(Stroke. 1998;29:824-829.)
© 1998 American Heart Association, Inc.
Treatment With the Competitive NMDA Antagonist GPI 3000 Does Not Improve Outcome After Cardiac Arrest in Dogs
Mark A. Helfaer, MD;
Rebecca N. Ichord, MD;
Lee J. Martin, PhD;
Patricia D. Hurn, PhD;
Alejandro Castro, BA;
Richard J. Traystman, PhD
From the Departments of Anesthesiology and Critical Care Medicine
(M.A.H., P.D.H., A.C., R.J.T.), Neurology (R.N.I.), and Pathology (L.J.M.),
Johns Hopkins Medical Institute, Baltimore, Md.
Correspondence to Richard J Traystman, PhD, Department of Anesthesiology/Critical Care Medicine, Blalock 1408, The Johns Hopkins Hospital, 600 N Wolfe St, Baltimore, MD 21287-4963. E-mail rtraystm{at}gwgate1.jhmi.jhu.edu
 |
Abstract
|
|---|
Background and Purpose—We previously
showed that treatment with a competitive
N-methyl-D-aspartate (NMDA) receptor
antagonist GPI-3000 (GPI) improved short-term
physiological recovery after incomplete global
cerebral ischemia complicated by dense acidosis. We tested the
hypothesis that GPI administered after resuscitation from cardiac
arrest would improve a more long-term recovery as measured by
neurobehavioral assessment and neuropathology 4 days after
resuscitation.
Methods—Anesthetized dogs were subjected to 7 minutes of
cardiac arrest followed by vest cardiopulmonary resuscitation.
Neurobehavioral outcomes were scored daily on a score ranging from 0
(normal) to 500 (worst). On the fourth day, the animals were killed,
and neuropathology was evaluated in a blinded manner in the hippocampus
and the neocortex by hematoxylin and eosin staining and by
determination of percentage of injured neurons. Three groups of animals
were treated in a randomized, blinded protocol with either saline
(SAL), low-dose GPI (5 mg/kg followed by 1 mg/kg per hour for 2 hours),
or high-dose GPI (25 mg/kg, followed by 5 mg/kg per hour for 2
hours).
Results—The mortality rate was higher in animals receiving GPI
than in saline-treated control animals (4 of 15 deaths in SAL, 6 of 15
in the low-dose GPI group, and 9 of 18 in the high-dose GPI group).
Neurobehavioral scores were depressed in GPI-treated animals compared
with saline-treated control animals in a dose-dependent manner, with
96-hour scores of essentially normal (9±2) in saline-treated animals
compared with those animals with significant impairment (181±47)
treated with high-dose GPI. Neuropathological damage in the neocortex
was most severe in GPI-treated animals, with the percentage of injured
neurons dependent on the dose: 8.3%±2.7% SAL, 13.2%±6.4% low-dose
GPI, and 39.4%±10.1%, high-dose GPI. CA1 neuronal damage was severe
regardless of treatment.
Conclusions—Contrary to results seen in experimental global and
focal cerebral ischemia, in which NMDA receptor antagonism may
improve responses to injury, receptor antagonism with GPI does not
improve brain outcome after cardiac arrest and resuscitation in the
dog. Behavioral and histological outcomes both were
worsened by GPI treatment at two doses, and mortality was higher
relative to saline control treatment. We speculate that systemic drug
effects, as well as potential neurotoxicity of the drug under
ischemic conditions, may be responsible for the deleterious
outcomes observed in our cardiac arrest model.
