The effect of dietary alpha-tocopherol on the experimental vasogenic brain edema

Alpha-Tocopherol Reduces Brain Edema and Protects Blood-Brain Barrier Integrity following Focal Cerebral Ischemia in Rats

OBJECTIVE

This study was conducted to examine the neuroprotective effects of α-tocopherol against edema formation and disruption of the blood-brain barrier (BBB) following transient focal cerebral ischemia in rats.

MATERIALS AND METHODS

Ninety-six male Sprague-Dawley rats were divided into 3 major groups (n = 32 in each), namely the sham, and control and α-tocopherol-treated (30 mg/kg) ischemic groups. Transient focal cerebral ischemia (90 min) was induced by occlusion of the left middle cerebral artery. At the end of the 24-hour reperfusion period, the animals were randomly selected and used for 4 investigations (n = 8) in each of the 3 main groups: (a) assessment of neurological score and measurement of infarct size, (b) detection of brain edema formation by the wet/dry method, (c) evaluation of BBB permeability using the Evans blue (EB) extravasation technique, and (d) assessment of the malondialdehyde (MDA) and reduced glutathione (GSH) concentrations using high-performance liquid chromatography methods.

RESULTS

Induction of cerebral ischemia in the control group produced extensive brain edema (brain water content 83.8 ± 0.11%) and EB leakage into brain parenchyma (14.58 ± 1.29 µg/g) in conjunction with reduced GSH and elevated MDA levels (5.86 ± 0.31 mmol/mg and 63.57 ± 5.42 nmol/mg, respectively). Treatment with α-tocopherol significantly lowered brain edema formation and reduced EB leakage compared with the control group (p < 0.001, 80.1 ± 0.32% and 6.66 ± 0.87 µg/g, respectively). Meanwhile, treatment with α-tocopherol retained tissue GSH levels and led to a lower MDA level (p < 0.01, 10.17 ± 0.83 mmol/mg, and p < 0.001, 26.84 ± 4.79 nmol/mg, respectively).

CONCLUSION

Treatment with α-tocopherol reduced ischemic edema formation and produced protective effects on BBB function following ischemic stroke occurrence. This effect could be through increasing antioxidant activity.

THERAPEUTIC PERSPECTIVES ON THE COMBINATION OF ALPHA-LIPOIC ACID AND VITAMIN E

Alpha-lipoic acid and vitamin E have synergistic effects, as determined in models of oxidant radical lesions. This review summarizes recent findings showing that the combination of alpha-lipoic acid plus vitamin E has beneficial effects in reducing oxidative damage in ischemic or other oxidation-related pathological events. Both antioxidants are common in the normal human diet and side effects are very rare. Therefore, alpha-lipoic acid and vitamin E can counteract oxidative processes and could have an important role in clinical medicine.

The antioxidant effect of N-acethylcysteine on experimental contusion in rats

N-acethylcysteine (NAC) is known to have direct and indirect antioxidant abilities. We investigated the potential protective effect of NAC on ICP, brain edema and contusion volume after Controlled Cortical Impact (CCI) injury. A moderate CCI injury was induced on the left hemisphere in 48 Sprague Dawley rats. The animals were treated with intraperitoneal injection of NAC (163 mg/kg/KG) or physiological saline. Measurements of intracranial pressure (ICP) were performed and brains were removed at 24 hours. Gravimetric analysis of post-traumatic edema and morphometric measurements (TTC staining) of contusion volume were carried out in 24 animals, respectively. ICP measurements increased significantly over time with no significant differences between both groups. The relative difference in water content in NAC treated animals (1.45 +/- 0.1%) did not differ significantly versus placebo (1.47 +/- 0.2%). The contusion volume was diminished by 19% in the NAC group (53.52 +/- 5.3 mm3) versus placebo (66.28 +/- 4.7 mm3) without showing statistical significance. The antioxidant properties of NAC did not affect intracranial pressure or posttraumatic brain edema formation, although the moderate reduction of contusion volume might reveal beneficial effects on focal contusion.

