(Stroke. 1995;26:1883-1887.)
© 1995 American Heart Association, Inc.
Articles |
From the University of Groningen, Department of Biological Psychiatry, Groningen, The Netherlands.
| Abstract |
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Methods Rats were treated for 14 days with 2 mg/kg and 10 mg/kg L-deprenyl or saline. After surgery a 20-minute hypoxia/ischemia period was induced by simultaneous occlusion of the left common carotid artery and reduction of the percentage of oxygen in the gas mixture to 10%. Rats were killed 24 hours later. Silver staining was used to reveal damage in several brain regions.
Results In the brain, both L-deprenyl dosages reduced damage up to 78% compared with the controls. Total brain damage was decreased from 23%-31% to 5%-9% with the L-deprenyl treatment (2 mg/kg: F1.13=6.956, P<.05; 10 mg/kg: F1.13=5.731, P<.05). In the striatum, significant treatment effects were found between both the L-deprenyl groups (2 mg/kg and 10 mg/kg, respectively) and the saline group (F1.13=14.870, P<.005; and F1.13=8.937, P=.01; respectively). In the thalamus, significant treatment effects were seen in the 2-mg/kg L-deprenyl group (F1.13=11.638, P<.005) and the 10-mg/kg group (F1.13=8.347, P<.05) compared with the control group. No significant damage decrease was seen in the hippocampus and the cortex.
Conclusions The results show that L-deprenyl is effective as a prophylactic treatment for brain tissue when it is administered before hypoxia/ischemia. Mechanisms responsible for the observed protection remain unclear. The regional differences in damage, however, are in accordance with the reported regional increase in superoxide dismutase and catalase activities after L-deprenyl treatment, suggesting the involvement of free radicals and scavenger enzymes.
Key Words: cerebral ischemia, transient free radicals monoamine oxidase inhibitors superoxide dismutase rats
| Introduction |
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Ischemic brain damage may involve several mechanisms, but calcium overload, glutamate toxicity, and generation of free radicals are most intensively investigated. Due to the rapid establishment of ischemic damage, pharmacological pretreatments should be considered. In our experimental hypoxia/ischemia model, several potential protective pretreatments were tested regarding their ability to reduce damage. The largest damage reduction was seen in rats that were deprived of food for 1 day despite significantly increased glutamate levels in the striatum after the hypoxia/ischemia.1
We explored L-deprenyl (Selegiline), an irreversible inhibitor of monoamine oxidase-B (MAO-b), as a potential neuroprotective agent against an ischemic/hypoxic episode. L-Deprenyl is a selective inhibitor of B-type MAO at moderate dosages and has several other characteristics that make it suitable as a prophylactic treatment in the prevention or reduction of neuronal damage.2 3 4 5 For example, L-deprenyl increases scavenger enzyme activity,3 6 and this may partially explain the described neuroprotection of L-deprenyl.4 7
In this article, the prophylactic effect of L-deprenyl on the cerebral damage of rats exposed to transient hypoxia/ischemia is described. Attention was especially focused on regional brain differences in total damage.
| Materials and Methods |
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Surgery
On day 14, rats were anesthetized with sodium
pentobarbital (50 mg/kg IP), and the left femoral artery was exposed
and cannulated for continuous mean blood pressure monitoring
(Hewlett-Packard pressure transducer). The left carotid artery was
exposed, and the rats were intubated, connected to a ventilator, and
stabilized during 10 minutes with a mixture of 30% O2 and
70% N2O (infant ventilator MK2, Loosco). After
stabilization, a 20-minute hypoxia/ischemia period was
induced by simultaneous occlusion of the left carotid
artery and reduction of the O2 content in the gas mixture
to 10%, followed by a 15-minute period of normoxia (30%
O2/70% N2O). During surgery, body
temperature was maintained between 36.5°C and 37.5°C with an
incandescent lamp and a heating pad.1
All treatments and surgical procedures were approved by a local animal ethics committee.
Histology
After a 24-hour survival period, rats were deeply
anesthetized with sodium pentobarbital (70 mg/kg IP) and
perfused transcardially with saline followed by 400 to 600 mL
ice-cold 4% paraformaldehyde in 0.1 mol/L borate
buffer (pH 9.5).10 Brains were post-fixed for 24 hours
and cryoprotected overnight in 20% sucrose in 0.1 mol/L phosphate
buffer, pH 7.4, at 4°C. Frontal sections 25 µm thick were cut on a
cryostat microtome and stored. Every fifth section was stained with an
improved silver impregnation procedure from Gallyas et
al,11 12 13 which labels degenerating cell bodies and their
processes. In brief, free-floating sections were rinsed three times
in quartz-distilled water and pretreated for 5 minutes in a
solution containing 1.1 mol/L NaOH and 75 mmol/L
NH4NO3 three times. Tissue was subsequently
impregnated for 10 minutes in 1.4 mol/L NaOH, 0.8 mol/L
NH4NO3, and 18 mmol/L AgNO3.
