Indian Journal of Biochemistry & Biophysics
Vol. 52, February 2015, pp. 29-33
Serum neuron-specific enolase and S-100β levels as prognostic follow-up markers
for oxygen administered carbon monoxide intoxication cases
Ali Osman Yildirim1, Murat Eroglu1, Umit Kaldirim2, Yusuf Emrah Eyi2, Kemal Simsek3*, Murat Durusu2, Levent
Yamanel2, Ibrahim Arziman2, Salim Kemal Tuncer2, Mehmet Toygar4, Arzu Balkan5, Tuncer Cayci6, Seref Demirbas7,
Sukru Oter8 and Cumhur Bilgi6
1
Department of Emergency Medicine, Gulhane Haydarpasa Training Hospital, Istanbul, Turkey
Departments of 2Emergency Medicine, 3Undersea & Hyperbaric Medicine, 4Forensic Medicine, 5Pulmonary Medicine,
6
Biochemistry, 7Internal Medicine, and 8Physiology, Gulhane Military Medical Academy, Ankara, Turkey
Received 01 May 2014 ; revised 21 December 2014
Serum neuron-specific enolase (NSE) and S-100β levels are considered novel biochemical markers of neuronal cell
injury. In this study, the initial and post-treatment levels of NSE and S-100β were compared in carbon monoxide (CO)
poisoning patients, who received normorbaric oxygen (NBO) or hyperbaric oxygen (HBO) therapy. Forty consecutive
patients with acute CO poisoning were enrolled in this prospective, observational study. According to their clinical
symptoms and observations, twenty patients were treated with NBO, and the other twenty with HBO. Serum S-100β and
NSE levels were measured both at time of admission and 6 h later (post-treatment). Serum NSE and S-100β values
decreased significantly in both of the therapeutic modalities. The initial and post-treatment values of NSE and S-100β in
NBO or HBO patients were comparable. A clear negative correlation was observed between the decrease of NSE and
S-100β levels and initial blood carboxyhemoglobin levels. In conclusion, the present results suggested the use of serum
S-100β and NSE levels as indicators for brain injury. Due to the significant increase of their values with oxygen therapy,
they may also be useful as prognostic follow-up markers. However, the current findings reflected no difference between the
efficacy of NBO or HBO therapy.
Keywords: Brain injury, Carbon monoxide poisoning, Hyperbaric oxygen, Neuron-specific enolase, Oxygen therapy, S-100β
Carbon monoxide (CO) is an agent that can cause
intoxication, mortality and morbidity worldwide1. CO
poisoning is responsible for 40,000 emergency
department visits each year in the USA; 600 are
attributable to unintentional causes and five to
ten-times to suicidal thoughts2-4. CO intoxication
accounts for approx. 31% of deaths, resulting from
poisoning4. Similarly, a study conducted in Turkey
has revealed that 15.7% of all forensic autopsies have
been performed due to asphyxial death, of which
8.2% are caused by CO poisoning5. The central
nervous system (CNS) is the most vulnerable region
_____________
*Corresponding author
Present address:
Gulhane Askeri Tip Akademisi
Sualti ve Hiperbarik Tip Anabilim Dali
06010 Etlik, Ankara, Turkey
E-mail: [email protected]
Phone: +90 312 3044797/3046132
GSM: +90 532 2834061
Abbreviations: CNS, central nervous system; HbCO,
carboxyhemoglobin; HBO, hyperbaric oxygen; NBO, normobaric
oxygen; NSE, neuron-specific enolase.
to CO inhalation6. Nonetheless, CO poisoning leads
also to early and permanent injuries in brain, heart,
muscle and kidney that also require high and constant
oxygen supplement function properly. Some of the
patients surviving after serious CO poisoning can stay
asymptomatic, while 67% of them experience
neurologic sequelae7-9.
The management of patients with CO poisoning
includes supportive and symptomatic treatments and
administration of supplemental oxygen. Although
hyperbaric oxygen (HBO) treatment may be useful to
prevent long-term neurologic sequelae in selected
patients, however, there is no biochemical marker
available which can be used to decide the usage of
HBO, instead of normobaric oxygen (NBO) treatment
in CO poisoning10. In fact, there is requirement for
prognostic biochemical markers in the evaluation and
management of patients with CO intoxication.
S-100β is a calcium-binding protein which is
produced and released by astroglial cells in the
CNS11. It exerts neuro- and gliotrophic effects and
may have an important role in the development and
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INDIAN J. BIOCHEM. BIOPHYS., VOL. 52, FEBRUARY 2015
recovery of CNS after injury12. It has been shown that
S-100β may be a useful biochemical marker of brain
damage in cardiac arrest, stroke, traumatic head injury
and subarachnoid hemorrhage13-16. Neuron-specific
enolase (NSE) is a glycolytic enzyme localized in
neuronal cytoplasm, which is not secreted
physiologically; its elevated level in serum and
cerebrospinal fluid can be associated with structural
damage to neuronal cells, indicating a traumatic brain
injury, cardiac arrest or Parkinson’s disease12,13,17.
