Polymorphonuclear leukocytes occlude capillaries following middle cerebral artery occlusion and reperfusion in baboons

Time-related changes in myeloperoxidase activity and leukotriene B4 receptor binding reflect leukocyte influx in cerebral focal stroke

In previous studies, we have used histological methods to characterize cellular changes, and validated the use of the myeloperoxidase (MPO) activity assay to quantitate increased neutrophil infiltration in ischemic stroke. We also identified increased leukotriene B4 (LTB4) binding sites as a potential marker for neutrophil infiltration into focal ischemic tissue. However, these studies were conducted at only one time-point, 24 h after ischemia. In the present study, we examined the full time-course of MPO activity and LTB4 receptor binding following middle cerebral artery occlusion (MCAO) made permanently (PMCAO) or transiently (160 min followed by reperfusion; TMCAO) in spontaneously hypertensive rats, and compared the results to previously characterized histologic changes in these models. Ischemic and contralateral (control) cortical tissue samples were assayed for MPO (U/g wet wt) and [3H]LTB4 receptor binding (fmol/mg protein). Following PMCAO, MPO activity significantly increased as early as 12 h and continued to increase over the next 5 d (p < 0.05). Following TMCAO, MPO activity was significantly elevated already after only 6 h of reperfusion and also continued to increase over the next 5 d of reperfusion (p < 0.05). LTB4 receptor binding and MPO activity were highly correlated during periods when both measures increased together (i.e., 0.5-5 d; p <0.01). However, by 15 d post-MCAO, LTB4 receptor binding remained elevated after MPO activity levels had returned to normal. This persistent LTB4 binding was associated with the significant gliosis that was characterized previously to persist in these models. The time-course of increased MPO activity and initially increased LTB4 binding post-MCAO correspond very well to our previous histological data that characterized the time-course for leukocyte infiltration under these conditions. Therefore, the increased MPO activity over time was associated with initial neutrophil and later mononuclear cell infiltration into ischemic tissue in these models. In addition, the present studies utilized histochemical analysis to demonstrate peroxidase activity in macrophages within the cerebral infarct following MCAO, thus validating that MPO activity originates from the later infiltrating mononuclear cells in addition to the early infiltrating neutrophils that had been previously characterized in the same manner. TMCAO produces a significantly larger and earlier increase in ischemic cortex MPO activity and a similar later increase in MPO activity compared to PMCAO treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Gross persistence of capillary plasma perfusion after middle cerebral artery occlusion in the rat brain

The densities of perfused and existing capillaries were measured in different cortical regions of rat brains after subtemporal occlusion of the middle cerebral artery (MCA). Capillary perfusion patterns (perfused capillaries versus nonperfused capillaries) were verified immediately after MCA occlusion in one group of rats and 1 h later in a second group using fluorescent double staining of capillary morphology and plasma perfusion in identical brain sections. In addition, local cerebral blood flow (CBF) was measured in another group of rats 1 h after MCA occlusion using the autoradiographic iodo-[14C]-antipyrine method. Although cortical CBF was decreased by up to 75% 1 h after MCA occlusion, plasma perfusion was not completely stopped in most capillaries (circulation time of Evans blue, 10 s). Only small patchy perfusion deficits (< 0.1 mm2 of brain section) were detected in the capillaries immediately and 1 h after MCA occlusion in all brains except for one that exhibited a more extensive lack of capillary perfusion. The data show that a drastic reduction of cortical CBF after MCA occlusion is not accompanied by a corresponding amount of nonperfused capillaries.

Polymorphonuclear leukocyte behavior in a nonhuman primate focal ischemia model

There is increasing interest in the role of polymorphonuclear (PMN) leukocytes in the evolution of focal cerebral infarction. Surgical preparation of focal cerebral ischemia models may alter leukocyte reactivity and thereby make interpretation of leukocyte function following ischemia/reperfusion difficult. The effects of surgical preparation and of experimental ischemia/reperfusion on granulocyte function have been examined prospectively in a baboon model. Twenty-six adolescent male baboons underwent surgical preparation, of which 21 underwent middle cerebral artery occlusion/reperfusion. Four additional animals served as nonsurgical controls. Peripheral venous blood specimens were taken for performing assays of leukocyte function at defined intervals before and after both the surgical preparation (i.e., the overall procedure for implantation of the middle cerebral artery occlusion device) and occlusion/reperfusion. A stress-related elevation in total leukocyte number was attributed mainly to an increase in the number of circulating PMN leukocytes. Values rose from 13.9 +/- 4.9 x 10(3) to 27.8 +/- 5.8 x 10(3)/microliters, (+/- SD; n = 21) for total leukocyte number, with p < 0.001, and from 4.3 +/- 2.1 x 10(3) to 15.9 +/- 4.7 x 10(3)/microliters (n = 21) for PMN leukocytes, with p < 0.001. Surgical preparation had no effect (p > or = 0.4) on the ability of PMN leukocytes, isolated 24 h after the implantation procedure, to display polarization, O2.- production, or beta-glucuronidase release when stimulated with human C5a. A moderate decrease in the chemotactic response to C5a resolved within the 7-day postsurgery (preocclusion) period. Three-hour middle cerebral artery occlusion and 1-h reperfusion resulted in a significant reduction in C5a-induced polarization.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibrin contributes to microvascular obstructions and parenchymal changes during early focal cerebral ischemia and reperfusion

BACKGROUND AND PURPOSE

Ischemic cerebral injury is associated with activation of the blood coagulation cascade. To elucidate the contribution of fibrin formation to microvascular injury during focal cerebral ischemia and reperfusion, we have studied the time course and the localization of fibrin deposition in cerebral microvessels and the surrounding tissues during ischemia/reperfusion in a well-described nonhuman primate model.

