Administration of Melatonin After Onset of Ischemia
Reduces the Volume of Cerebral Infarction in a Rat Middle
Cerebral Artery Occlusion Stroke Model
Zhong Pei, MBBS, MMed; Shiu Fun Pang, PhD; Raymond Tak Fai Cheung, MBBS, PhD
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Background and Purpose—In both permanent and transient 3-hour middle cerebral artery occlusion rat stroke models, a
single intraperitoneal injection of melatonin at 5 or 15 mg/kg given before ischemia was shown to reduce infarct volume
at 72 hours. The present study was conducted to examine the treatment time window when melatonin was commenced
after onset of ischemia.
Methods—Adult male Sprague-Dawley rats were anesthetized to undergo right-sided middle cerebral artery occlusion for
3 hours. A single intraperitoneal injection of vehicle or melatonin at 5 mg/kg was given at 0, 1, or 3 hours after onset
of ischemia. Other groups received multiple injections of vehicle or melatonin at 5 mg/kg with the first injection given
at 1, 2, or 3 hours after onset of ischemia and the second and third injections at 24 and 48 hours, respectively. Multiple
injections of melatonin at 15 mg/kg with the first injection given at 3 hours were also made. The infarct volume was
determined at 72 hours.
Results—A single dose of melatonin at 5 mg/kg given at 0 or 1 but not 3 hours after onset of ischemia reduced the infarct
volume. Multiple doses of melatonin at 5 mg/kg also reduced the infarct volume when the first dose was given at 1 or
2 but not 3 hours after onset. Significant hemodynamic effects were not observed.
Conclusions—Our results indicate that melatonin at 5 mg/kg given as a single injection or multiple injections protects
against focal cerebral ischemia when commenced within 2 hours of onset. (Stroke. 2003;34:770-775.)
Key Words: melatonin 䡲 middle cerebral artery occlusion 䡲 neuroprotection 䡲 stroke, experimental 䡲 rats
M
ost stroke patients are ineligible for recombinant tissue
plasminogen activator (rtPA),1–3 and the risk of hemorrhagic transformation becomes unacceptable if rtPA is
given to ineligible patients.3,4 Although remarkable insight
into the pathogenic mechanisms of ischemic brain damage
has been achieved in the last decade,5– 8 no cerebroprotective
agent is proven to be efficacious in controlled clinical trials.1
There is a need for safe and effective cerebroprotective agents
that will benefit all stroke patients. In addition, cerebroprotective treatment can potentially extend the therapeutic time
window and/or enhance the efficacy of rtPA.
Oxidative damage due to overproduction of reactive free
radicals plays a key role in the pathogenesis of ischemic brain
damage, and free radicals are generated during both ischemia
and reperfusion.5,7 Accumulating evidence suggests that oxidative damage does not occur in isolation but has complex
interactions with excitotoxicity, apoptosis, and inflammation.8 Pharmacological modification of oxidative damage
may protect against ischemia. Melatonin (N-acetyl-5methoxytryptamine) is a potent free radical scavenger as well
as indirect antioxidant.9 It is produced from L-tryptophan in a
limited number of mammalian organs such as the pineal
gland, retina, and gastrointestinal tract.9 Melatonin has been
shown to be protective in gastrointestinal, myocardial, and
cerebral models of ischemia/reperfusion injury when melatonin is given before ischemia10 –14 and/or repeated doses are
started before reperfusion.11–16
In both permanent and transient 3-hour middle cerebral
artery occlusion (MCAO) rat stroke models, a single intraperitoneal injection of melatonin at 5 or 15 mg/kg given at 30
minutes before MCAO significantly reduces infarct volume
at 72 hours.17,18 The present study was conducted to document the benefit of melatonin given after onset of ischemia
and to identify the therapeutic time window.