Key Words: cardiopulmonary resuscitation • cerebral ischemia • glutamates • hippocampus • N-methyl-D-aspartate receptor • neocortex
|
Introduction
|
|---|
Multiple mechanisms
of cerebral ischemia and reperfusion injury have been proposed,
but one consistent finding is the rise in
interstitial glutamate concentration associated with
cerebral ischemia.1 2 3 et> Excessive
activation of NMDA receptors under conditions of energy substrate
depletion leads to neuronal death.4 5 et> Treatment
of focal ischemia with a noncompetitive NMDA receptor
antagonist such as MK-801 can reduce neuronal injury,
albeit with significant adverse effects.6 7
Although non-NMDA (glutamate) receptor antagonists have
been efficacious in global cerebral ischemia,8 NMDA receptor antagonism has yielded
variable results.9 10 11 12 13 14 15 Competitive NMDA
receptor antagonists are effective in animal stroke models
and avoid some of the undesirable behavioral effects of noncompetitive
antagonists, such as ataxia, hyperactivity,
hyperreactivity, and motoric stereotypes.16 17 18 19
GPI, formerly known as NPC 17742
(2R,4R,5S-[2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoic acid]),
is a specific competitive NMDA receptor
antagonist20 that reduces infarction
volume after transient focal ischemia.21
We have also shown that treatment with this agent during or after
severe incomplete global cerebral ischemia complicated by
intense acidosis ameliorates secondary deterioration of cerebral blood
flow and high-energy phosphates during early reperfusion.12
However, the importance of NMDA receptor–mediated mechanisms of injury
in the brain after cardiac arrest is unclear. Therefore, we examined
the effect of GPI on neurological and histological
outcomes from cardiac arrest (7 minutes) followed by resuscitation and
96 hours of recovery.
|
Materials and Methods
|
|---|
This study is in compliance with the guidelines of the National
Institutes of Health for care and handling of animals and was approved
by our institutional animal care and use committee. Fifty-one
preconditioned 8- to 15-kg mongrel dogs were anesthetized with
12.5 mg/kg thiopental and 0.2 mg/kg pancuronium, intubated, ventilated
with <1% halothane in 70% nitrous oxide and 30% oxygen, and
monitored through capnography (model 78356A capnograph,
Hewlett-Packard) to maintain end-tidal CO2
concentration between 35 and 40 mm Hg. One gram ampicillin,
1 g cefazolin, and 2 mg/kg gentamicin were administered
intramuscularly. Strict sterile procedures were used to place two
0.07-in (OD) Tygon catheters (Norton Performance Plastics) in
the femoral vein and artery. These were tunneled to emerge between the
shoulders to prevent removal on recovery. Temperature was measured with
a thermometer placed in the mid esophagus, and maintained between
37.8°C and 38.4°C with the use of a heating lamp and warming
blanket. Arterial blood gases were adjusted to maintain
PaO2 between 100 and 150 mm Hg
and PaCO2 between 35 and 40
mm Hg.
A 16-V AC 100 mA shock was administered through a pacing catheter
(V-Probe, Baxter) placed into the right ventricle through a venous
catheter that initiated 7 minutes of normothermic
ventricular fibrillation cardiac arrest. One and one-half
minutes into the arrest, 0.8 mg of epinephrine and 1 mEq/kg of
sodium bicarbonate were administered intravenously.
Beginning 7 minutes after initiation of cardiac arrest, vest chest
compressions were initiated at 60 times per minute and maintained a
diastolic blood pressure of 60 mm Hg. Five
compressions were linked to one ventilation. After 1.5 minutes of CPR,
100 J was delivered (Life Pack, Physiocontrol Corp) via previously
placed chest pads (R2 Peds Pads, R2 Medical Systems Inc). If there was
no ROSC, repeat shocks were instituted. If two repeat shocks failed to
resuscitate the animal, additional doses of epinephrine were
administered every minute of continued CPR. Shocks were repeated every
minute. If ROSC was not established within 7 minutes, the animal was
excluded from the study.
The time to ROSC was defined as the time from initiation of cardiac
arrest to the time when mean PaO2
equaled 60 mm Hg. On ROSC, treatment was administered in a
randomized investigator-blinded fashion: (1) intravenous
saline (40 mL/kg over 15 minutes, then 3 mL/kg per hour for 2 hours);
SAL, (2) low-dose GPI (5 mg/kg in a comparable amount of saline over 15
minutes then 1 mg/kg per hour for 2 hours); and (3) high-dose GPI (25
mg/kg in a comparable amount of saline over 15 minutes then 5 mg/kg per
hour for 2 hours). These dosages were chosen on the basis of our
previous study.12 The animals then remained
intubated until they had a cough and gag and were able to breathe
spontaneously. They were physiologically
monitored and supported to maintain normal vital signs for 4 days.
The animals underwent daily neurobehavioral scoring with use of the
rating scale developed by Safar and colleagues22
to evaluate recovery in dogs after CPR. Neurological examination and
neurobehavioral scoring were carried out at 24, 48, 72, and 96 hours
after ROSC by a single examiner who was blinded to treatment group and
the details of the surgery and resuscitation. The scores ranged from a
normal score of 0 for no deficit to the worst score of 500 for a
maximal deficit. Animals with neurobehavioral scores of 5 to 100 had
normal consciousness and gait abnormalities that were minimal to none.