METHODS

Cerebral tissues from adolescent male baboons were examined after 2-hour middle cerebral artery occlusion (n = 3) and after 3 hours of middle cerebral artery occlusion and 1-hour (n = 6), 4-hour (n = 3), and 24-hour (n = 4) reperfusion; tissues from control primates (n = 3) also were examined. Fibrin deposition was detected by immunohistochemical techniques using the fibrin-specific monoclonal antibody MH-1. The number and size distribution of microvessels associated with fibrin were quantified by video-imaging microscopy.

RESULTS

Fibrin was associated with microvessels only in the ischemic zone where severe neuronal injury was documented, its frequency increasing with the reperfusion period (F4,26 = 3.80, P < .05). Extravascular fibrin deposition was significantly increased by 24-hour reperfusion compared with the other subjects (P < .05). Preischemia infusion of the anti-tissue factor monoclonal antibody TF9-6B4 resulted in significant reduction of intramicrovascular fibrin (P < .038 versus no intervention) at 1-hour reperfusion but had no effect on extravascular fibrin deposition.

CONCLUSIONS

These results suggest that microvascular fibrin deposition accumulates in a time-dependent manner during focal cerebral ischemia/reperfusion and that exposure of focal cerebral ischemia/reperfusion and that exposure of plasma to perivascular tissue factor is partially responsible for occlusion formation. During ischemia the large plasma protein fibrinogen extravasates and interacts with parenchymal tissue factor, forming significant extravascular fibrin by 24 hours of reperfusion.

The effect of hypothermia on transient focal ischemia in rat brain evaluated by diffusion- and perfusion-weighted NMR imaging

The effect of moderate whole-body hypothermia (30 degrees C) on transient middle cerebral artery (MCA) occlusion in the rat was evaluated using diffusion- and perfusion-weighted magnetic resonance imaging. Two hours of transient MCA occlusion was induced by intracarotid insertion of a nylon filament under normothermic (n = 14) and hypothermic (n = 7) conditions. Diffusion- and perfusion-weighted imaging were performed before, during, and after focal ischemia from 30 min up to 7 days. In hypothermic animals, scattered neuronal necrosis was localized to select areas of the caudate putamen and the parietal and insular cortex. In contrast, the normothermic ischemic animals exhibited pan-necrosis and infarct encompassing the damaged area. The diffusion and perfusion data measured from caudate putamen indicate that hypothermia causes a significant reduction in the apparent diffusion coefficient of water (ADCw) and CBF values from normothermic control values (p < 0.01). In both normothermic and hypothermic animals after onset of MCA occlusion, ADCw and CBF values in the core of the ischemic region (striatum) significantly declined from the preischemic and homologous contralateral control ADCw and CBF values (p < 0.05). However, ADCw and CBF in the hypothermic group returned toward control more rapidly than in the normothermic group. These results suggest that the protective effect of hypothermia on ischemic cell damage is reflected in the early return of ADCw during reperfusion and the reduction of ischemic cell damage by hypothermia may be mediated by the improved CBF during acute reperfusion.

Temporal profile of ischemic tissue damage, neutrophil response, and vascular plugging following permanent and transient (2H) middle cerebral artery occlusion in the rat

We investigated the temporal profile of ischemic tissue damage, neutrophil response, and vascular occlusion after permanent and transient middle cerebral artery occlusion in the rat. Focal cerebral ischemia was induced by advancing a nylon monofilament to occlude middle cerebral artery (MCA). Two groups of rats were investigated: (1) those with permanent MCA occlusion (n = 29), and (2) and those having the arterial occlusion released after 2 h (n = 34). Experiments were terminated at 6, 12, 24, 48, 72, 96 and 168 h after the onset of ischemia, and brain sections were stained with hematoxylin and eosin for histological evaluation. Initially, the cortical lesion was smaller in rats subjected to transient MCA occlusion than in rats subjected to permanent MCA occlusion (p < 0.02). The surface area of the lesion was identical in both groups at 48 h after the onset of ischemia. Neutrophil infiltration into tissue and the time of peak neutrophil infiltration occurred earlier after transient MCA occlusion than after permanent MCA occlusion (6 h, 48 h in transient; 12 h, 72 h in permanent). Within the lesions, the number of occluded vessels was significantly lower in the transient ischemia group than in the permanent ischemia group during the time interval between 12-48 h (p < 0.01). Our data suggest that the temporal evolution of the lesion, the pattern of neutrophil infiltration and the chronology of microvascular occlusion differs depending on whether the MCA occlusion is transient (2 h) or permanent; however, significant differences in the size of the brain lesion disappeared 48 h after onset of ischemia.

Increased expression of ICAM-1 during reoxygenation in brain endothelial cells

BACKGROUND AND PURPOSE

Thrombolysis is a promising therapy for acute ischemic stroke. However, there is evidence that neutrophils may physically plug cerebral microvessels on reperfusion, preventing the full benefit of thrombolysis. We undertook this study to determine whether there was increased endothelial expression of the intercellular adhesion molecule-1 (ICAM-1) gene during hypoxia-reoxygenation.