Materials and Methods
Animal Preparation
All experiments were conducted according to the institutional
guidelines with the protocol approved by the Committee on the Use
of Live Animals in Teaching and Research, the University of Hong
Kong. Adult male Sprague-Dawley rats, weighing between 280 and
360 g, were purchased from the Laboratory Animal Unit, the
University of Hong Kong. The rats were maintained under a diurnal
Received March 1, 2002; final revision received August 23, 2002; accepted September 23, 2002.
From the Division of Neurology, Department of Medicine (Z.P., R.T.F.C.), and Department of Physiology (S.F.P.), Faculty of Medicine, University
of Hong Kong, Pokfulam, Hong Kong.
Reprint requests to Dr Raymond T.F. Cheung, Division of Neurology, University Department of Medicine, Queen Mary Hospital, Pokfulam, Hong
Kong. E-mail [email protected]
© 2003 American Heart Association, Inc.
Stroke is available at http://www.strokeaha.org
DOI: 10.1161/01.STR.0000057460.14810.3E
770
Pei et al
Melatonin Treatment Protects Against Experimental Stroke
lighting condition (12 hours of light beginning at 6 AM) with free
access to food and water for a minimum of 4 days before
experimentation.
Experiments were performed during the light period. Rats were
anesthetized with an intraperitoneal injection of sodium pentobarbital (Rhone Merieux, Pinkenba) at a dose of 60 mg/kg. Most rats
required an additional bolus of 20 mg/kg to ensure stable anesthesia.
Rectal temperature was monitored continuously and maintained
between 36.5°C and 37.5°C throughout the anesthesia via a
feedback-regulated heating pad (FHC) placed underneath the rat.
The right femoral artery was cannulated with PE-50 polyethylene
tubing for monitoring of arterial blood pressure (BP) and heart rate
(HR) (Powerlab/16 Data Acquisition System, AD Instruments Pty
Ltd). These parameters were monitored continuously before and
during the 3-hour MCAO as well as in the first 30 minutes of
reperfusion.
Monitoring of Regional Cerebral Perfusion
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Regional cerebral perfusion was monitored with a laser-Doppler
flowmeter (MBF3D, Moor Instruments Ltd). With the help of a
stereotaxic device (SR-6N, Narishige Scientific Instrument Laboratory) and a low-speed dental drill, a burr hole of 2 mm in diameter
was made over the skull at 2 mm posterior and 5 mm lateral to the
bregma on the right side. A needle-shaped laser probe was placed on
the dura away from visible cerebral vessels. Steady state baseline
values were recorded before MCAO. The regional cerebral perfusion
was monitored continuously during focal ischemia until the first 30
minutes of reperfusion. Data on regional cerebral perfusion were
normalized and expressed as percentages of the respective baseline
values.
Experimental Protocols
This study consisted of 2 parts with melatonin or its vehicle given
either as a single injection or multiple intraperitoneal injections in
different groups of rats. In the first part of this study, a single dose
of melatonin at 5 mg/kg was injected at the onset, 1 hour, or 3 hours
of focal cerebral ischemia. A control group of rats received an
intraperitoneal injection of vehicle at the onset of MCAO. In the
second part of this study, 3 doses of melatonin at 5 mg/kg or vehicle
were administered in which the first injection was made at 1, 2, or 3
hours of MCAO and the second and third injections at 24 and 48
hours, respectively. Some rats received 3 doses of melatonin at 15
mg/kg given at 3, 24, and 48 hours of ischemia. Melatonin (Sigma
Chemical) was dissolved in 1 mL of normal saline containing 5% of
dimethyl sulfoxide (Sigma Chemical). Normal saline containing 5%
of dimethyl sulfoxide was the vehicle.