Bradykinin B2, but not B1, receptor antagonism has a neuroprotective effect after brain injury

The aim of the present study was to measure the therapeutic effects of bradykinin antagonists on lesion volume and brain swelling induced by cold injury in the parietal cortex of rat and mouse, respectively. Cold lesion was induced by application of a precooled (-78 degrees C) copper cylinder (3 mm diameter) to the intact dura of rat and mouse for 6 and 30 sec, respectively. At 24 h after the injury, the brains were removed and lesion volume was determined by the triphenyltetrazolium chloride method in rats. In the mouse, brain swelling was expressed as percentage increase in weight of the injured hemisphere which is compared to the contralateral side. After a subcutaneous priming dose of 18 microg/kg, a 1-h pretreatment and 24-h posttreatment using osmotic minipumps (300 ng/kg x min) was applied. Hoe140, a bradykinin receptor 2 antagonist, revealed a 19% reduction of lesion volume (p < 0.05) in the rat and a 14% diminution of brain swelling (p < 0.05) in the mouse. In contrast, the bradykinin receptor 1 antagonist, B 9858, had no effect on lesion volume compared to sham treated rats. When B 9858 was given in combination with Hoe140, a significant reduction in lesion volume was seen which was equivalent to and not different from that seen with Hoe140 alone in the rat. We conclude that brain injury after cold lesion is partially mediated by bradykinin and can be successfully treated with B2 antagonists.

Role of nitric oxide in the secondary expansion of a cortical brain lesion from cold injury

We have investigated the role of nitric oxide (NO) as mediator of the secondary growth of a traumatic cortical necrosis. For this purpose, a highly standardized focal lesion of the brain was induced in 46 Sprague-Dawley rats by cold injury. Twenty-four hours later--the timepoint of maximal lesion spread--the animals were sacrificed and brains were removed for histomorphometry of the maximal necrosis area and volume. The animals were divided into five experimental groups. Group I received the NO donor L-arginine as i.v. bolus 10 min prior to trauma (300 mg/kg body weight; n = 10) and a second bolus of the same dosage intraperitoneally 1 h after trauma. Group II (n = 10)--serving as control of group I--was infused with an i.v. bolus of 1 mL/kg isotonic saline 10 min prior to and a subsequent bolus i.p. 1 h after trauma. Group III (n = 8) received 100 mg/kg b.w. of the inducible NOS (iNOS) inhibitor aminoguanidine (AG) 1 h before and 8 h after trauma by intraperitoneal route. Group IV was administered with the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine (L-NNA; 100 mg/kg b.w., i.p.; n = 8); group V--the controls of group III and IV--was administered with isotonic saline (1 mL/kg b.w. i.p.; n = 10) 1 h before and 8 h after trauma. In the control group with i.v./i.p. sham treatment (II), the focal lesion led to a cortical necrosis with a maximum area of 3.1 +/- 0.3 mm2 and a lesion volume of 5.7 +/- 0.5 mm3 at 24 h after trauma. In animals with administration of L-arginine, the focal lesion had a maximum area of 3.1 +/- 0.3 mm2 and a volume of 5.3 +/- 0.5 mm3. Hence, the NO donor did not affect the secondary growth of necrosis. Animals with i.p. sham treatment (group V) had a maximal lesion area of 3.6 +/- 0.2 mm2 and lesion volume of 6.2 +/- 0.4 mm3. Administration of aminoguanidine afforded significant attenuation of the lesion growth. Accordingly, the maximal area of necrosis spread only to 2.8 +/- 0.2 mm2 with a volume of 4.5 +/- 0.5 mm3, respectively, at 24 h after trauma (p < 0.01 vs group V). On the other hand, administration of L-NNA did not influence the maximal lesion area (3.7 +/- 0.2 mm2) or lesion volume (6.5 +/- 0.5 mm3) evolving at 24 h after trauma. Thus, neither the enhancement of the formation of NO by L-arginine nor gross inhibition of the synthesis of NO by L-NNA did affect the secondary spread of the necrosis from a focal trauma. The marked attenuation of the posttraumatic necrosis growth by the iNOS inhibitor aminoguanidine strongly indicates an important role of iNOS product in this phenomenon. These findings, thus, demonstrate that the expansion of a primary necrotic focal lesion is a secondary process which can be therapeutically inhibited. Thereby, the growth of a focal tissue necrosis from trauma is clearly identified as a manifestation of secondary brain damage. This information is deemed important for the better understanding of the pathophysiology of traumatic brain injury and for the targeted development of specific treatment modalities.