METHODS

We isolated and cultured human brain microvascular endothelial cells and subjected them to hypoxia (PO2 < 10 mm Hg) in an anaerobic chamber followed by variable periods of reoxygenation.

RESULTS

Twenty-hour periods of hypoxia did not lead to endothelial cytotoxicity as measured by a chromium-release assay. By Northern blot analysis, ICAM-1 mRNA transcripts were dramatically increased at 4 hours of reoxygenation but fell toward baseline (normoxia) by 12 and 24 hours. Hypoxia alone did not lead to an increase in mRNA levels. Western blot analysis showed an increased expression of ICAM-1 at 4, 12, and 24 hours of reoxygenation. The 4-hour increase in mRNA levels was not attenuated by pretreatment with 100 mumol/L allopurinol but was reduced by 30% with the addition of 20 mmol/L N-acetyl-L-cysteine at the time of reoxygenation and completely prevented by pretreatment with N-acetyl-L-cysteine.

CONCLUSIONS

Hypoxia-reoxygenation leads to an increase in ICAM mRNA levels that peaks at 4 hours in human brain microvascular endothelial cells. Pretreatment with N-acetyl-L-cysteine can completely block the increase in ICAM-1 mRNA levels.

Reduction of central nervous system reperfusion injury in rabbits using doxycycline treatment

BACKGROUND AND PURPOSE

Activated leukocytes appear to potentiate central nervous system reperfusion injury, and agents that block leukocyte adhesion have shown neuroprotective efficacy in experimental models. Doxycycline, a tetracycline antibiotic, inhibits leukocyte function in vitro, presumably through divalent cation binding. We used a model of focal central nervous system reperfusion injury to determine the efficacy of doxycycline treatment in preserving neurological function.

METHODS

Rabbits randomly received 10 mg/kg i.v. doxycycline 30 minutes before ischemia (pretreatment group) or 45 minutes after ischemia (posttreatment group) or received phosphate-buffered saline vehicle (control group) followed by 10 mg/kg q 8 hours times two. The average length of reversible spinal cord ischemia required to produce paraplegia (P50) at 18 hours was calculated for each group.

RESULTS

For the control group (n = 13), the P50 was 22.8 +/- 2.2 minutes; for the pretreatment group (n = 14), 35.5 +/- 2.4 minutes (P < .01; t = 3.8); and for the posttreatment group (n = 13), 31.4 +/- 4.2 minutes (not significant; t = 1.6). Doxycycline also attenuated postischemic decreases in vivo leukocyte counts and inhibited in vitro leukocyte adhesion. Therapeutic doxycycline levels at 24 hours were confirmed in the plasma and spinal cord.

CONCLUSIONS

This significant protective effect suggests that doxycycline, a safe and readily available agent, may play a role in reducing clinical central nervous system reperfusion injury.

Effects of neutropenia on edema, histology, and cerebral blood flow after traumatic brain injury in rats

Neutrophils accumulate during the acute inflammatory response to brain injury, but their role in the injury process remains controversial. We tested the hypothesis that neutrophils contribute to cerebral edema, tissue injury, and disturbed cerebral blood flow (CBF) (hyperemia or ischemia) during the first 24 h after traumatic brain injury. Wistar rats (n = 51) were injected with either vinblastine sulfate to induce neutropenia or the saline vehicle. Five days later, under halothane anesthesia, right hemispheric trauma was produced by weight drop (10 g x 5 cm) onto exposed dura. At 24 h after trauma, brain water (wet-dry weight), traumatic infarct size (percent of hemispheric section infarcted), or local CBF (lCBF, 14C-iodoantipyrine autoradiography) was assessed. Vinblastine treatment produced profound neutropenia on the day of trauma (absolute neutrophil count 0.024 +/- 0.008 x 10(9)/L vs 1.471 +/- 0.322 x 10(9)/L, p < 0.05 in neutropenic vs saline, respectively, mean +/- SEM). Neutropenia did not reduce the development of brain edema in the injured hemisphere (brain water 82.38 +/- 0.29% vs 82.73 +/- 0.37% in neutropenic and saline, respectively, mean +/- SEM) or traumatic infarct size (34.5 +/- 3.3% vs 33.2 +/- 2.1% in neutropenic vs saline respectively). In contrast, neutropenic rats exhibited 52%, 41%, and 57% reductions in lCBF in the frontal cortex, parietal cortex, and amygdala, respectively, of the injured hemisphere 24 h after trauma (all p < 0.05 vs nonneutropenic controls). These data suggest that neutrophils and the acute inflammatory process contribute to the level of CBF observed 24 h after trauma, but effects on edema or early posttraumatic infarct size could not be demonstrated.

