(Stroke. 1997;28:708-710.)
© 1997 American Heart Association, Inc.
Articles |
Duration of Glutamate Release After Acute Ischemic Stroke
From the Section of Neurology, Hospital Universitari Doctor Josep Trueta, Girona (A.D., J.S.), and Department of Neurology, Hospital General de Galicia, Clínico Universitario, Santiago de Compostela (J.C., M.N.), Spain.
Correspondence to Antoni Dávalos, MD, Section of Neurology, Hospital Universitari Doctor Josep Trueta, 17007 Girona, Spain. E-mail adavalose{at}meditex.es
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Abstract |
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 Top Abstract IntroductionSubjects and MethodsResultsDiscussionReferences |
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Background and Purpose High levels of glutamate in plasma and cerebrospinal fluid (CSF) have been demonstrated in patients with acute ischemic stroke. The duration of this excitatory amino acid release has not been studied, and therefore the window of opportunity of treatment with glutamate antagonists is unknown. The aim of this investigation was to study the duration of the glutamate increase in patients with stable and progressing ischemic stroke.
Methods Glutamate in CSF was measured by high-performance liquid chromatography in 184 patients with an acute cerebral infarction of less than 24 hours' duration and in 43 control subjects.
Results Among the 120 patients with stable ischemic stroke, median glutamate levels were significantly lower—and within the reference range of control subjects—in those patients studied 6 to 24 hours from onset of symptoms than in patients studied in the first 6 hours (3 [range, 2 to 10] versus 5 µmol/L [range, 2 to 17]; P<.0001). In 64 patients with progressing ischemic stroke, glutamate concentrations measured at any time interval during the first 24 hours from onset were significantly higher than in the stable stroke and control groups.
Conclusions The presence of glutamate increase in the CSF cannot be documented for greater than 6 hours in stable ischemic stroke. The sustained elevation of glutamate observed in progressing stroke suggests that the window to prevent neurological deterioration may be wider.
Key Words: excitotoxicity • stroke outcome • neuroprotection • glutamate
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Introduction |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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There is increasing evidence that excitotoxic neuronal damage related to glutamate release plays a key role in the pathogenesis of focal cerebral ischemia.1 Drugs that antagonize the mechanisms of abnormal glutamate accumulation reduce the infarct volume in experimental stroke.2 The use of glutamate antagonists in clinical trials is based on the hypothesis that excitotoxicity persists for at least several hours after stroke onset.3 However, the duration of the excitatory amino acid (EAA) release in humans has not been studied, and therefore the window of opportunity of treatment with glutamate release inhibitors or glutamate receptor antagonists is unknown. In animal stroke models, the increase of EAA is brief4 (shorter than 2 hours), although it may be more prolonged in sustained cerebral ischemia.5
We previously described an elevation of glutamate in plasma and cerebrospinal fluid (CSF) of patients with an acute cerebral infarction,6 particularly in those with early neurological deterioration.7 The aim of this investigation was to study the duration of the glutamate increase in patients with stable ischemic stroke and in those with progressing ischemic stroke.
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Subjects and Methods |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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The study included 184 patients (117 men and 67 women; mean age, 68±10 years; age range, 38 to 89 years) admitted consecutively between October 1992 and December 1995 with a first episode of hemispheric ischemic stroke within 24 hours after the onset of symptoms. The protocol was approved by the Ethics Committee of the General Hospital of Galicia and has been described elsewhere.6 In summary, all patients had a persistent focal neurological deficit and absence of important mass effect or cerebral hemorrhage on the cranial CT performed before inclusion. The mean time from the onset of symptoms to the arrival at the hospital was 8.1±5.5 hours (range, 1.5 to 23 hours). After informed consent was obtained and the cerebral CT was completed, a spinal tap was performed in all patients. There were no medical or neurological complications of lumbar puncture. The mean time between admission and the CSF sampling was 1.3±0.8 hours. Type of stroke was classified as atherothrombotic in 77 patients, cardioembolic in 63, lacunar in 25, and of undetermined origin in 19 patients. Stroke severity was quantified by a neurologist using the Canadian Stroke Scale (CSS) at inclusion and after 48 hours. According to already published criteria,8 progressing stroke was diagnosed when the CSS score dropped
1 point between both examinations; patients
whose condition worsened exclusively in the area of orientation or
remained stable or improved during that 48-hour period were classified
as having stable ischemic stroke. Glutamate concentrations in
CSF were analyzed by high-performance liquid
chromatography with the same method used in a previous
study.6 The range of normality in the general population
was obtained from 43 control subjects without neurological disorders
subjected to epidural anesthesia (26 men and 17 women; mean
age, 56±17 years; age range, 19 to 81 years). Results are expressed as median and range. The Mann-Whitney-Wilcoxon test was used for comparison of two groups since glutamate values were not normally distributed. We used Spearman's correlation to analyze the relationship between glutamate concentrations and the inclusion delay.
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Results |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Glutamate concentrations in CSF were significantly higher in patients than in control subjects (6 [range, 2 to 22] versus 3 µmol/L [range, 2 to 7]; P<.0001). Among patients, glutamate was higher in the 64 with progressing ischemic stroke than in the 120 with stable ischemic stroke (12.5 [range, 5 to 22] versus 4.0 µmol/L [range, 2 to 17]; P<.0001) and in the 79 patients with early focal hypodensity than in the 105 without early signs on baseline cranial CT (10 [range, 2 to 21] versus 5 µmol/L [range, 2 to 22]; P=.004). No differences were found in glutamate levels between types of stroke, CSS score on admission <5 or
5 points, age 
65 or >65 years, or
between men and women.
