Anti-ICAM-1 antibody reduces ischemic cell damage after transient middle cerebral artery occlusion in the rat

Ischemic stroke is associated with a systemic increase of blood mononuclear cells expressing interleukin-8 mRNA

BACKGROUND AND PURPOSE

Ischemic brain injury secondary to an arterial occlusion is characterized by acute local inflammation. Blood polymorphonuclear leukocytes (PMNL), primarily neutrophils, adhere to endothelial cells and rapidly invade the injured brain after the arterial occlusion. This neutrophilic invasion might correlate with the production of certain chemoattractants by blood mononuclear cells (MNC). We evaluated mRNA expression of the CXC chemokine interleukin (IL)-8, and the CC chemokines monocyte chemoattractant protein-1, macrophage inflammatory protein (MIP)-1alpha, and MIP-1beta in blood MNC from patients with ischemic stroke.

METHODS

Peripheral blood was obtained at 8 AM on days 1 to 7 (mean, day 3) after onset of symptoms. In situ hybridization with radiolabeled synthetic oligonucleotide probes for the chemokines was adopted to measure chemokine mRNA expression in MNC. An enzyme-linked immunosorbent assay for IL-8 was used to measure IL-8 levels in plasma.

RESULTS

Most patients with ischemic stroke had high numbers of IL-8 mRNA expressing blood MNC, regardless of the time interval between onset of clinical symptoms and examination. There was a marked difference between patients with ischemic stroke and healthy subjects (median, 6228 versus 885 positive cells per 10(5) MNC; P<.0001). IL-8 levels in plasma correlated positively to IL-8 mRNA expression in examined patients (n=7) with ischemic stroke (r=.78, P<.05). In contrast, mRNA expression for the CC chemokines showed no significant difference between patients with ischemic stroke and healthy control subjects.

CONCLUSIONS

This study demonstrated a systemic increase of IL-8 mRNA expressing MNC and IL-8 levels in plasma from patients with ischemic stroke, suggesting that IL-8 could be involved in recruiting blood PMNL to the sites of cerebral ischemia.

Tissue plasminogen activator (tPA) increases neuronal damage after focal cerebral ischemia in wild-type and tPA-deficient mice

Intravenous tissue plasminogen activator (tPA) is used to treat acute stroke because of its thrombolytic activity and its ability to restore circulation to the brain. However, this protease also promotes neurodegeneration after intracerebral injection of excitotoxins such as glutamate, and neuronal damage after a cerebral infarct is thought to be mediated by excitotoxins. To investigate the effects of tPA on cerebral viability during ischemia/reperfusion, we occluded the middle cerebral artery in wild-type and tPA-deficient mice with an intravascular filament. This procedure allowed us to examine the role of tPA in ischemia, independent of its effect as a thrombolytic agent. tPA-deficient mice exhibited approximately 50% smaller cerebral infarcts than wild-type mice. Intravenous injection of tPA into tPA-/- or wild-type mice produced larger infarcts, indicating that tPA can increase stroke-induced injury. Since tPA promotes desirable (thrombolytic) as well as undesirable (neurotoxic) outcomes during stroke, future therapies should be aimed at countering the excitotoxic damage of tPA to afford even better neuroprotection after an acute cerebral infarct.

Reproducibility and reliability of middle cerebral artery occlusion using a silicone-coated suture (Koizumi) in rats

The best technical approach to rat middle cerebral artery occlusion (MCAO) using a nylon-monofilament suture remains unsettled, regarding the usefulness of coated or uncoated sutures. Three investigators with different degrees of experience: A, well skilled; B, 2 years of experience; C, a novice with 6 months of experience, each subjected 10 Sprague-Dawley rats to permanent MCAO using low-viscosity silicone-coated sutures with a mean diameter 0.468+/-0.013 mm (mean+/-S.D.) at the tip and 0.361+/-0.013 mm in the body. Post-mortem corrected infarct size 24 h after MCAO was similar among the three investigators: A, 204.7+/-33.2 mm3; B, 212.6+/-42.8, and C, 195.9+/-44.4. The coefficient of variation was 16.2% to 22.7%, and 19.4% for the three investigators. This study suggests that experimental stroke with silicone-coated sutures (Koizumi's method) provides good reproducibility and reliability, among investigators of varying experience.