Uptake of C5a by polymorphonuclear leukocytes (PMNs) after focal cerebral ischemia. I. Effect of tirilazad mesylate intervention on C5a uptake by PMNs

PMNs are believed to play an important role in ischemia and C5a uptake is an important functional indicator for G protein-coupled receptor trafficking. The ability of PMNs to internalize 125I-labeled C5a in vitro is an index of the functional state of these cells. We evaluated the effects of model preparation and focal cerebral ischemia by middle cerebral artery occlusion and reperfusion (MCA:O/R) on internalization of C5a by PMNs isolated from baboons (Papio anubis/cynocephalus). Similar assays were performed on PMNs isolated before and after exposing the animals undergoing MCA:O/R to an anti-inflammatory 21-aminosteroid, tirilazad mesylate (U74006F). Surgical implantation of the MCA occlusion device had no measureable effect on uptake of C5a to the cytosol by the PMN. In contrast, MCA:O/R appeared to decrease uptake of C5a. Both in vivo and in vitro administration of tirilazad, to otherwise untreated animals and to isolated cells, respectively, reduced baseline values of C5a uptake in the PMNs. Cytosolic uptake of C5a was also reduced in PMNs isolated from subjects that had undergone MCA:O/R and tirilazad treatment. These results suggest that focal cerebral ischemia, with or without exposure to tirilazad mesylate, may inhibit internalization of C5a by the PMN receptors. The effects of stroke on the ability of C5a to gain entry into the PMN may result from receptor down-regulation or "desensitization" of the cell, possibly due to activation of complement and generation of C5a which occupied the receptors. Alternatively, the effect of tirilazad presumably results from the ability of this drug to enter the membrane lipid layer and reduce fluidity.

Cortical hypoperfusion after global forebrain ischemia in rats is not caused by microvascular leukocyte plugging

BACKGROUND AND PURPOSE

We tested the hypothesis that cerebral hypoperfusion after experimental global cerebral ischemia is caused by plugging of the microcirculation with activated leukocytes using in vivo microscopic observation of the behavior of leukocytes in the cortical microcirculation during the transition from postischemic hyperperfusion to hypoperfusion.

METHODS

Anesthetized and ventilated rats (n = 24) were equipped with a closed cranial window. Physiological variables and cortical regional cerebral blood flow (laser-Doppler flowmetry) were measured continuously. Leukocytes were labeled intravitally with rhodamine 6G and visualized in the microcirculation of the brain surface and outer layers of the cortex with confocal laser scanning microscopy from preischemia to 4 hours after reperfusion that followed 10 minutes of global cerebral ischemia (rCBF < 10% of control).

RESULTS

In controls (n = 8), there were no signs of leukocyte activation over the 4-hour observation period. In ischemic rats (n = 16), during the transition from hyperperfusion to hypoperfusion there was no change in the behavior of leukocytes. Most notably, no capillary pluggers were seen. In the postischemic period only a slight increase of the number of leukocytes rolling along or sticking to the venular endothelium was seen, and very few capillaries were plugged by leukocytes. Extravasation of leukocytes into the brain tissue was observed in 8 rats beginning 2 hours after ischemia with a variable degree between animals.

CONCLUSIONS

Because there was only mild activation of leukocyte-endothelium interaction within the first hours of reperfusion after 10 minutes of global forebrain ischemia, because no leukocytes plugged superficial cortical capillaries during the transition from hyperperfusion to hypoperfusion, and because the regional cerebral blood flow transition was very rapid, we speculate that leukocyte plugging is not responsible for the early cortical hypoperfusion seen after brief global ischemia in rats.

Postischemic administration of an anti-Mac-1 antibody reduces ischemic cell damage after transient middle cerebral artery occlusion in rats

BACKGROUND AND PURPOSE

Postischemic cerebral inflammation may contribute to ischemic cell damage. The CD11b/18 (Mac-1) integrin mediates stimulated neutrophil binding to endothelia. We therefore investigated the effect of administration of an anti-Mac-1 monoclonal antibody on cerebral ischemic cell damage in the rat.

METHODS

Rats (n = 10) were subjected to 2 hours of middle cerebral artery occlusion; the anti-Mac-1 antibody was administered at a dose of 2 mg/kg i.v. at 1 hour of reperfusion and 1 mg/kg i.v. at 22 hours of reperfusion or an isotype-matched control antibody (n = 10) was administered using the same experimental protocol. Rats were killed at 46 hours of reperfusion, and brain sections were stained with hematoxylin and eosin for histological evaluation. In a separate population of rats given either vehicle (n = 8) or anti-Mac-1 antibodies (n = 9), intraparenchymal neutrophils were measured by means of a myeloperoxidase assay.

RESULTS

The lesion volume was significantly smaller (28%) in the anti-Mac-1 antibody group compared with the vehicle control group (P < .01). Numbers of intraparenchymal polymorphonuclear cells were significantly reduced (P < .05) in the cortex of the anti-Mac-1 antibody group compared with the vehicle control group.

CONCLUSIONS

Our data demonstrate that administration of anti-Mac-1 antibody 1 hour after onset of reperfusion results in significant reductions of ischemic cell damage and intraparenchymal neutrophils after transient (2-hour) focal cerebral ischemia in the rat.

Role of neutrophil-endothelial cell adhesion in inflammatory disorders

Polymorphonuclear leukocytes are armed with an impressive arsenal of bactericidal agents that allow these cells to play a vital role in host defense against invading pathogens. However, these same agents can produce extensive cellular damage in host tissues when leukocytes are activated during inflammatory conditions. Recognition of this fact, when coupled with the observation that leukocyte adhesion to post-capillary venules is a critical first step in the inflammatory process, has led to the development of the concept that inhibition of neutrophil-endothelial cell adhesion (NECA) may represent a novel therapeutic strategy for the prevention of leukocyte-dependent injury in inflammatory conditions. Indeed, pharmacological or immunologic inhibition of NECA reduces cellular injury, dysfunction, and necrosis induced by ischemia/reperfusion, circulatory shock and resuscitation, organ transplantation, cardiopulmonary bypass, frostbite, and thermal trauma. NECA also appears to play an important role in the pathobiology of airway inflammation and asthma, pulmonary oxygen toxicity, arthritis, bacterial meningitis, and cerebral malaria. The aim of this review is to summarize the evidence implicating NECA in the pathogenesis of these inflammatory conditions.