Transient Focal Cerebral Ischemia With Reperfusion
The rats were subjected to transient focal cerebral ischemia for 3
hours with reperfusion for 69 hours with the use of the endovascular
MCAO method.19 Briefly, the right carotid arteries were exposed
through a midline cervical incision. The right external carotid artery
was dissected free and isolated distally by coagulating its branches
(Bipolar Electric Coagulation, GN60, Aesculap AG & Co) as well as
placing a distal ligation before transection. A piece of 4-0 monofilament nylon suture (Ethicon, Johnson & Johnson), with its tip
rounded by gentle heating, was introduced via the lumen of right
external and internal carotid arteries to embed into the right anterior
cerebral artery so that the right middle cerebral artery (MCA) was
occluded. Three hours after focal ischemia, the intraluminal suture
was withdrawn from the right anterior cerebral artery and right
internal carotid artery to permit reperfusion. Achievement of focal
ischemia and reperfusion was confirmed by appropriate changes in
the regional cerebral perfusion. Wounds were closed with surgical
clips. Finally, the rats were allowed to recover from the anesthesia
before returning to their cages with free access to food and water.
Determination of Infarct Volume
Seventy-two hours after onset of ischemia, the rats were deeply
reanesthetized with sodium pentobarbital at a dose of 100 mg/kg.
771
Their brains were collected after decapitation. Brains were cut into
2-mm-thick coronal slices with a rodent brain matrix. Extent of
ischemic infarction was revealed by reaction with a 2% solution of
2,3,5-triphenyltetrazolium chloride (TTC; Sigma Chemical) for 20 to
30 minutes. After TTC reaction, the brain slices were fixed in 10%
formalin at pH 7.4. The hemispheric volumes and volume of
infarction between the bregma levels of ⫹4 (anterior) and ⫺6 mm
(posterior) were integrated from the respective calibrated area
measurements20 made on the digitalized images of the TTC-reacted
brain slices with a computer-assisted image analysis system (SigmaScan Pro 4.0, SPSS Inc). To correct for swelling due to cerebral
edema, the infarct volume was normalized and expressed as a percentage of the ipsilateral hemispheric volume. A cerebral edema index was
generated from the ratio of the right to left hemispheric volume.21,22
Statistical Analysis
There was no significant difference in the hemodynamic parameters
and brain infarct volume between the control groups injected with
vehicle at 30 minutes before or at the onset of MCAO. Thus, results
of the control group (n⫽6) receiving an intraperitoneal injection at
the onset of MCAO were combined with those of a previous control
group (n⫽14) in which an intraperitoneal injection was made at 30
minutes before 3-hour MCAO.18 Data on regional cerebral perfusion
were available from 5 rats of the previous control group. The data
were analyzed with SPSS (Windows version 10.0) with the general
linear model for univariate or repeated-measures 1-way or 2-way
ANOVA because of the unequal number of rats in each group. For
the groups receiving a single injection, the relative infarct volume
and cerebral edema index were compared with univariate 1-way
ANOVA, and the mean BP, HR, and normalized regional cerebral
perfusion data were compared with repeated-measures 1-way
ANOVA. The Dunnett post test was used to reveal any significant
difference between any of the melatonin-treated groups and the
combined vehicle-treated control group. For the groups receiving
multiple injections at 1, 2, or 3 hours (including the groups treated
with melatonin at 5 or 15 mg/kg) of ischemia, the relative infarct
volume and cerebral edema index were compared with univariate
2-way ANOVA, and the mean BP, HR, and normalized regional
cerebral perfusion data were compared with repeated-measures
2-way ANOVA. Additional comparisons were made for generating
hypotheses only; Student’s t test was applied to reveal any significant
difference in the relative infarct volume between each of the
melatonin-treated groups and the respective vehicle-treated control
group of part 2 of this study as well as between single and multiple
injections of melatonin at 5 mg/kg with the first injection made at 1
or 3 hours of ischemia, and univariate 1-way ANOVA with the
Dunnett post test was used to reveal any difference in the relative
infarct volume among 0 (ie, vehicle only), 5, and 15 mg/kg of
melatonin in the groups receiving multiple injections, with the first
injection made at 3 hours of ischemia. A 2-tailed probability value of
ⱕ0.05 was taken to indicate statistical significance.
