodynamic, inflammatory and
metabolic factors contribute to brain cell dysfunction
and death during septic shock, and may account for
sepsis associated brain dysfunction, which is associated
with increased mortality [46]. More research is needed
to understand the pathogenic significance of these fac-
tors and how they may be modulated to therapeutic
ends.
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Key messages
•In septic shock patients microglia is strongly
activated.
•Hemodynamic, inflammatory and metabolic factors
contribute to brain cell dysfunction and death during
septic shock.
•Hyperglycaemia is associated with microglial apop-
tosis while neuronal apoptosis is preferentially asso-
ciated with endothelial iNOS expression.
•Hyperglycaemia may contribute to the complex
web of abnormal signaling which causes sepsis asso-
ciated brain dysfunction.
Abbreviations
iNOS: inducible Nitric Oxide Synthase; AUBGC: area under the BG curve;
Beta-APP: amyloid precursor protein A4; BG: blood glucose; GLUT: glucose
transporter; IQR: interquartile range; ISEL: in-situ end labelling; LPS:
lipopolysaccharide; SAPS II: Simplified Acute Physiologic Score II; SOFA:
Sequential Organ Failure Assessment; TNF-α: tumor necrosis factor α.
Author details
1
General Intensive Care Medicine, Raymond Poincaré Hospital (AP-HP),
University of Versailles Saint Quentin en Yvelines, 104 bd R. Poincaré,
Garches 92210, France.
2
Department of Pathology, Lariboisière Hospital (AP-
HP), University Denis Diderot-Paris 7, 2 rue Ambroise Paré, Paris 75010,
France.
3
Departement of Biostatistic and Medical Informatics, Saint-Louis
Hospital (APHP), University Denis Diderot-Paris 7, 47-83, boulevard de
l’Hôpital, Paris 75010, France.
4
Department of Anesthesiology and Critical
Care Medicine, Johns Hopkins University School of Medicine, 600 North
Wolfe Street, Baltimore, MD 21287, USA.
5
Department of Pathology,
Raymond Poincaré Hospital (AP-HP), University of Versailles Saint Quentin en
Yvelines, 104 bd R. Poincaré, Garches 92210, France.
6
HISTO, Human
Histopathology and Animal Models; Institut Pasteur; Département Infection
et Epidémiologie, 25 rue du Dr Roux, 75015 Paris.
Authors’contributions
AP conceived the study, acquired data and wrote the manuscript. JPB
helped in interpretation of the data and in drafting the manuscript. RP
participated in the design of the study, performed the statistical analysis and
helped to draft the manuscript. RS helped to draft the manuscript. SS
helped in acquisition of data and revising the manuscript, while RDS also
helped to revise the manuscript. CG, FC, FG, DA and VM helped to draft the
manuscript. GLG helped in acquisition and interpretation of data. TS
conceived the study, participated in the design of the study and helped to
draft the manuscript. All the authors read and approved the final
manuscript.
Competing interests
The authors declare that they have no competing interests.
Received: 15 February 2011 Revised: 3 April 2011
Accepted: 25 May 2011 Published: 25 May 2011
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doi:10.1186/cc10244
Cite this article as: Polito et al.: Hyperglycaemia and apoptosis of
microglial cells in human septic shock. Critical Care 2011 15:R131.
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