ICAM-1 expression on human brain microvascular endothelial cells

There is evidence that leukocytes play an important role in mediating tissue injury during acute ischemic stroke. Endothelial cell adhesive molecules such as ICAM-1 are required for the migration of leukocytes into the brain. Using an Elisa, we compared the expression of ICAM-1 by human brain microvascular endothelial cells with human umbilical vein endothelial cells. There was constitutive surface expression of ICAM-1 on both brain and umbilical vein endothelial cells. With cytokine (IL-1 beta or TNF) or lipopolysaccaride stimulation, ICAM-1 surface expression increased to a greater extent on brain than on umbilical vein endothelial cells. Dexamethasone at doses up to 100 microM had no effect on inhibiting cytokine-mediated upregulation of ICAM-1 on human brain microvascular endothelial cells.

Reperfusion following focal stroke hastens inflammation and resolution of ischemic injured tissue

Previously, we described cellular changes following Permanent Middle Cerebral Artery Occlusion (PMCAO) in spontaneously hypertensive rats. Ischemic changes following PMCAO included a time-related focal pan necrosis, inflammatory cell infiltration, gliosis, and eventual loss of necrotic tissue post PMCAO. We have now characterized changes which occur after Temporary Middle Cerebral Artery Occlusion (TMCAO; 80 or 160 min) followed by reperfusion and compared these changes to those which occur following PMCAO. TMCAO with reperfusion results in cortical infarcts which vary in size in an occlusion-time-dependent manner. After 1 h of reperfusion, ischemic changes were observed histologically, including microhemorrhages and the beginning of a slight inflammatory infiltration in and around the meningeal vasculature. This infiltrate consisted primarily of neutrophils, which by 6 h of reperfusion was significant with infiltration from deep blood vessels into brain tissue, including the presence of some monocytes adhering within blood vessels. Neutrophil infiltration occurred sooner and to a greater extent in reperfused tissues than in permanently occluded tissues, where it only began at 12 h post PMCAO. As occurred following PMCAO, increased Glial Fibrillary Acidic Protein (GFAP) immunoreactivity indicating astrogliosis was first observed at 12 h postTMCAO. Over 1-3 days of reperfusion, a heavy macrophage infiltrate was observed in the reperfused tissues in addition to a continued influx of neutrophils. Following 5 days of reperfusion, the lesion was completely replaced with inflammatory cells, of which macrophages predominated. Unlike PMCAO, which resulted in focal spots of neutrophil accumulation, neutrophils were more distributed throughout the infarcted cortex following TMCAO.(ABSTRACT TRUNCATED AT 250 WORDS)

Polymorphonuclear leukocytes in ischemic vascular disease

Over the last decade, an extensive amount of evidence has accumulated which implicates PMN in the etiology and pathophysiology of ischemic/thrombotic diseases. It has become apparent that PMN infiltration is not, as once thought, an innocent secondary phenomenon following ischemia. Rather, PMN are active participants in the pathophysiology of infarction, exacerbating the tissue damage. Since the development of means to achieve reperfusion after thrombosis, this phenomenon has become of critical importance. Many different approaches, targeted at prevention of PMN trapping in the capillaries of the ischemic, area, have been shown to effectively reduce the final infarct size, and will likely prove valuable adjuncts to reperfusion. However, perhaps the most significant aspect of the realization that PMN play a significant role in thrombotic disease may prove to be the potential for early intervention: Elevated PMN counts are predictive of ischemic events, and there is preliminary evidence that the elevated PMN count may be also associated with increased PMN activation, suggesting that research directed at the prophylactic use of anti-PMN agents might someday prove effective in reducing the incidence of MI and stroke.

P-selectin and intercellular adhesion molecule-1 expression after focal brain ischemia and reperfusion

BACKGROUND AND PURPOSE

Polymorphonuclear leukocytes have been implicated in the development of the "no-reflow" phenomenon after focal cerebral ischemia and reperfusion. To further understand the role of granulocytes in microvascular occlusions, the responses of the granulocyte-endothelial cell adhesion molecules P-selectin and intercellular adhesion molecule-1 during middle cerebral artery ischemia and reperfusion were examined in a primate model.

METHODS

Twelve adolescent male baboons were used for 2-hour middle cerebral artery occlusion (n = 3) or for 3-hour occlusion with 1-hour (n = 3), 4-hour (n = 3), and 24-hour (n = 3) reperfusion, and three separate unoperated primates served as controls. A quantitative immunohistochemical study of the microvascular distribution of P-selectin and intercellular adhesion molecule-1 was performed using 10-microns frozen sections from basal ganglia analyzed with computerized light microscopy video imaging.

RESULTS

Significant (P < .05) persistent upregulation of P-selectin (beginning during ischemia) and transient upregulation of intercellular adhesion molecule-1 (at 1 and 4 hours of reperfusion) were observed on endothelium of selected post-capillary microvessels of the ischemic lenticulostriate artery territory. Platelet accumulation also occurred in this territory and was responsible for a significant proportion of the nonendothelial P-selectin signal at 24 hours after reperfusion.