Results
Groups With Single Injection
Table 1 summarizes the relative infarct volume and cerebral
edema index after 3 hours of focal ischemia and 69 hours of
reperfusion plus single or multiple injections of melatonin or
its vehicle. Compared with the relative infarct volume of
32.7⫾2.7% in the combined control group, a single intraperitoneal injection of melatonin at 5 mg/kg at 0, 1, or 3 hours of
ischemia reduced the relative infarct volume by 37.6%,
38.8%, and 17.4%, respectively (P⬍0.05 with a significant
difference between the melatonin-treated groups at 0 or 1
hour of ischemia and the combined control group). There was
no significant difference in the cerebral edema index (Table 1).
There was no significant difference in the mean BP (data not
shown), HR (data not shown), or normalized regional cere-
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March 2003
TABLE 1.
Relative Infarct Volume (%) and Cerebral Edema Index
Single IP Injection
0 h of Ischemia
1 h of Ischemia
3 h of Ischemia
Vehicle only
32.7⫾2.7% (20)
䡠䡠䡠
䡠䡠䡠
1.073⫾0.025
Melatonin
20.4⫾3.6%* (8)
20.0⫾2.8%* (9)
1.014⫾0.014
1.042⫾0.010
27.0⫾5.3% (9)
1.042⫾0.009
Multiple IP Injections 1, 24, 48 h of Ischemia 2, 24, 48 h of Ischemia 3, 24, 48 h of Ischemia
Vehicle only
30.4⫾7.4% (6)
31.3⫾5.6% (8)
1.050⫾0.032
Melatonin
1.070⫾0.019
13.8⫾3.4%† (8)
1.033⫾0.007
13.4⫾1.5%† (9)
1.023⫾0.007
31.2⫾5.4% (10)
1.042⫾0.013
24.1⫾3.1%‡ (14)
1.072⫾0.016
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Relative infarct volume (%) and cerebral edema index in different groups of rats following the
middle cerebral artery occlusion (MCAO) for 180 minutes plus a single intraperitoneal (IP) injection of
vehicle given at 0.5 hours before or at the onset of ischemia or of melatonin given at 0, 1, or 3 hours
of ischemia or plus multiple IP injection of vehicle or melatonin with the first dose given at 1, 2, or
3 hours of ischemia in the rat. Data are expressed in mean⫾SEM. Number of rats in each group is
indicated inside parentheses.
*Significant difference among the groups with Dunnett’s post test showing significant difference
between the vehicle-treated group and these melatonin-treated groups.
†Significant treatment effect due to melatonin but no effect due to the different timing of injections
with Student’s t test showing possible difference between the vehicle-treated groups and the
respective melatonin-treated groups.
‡This includes 8 rats receiving 3 injections of melatonin at 5 mg/kg (23.3⫾4.8%) and 6 rats given
melatonin at 15 mg/kg (25.2⫾5.9%).
bral perfusion (Table 2) among the different groups. In
addition, the normalized regional cerebral perfusion
(P⬍0.001) but not the mean BP or HR showed significant
change at different time points; the mean regional cerebral
perfusion was suppressed to ⬍30% during MCAO and
rapidly restored on reperfusion (Table 2).
Groups With Multiple Injections
Compared with the respective relative infarct volume of
30.4⫾7.4%, 31.3⫾5.6%, and 31.2⫾5.4% in the vehicle groups
when the first injection was made at 1, 2, and 3 hours,
TABLE 2.
respectively (Table 1), multiple intraperitoneal injections
of melatonin with the first injection given at 1, 2, or 3
hours of ischemia reduced the relative infarct volume by
54.5%, 42.9%, and 22.7%, respectively (P⬍0.001 for
treatment with melatonin and P⫽0.362 for timing of
injections). There was no significant difference in the
cerebral edema index (Table 1).