Animals with scores 100 to 200 had normal consciousness but were
apathetic hypoactive and had mild to moderate tone and gait
abnormalities. Animals with scores 200 to 300 were somnolent or
stuporous and had severe motor abnormalities (tone and movement) but
intact brain stem reflexes. Animals with scores >300 were deeply
depressed or comatose, had severe motor deficits, and in some cases had
brain stem reflex deficits. The recovering animals that demonstrated
marked stereotypical motor behaviors, such as tonic limb extensor
paroxysms, running movements, neck extensor dystonias, and oral-lingual
dyskinesias, also underwent concurrent EEG recordings (Grass
Instruments, models 6 to 6ES 825B). Four scalp needle electrodes were
placed to record two bipolar channels (right and left, frontal and
occipital) and ECG with use of a Grass electroencephalograph at a
sensitivity of 7 µV/mm.
On the fourth day, the dogs that survived a 4-day recovery period were
used to determine neuropathological scores. The dogs were deeply
anesthetized with sodium pentobarbital and then perfused (20
minutes) intra-aortically with cold (4°C) 4%
paraformaldehyde prepared in 0.1 mol/L phosphate buffer
(pH 7.4). Neurodegeneration was assessed in 10-µm sections stained
with hematoxylin and eosin. Profile counting was used to estimate
ischemic neuronal damage in septal hippocampus (striatum
pyramidale of CA1) and motor cortex (layers II and II) of
vehicle- and drug-treated animals. Neuropathological scores were
determined by an observer unaware of treatment. In each microscopic
field, the fraction of neurons with ischemic cytopathology (ie,
the percentage of neuronal damage) was determined in each animal. The
criteria for ischemic cytopathology were an eosinophilic
cytoplasm, cytoplasmic vacuolation, perikaryal shrinkage, and nuclear
pyknosis.
In addition, 3 animals served as nonischemic control animals to
evaluate the effects of GPI (25 mg/kg) on the neurobehavior and
neuropathology in the absence of cardiac arrest. All 3 animals
demonstrated temporary neurobehavioral effects that resolved between 48
and 72 hours. No obvious injury or inflammatory changes were identified
in any brain region by light microscopy.
Data are presented as mean±SEM. Statistical analysis
was performed with CRUNCH (Crunch Software Inc), using multiple ANOVA
(with repeated measures) with the Newman Keuls test to evaluate
differences with P set at 
.05. Mortality was
analyzed with the nonparametric Kruskal-Wallis
test.
|
Results
|
|---|
Three animals could not be resuscitated and were excluded from
randomization and treatment. Of those randomized, the mortality rate
was greater among GPI-treated animals than saline-treated ones and
correlated with drug dose. Mortality in saline-treated dogs was 4 of 15
and occurred 2±0.6 days after arrest. The low-dose GPI group mortality
was 6 of 15 and occurred 1±0 days after arrest. The high-dose GPI
group suffered a mortality rate of 9 of 18 and occurred1.4±0.3 days
after arrest. Of the survivors, there were no differences among the
three groups related to resuscitation events (Table 1
).
In all three groups, neurobehavioral scores improved from 24 to 96
hours of recovery (Fig 1). However,
neurobehavioral scores in high-dose GPI were poor (181±47) compared
with those in animals treated with saline (9±2) or from the low-dose
GPI group (70±29). Seizures were not observed in any animals. In some
cases, GPI-treated animals manifested stereotypic motor behaviors that
were not associated with epileptiform discharges on EEG. Postoperative
vital signs were similar in the three groups (Table 2),
but heart rate was initially elevated in the high-dose GPI
group, which resolved on day 2 after extubation. Likewise,
arterial blood gases and hemoglobin levels were similar in
the three groups (Table
3).
PaO2 was higher on the first
postoperative day in the high-dose GPI animals, because of the need for
prolonged intubation and ventilation in these animals.
View larger version (25K):
[in this window]
[in a new window]
|
Figure 1. Behavioral scores improve over time in all groups.