CONCLUSIONS

Focal cerebral ischemia/reperfusion stimulates endothelial P-selectin and intercellular adhesion molecule-1 expression in brain microvessels in the ischemic zone, which may contribute to enhanced leukocyte adherence and persistent activation.

Cerebral endothelial nitric oxide synthase expression after focal cerebral ischemia in rats

BACKGROUND AND PURPOSE

The purpose of this study was to measure the temporal profile of expression of the endothelial nitric oxide synthase (NOS) in cerebral microvessels after middle cerebral artery occlusion in the rat.

METHODS

Middle cerebral artery occlusion was performed on 24 male Wistar rats by extracranial insertion of a 4-0 nylon monofilament into the internal artery. Three additional rats were used as controls. Animals were killed at 1, 2, 4, 6, 24, 48, 72, and 168 hours after middle cerebral artery occlusion (n = 3 per time point). Rat brains were perfused with buffer, frozen, sectioned, and stained with a monoclonal antibody against endothelial NOS. Adjacent sections were stained with hematoxylin and eosin for evaluation of neuronal damage.

RESULTS

The endothelial NOS in the cerebral vessels was upregulated at 1 hour after induction of ischemia throughout the ischemic region. The induction of the endothelial NOS progressively increased up to 24 hours of ischemia. In the periphery of the area of necrosis in the cortex, a delayed (24-hour) upregulation of the endothelial NOS remained constant throughout the duration of ischemia.

CONCLUSIONS

The rapid and intense differential expression of the endothelial NOS in the core and peripheral areas of the lesion indicates a role for endothelial NOS in ischemic cell damage and suggests that the increased expression of NOS may mediate changes in the cerebral blood flow.

Effect of phorbol myristate acetate on cerebral blood flow in normal and neutrophil-depleted rats

BACKGROUND AND PURPOSE

Recent evidence suggests a possible role for leukocytes in ischemic brain injury. This study examined the effect of activation of endogenous circulating leukocytes on cerebral blood flow in normal and neutrophil-depleted rats.

METHODS

Leukocytes were activated by rapid injection of either 50 micrograms/kg phorbol 12-myristate 13-acetate, a protein kinase C activator, or an equimolar amount of the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine, into the right carotid artery. Control rats received an equal volume of dimethyl sulfoxide in saline vehicle. H2-clearance cerebral blood flow was measured in each of the three groups and in vinblastine-treated, neutrophil-depleted rats after carotid artery injection of phorbol.

RESULTS

Phorbol 12-myristate 13-acetate dramatically decreased circulating leukocyte and platelet counts from 5 to 120 minutes after infusion and decreased regional cerebral blood flow in the ipsilateral parietal cortex from a baseline of 119 +/- 14 mL.min-1.100 g-1 (mean +/- SEM) to 49 +/- 5 mL.min-1.100 g-1 at 30 minutes (P < .05). Decreased flow persisted for the 2-hour study. Neither N-formyl-methionyl-leucyl-phenylalanine or vehicle had an effect on cerebral blood flow. In the neutrophil-depleted rats the initial decrease in cerebral blood flow at 30 and 60 minutes after infusion of phorbol was observed, but cerebral blood flow was restored to 70% to 80% of its baseline value (P > .05 versus baseline) by 90 to 120 minutes.

CONCLUSIONS

The early phorbol 12-myristate 13-acetate-induced decrease in cerebral blood flow may be due to the effects of protein kinase C activation on vascular smooth muscle or on platelet aggregation, whereas the persistent decrease in cerebral blood flow appears to be mediated in part by neutrophil activation.

Inhibition of inflammatory cell-mediated myelin oxidation and interleukin-1 beta generation by a 21-aminosteroid, U74500A

Inflammatory cell-mediated myelin injury may be an important cause of tissue damage in both acute and chronic central nervous system (CNS) disorders. The 21-aminosteroids are novel derivatives of methylprednisolone without obvious glucocorticoid or mineralocorticoid side effects. We evaluated the ability of 21-aminosteroid, U74500A, to inhibit oxidation of rat brain myelin by human polymorphonuclear leukocytes (PMN) and monocytes. Myelin samples, as confirmed by SDS-PAGE, were incubated with PMN or monocytes and 100 microM U74500A or vehicle. Myelin oxidation by both PMN and monocytes was significantly reduced by U74500A. These observations demonstrate that U74500A can inhibit myelin oxidation by inflammatory cells. Additionally, 100 microM U74500A significantly reduced production of interleukin 1-beta by monocytes exposed to myelin. The aminosteroids may be beneficial in CNS disorders where myelin injury by inflammatory cells appears to contribute, such as acute focal ischemia or multiple sclerosis.

Serial determinations of leukocyte aggregation in patients with ischemic stroke

The pattern of leukocyte aggregation and its possible relationship with the clinical outcome were evaluated in 35 untreated patients with acute cerebrovascular disease during each of the first three days of hospitalization. Although statistically significant differences were found when comparing patients and age and sex matched controls during any of the 3 days, a large overlapping of values was noted in each comparison. The overlapping was strongly reduced when the average 3-day value was compared. Similarly, when comparing subgroups of patients classified on the basis of their clinical status, the overlap of values observed during any of the 3 days dropped from 70% to 30% when considering the average 3-day levels of leukocyte aggregation. Furthermore, the level of correlation between leukocyte aggregation and size of cerebral infarction was better when considering the average 3-day value (p = .005) than the best single-day correlation (p = .01). These data suggest that the association between acute cerebrovascular ischemia and leukocyte rheology is better discovered when repeated evaluation of the latter are performed.