There was no significant difference in the mean BP (data
not shown), HR (data not shown), or normalized regional
cerebral perfusion (Table 2) among the different groups. In
addition, the normalized regional cerebral perfusion
Normalized Regional Cerebral Perfusion (%)
Group (No. of Rats)
Before
MCAO
5 min of
MCAO
60 min of
MCAO
120 min of
MCAO
5 min of
Reperfusion
Vehicle at ⫺0.5 or 0 h (11)
100.0
29.3⫾5.3
28.3⫾3.8
28.3⫾3.6
113.2⫾12.8
Melatonin at 0 h (8)
100.0
22.8⫾2.9
25.2⫾3.5
21.8⫾2.9
101.4⫾11.3
Melatonin at 1 h (9)
100.0
29.9⫾2.4
30.1⫾4.0
29.9⫾5.6
89.7⫾13.3
Melatonin at 3 h (9)
100.0
26.9⫾2.9
24.1⫾2.8
26.8⫾2.9
86.1⫾19.4
Vehicle at 1, 24, 48 h (6)
100.0
26.3⫾4.9
22.5⫾4.8
22.7⫾5.1
90.4⫾10.3
Melatonin at 1, 24, 48 h (8)
100.0
21.9⫾5.2
19.6⫾3.5
21.3⫾2.9
81.9⫾13.5
Vehicle at 2, 24, 48 h (8)
100.0
23.2⫾4.6
22.9⫾6.1
21.1⫾5.2
81.6⫾10.7
Melatonin at 2, 24, 48 h (9)
100.0
24.7⫾2.9
26.9⫾2.9
17.8⫾2.6
78.3⫾10.7
Vehicle at 3, 24, 48 h (10)
100.0
26.9⫾5.2
14.7⫾2.9
17.6⫾2.8
84.2⫾8.5
Melatonin at 3, 24, 48 h (14)*
100.0
23.5⫾2.6
20.0⫾2.3
17.1⫾2.1
83.3⫾9.6
Normalized regional cerebral perfusion (%) at time points in different groups of rats in relation to the middle
cerebral artery occlusion (MCAO) for 180 minutes plus a single intraperitoneal (IP) injection of vehicle given at 0.5
hours before or at the onset of ischemia or of melatonin given at 0, 1, or 3 hours of ischemia or plus multiple IP
injection of vehicle or melatonin with the first dose given at 1, 2, or 3 hours of ischemia in the rat. Data are expressed
in mean⫾SEM.
*Each dose of melatonin is at 5 mg/kg except in this group: 6 rats received 3 doses of melatonin at 15 mg/kg.
Pei et al
Melatonin Treatment Protects Against Experimental Stroke
(P⬍0.001) but not the mean BP or HR showed significant
change at different time points; the mean regional cerebral
perfusion was suppressed to ⬍30% during MCAO and
rapidly restored on reperfusion (Table 2).
Hypotheses-Generating Additional Comparisons
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Student’s t tests comparing the relative infarct volume between each of the melatonin-treated groups and corresponding vehicle-treated groups of part 2 of this study (Table 1)
revealed the following probability values: 0.045, 0.005, and
0.265 with the first injection given at 1, 2, and 3 hours,
respectively. Three groups of rats received multiple injections
with the first one given at 3 hours of ischemia: vehicle,
melatonin at 5 mg/kg, and melatonin at 15 mg/kg (Table 1);
the difference in infarct volume was not significant. Two
groups of rats received an injection of melatonin at 5 mg/kg
at 1 hour of ischemia; 1 had 1 injection, and another had 3
injections (Table 1); the difference in infarct volume was not
significant. In addition, 2 groups of rats received an injection
of melatonin at 5 mg/kg at 3 hours of ischemia; there was no
significant difference in the infarct volume.
Discussion
The main findings of the present study are that (1) a single
dose of melatonin at 5 mg/kg given at 0 or 1 but not 3 hours
of ischemia significantly reduces infarct volume at 72 hours
by approximately 40%; (2) multiple doses of melatonin at 5
mg/kg started after onset of ischemia significantly reduce the
infarct volume by approximately 40%, and this benefit seems
to disappear when the first dose is commenced at 3 hours of
ischemia; (3) there may not be any additional benefit from
giving the second and third doses of melatonin at 24 and 48
hours of ischemia; (4) treatment with melatonin does not
significantly affect the cerebral edema index; and (5) treatment with melatonin does not produce significant hemodynamic effects during ischemia and the first 30 minutes of
reperfusion.