Effects of plasma from hibernating ground squirrels on monocyte-endothelial cell adhesive interactions

Adhesion and subsequent penetration of leukocytes into central nervous system ischemic tissue proceeds via a coordinated inflammatory mechanism involving adhesion molecules at the blood-endothelium interface. Mammalian hibernation is a state of natural tolerance to severely reduced blood flow-oxygen delivery (i.e., ischemia). Hibernating thirteen-lined ground squirrels were investigated in an attempt to identify factors responsible for regulating this tolerance. Since leukocytopenia is closely associated with entrance into hibernation, the role of leukocyte adhesion to endothelium in this phenomenon was examined. Intercellular adhesion molecule-1 (ICAM-1) is expressed by endothelium and regulates interactions with circulating leukocytes that may result in margination or extravasation. ICAM-1 expression by rat cerebral microvascular endothelial cells (EC) cultured with plasma from hibernating (HP) or nonhibernating (NHP) thirteen-lined ground squirrels was dose dependently increased by HP and, to a lesser extent, by NHP. Treatment of EC with HP coincidentally induced significantly greater increases in monocyte adhesion to EC (37.2%) than were observed with NHP (23.9%). Study of the effects of HP and NHP on monocyte adhesion to EC may identify mechanisms responsible for ischemic tolerance in hibernators and could lead to the development of novel therapeutic approaches to the treatment of stroke.

Ischemic stroke injury is reduced in mice lacking a functional NADPH oxidase

BACKGROUND AND PURPOSE

Free radicals account for a significant proportion of the brain damage that occurs during ischemic stroke. Using mutant mice (X-CGD) with a dysfunctional phagocytic NADPH oxidase, we investigated the role of this superoxide-generating enzyme as a mediator of the reperfusion injury in a mouse model of middle cerebral artery occlusion.

METHODS

Transient (2 hour) middle cerebral artery occlusion was performed in X-CGD or wild-type litter mates (8- to 10-week-old). After 22 hours of reperfusion, brains were harvested and infarct volume delineated using 2,3,5-triphenyl-tetrazolium chloride. To elucidate the origin of the damaging NADPH oxidase, transient ischemia was also performed in X-CGD or wild-type mice transplanted with wild-type C57 B1/6J or X-CGD bone marrow, respectively.

RESULTS

The infarct volume induced by transient ischemia was significantly less in X-CGD mice (29.1 +/- 5.6 mm3; n = 13) than wild-type littermates (54.0 +/- 10.6 mm3; n = 10; P < .05). The elimination of a functional NADPH oxidase from either the circulation or the central nervous system, by performing the appropriate bone marrow transplant experiments, did not reduce the infarct size induced by transient ischemia. This suggests that in order to confer protection against transient ischemia and reperfusion, a putative neuronal and circulating NADPH oxidase need to be inactivated.

CONCLUSIONS

Brain injury was reduced in mice lacking a functional NADPH oxidase in both the central nervous system and peripheral leukocytes, suggesting a pivotal role for the NADPH oxidase in the pathogenesis of ischemia-reperfusion injury in the brain.

Inflammatory gene expression in cerebral ischemia and trauma. Potential new therapeutic targets

This review summarized evidence in support for the case that ischemia elicits an inflammatory condition in the injured brain. The inflammatory condition consists of cells (neutrophils at the onset and later monocytes) and mediators (cytokines, chemokines, others). It is clear that de novo upregulation of proinflammatory cytokines, chemokines and endothelial-leukocyte adhesion molecules in the brain follow soon after the ischemic insult and at a time when the cellular component is evolving. The significance of the inflammatory response to brain ischemia is not fully understood. Evidence is emerging in support of the possibility that the acute inflammatory reaction to brain ischemia may be causally related to brain damage. This evidence includes: 1) the capacity of cytokines to exacerbate brain damage; 2) the capacity of specific cytokine antagonists such as IL-1ra to reduce ischemic brain damage; 3) that depletion of circulating neutrophils reduces ischemic brain injury; 4) and that antagonists of the endothelial-leukocyte adhesion interactions (e.g., anti-ICAM-1) reduce ischemic brain injury. However, it should be kept in mind that cytokines were also argued to provide beneficial effects in brain injury as inferred from studies with TNF-receptor knock-out mice (p55 and p75 knock-out), which display increased sensitivity to brain ischemia, and the capacity of IL-1 to elicit the state of ischemic tolerance upon repeated administration. Nevertheless, the recent revelation on the capacity of ischemia to induce acute inflammation in the brain provides a new and fertile ground for new explorations for novel therapeutic agents that could confine the neuronal damage that follows ischemia. Furthermore, many of the genes that are upregulated by ischemia have growth-promotion capacity and therefore raise the possibility that such gene products may be useful in counteracting brain damage by enhancing repair and establishing compensatory mechanisms that enhance histological and functional recovery.