Temporal profile of expression and cellular localization of inducible nitric oxide synthase, interleukin-1beta and interleukin converting enzyme after cryogenic lesion of the rat parietal cortex

We used in situ hybridization, RT PCR and immunohistochemistry to study the time course of expression and the cellular localization of inducible nitric oxide synthase (iNOS) and interleukin-1beta (IL-1beta) during the first 7 days after induction of a standardized cryogenic lesion on the right parietal cortex in male rats. Cryogenic lesion induced iNOS mRNA in the lesioned hemisphere after 6 to 72 h with a maximum (15+/-2 cells/mm2, n=4, p<0.01 vs. sham) at 24 h. Microglia, invading monocytes and granulocytes in and around the lesion expressed iNOS immunoreactivity starting at 12 h and peaking (29+/-10 cells/mm2, n=4, p<0.05 vs. sham) at 24 h after lesion. Induction of IL-1beta mRNA expression was immediate with a peak (9+/-1 cells/mm2, n=4, p<0.01 vs. sham) at 24 h after cryogenic lesion. The number of round cells with IL-1beta immunoreactivity around the lesion was maximal (8+/-2 cells/0.1 mm2, n=3, p<0.01 vs. sham) at 24 h. A weak astrocytic expression of IL-1beta-immunoreactivity was seen in sham animal brains. Astrocytic IL-1beta-expression was significantly increased in the lesion hemisphere and both hippocampi. Interleukin converting enzyme (ICE) was expressed in astrocytes and microglia around the lesion 6 h after injury. The number of ICE immunoreactive cells (8+/-2 cells/0. 1 mm2, n=3, p<0.05 vs. sham) peaked at 72 h after lesion. Neuronal expression of ICE and IL-1beta was seen in the lesion periphery 72 h and 7 days after injury. At this time, morphological features of apoptosis were evident in cells in the lesion periphery. The data indicate an early activation of microglia and monocyte invasion into the lesion hemisphere leading to multicellular expression of iNOS, ICE, and IL-1beta. These events may contribute to the expansion of neuronal damage after brain injury.

Delayed loss of ETB receptor-mediated vasorelaxation after cold lesion of the rat parietal cortex

The aim of this study was to investigate the involvement of endothelins (ET) in brain injury. The effect of ET was studied in the isolated basilar artery (BA) taken from control, sham-operated, and cold-lesioned rats. Cold lesion was induced by application of a precooled (-78 degrees C) copper cylinder (outer diameter 5 mm) for 60 seconds to the intact dura over the parietal cortex. After precontraction with prostaglandin (PG) F2alpha, ET-3 (10(-10) to 10(-8) mol/L) dilated BA with a pD2 (negative log of the half-maximal concentration) of 9.06+/-0.031 (mean +/- SD) and a maximal effect (Emax) of 1.64+/-1.0 mN at 3 x 10(-9) mol/L in sham-operated animals. This dilation was reduced 24 and 48 hours after cold lesion by 33% and 73%, respectively, at 3 x 10(-9) mol/L. The effects of acetylcholine (10(-8) to 10(-4) mol/L) and sodium nitroprusside (10(-3) mol/L) were unaltered. Activation of the ETB receptor in thoracic aorta by the specific agonist IRL 1620 also resulted in a reduced dilation (51% by 48 hours after cold lesion). Reverse transcriptase-polymerase chain reaction of the BA showed unaltered expression of mRNA for the ETB receptor after cold lesion whereas ETB immunoreactivity in BA and in its intraparenchymal arteries was reduced at 24 and 48 hours. In contrast to the reduction of ET-3-induced dilation, the constrictor effects of ET-1 and ET-3 were retained after cold lesion. Endothelin-1 (10(-12) to 10(-6) mol/L) dose-dependently contracted segments of untreated control BA segments under resting conditions with a pD2 of 8.03+/-0.22 and an Emax of 6.35+/-0.70 mN. Further evidence that the constrictor ability of BA was not influenced by cold lesion is given by the unaltered response to 124 mmol/L K+ and 10(-6) mol/L serotonin. We conclude that the ETB receptor of BA after cold lesion is downregulated specifically, apparently at the posttranscriptional level. Because the ETB-mediated dilation in thoracic aorta was also reduced, downregulation of the ETB receptor apparently is not restricted to cerebral arteries. The nitric oxide-cyclic guanosine monophosphate system in BA is, however, intact.