In the medical literature, only few clinical studies
are available on the possible association of serum
NSE and S-100β levels with CO poisoning-dependent
brain injuries10,18,19. In the present study, we have
aimed to investigate the relationship between NSE
and S-100β with regard to carboxyhemoglobin
(HbCO) levels and the clinical outcome of CO
intoxication patients. In addition, the follow-up values
for NSE and/or S-100β have been compared in the two
different therapeutic modalities, i.e. HBO and NBO.
Materials and Methods
Patients
A total of 40 CO poisoning cases admitted to the
emergency service of the Gulhane Military Medical
Academy Hospital, Ankara, Turkey over a period of
4 months were included in the study. In relation to the
cause of intoxication, duration of exposure, symptoms
and findings at admission, the estimated Glasgow
coma scale20 (GCS) and blood HbCO levels. Twenty
of these patients (12 male, 8 female; mean age
33.95 ± 16.83) were treated with NBO and the other
20 (11 male, 9 female; mean age 37.05 ± 12.78) were
administered HBO. The selection for NBO or HBO
treatment was assessed according to universally
accepted guidelines21 as shown in Table 1. All
patients enrolled in the study gave their consent for
the usage of their data. The study was performed in
accordance with the ethical standards laid down in the
1964 Declaration of Helsinki and with the approval of
the Institutional Ethical Committee.
Therapeutic interventions
All cases were treated with pure oxygen via a nonrebreather face-mask. NBO was administered at a flow
rate of 15 l/min throughout the therapy period with
5-min air break intervals after every 25 min of oxygen
breathing. The HBO pressure/duration range was set as
2.4 atm/90 min during which the patients breathe
pure oxygen with the same scheme of NBO patients;
after HBO exposure, the patients continued receiving
NBO until end of the treatment procedure (6 h).
Biochemical measurements
Blood samples were collected from the patients
twice; at the time of arrival in the emergency service
and at 6 h later (after therapeutic approach). Serum
NSE and S-100β values were estimated along with the
routine hematologic parameters, such as blood cell
count, hematocrit and hemoglobin. Enzyme-linked
immunoassay (ELİSA) was used for S-100β and NSE
measurements.
Statistical analysis
Data analysis was performed with the Statistical
Package for the Social Sciences (SPSS version 15.0)
software. The mean plus standard deviation and
median values were used for data defining. Normality
analysis for data distribution was done by the
Kolmogorov-Smirnov test; since the test reflected
non-normal distribution, non-parametric tests were
used. The Mann-Whitney U test was used for
group-to-group comparisons of the same parameter,
while the Wilcoxon test was used for comparing
continuous variables within the same group and the
Chi-square test was used to compare discrete
variables. In addition, the possible relation between
variables was evaluated by using the Pearson's
correlation test. P levels less than 0.05 were
considered statistically significant.
Results
The baseline symptoms and their values in
selection of patients to HBO or NBO therapies are
presented in Table 1. In brief, demographic
characteristics, such as age and gender were similar
between the two groups. As expected, headache and
syncope were significantly more in the HBO
treatment group (P = 0.006 for both). Although
statistically insignificant, dizziness was also more
often observed in the HBO patients. The patients who
received HBO treatment showed a relative longer
exposure time to CO and their Glasgow coma scale
was also slightly lower than the NBO patients
(not significant).
Table 2 represents the HbCO, NSE and S-100β
levels at time of arrival and 6 h post-treatment. The
patients of HBO group had significantly higher mean
blood HbCO levels (P = 0.017, HBO vs NBO group);
the HbCO levels of both HBO and NBO groups were
diminished after the therapy (P < 0.001 and P = 0.008
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YILDIRIM et al.: SERUM NSE AND S-100β LEVELS AS PROGNOSTIC FOLLOW-UP MARKERS
respectively, compared with levels at arrival). The
serum NSE and S-100β levels were found to be
slightly (but not significant) higher in the HBO
treated patients. At 6 h after treatment, both NSE and
S-100β values were significantly lowered in HBO and
NBO groups (HBO group, P = 0.002 for NSE and
P = 0.018 for S-100β; NBO group, P = 0.004 for NSE
and P = 0.001 for S-100β). There were no differences
for the post-treatment values of these markers
between HBO and NBO patients. A negative
moderate (r = –0.324) and statistically significant
(P = 0.008) correlation was found between blood
HbCO values at arrival and serum NSE level (Fig. 1).
Similarly, a negative moderate (r = –0.398) and
significant (P = 0.032) correlation was observed
among HbCO and S-100β levels (Fig. 2).