Tissue factor contributes to microvascular defects after focal cerebral ischemia

BACKGROUND AND PURPOSE

Microvascular perfusion defects occur after occlusion and reperfusion of the middle cerebral artery in examples of focal cerebral ischemia. In addition to cellular (eg, polymorphonuclear leukocyte) contributors to the focal "no-reflow" phenomenon, activation of coagulation may also play a role. We have tested a potential role of tissue factor-mediated coagulation in the microvascular perfusion defects seen after focal cerebral ischemia-reperfusion in a baboon model of reversible middle cerebral artery occlusion with the murine anti-tissue factor monoclonal antibody TF9-6B4. Tissue factor is the principal resident procoagulant substance in cerebral tissues and has a distinct perivascular distribution.

METHODS

Microvascular patency in the basal ganglia after 3-hour middle cerebral artery occlusion and 1-hour reperfusion was quantified by computerized video imaging of carbon-tracer perfused tissues. Animals were randomized to receive intravenous TF9-6B4 (10 mg/kg) 10 minutes before middle cerebral artery occlusion (n = 6) or no treatment (n = 6) in an open study.

RESULTS

In the control animals, a significant decrease in patency was confirmed in microvessels less than 30 microns in diameter. Infusion of TF9-6B4 before middle cerebral artery occlusion produced a stable maximal level of circulating antibody within 10 minutes, which lasted the duration of ischemia and reperfusion. An increase in reflow in microvessels of all size classes occurred after TF9-6B4 infusion, which was significant in those 7.5 to 30 microns (P = .038) and 30 to 50 microns (P = .013) in diameter.

CONCLUSIONS

These results indicate that tissue factor-mediated events may also contribute to no-reflow in noncapillary microvessels after focal cerebral ischemia.

Circulating intercellular adhesion molecule-1 levels and neutrophil adhesion in stroke

To examine whether changes in leukocyte adhesion properties occur during stroke, we measured circulating serum intercellular adhesion molecule 1 (cICAM-1) levels and neutrophil adhesion in acute stroke, patients at high risk of stroke, and in matched controls. Levels of cICAM-1 were significantly lower in the stroke group (186.2 +/- 15.6 ng ml-1) compared to controls (257.7 +/- 24.8) and risks (257.7 +/- 16.5). Neutrophil adhesion was significantly higher in the stroke group (23.6 +/- 4.3%; n = 14) compared to controls (9.7 +/- 2.3%; n = 12) and risks (12.7 +/- 2.5%; n = 13). These data suggest that changes in leukocyte adhesion dynamics are occurring in acute stroke.

Leukocyte infiltration in acute hemispheric ischemic stroke

BACKGROUND AND PURPOSE

The dynamics of leukocyte infiltration in human cerebral ischemia were studied using technetium-99m hexamethylpropyleneamine oxime (99mTc HMPAO)-labeled leukocyte brain single-photon emission computed tomography (SPECT).

METHODS

Twenty-two patients diagnosed as having hemispheric ischemic stroke were examined with 99mTc HMPAO brain SPECT for cerebral blood flow study and 99mTc HMPAO-labeled leukocyte brain SPECT for the study of leukocyte infiltration. Three patients with chronic hemispheric ischemic stroke received one examination. Nineteen patients with acute hemispheric ischemic stroke received their initial examination within the first after onset. Follow-up examinations were performed at intervals of 1-3 weeks whenever possible.

RESULTS

In patients with chronic hemispheric ischemic stroke, leukocyte infiltration was not seen in areas of perfusion defect. In patients with acute hemispheric ischemic stroke, leukocyte infiltration was seen in areas of perfusion defect during the acute stage, which persisted for no less than 5 weeks after onset and then declined.

CONCLUSIONS

A new method to study and monitor the process of leukocyte infiltration in acute cerebral ischemia using 99mTc HMPAO-labeled leukocyte brain SPECT is described. This method shows that leukocyte infiltration in acute hemispheric ischemic stroke is a dynamic process that persists for no less than 5 weeks and then declines.

The damaging potential of leukocyte activation in the microcirculation

Traditionally leukocytes have been regarded as beneficial cells, owing to their immunologic and antimicrobial activity. Recent evidence suggests, however, an additional role of granulocytes and monocytes as mediators of cardiovascular complications, such as ischemia, reperfusion, diabetes, physiologic shock, venous ulceration, and other conditions. Granulocytes and monocytes have a large volume, and stiff cytoplasm; they have the ability to adhere to endothelium and to other substrates; and they exert several forms of cytotoxicity. Granulocytes and monocytes may be trapped in the microcirculation, may obstruct capillaries and thereby induce a no-reflow phenomenon, and may initiate organ dysfunction via oxygen free radical production and proteolytic cleavage. Few organs seem to be spared from the potential destructive actions of these cells, and novel approaches are required to interfere with leukocyte accumulation in local regions of the peripheral circulation.