In the total series of patients, glutamate values were not related to
the time elapsed from the onset of symptoms (Spearman coefficient=.18).
In patients with stable stroke, glutamate concentrations decreased with
time (Spearman coefficient=-.54, P<.001) (Fig 1
). In those patients studied 6 to 24 hours after onset
of symptoms, mean CSF glutamate levels were within the range of values
of control subjects and significantly lower than in patients studied
within the first 6 hours (3 [range, 2 to 10] versus 5 µmol/L
[range, 2 to 17]; P<.0001). In patients with progressing
stroke, glutamate values did not correlate significantly with the
inclusion delay (Spearman coefficient=-.09, P=.46) (Fig 1);
the median values determined at any time interval during the first 24
hours from onset were higher than those obtained in the stable stroke
and control groups (Fig 2).
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) and progressing (
) ischemic stroke.
Horizontal lines represent 90th and 10th percentiles. There was
a negative correlation between glutamate and inclusion delay in
patients with stable ischemic stroke (Spearman
coefficient=-.54, P<.0001) but not in patients with
progressing ischemic stroke (Spearman coefficient=-.09,
P=.46).
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Discussion |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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The elevation of EAA concentrations in in vivo focal ischemia models is transient, lasting only 1 to 2 hours.4 5 9 However, in contrast to experimental stroke, sustained elevation of glutamate has been observed for up to 4 days in patients with prolonged global posttraumatic ischemic brain damage.10 11 Recently, Bullock et al12 detected by microdialysis levels of glutamate at least 300 times higher than normal for several days after stroke onset in the cortex of a patient with a massive cerebral infarction due to internal carotid occlusion. Our results confirm that glutamate increase persists for at least 24 hours in patients with an acute ischemic stroke and early neurological deterioration. This maintained excitotoxicity is presumably related to the progression of the ischemic process in the penumbra over a period of several hours, since in those patients with stable ischemic stroke glutamate levels dropped to within the normal values in less than 6 hours from onset. Although the patients with important mass effect on CT were excluded from this study, glutamate was significantly higher in those with focal hypodensity at the initial CT, a sign that reflects intracellular edema and that has been related to neurological deterioration.13 14 15 Persistent glutamate release may promote cell swelling16 ; thus, the association between early CT signs of cerebral infarction and progression may be in part an epiphenomenon, as a result of the glutamate release that leads to a delayed neuronal death in the ischemic penumbra.
Our findings support the idea that a wide window of opportunity exists for glutamate antagonists in preventing early deterioration in patients with acute ischemic stroke. However, the interpretation of our results must be carefully evaluated. First, we did not study the profile of CSF glutamate levels at repeated intervals because this would have been unethical in clinical practice. Second, to our knowledge, there are no data regarding the relationship between glutamate release from ischemic tissue and its clearance dynamics into and from the CSF in focal cerebral ischemia. In normal conditions, glutamate is cleared from the extracellular space by a sodium-dependent reuptake system and moved into astrocytes and neurons; however, during ischemia the sodium gradient breaks down and extracellular glutamate is not transported back into the intracellular compartment.17 The diffusion of glutamate from the cortex to the CSF was low and delayed in an experimental model of global brain ischemia.18 Third, it cannot be ruled out completely that glutamate release might simply be a consequence of larger cerebral infarcts in progressing stroke, although in a previous study we found that the relationship between glutamate and progression was independent of the initial stroke severity and of the final infarct volume after progression had occurred.7 Finally, even if we assume that clinical deterioration is caused by glutamate release, its blockade beyond an unknown time window may be ineffective if the ischemic cascade has been fully triggered. Our results warrant confirmation by larger prospective clinical trials with glutamate antagonists.
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Acknowledgments |
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This study was supported by a grant from the Xunta de Galicia (investigation project XUGA 20802B93). The authors wish to extend their gratitude to Dr Jaume Marrugat (Lipid and Cardiovascular Epidemiology Unit, Institut Municipal d'Investigació Mèdica de Barcelona, Spain) for his helpful comments on design and statistical analysis.
Received October 21, 1996; revision received January 7, 1997; accepted January 7, 1997.
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References |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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1. Rothman SM, Olney JW. Glutamate and the pathophysiology of hypoxic-ischemic brain damage. Ann Neurol. 1986;19:105-111. [Medline] [Order article via Infotrieve]
2. Hossmann K-A. Mechanisms of ischemic injury: is glutamate involved? In: Krieglstein J, Oberpichler-Schwenk H, eds. Pharmacology of Cerebral Ischemia 1994. Stuttgart, Germany: Medpharm Scientific Publishers; 1994:239-251.
3.
Muir KW, Lees KR. Clinical experience with
excitatory amino acid antagonist drugs.
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4. Takagi K, Ginsberg MD, Globus MYT, Dietrich D, Martinez E, Kraydieh S, Busto R. Changes in amino acid neurotransmitters and cerebral blood flow in the ischemic penumbral region following middle cerebral artery occlusion in the rat: correlation with histopathology. J Cereb Blood Flow Metab. 1993;13:575-585. [Medline] [Order article via Infotrieve]
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Castillo J, Dávalos A, Naveiro J, Noya M.
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