Reduced reactivity of the middle cerebral artery and its large branches after cold lesion

The aim of this study was to measure vascular reactivity in the isolated middle cerebral artery (MCA) after brain injury. Segments of MCA were prepared from control, sham-operated, and cold-lesioned rats. Cold lesion was induced by application of a precooled (-78 degrees C) copper cylinder (diameter 5 mm) for 60 sec to the intact dura over the parietal cortex. Endothelin-1 (ET-1) (10(-12) to 3 x 10(-7) M) induced a dose-dependent contraction with a pD2 (-log10 EC50) of 8.36+/-0.12 (mean+/-SEM) and an Emax (maximal response) of 2.41+/-0.15 mN (millinewton) at 10(-7) M in sham-operated animals under resting conditions. This maximum contraction induced by 10(-7) M ET-1 was significantly (p < 0.05) reduced 24 and 48 h after cold lesion by 41% and 30%, respectively. After precontraction with 10(-5) M prostaglandin (PG) F2alpha, ET-3 (10(-12) to 10(-8) M) relaxed the MCA with an Emax of 0.42+/-0.07 mN at 10(-8) M and a pD2 of 9.20+/-0.19 in sham-operated animals. This relaxation was reduced 24 and 48 h after cold lesion by 19% and 62% at 10(-8) M, respectively. Concentration-effect curves for bradykinin (BK, 10(-8) to 10(-5) M) in uridine triphosphate (UTP, 10(-4) M)-precontracted MCA segments revealed relaxation with a pD2 of 7.08+/-0.10 and an Emax of 0.65+/-0.06 mN at 10(-6) M in sham-treated animals. This effect of BK was reduced by 35% and 20% at 10(-6) M 24 and 48 h after cold lesion, respectively. In addition, the contractile responses to 124 mM K+, 10(-5) M PGF2alpha and the dilation induced by 10(-3) sodium nitroprusside (SNP) were reduced in MCA segments taken 24 and 48 h after lesion compared with shams. We conclude that attenuation of ET effects can be explained, at least in part, by tachyphylaxis to ETs. The unspecific reduction of vascular reactivity may result from spreading depression.

Novel pharmacologic strategies in the treatment of experimental traumatic brain injury: 1998

The mechanisms underlying secondary or delayed cell death following traumatic brain injury are poorly understood. Recent evidence from experimental models suggests that widespread neuronal loss is progressive and continues in selectively vulnerable brain regions for months to years after the initial insult. The mechanisms underlying delayed cell death are believed to result, in part, from the release or activation of endogenous "autodestructive" pathways induced by the traumatic injury. The development of sophisticated neurochemical, histopathological and molecular techniques to study animal models of TBI have enabled researchers to begin to explore the cellular and genomic pathways that mediate cell damage and death. This new knowledge has stimulated the development of novel therapeutic agents designed to modify gene expression, synthesis, release, receptor or functional activity of these pathological factors with subsequent attenuation of cellular damage and improvement in behavioral function. This article represents a compendium of recent studies suggesting that modification of post-traumatic neurochemical and cellular events with targeted pharmacotherapy can promote functional recovery following traumatic injury to the central nervous system.

Protective effects of free radical inhibitors in intracerebral hemorrhage in rat

Iron compounds formed in the degradation of a hematoma can accelerate the formation of free radicals in adjacent ischemic or hypoperfused tissue. The purpose of this study was to examine the efficacy of compounds that quench free radicals in improving the outcome in rats with experimental intracerebral hemorrhage. Intracerebral hemorrhage was induced in rats by injection of bacterial collagenase and heparin into the caudate nucleus. Rats were treated with alpha-tocopherol plus ascorbic acid starting before hemorrhage, or with dimethylthiourea or alpha-phenyl-N-tert-butyl nitrone starting 2 h after hemorrhage, with treatment continued for 10 days after induction of hemorrhage. Outcome was assessed by behavioral analyses, magnetic resonance imaging, and histopathology. A trend towards behavioral improvement was found for rats treated with alpha-tocopherol/ascorbic acid, while behavior was significantly improved following intracerebral hemorrhage in rats treated with dimethylthiourea or alpha-phenyl-N-tert-butyl nitrone. These results suggest that free radicals may play a role in the development of brain injury following intracerebral hemorrhage, and that compounds that interrupt the free radical cascade may improve outcome. However, treatment did not significantly affect edema, resolution of the hematoma, or neuronal injury in tissue adjacent to the hemorrhage.