In primary cultures, melatonin as a cotreatment was shown
to protect rat cerebellar granule neurons against excitotoxicity
due to kainate but not N-methyl-D-aspartate.23 Nevertheless,
melatonin did not affect binding of glutamate to rat cerebellar
membranes or kainate-stimulated inward currents or rise in
free cytosolic calcium. Subsequently, 4 intraperitoneal injections of melatonin at 2.5 mg/kg, with the first injection made
at 20 minutes before an intraperitoneal injection of kainate
and other injections at 0, 1, and 2 hours after the injection of
kainate, was found to ameliorate the kainate-induced neuronal death and apoptosis in the hippocampus, amygdala, and
pyriform cortex as well as behavioral and biochemical disturbances in rats.24,25 Melatonin protects against kainateinduced excitotoxicity because of its direct and indirect
antioxidant effects.26
When melatonin deficiency was induced in rats by pinealectomy, melatonin-deficient rats were more susceptible to
kainate-induced excitotoxicity (with rats killed at 72 hours),
photothrombotic brain injury (with rats killed at 24 hours), or
focal ischemia (with rats killed at 4 or 6 hours) due to
microsurgical clipping of both common carotid arteries and 1
MCA for 1 hour.27 In a follow-up study on the effects of
773
pinealectomy and melatonin in the 3-vessel occlusion model
of focal ischemia for 90 minutes, the extent of DNA damage
and infarct volume at 6 or 24 hours after focal ischemia was
increased in pinealectomized rats, and these effects of pinealectomy were reversed by 4 intraperitoneal doses of melatonin at 2.5 mg/kg (given at 30 minutes before as well as at 0,
1, and 2 hours after focal ischemia).28 The opposing effects of
pinealectomy and melatonin on brain damage at 24 hours of
ischemia in rats were confirmed in another study in which
hemodynamic factors were also monitored and focal ischemia
was induced by endovascular MCAO for 2 hours.12 In
addition, melatonin at 4 mg/kg given before ischemia and
reperfusion was shown to reduce infarct volume by 40% in
both pinealectomized and sham-pinealectomized rats, suggesting a neuroprotective action of exogenous melatonin.12
Three intraperitoneal injections of melatonin at 10 mg/kg
in rats protected CA1 hippocampal neurons against forebrain
ischemia for 10, 20, or 30 minutes only when the first
injection was made immediately at reperfusion but not at 30
minutes before or 1 hour after reperfusion; the second and
third injections were made at 2 and 6 hours of reperfusion.29
An intraperitoneal injection of melatonin at 10 mg/kg given at
30 minutes before ischemia was found to inhibit brain nitric
oxide (NO) production and suppress NO synthase in a
10-minute gerbil model of forebrain ischemia and reperfusion.30 In another study, 4 intraperitoneal injections of melatonin at 10 mg/kg (given at 30 minutes before as well as 1, 2,
and 6 hours after reperfusion) were shown to reduce NO
levels in the plasma at 4 hours, lipid peroxidation in the brain
at 1 hour, cerebral edema at 48 hours, and CA1 neuronal loss
at 96 hours after reperfusion in a 5-minute gerbil model of
forebrain ischemia.14
Taken together, previous studies have shown the neuroprotective effects of exogenous melatonin in kainate-induced
excitotoxicity in rats, focal cerebral ischemia in pinealectomized rats, and forebrain ischemia in rats and gerbils only
when melatonin was given as multiple doses with the first one
as a pretreatment or cotreatment. Two recent studies show
that pretreatment with a single intraperitoneal injection of
melatonin at doses between 5 and 15 mg/kg significantly
reduces the infarct volume at 72 hours by approximately 40%
without affecting the mean BP, HR, and regional cerebral
perfusion in both permanent and 3-hour transient MCAO
stroke models in rats.17,18 Compared with these studies,17,18
commencement of single melatonin injection at 1 hour or less
after onset of ischemia produces a similar reduction in infarct
volume. Addition of the second and third doses at 24 and 48
hours of ischemia may not achieve a larger reduction in
infarct volume or an extension of the treatment time window
beyond 2 hours of ischemia. Increasing the individual dose of
melatonin from 5 to 15 mg/kg may not extend the treatment
time window to 3 hours of ischemia. The relatively short time
window of ⬍3 hours for both single and multiple injections
as well as the absence of significant effects on cerebral edema
and hemodynamic parameters suggests that melatonin mediates its cerebroprotective actions against the early pathophysiological events of severe focal ischemia. On the other hand,
the treatment regimen can be as simple as a single dose given
within 2 hours of ischemia.