Scores ranged from normal (0) to 500 (most severely injured). Open
circles represent saline-treated control animals, squares
represent animals receiving low-dose GPI, and triangles
represent animals receiving the high dose of GPI. The filled
symbols represent the mean with standard error bars. For all
groups, improvement is statistically significant over time. At all time
points, the animals receiving saline had scores better than those
receiving the high-dose GPI. At 24 hours, the animals receiving saline
had a better score than those receiving the low-dose GPI. At 48, 72,
and 96 hours, the scores of the animals receiving high-dose GPI were
worse than those of animals receiving low-dose GPI.
|
|
Hippocampal injury (Fig 2) was severe in
all groups (84.6%±7.8% for saline-treated control animals,
93.7%±2.8% for the low-dose GPI group, and 94.8%±0.8% the
high-dose GPI group). Cortical neuronal damage correlated with GPI dose
(8.3±2.7% for saline-treated animals, 13.2±6.4% for low-dose GPI,
and 39.4±10.1% for high-dose GPI, Fig 2).
View larger version (17K):
[in this window]
[in a new window]
|
Figure 2. Neocortex damage is dependent on GPI dose.
Hippocampal and neocortex neuronal dropout percentages are
represented by open circles and open squares, respectively.
Filled symbols represent the mean and SEM. There are no
differences between the three treatment groups in terms of hippocampal
neuronal dropout. The dose-response relationship with neocortex
neuronal dropout percentages follows a linear regression model with
r2=.99.
|
|
|
Discussion
|
|---|
The major findings of this study are that competitive NMDA
receptor antagonism after 7 minutes of cardiac arrest and resuscitation
in dogs impairs neurobehavioral and neuropathological outcomes compared
with those in saline-treated animals. Furthermore, the deleterious
effects of the administration of this agent (GPI 3000) on mortality are
strongly dose dependent. Surprisingly, these results differ from those
obtained with focal5 and incomplete
global12 cerebral ischemias and suggest
that systemic effects of NMDA receptor antagonists may
influence recovery.
We chose the present experimental cardiac arrest model in a large
animal for its clinical applicability, its low overall mortality rate,
its reproducible neocortical and hippocampal pathology, and the lack of
dependence on cardiopulmonary bypass procedures. Because the
arrest time is short, neurobehavioral deficits are mild and typically
short-lived. In addition, because excitatory amino acid release occurs
early in ischemia,2 inhibition of these
mechanisms should be instituted in short-duration ischemias.
This model is advantageous in that both beneficial (or in the case of
GPI-treated groups, deleterious) outcomes can be measured.
NMDA blockade with GPI depressed recovery after cardiac arrest. The
increased mortality rates associated with GPI treatment may result in
part from effects outside the central nervous system. NMDA receptors
have been identified in the lung,23 but the
effects of blockade of these lung receptors on resuscitation after
cardiac arrest are not known. Similarly, NMDA receptor blockade with
ketamine in the myocardium causes diminution of
contractile force, the spontaneous rate of contraction, and the
transsarcolemmal calcium currents.24 The
widespread physiological consequences of cardiac
arrest and resuscitation25 in concert with the
potential for cardiopulmonary dysfunction from NMDA receptor
blockade are a potential explanation for a higher mortality rate in
GPI-treated animals.
NMDA antagonism has been evaluated in the setting of cardiac
arrest. Using a model of normothermic
ventricular fibrillation cardiac arrest with a 96-hour
recovery, Sterz and colleagues26 evaluated the
efficacy of the noncompetitive NMDA receptor antagonist
MK-801. In this global cerebral ischemia model, no improvement
was demonstrated in neurobehavioral or neuropathological outcome with
MK-801 treatment. The authors concluded that their results do not
negate the hypothesis that neuronal hyperexcitability mediated by
excitatory amino acids causes neuronal injury in the face of global
cerebral ischemia. They interpreted their negative result to
emphasize the existence of multiple mechanisms mediating secondary
brain injury. Using GPI, we have demonstrated improvements in acute
bioenergetics and neurophysiological recovery
associated with a severe model of incomplete global cerebral
ischemia induced by elevation in intracranial
pressure.12 In that study, the administration of
GPI (25 mg/kg bolus followed by 5 mg/kg per hour) after 30 minutes of
global cerebral ischemia resulted in improvement in high-energy
phosphates in the brain. Since we demonstrated that NMDA receptors may
have a role in the neuropathophysiology associated with this cerebral
injury,12 we were prompted to evaluate this agent
in a more clinically applicable model and to evaluate chronic outcomes.