Doxycycline treatment reduces ischemic brain damage in transient middle cerebral artery occlusion in the rat

Agents that inhibit leukocyte adhesion including intercellular adhesion molecule-1 antibodies (anti-ICAM-1) have shown beneficial effects in experimental central nervous system (CNS) ischemia. Doxycycline inhibits leukocyte function in vitro by binding divalent cations and reduces spinal cord reperfusion injury. The authors used a clinically relevant model of focal CNS reperfusion injury to test whether treatment with doxycycline would reduce cerebral ischemic damage and improve functional outcome. Reversible middle cerebral artery occlusion was produced in adult Sprague-Dawley rats by advancing a filament into the internal carotid artery for 2 h. Animals received either i.p. doxycycline (10 mg/kg) (N = 13) or saline (N = 11) 30 min before ischemia, followed by 10 mg/kg every 8 h x 6. Both functional assessment (5 point neurologic scale) and infarct volume was evaluated at 48 h. Functional efficacy: doxycycline 0.5 +/- 0.2 (mean +/- SE) vs control 1.3 +/- 0.3 (p = 0.03). Infarct volume: doxycycline 56 +/- 18 mm3 vs control 158 +/- 44 mm3 (p = 0.03); This protective effect supports the role of doxycycline in reducing CNS reperfusion injury.

Inhibition of experimental vasospasm with anti-intercellular adhesion molecule-1 monoclonal antibody in rats

BACKGROUND AND PURPOSE

Inflammation may play a role in delayed chronic vasospasm after aneurysmal subarachnoid hemorrhage. We investigated the role of intercellular adhesion molecule-1 (ICAM-1) and macrophage/granulocyte infiltration in the rat femoral artery model of vasospasm using systemic administration of a murine anti-ICAM-1 monoclonal antibody (MAb).

METHODS

The femoral arteries (n = 72) in Sprague-Dawley rats (n = 36) were enclosed in latex pouches bilaterally. Autologous blood was injected into the pouch on one side, and saline was injected on the contralateral side. Chronic vessel narrowing was evaluated with the use of 29 rats, which were randomized into one of three groups for intraperitoneal injections: (1) anti-ICAM-1 MAb (2 mg/kg per dose, n = 10), (2) isotype-matched MAb (2 mg/kg per dose, n = 9), or (3) saline (n = 10), given at 3 hours and 3, 6, and 9 days after blood exposure. These rats were killed 12 days after blood exposure, and femoral artery lumen cross-sectional areas were determined by computerized image analysis. Saturation of ICAM-1 binding sites with this dosing schedule was evaluated by fluorescence-activated cell sorter (FACS) analysis of splenocytes. Immunohistochemical studies with objective cell counts were performed to evaluate macrophage/granulocyte infiltration at 24 hours in 7 rats, comparing anti-ICAM-1 MAb treatment (n = 4) with isotype-matched control MAb (n = 3).

RESULTS

Animals treated with anti-ICAM-1 MAb showed a significant inhibition of arterial narrowing at 12 days (P = .0081), with lumen patency of 96.5 +/- 5.3% (mean +/- SEM), compared with 77.3 +/- 5.6% for isotype-matched MAb and 72.2 +/- 5.3% for saline-treated controls. FACS analysis of splenocytes from animals treated with anti-ICAM-1 MAb confirmed saturation of ICAM-1 binding sites. Vessels treated with anti-ICAM-1 MAb showed a significant decrease in inflammatory cell infiltrates, with objective macrophage/granulocyte counts of 31.3 +/- 26.6 (mean +/- SEM) per high-powered field, compared with 171.4 +/- 30.7 for isotype-matched control MAb (P = .0027).