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Melatonin probably ameliorates oxidative damage of reactive free radicals generated during both ischemia and reperfusion.31 In addition to being a direct free radical scavenger
and an indirect antioxidant,9,31,32 melatonin may help to
preserve mitochondrial function during ischemia and reperfusion. Mitochondrial dysfunction is an important mediator of
ischemic cell death.33 When mitochondria generate ATP
through the mitochondrial respiratory chain, reactive oxygen
species are produced by complex I and complex III.34 When
mitochondrial respiration is disturbed during ischemia, ATP
synthesis is impaired, and excessive generation of reactive
oxygen species occurs.34 Melatonin preserves mitochondrial
function by improving the electron transport chain, ameliorating mitochondrial oxidative stress, maintaining ATP production, and restoring glutathione levels.35
Melatonin possesses anti-inflammatory effects via indirect
inhibition of NO synthase, suppressed induction of inducible
NO synthase and cyclooxygenase-2, and inhibition of neutrophil infiltration,36 –38 but the present results do not support
an important role of its anti-inflammatory effects in protection against focal ischemia because inflammation is important
in the delayed evolution of ischemic infarction.39 – 41
Melatonin is a lipid soluble molecule and a relatively safe
drug with excellent oral absorption and tissue bioavailability.
It is hypothesized that melatonin can be used in stroke
patients to alleviate the ischemic lesion. The possibility of
high-risk patients, who are willing to keep melatonin pills or
patches, being treated immediately with melatonin after any
signs of stroke should be considered. A reduction of the
infarct volume in stroke patients would lessen the brain
damage and facilitate recovery after appropriate hospital care.
Moreover, melatonin may be used in combination with other
cerebroprotectants or with rtPA to improve the treatment
effects as well as extend the treatment time window of rtPA.
For example, melatonin can be offered as a prehospital
treatment in combination with other strategies. Melatonin
may be an important cerebroprotective agent against ischemic
and reperfusion injury because of its excellent diffusion in
brain tissue after either systemic injection or oral administration and lack of toxic effects in animals and humans.9,42,43
Both rtPA and melatonin have a short treatment time window,
but the treatment with melatonin is very simple and
convenient.
In conclusion, melatonin as single or multiple intraperitoneal injections of 5 mg/kg given as late as 2 hours after
ischemia significantly reduces infarct volume without affecting cerebral edema and hemodynamic parameters. It appears
that a single dose of melatonin at 5 mg/kg given as late as 2
hours after ischemia is sufficient and that subsequent dosing
or higher doses of melatonin may be unnecessary. In vitro
studies using neuronal cell culture are useful in unraveling the
cerebroprotective mechanisms of melatonin in focal cerebral
ischemia. Further studies should also be conducted to explore
the benefit of combining melatonin with other cerebroprotectants or rtPA.
Acknowledgment
This study was supported by a grant (10203847) from the Committee
of Research and Conference Grants, University of Hong Kong.
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Infarction in a Rat Middle Cerebral Artery Occlusion Stroke Model
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Stroke. 2003;34:770-775; originally published online February 6, 2003;
doi: 10.1161/01.STR.0000057460.14810.3E
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