In the present study, we found the unexpected result that this
agent worsened outcome compared with saline. The dramatically different
results compared with our previous study12 are
due to differences in the methods used to produce cerebral
ischemia, the acute versus chronic recovery period during which
observations were made, and the use of histological and
neurobehavioral outcomes in the present study. In our early
observations of GPI efficacy,12 we used global
cerebral ischemia induced by reversible intracranial
hypertension, which results in few adverse systemic effects. The
ischemic insult is limited to the cerebral vascular bed in that
model. In contrast, cardiac arrest results in both cerebral and
systemic low-flow conditions and likely affects numerous noncerebral
factors that alter cell injury mechanisms. Furthermore, our previous
evaluation of the efficacy of GPI was determined over only the first 3
hours of reperfusion in the anesthetized dog and used
hemodynamic and bioenergetic measures of brain
outcomes. The present findings reflect a longer observation period
(96 versus 3 hours) that likely allowed initial injury maturation
reflected by loss of neuronal viability and depressed functional
recovery in the awake animal.
Upregulation of presynaptic excitatory amino acid transporters
has been demonstrated to increase within 5 minutes of bilateral common
carotid occlusion. This upregulation transports the excess excitatory
amino acids that are released into the extracellular space from the
intracellular space in response to ischemia. This upregulation
has a biphasic time course, with partial return to control levels at 1
hour of reperfusion followed by a second increase at 48 hours only to
fall to control levels within 7 days.27 In
addition, it is likely that glutamate receptor desensitization occurs
after exposure to elevated neurotransmitters during or after
ischemia,27 an effect that could be
altered by the administration of a glutamate receptor
antagonist. Others28 29 have shown
that NMDA receptor–blockade alters receptor density and may thereby
affect receptor activity after the antagonist is no longer
present. The balance of excitatory and inhibitory amino
acids shifting between the intra- and extracellular compartments has
been shown to modulate neuronal injury associated with cerebral
injury.2 In this more prolonged setting, it is
conceivable that administration of GPI causes the balance of amino acid
binding and transporting to lead to the deleterious effects seen in the
present study.
Previous work has documented neurotoxicity associated with NMDA
receptor blockade (MK-801) in the brain. This toxicity is most
prominent in the posterior cingulate and retrosplenial cortices and is
seen on light microscopy in very high doses, with electron microscopy
necessary for demonstration of the vacuolization seen at smaller
doses.6 30 Olney et al31 suggested
that NMDA receptor blockade decreases GABAergic inhibition of
excitatory synaptic pathways with resulting neurotoxicity. In our
study, we did not show signs of toxicity on a light microscopic
evaluation with high doses of GPI in the absence of ischemia.
Nevertheless, we cannot fully exclude this possibility. What is clear
from our data is the potential for deleterious outcome when there is an
interaction between ischemia and competitive NMDA receptor
antagonism.
In this study, we have defined a chronic model of 7 minutes of cardiac
arrest, 1.5 minutes of CPR followed by external defibrillation without
extracorporeal resuscitation, and a 96-hour recovery that mimics the
clinical situation in humans. With an acceptable mortality rate (27%),
we demonstrated the utility of this chronic model in defining the
neurobehavioral and neuropathological effects after saline
administration. This model results in nearly complete recovery of
neurobehavioral function by the 4th postoperative day, and hippocampal
and neocortical neuronal damage at 84.6%±7.8% and 8.3%±2.7%,
respectively. Furthermore, blockade of the NMDA receptor with GPI
worsens mortality rates, neurobehavioral outcome, and neocortical
neuropathology in a dose-dependent manner.
|
Selected Abbreviations and Acronyms
|
|---|
| CPR |
= |
cardiopulmonary resuscitation |
| EEG |
= |
electroencephalogram |
| GPI |
= |
GPI 3000 |
| NMDA |
= |
N-methyl-D-aspartate |
| ROSC |
= |
return of spontaneous circulation |
|
|
Acknowledgments
|
|---|
This study was supported by grants from the National Institutes
of Health (NR-03521 and NS 20020) and a gift from Guilford
Pharmaceuticals (Baltimore, Md).