After being rinsed three times for 5 minutes in 47 mmol/L
Na2CO3, 1.5 mmol/L
NH4NO3, and 30% ethanol, the sections
were developed for 1 minute in 0.07% citric acid, 0.55% formalin,
9.6% ethanol, 0.675 mol/L NaOH, and 0.75 mmol/L
NH4NO3. Silver deposits were fixed for 4
minutes in 1.5 mol/L
Na2S2O3·5H2O,
rinsed three times for 5 minutes in distilled water, and stored in 0.1
mol/L phosphate buffer (pH 7.4) before being mounted on
gelatin-coated slides.
Data Analysis
Investigators were blinded to the procedures during
surgery and analysis of the histology. Rats with a blood
pressure drop during hypoxia/ischemia of less than 60%
of normal blood pressure were excluded from the analysis. In
frontal sections of the brain, both total and regional damage was
determined with light microscopy. Camera lucida drawings of the silver
staining in the side ipsilateral and contralateral to the clamped
artery were made on millimeter graph paper and used for calculations of
the size of the damaged area. Silver-stained area in square
millimeters served as the numerator, and the total square millimeters
of the area functioned as denominator. This was specified for the
following brain areas: hippocampus, striatum, cortex, and thalamus.
Attention was especially focused on four coronal sections: 5.7, 6.7,
7.7, and 9.2 mm rostral from the interaural line. All data shown are
presented as the mean±SEM. Silver-staining data were
statistically evaluated using an ANOVA with repeated measures followed
by the post hoc corrected (according to Newman-Keuls) Student's
t test. Changes in weight, daily food intake, and blood
pressure were analyzed with a two-tailed Student's
t test. The average silver-staining data were
analyzed with ANOVA. A probability level of P<.05
was considered significant for all tests.
| Results |
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weight) in the 10-mg L-deprenyl group (19.1±3.5 g)
was markedly reduced when compared with the control group (46.9±3.1 g,
P=.0001) and the 2-mg L-deprenyl group
(40.3±3.0 g, P<.001), although daily food intake and food
intake per gram of body weight (not shown) did not differ between the
groups. Blood glucose levels in the control group were 6.3±0.3 mmol/L
and were not significantly different from levels found in the 2-mg/kg
and 10-mg/kg L-deprenyltreated rats (6.0±1.0 and
6.3±0.2 mmol/L, respectively). Also, the mean arterial
blood pressures before, during, and after the hypoxic period of
controls and deprenyl-treated rats were not significantly
different.
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The percentage of damaged area when averaged over several levels showed
that the forebrain in total and all regions studied, except the
hippocampus and the cortex, had significantly less silver-stained
surface (Fig 1
). In the striatum and thalamus, this
damage reduction was at least 50% and at most 79%. The percentage of
total damaged area in the forebrain of control rats was 27%, and this
was reduced in the L-deprenyltreated groups to 6%
(2 mg/kg) and 8% (10 mg/kg).
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Forebrain
The silver-stained surface specified at different levels
rostral from the interaural line showed in some regions an
anterior-posterior damage gradient. In the saline group, the brain
hemisphere ipsilateral to the occluded artery was damaged for 23% to
31% of the total brain area (Fig 1A
). A significant reduction of this
damage (by approximately 75%) to about 5% to 9% of the total brain
area was seen at all four coronal levels studied in the group treated
with 2 mg/kg deprenyl (F1.13=6.956, P<.05) (Fig 1A
). The damage in the 10-mg/kgtreated group was also
significantly less (F1.13=5.731, P<.05)
compared with the saline group. The Newman-Keuls test indicated that
there was a significant damage difference at the most anterior
(17.5±7.9%, P<.05) and posterior (15.6±3.7%,
P<.05) level. The total brain damage in the other two
sections, however, was not significantly different (21.8±4.9,
P=.070; and 23.1±10.8, P=.071;
respectively).
The localization of the silver staining in the control brain was most
pronounced in the dorsolateral parts of the striatum, cortex, and
thalamus (Fig 2
). The hippocampal area (Fig 1B
) in the
control animals was damaged on average for 30% to 38%. In the
hippocampus, no reduction of damage was seen by any of the
L-deprenyl treatments.
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Cortex
In the saline group, silver staining was detectable in
19.6% to 24.3% of the cortical areas (Fig 1C
). In the
L-deprenyl (2 and 10 mg/kg) groups, the cortical damage
was highest at the most frontal levels (4.2% and 7.1%, respectively)
but decreased gradually to 2.1% and 1.7%, respectively, at
the more caudal sections. These differences were significant
(P<.001) at the most caudal levels.