Table 1—Basic demographic data of cases and selection criteria for the therapeutic modality
HBO
Age (Mean ± SD)
Gender (Male/Female)
Headache (n) (%)
Syncope (n) (%)
Dizziness (n) (%)
Exposure time (Mean ± SD) (Median)
Glasgow coma scale (Mean ± SD) (Median)
NBO
37.05 ± 12.78
11/9
17 (89)
9 (52.9)
11 (57.9)
4.34 ± 5.18 (1)
13.93 ± 2.12 (15)
33.95 ± 16.83
12/8
8 (47.1)
2 (10.5)
6 (33.3)
4.22 ± 2.5 (4)
14.95 ± 0.23 (15)
P
0.285*
0.749*
0.006**
0.006**
0.175**
0.336*
0.067*
*Mann-Whitney U test; **Chi-square test
Table 2—Carboxyhemoglobin (HbCO), neuron-specific enolase and S-100β levels at time of arrival and 6 h post-treatment
HBO
HbCO (Mean ± SD) (Median)
P**
NSE (Mean ± SD) (Median)
P**
S100β (Mean ± SD) (Median)
First
Control
First
Control
First
Control
P**
*Mann-Whitney U test; **Wilcoxon test
NBO
29.6 ± 10.2 (30.9)
4.4 ± 3 .6 (3.6)
< 0.001
6.82 ± 5.84 (5.14)
3.69 ± 2.21 (2.9)
0.002
4.57 ± 3.07 (2)
2.12 ± 1.31 (2.42)
0.018
Fig. 1–Relation between blood HbCO values and difference
between serum NSE levels at admission and 6 h post-treatment
(Chi-square test; r = –0.324, r2 = 0.105, P = 0.008)
21.7 ± 8.6 (20.95)
3.6 ± 2.03 (2.95)
0.008
5.51 ± 4.64 (4.27)
3.27 ± 2.17 (2.75)
0.004
3.61 ± 1.63 (3)
2.54 ± 1.57 (2.42)
0.001
P*
0.017
0.982
0.31
0.425
0.461
0.545
Fig. 2–Relation between blood HbCO values and difference
between serum S-100β levels at admission and 6 h post-treatment
(Chi-square test; r = –0.398, r2 = 0.159, P = 0.032)
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INDIAN J. BIOCHEM. BIOPHYS., VOL. 52, FEBRUARY 2015
Discussion
Oxygen therapy is the cornerstone for the
management of CO intoxication; in selected cases,
the use of HBO is also considered22-24. One of the
main targets affected by CO poisoning is the central
nervous system (CNS). HBO therapy is
recommended to the patients presenting with
syncope, coma, seizures, focal neurologic deficits,
and patients having a HbCO level higher than 25%
(or 15% for pregnant women)8,21. The majority of the
HBO therapy suggested symptoms, such as
headache, dizziness or syncope are clinical
presentations caused by the brain. Thus, biochemical
markers demonstrating the brain damage can provide
additional evidence in determining neurological
response and can guide for HBO therapy in patient
selection25.
In literature, only a limited number of studies are
available comparing NSE and S-100β and their
levels in CO poisoning. In an experimental CO
poisoning model, Brvar et al26 have reported that
serum S-100β levels are significantly increased after
exposure and that this difference is particularly more
pronounced in patients with loss of consciousness.
Another study of the same group has suggested that
S-100β may be a compatible marker for the brain
injury in CO poisoning18. By comparing S-100β and
NSE levels in 70 CO poisoning cases and 20 control
individuals, Yardan et al10 have reported
significantly increased S-100β levels in CO
intoxication cases; the significant rise of S-100β
levels10 is found to be significantly higher in patients
with loss of consciousness, similar to the report of
Brvar et al26. On the other hand, NSE levels are
increased and a positive correlation has been found
between S-100β and NSE levels10. In another study,
where NSE and S-100β levels have been compared
at 0, 3 and 6 h in 30 CO poisoning cases, a marked
decrease of their levels is reported with oxygen
treatment; the decrease rate is more pronounced in
S-100β levels19.
The significantly decreased levels of serum S-100β
and NSE compared to their initial values in the
present study was in line with the previous findings of
other groups. Both HBO and NBO therapies resulted
in lowering HbCO rates, as well as S-100β and NSE
levels; however, the present findings could not
provide an advantage of one therapy modality to the
other. Since the values of NSE and S-100β at
admission were comparable, using these biomarkers
to make a decision between HBO and NBO therapies
could not be confirmed.
In conclusion, the present results provided
evidence for the usefulness of serum S-100β and NSE
levels as indicators for brain injury in CO poisoning.
These markers could also be used as follow-up
parameters during the therapeutic process, i.e. lower
their values, the better the clinical outcome. But, they
seemed unable to provide information regarding the
decision for using NBO or HBO therapy in CO
intoxication cases. However, due to the relative low
number of patients in the present work, further
large-scale studies are needed to confirm the possible
benefits of S-100β and NSE as prognostic markers for
CO poisoning.
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