Polymorphonuclear leukocytes and monocytes/macrophages in the pathogenesis of cerebral ischemia and stroke

BACKGROUND

The extent to which polymorphonuclear leukocytes and monocytes/macrophages contribute to the pathobiology of cerebral ischemia and stroke is an issue of long-standing contradiction and controversy. Recent developments in the ability to selectively modify leukocyte adhesion with antiadhesion antibodies and the potential clinical application of this therapeutic approach have spurred a resurgence of experimental studies examining the role of leukocytes in cerebral ischemia and stroke.

SUMMARY OF REVIEW

We review studies examining leukocyte accumulation, initiation of thrombosis, and exacerbation of ischemic brain injury in stroke, and we examine other proposed contributions of leukocytes to cerebrovascular pathophysiology.

CONCLUSIONS

The importance of specific characteristics of a given ischemia model and of underlying stroke risk factors in determining the degree of leukocyte involvement and effectiveness of therapies directed against these cells is discussed.

Inhibition of polymorphonuclear leukocyte adherence suppresses no-reflow after focal cerebral ischemia in baboons

BACKGROUND AND PURPOSE

While polymorphonuclear leukocytes may contribute to the "no-reflow" phenomenon after focal cardiac and skeletal muscle ischemia/reperfusion, their contribution to acute focal cerebral ischemia is unresolved. We have examined the role of polymorphonuclear leukocytes in microvascular perfusion defects after focal cerebral ischemia/reperfusion in a baboon model of reversible middle cerebral artery occlusion with the anti-CD18 monoclonal antibody IB4, which inhibits neutrophil adherence to endothelium.

METHODS

Microvascular patency in the basal ganglia after 3-hour middle cerebral artery occlusion and 1-hour reperfusion (by india ink tracer perfusion) was quantified by computerized video imaging. Animals were randomized to receive intravenous IB4 infusion 15 minutes before reperfusion (n = 7) or to receive no treatment (n = 6). Binding of IB4 to baboon leukocytes was maximal within 5 minutes of infusion.

RESULTS

In the untreated group, a significant reduction in patency was observed in microvessels less than 30 microns diameter: mean percent reflow was 51% in the capillary diameter class (4.0-7.5 microns) and 39% in the precapillary arteriole and postcapillary venule diameter class (7.5-30 microns). Infusion of IB4 before middle cerebral artery reperfusion increased reflow in microvessels of all size classes, most significantly in those 7.5-30 microns (p = 0.049) and 30-50 microns (p = 0.034) in diameter.

CONCLUSIONS

These results suggest that CD18-mediated polymorphonuclear leukocyte-endothelium adherence contributes to no-reflow predominantly in noncapillary microvessels and at least partially to that in capillaries.

Assessment of posttraumatic polymorphonuclear leukocyte accumulation in rat brain using tissue myeloperoxidase assay and vinblastine treatment

Polymorphonuclear leukocytes (PMN) are implicated in the pathogenesis of traumatic brain injury. We tested the following hypotheses: (1) leukocyte accumulation is present in brain tissue 24 h posttrauma, (2) leukocyte accumulation represents PMN, and (3) prior systemic PMN depletion attenuates brain tissue PMN accumulation. Trauma was induced in exposed right parietal cortex by weightdrop in anesthetized Wistar rats (n = 24). Of the traumatized rats, 12 were PMN-depleted with vinblastine sulfate i.v. Controls were 12 normal rats and 5 sham-operated rats (craniotomy). Sections of traumatized and contralateral hemispheres were analyzed for myeloperoxidase (MPO) activity. Brain MPO activity was increased fivefold at 24 h posttrauma, but only in the traumatized hemisphere (0.448 +/- 0.133 U/g vs 0.090 +/- 0.022 U/g in trauma vs normal, respectively, p < 0.05, mean +/- SEM). PMN depletion attenuated this increase in MPO activity and decreased circulating PMN counts (0.07 +/- 0.032 x 10(9)/L vs 0.894 +/- 0.294 x 10(9)/L PMN-depleted-trauma vs trauma rats, respectively, p < 0.05). Leukocyte accumulation in the brain posttrauma was confirmed by MPO assay. Inhibition of MPO activity in the PMN-depleted group and the specificity of vinblastine treatment for depletion of circulating PMN suggest that leukocyte accumulation in the brain at 24 h posttrauma is largely due to PMN.

Attenuation of spontaneous pseudopod formation in human neutrophils by pentoxifylline

The effects of pentoxifylline (PTX) on spontaneous pseudopod formation in neutrophils in response to the tripeptide formyl-Met-Leu-Phe (fMLP), endotoxin, human complement C5a, and leukotriene B4 (LTB4) were examined in autologous plasma. Unseparated supernatant leukocyte suspensions from fresh heparinized venous human blood were incubated with PTX (0-5 mM) for 25 min and then stimulated for 5-25 min within a range of concentrations of fMLP, endotoxin, complement C5a, and LTB4. The cell suspensions were fixed with glutaraldehyde and stained with crystal violet in acetic acid; the percentage of neutrophils with pseudopods was determined under high-resolution light microscope. The results show that PTX significantly decreases formation of pseudopods in the presence of all four stimulators. The mechanism of pseudopod suppression appears to be independent of the adenosine receptor. PTX and its analogues, HWA 138 and HWA 448, decreased pseudopod formation by similar amounts when stimulated with 10(-8)M fMLP. These results suggest that PTX may improve microvascular perfusion and attenuate neutrophil-mediated injury by reducing the degree of neutrophil pseudopod formation in free suspension and microvascular entrapment.