Thalamus
The caudal thalamic levels (Fig 1E
) of saline-treated animals
showed a larger silver-stained area (50.5%) than the more frontal
levels (16.7%). In the L-deprenyltreated groups,
this gradual decrease of silver staining from caudal to frontal levels
was less pronounced. Both the 2- and 10-mg/kg
L-deprenyltreated groups, compared with the saline
group, showed a significant neuroprotective effect in the thalamus
(F1.13=11.638, P<.005; F1.13=8.347,
P<.05; respectively). The thalamic damage after 2-mg/kg and
10-mg/kg deprenyl treatment was significantly reduced at the most
caudal levels, at 5.7 (12.1±6.2, P<.01; and 13.6±5.9,
P<.01; respectively) and 6.7 mm (9.8±3.8,
P<.01; and 11.1±6.4, P<.05; respectively)
rostral from the interaural line.
Striatum
Of all brain areas examined, the percentage of damage was the
highest in the striatal areas of the saline group (Fig 1D
), between
52.1% and 54.6% in the various coronal sections. In the group
injected with 10 mg/kg L-deprenyl, the damage was
significantly reduced (F1.13=8.937, P=.01)
compared with the saline group. The Newman-Keuls test in this group
showed a significant damage reduction at 9.2, 7.7, and 6.7 mm rostral
from the interaural line. The group treated with the low-dose
L-deprenyl showed significantly less
(F1.13=14.870, P<.005) silver-stained area at
all rostrocaudal levels compared with the controls and was affected on
average by 21%.
| Discussion |
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The mechanism through which L-deprenyl diminishes damage is unclear. However, a few possibilities for the protective effects of L-deprenyl should be taken into consideration.
Previously we have shown that rats fasted for 24 hours are protected
against ischemic-hypoxic damage in the presently used
model.1 The reduced
weight of the
L-deprenyltreated animals versus the
saline-treated animals might suggest a chronic fasting state for
the L-deprenyltreated animals. However, the gradual
gain in body weight, the unchanged food intake seen in the
L-deprenyltreated rats, and the comparable blood
glucose levels are in disagreement with the idea that
L-deprenyl treatment induces a hypoglycemic state in
rats. This idea of a chronic fasting state is furthermore rejected by a
study that has shown that the beneficial effects of
L-deprenyl on life expectancy were not mediated by way of
food restriction.15
The regional differences in damage protection by L-deprenyl are in agreement with MAO-b independent effects of L-deprenyl on free radical scavenger enzymes, ie, catalase and superoxide dismutase.3 6 Cortical areas showed a tendency for increased activity, but the increase in the activity of the scavenger enzymes was most pronounced in striatum and thalamus, the areas that were most protected by L-deprenyl in the present study. The hippocampal scavenger enzyme activities, however, were not changed corresponding to the lack of effect of L-deprenyl on hippocampal ischemic damage. This ability of scavenger enzymes to protect against ischemia-induced damage has been described by numerous studies. Not only exogenously applied scavenger enzymes16 but also intrinsically increased expression of these enzymes had beneficial effects on damage outcome. For instance, an increased superoxide dismutase expression in transgenic mice offered protection against radicals generated through ischemia17 18 and/or N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.19
However, other MAO-b inhibitors were shown to eliminate the rise of toxic H2O2 in the reperfusion period in a rat ischemia model.20 So it seems that L-deprenyl can prevent the damaging effects of radicals by either preventing the rise of H2O2, which can quickly be converted to the most damaging OH radical, or by increasing the enzymatic radical scavenging capacity.
Although no significant differences in protection between both doses of L-deprenyl could be found, the low dose of L-deprenyl appears to be the most effective in damage reduction. An explanation for this phenomenon might be given by the fact that L-deprenyl influences the superoxide dismutase and catalase activity in an inverted U-shaped way,3 with an optimal scavenger activity increase after administration of 2 mg/kg L-deprenyl.
Long-term L-deprenyl treatment also has several other beneficial effects: it slows down significantly the age-related decline of sexual functioning in male rats, and it proved to be beneficial for performance in a learning test.21 Finally, it also improved the lifespan of L-deprenyltreated rats compared with their saline-treated peers.9 22
In short, a 14-day L-deprenyl pretreatment in the 2- and 10-mg/kgtreated animals offers substantial protection against an oxygen shortage. Therefore, more should be known about the exact mechanisms behind this protection, the dose responsiveness of this phenomenon, and the protective effects after prolonged L-deprenyl administration, as well as whether L-deprenyl reduces damage when given after hypoxia/ischemia.
| Acknowledgments |
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| Footnotes |
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Received September 22, 1994; revision received June 26, 1995; accepted June 28, 1995.
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