Received September 29, 1997;
revision received January 23, 1998;
accepted January 23, 1998.
|
References
|
|---|
1.
Globus MY, Busto R, Martinez E, Valdes I,
Dietrich WD, Ginsberg MD. Comparative effect of transient global
ischemia on extracellular levels of glutamate, glycine, and
gamma-aminobutyric acid in vulnerable and nonvulnerable brain regions
in the rat. J Neurochem. 1991;57:470–478.[Medline]
[Order article via Infotrieve]
2.
Hagberg H, Lehmann A, Sandberg M, Nystrom B, Jacobson
I, Hamberger A. Ischemia-induced shift of
inhibitory and excitatory amino acids from intra- to
extracellular compartments. J Cereb Blood Flow Metab. 1985;5:413–419.[Medline]
[Order article via Infotrieve]
3.
Matsumoto K, Lo EH, Pierce AR, et al Secondary
elevation of extracellular neurotransmitter amino acids in the
reperfusion phase following focal cerebral ischemia.
J Cereb Blood Flow Metab. 1996;16:114–24.
Abstract.[Medline]
[Order article via Infotrieve]
4.
Lipton SA, Rosenberg PA. Excitatory amino acids as a
final common pathway for neurologic disorders [see comments].
N Engl J Med. 1994;330:613–22.[Free Full Text]
5.
Nishikawa T, Kirsch JR, Koehler RC, Miyabe M,
Traystman RJ. Competitive N-methyl-D-aspartate
receptor blockade reduces brain injury following transient focal
ischemia in cats. Stroke. 1994;25:2258–2264.[Abstract]
6.
Olney JW, Labruyere J, Price MT. Pathological changes
induced in cerebrocortical neurons by phencyclidine and related drugs.
Science. 1989;244:1360–1362.[Abstract/Free Full Text]
7.
Sharp FR, Jasper P, Hall J, Noble L, Sagar SM. MK-801
and ketamine induce heat shock protein HSP72 in injured neurons
in posterior cingulate and retrosplenial cortex. Ann Neurol. 1991;30:801–809.[Medline]
[Order article via Infotrieve]
8.
Sheardown MJ, Nielsen EO, Hansen AJ, Jacobsen P,
Honore T. 2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline: a
neuroprotectant for cerebral ischemia. Science. 1990;247:571–574.[Abstract/Free Full Text]
9.
Block GA, Pulsinelli WA. Excitatory amino acid
receptor antagonists: failure to prevent ischemic
neuronal damage. J Cereb Blood Flow Metab. 1987;7(suppl
1):S149.
10.
Boast CA, Gerhardt SC, Pastor G, Lehmann J, Etienne PE,
Liebman JM. The N-methyl-D-aspartate
antagonists CGS.5 and CPP reduce ischemic brain
damage in gerbils. Brain Res. 1988;1975:442:345–348.
11.
Buchan A, Pulsinelli WA. Hypothermia but not the
N-methyl-D-aspartate antagonist, MK-801,
attenuates neuronal damage in gerbils subjected to transient global
ischemia. J Neurosci. 1990;10:311–316.[Abstract]
12.
Davis S, Helfaer MA, Traystman RJ, Hurn PD. Parallel
antioxidant and antiexcitotoxic therapy improves outcome after
incomplete global cerebral ischemia in dogs. Stroke. 1997;28:198–205.[Abstract/Free Full Text]
13.
Lanier WL, Perkins WJ, Karlsson BR, Milde JH,
Scheithauer BW, Shearman GT, Michenfelder JD. The effects of
dizocilpine maleate (MK-801), an antagonist of the
N-methyl-D-aspartate receptor, on neurologic recovery and
histopathology following complete cerebral ischemia in
primates. J Cereb Blood Flow Metab. 1990;10:252–261.[Medline]
[Order article via Infotrieve]
14.
Swan JH, Evans MC, Meldrum BS. Long-term development of
selective neuronal loss and the mechanism of protection by
2-amino-7-phosphonoheptanoate in a rat model of incomplete forebrain
ischaemia. J Cereb Blood Flow Metab. 1988;8:64–78.[Medline]
[Order article via Infotrieve]
15.
Swan JH, Meldrum BS. Protection by NMDA
antagonists against selective cell loss following transient
ischaemia. J Cereb Blood Flow Metab. 1990;10:343–351.[Medline]
[Order article via Infotrieve]
16.
Bullock R, Graham DI, Chen MH, Lowe D, McCulloch
J. Focal cerebral ischemia in the cat: pretreatment with a
competitive NMDA receptor antagonist, D-CPP-ene.
J Cereb Blood Flow Metab. 1990;10:668–674.[Medline]
[Order article via Infotrieve]
17.
Hargreaves EL, Cain DP. Hyperactivity,
hyper-reactivity, and sensorimotor deficits induced by low doses of the
N-methyl-D-aspartate non-competitive channel blocker MK801.
Behav Brain Res. 1992;47:23–33.[Medline]
[Order article via Infotrieve]
18.
Sauer D, Weber E, Luond G, Da Silva F, Allegrini PR.
The competitive NMDA antagonist CGP 40116 permanently
reduces brain damage after middle cerebral artery occlusion in rats.
J Cereb Blood Flow Metab. 1995;15:602–610.[Medline]
[Order article via Infotrieve]
19.
Willetts J, Balster RL, Leander JD. The behavioral
pharmacology of NMDA receptor antagonists. Trends
Pharmacol Sci. 1990;11:423–428.[Medline]
[Order article via Infotrieve]
20.
Ferkany JW, Hamilton GS, Patch RJ, Huang Z, Borosky SA,
Bednar DL, Jones BE, Zubrowski R, Willetts J, Karbon EW.
Pharmacological profile of NPC 17742, a potent, selective and
competitive N-methyl-D-aspartate receptor
antagonist. J Pharmacol Exp Ther. 1993;264:256–264.[Abstract/Free Full Text]
21.
Nishikawa T, Kirsch JR, Koehler RC, Bredt DS,
Snyder SH, Traystman RJ. Effect of nitric oxide synthase inhibition on
cerebral blood flow and injury volume during focal ischemia in
cats. Stroke. 1993;24:1717–1724.[Abstract/Free Full Text]
22.
Leonov Y, Sterz F, Safar P, Radovsky A, Oku K,
Tisherman S, Stezoski SW. Mild cerebral hypothermia during and after
cardiac arrest improves neurologic outcome in dogs. J Cereb
Blood Flow Metab. 1990;10:57–70.[Medline]
[Order article via Infotrieve]
23.
Said SI, Berisha HI, Pakbaz H. Excitotoxicity in the
lung: N-methyl-D-aspartate-induced, nitric oxide-dependent,
pulmonary edema is attenuated by vasoactive intestinal peptide
and by inhibitors of poly(ADP-ribose) polymerase.
Proc Natl Acad Sci U S A. 1996;93:4688–4692.[Abstract/Free Full Text]
24.
Sekino N, Endou M, Hajiri E, Okumura F.
Nonstereospecific actions of ketamine isomers on the force of
contraction, spontaneous beating rate, and Ca2+ current in
the guinea pig heart. Anesth Analg. 1996;83:75–80.[Abstract]
25.
Cerchiari EL, Safar P, Klein E, Diven W. Visceral,
hematologic and bacteriologic changes and neurologic outcome after
cardiac arrest in dogs. The visceral post-resuscitation syndrome.
Resuscitation. 1993;25:119–136.[Medline]
[Order article via Infotrieve]
26.
Sterz F, Leonov Y, Safar P, Radovsky A, Stezoski
SW, Reich H, Shearman GT, Greber TF. Effect of excitatory amino acid
receptor blocker MK-801 on overall, neurologic, and morphologic outcome
after prolonged cardiac arrest in dogs. Anesthesiology. 1989;71:907–918.[Medline]
[Order article via Infotrieve]
27.
Anderson KJ, Nellgard B, Wieloch T.
Ischemia-induced upregulation of excitatory amino acid
transport sites. Brain Res. 1993;622:93–98.[Medline]
[Order article via Infotrieve]
28.
Wed Zong K, Mackowiak M, Czyrak A, Fijal K, Michulsak
B. Single doses of MK-801, a non-competitive antagonist of
NMDA receptors, increase the number of 5-HTIA serotonin
receptors in the rat. Brain Res. 1997;756:84–91.[Medline]
[Order article via Infotrieve]
29.
White BH, and Vogel MW. CGP 39653 binding in the chick
CNS after NMDA receptor antagonist treatment. J
Neural Transmission. 1996;103:1247–1253.
30.
Fix AS, Horn JW, Wightman KA, Johnson CA, Long GG,
Storts RW, Farber N, Wozniak DF, Olney JW. Neuronal vacuolization and
necrosis induced by the noncompetitive N-methyl-D-aspartate
(NMDA) antagonist MK(+)801 (dizocilpine maleate): a light
and electron microscopic evaluation of the rat retrosplenial cortex.
Exp Neurol. 1993;123:204–215.[Medline]
[Order article via Infotrieve]
31.
Olney JW, Labruyere J, Wang G, Wozniak DF, Price MT,
Sesma MA. NMDA antagonist neurotoxicity: mechanism and
prevention. Science. 1991;254:1515–1518.[Abstract/Free Full Text]
Editorial Comment
Giora Feuerstein, MD, MSc, Guest Editor
Director,
Cardiovascular Pharmacology WW,
SmithKline Beecham Pharmaceuticals,
Philadelphia, Pennsylvania
|
Introduction
|
|---|
The article by Helfaer et al reports on a pharmacological study
that resulted in "negative" data (ie, the kind of data
investigators usually try not to produce, as the premise of
pharmacological studies is that "we try to demonstrate some
usefulness of the chemical in view of proving a research hypothesis or
supporting eventual clinical utility"). However, the study by Helfaer
et al is, in my opinion, a very important one because publications of
pharmacological studies are heavily biased toward the "good news".
Although we do not know exactly the ratio of reporting positive versus
negative results with a compound (many journals/reviewers have little
patience with pharmacological studies that "did not work"), it is
nevertheless extremely important to report such data. The
NMDA/glutamate hypothesis in neuroinjury has been an intriguing example
in which early optimism (mid-1980s) ran into a perplexing stage
(mid-1990s), during which expectations for positive clinical studies in
stroke and neurotrauma have been difficult to realize—and, as the
decade closes, may not be counted as 20th century
pharmaceutical/academic achievement in drug discovery and development.
Is it possible that, early on, too little has been reported on negative
data for this class of agents as well as for other compounds that block
the glutamate/NMDA receptor/channel complex (noncompetitive
antagonists)?
In this light, the demonstration by Halfaer et al (in a well-designed
and well-executed study) that a compound which possesses the primary
pharmacology of competitive NMDA receptor antagonists in
fact worsens the outcome (histologically and
functionally) of cerebral insult (ischemia and reperfusion) may
call attention to the need for thorough analysis of the reasons
for this detrimental effect. Although the study has not explored the
mechanism of the negative results (an endeavor that needs to be
undertaken), several possibilities must be entertained: (1) Is the
reported data particular to the specific agent used? It would be useful
to compare other competitive NMDA antagonists of diverse
chemical structures in the same models. (2) Do noncompetitive
antagonists behave the same way in this model (ie, is this
a model/species-specific issue? Other species and models of global
ischemia and reperfusion need to be used. (3) Does the compound
(or the class) act on central versus peripheral target
organs? The authors alluded to this possibility but have not explored
it. (4) Are certain metabolites of the compound responsible for the
toxic effects? Better understanding of the pharmacokinetics and
pharmacodynamics of the compound need to be reviewed before broad
implications are made.
These issues are important points that need to be better addressed in
pharmacological studies, regardless of the compound tested. It is
highly advisable that researchers design their studies up front to
address these concerns. This reviewer's opinion is that
Stroke explores principles of pharmacological conduct to be
recommended to scientists interested in pharmacological studies to
ensure that pharmacological observations in vivo are provided with more
complete insights on the issues addressed above. Such standards could
be very instrumental in reducing the "noise" of apparently
conflicting data that confuse pharmacological efficacy based on
mechanism of action with confounding issues of metabolism,
pharmacokinetics and pharmacodynamics, site of action, and species and
models particularities.
|
Selected Abbreviations and Acronyms
|
|---|
| CPR |
= |
cardiopulmonary resuscitation |
| EEG |
= |
electroencephalogram |
| GPI |
= |
GPI 3000 |
| NMDA |
= |
N-methyl-D-aspartate |
| ROSC |
= |
return of spontaneous circulation |
|
Received September 29, 1997;
revision received January 23, 1998;
accepted January 23, 1998.
Top
Abstract
Introduction