CONCLUSIONS

Anti-ICAM-1 MAb administered systemically starting 3 hours after blood exposure results in significant inhibition of chronic vasospasm in the rat femoral artery model and is correlated with a reduction in the number of infiltrating macrophages and granulocytes in the periadventitial region of blood-exposed arteries. We conclude that inflammatory changes associated with ICAM-1-mediated macrophage and granulocyte migration play an important role in the development of posthemorrhagic chronic vasospasm in this model.

Autonomic and vasomotor regulation

The cerebellum not only modulates the systemic circulation, but also profoundly influences cerebral blood flow (rCBF) and metabolism (rCGU), and initiates long-term protection of the brain from ischemia. Electrical stimulation of the rostral ventral pole of the fastigial nucleus (FN), elevates arterial pressure (AP), releases vasoactive hormones, elicits consummatory behavioral and other autonomic events and site specifically elevates rCBF independently of changes in rCGU. Cerebral vasodilation results from the antidromic excitation of axons of brain stem neurons which innervate cerebellum and, through their collaterals, neurons in the rostral ventrolateral reticular nucleus (RVL). RVL neurons initiate cerebral vasodilation over polysynaptic vasodilator pathways which engage a population of vasodilator neurons in the cerebral cortex. In contrast, intrinsic neurons of FN, when excited, elicit widespread reductions in rCGU and, secondarily, rCBF, along with sympathetic inhibition. Electrical stimulation of FN can reduce the volume of a focal cerebral infarction produced by occlusion of the middle cerebral artery by 50%. This central neurogenic neuroprotection is long lasting (weeks) and is not due to changes in rCBF or rCGU. Rather, it appears to reflect alterations in neuronal excitability and/or downregulation of inflammatory responses in cerebral vessels. The FN, therefore, appears to be involved in widespread autonomic, metabolic, and behavioral control, independent of motor control. The findings imply that the FN receives inputs from neurons, probably widely represented in the central autonomic core, which may provide continuing information processing of autonomic and behavioral states. The cerebellum may also widely modulate the state of cortical reactivity to ischemia, hypoxia, and possibly other neurodegenerative events.

Microvascular responses to cerebral ischemia/inflammation

Experimental occlusion of a brain-supplying artery triggers tissue ischemia and subsequent inflammatory events that are initiated at the blood microvessel interface. Cytokine production and molecular adhesive events occur in the early moments following cerebral blood flow reduction, which underlie the transition from ischemic to inflammatory injury. Events both within the microvascular lumen and in the immediately surrounding tissue are involved. Cytokines, including TNF-alpha, IL-1 beta, IL-6, and PAF, are produced from the ischemic parenchyma and contribute to the endothelial cell expression of P-selectin, ICAM-1, and E-selectin. Platelet activation occurs paris passu and probably involves alpha-granule P-selectin to mediate PMN leukocyte-platelet interactions. Other integrin heterodimers are also involved in the early microvascular responses to ischemia. The response of the basal lamina and ECM is somewhat slower, entailing yet unproven mechanisms that most probably include the proteolytic processes of leukocyte transmigration. The modifications to microvascular structure are likely to affect both endothelial and astrocyte relationships, promote erythrocyte extravasation and hemorrhage, and contribute to tissue injury. Remodeling of the microvasculature, apparent in other tissues, involves a number of these processes. However, the enzymatic participants and regulating mechanisms are coming under study: the unraveling of regulatory mechanisms of adhesion receptor expression and their modulation, and the companion roles of integrins as mediators of structural integrity and intercellular signaling.

Cerebral lupus vasculopathy. Mechanisms and clinical relevance

The most common neuropathological findings in SLE are a small vessel cerebral vasculopathy and microinfarcts. These findings may reflect the end result of repeated episodes of acute inflammation in the small vessels in the brain. There is experimental support for the local Shwartzman reaction as a paradigm to explain some of the CNS manifestations in SLE. Activation or "priming" of cerebral microvascular endothelial cells by anticardiolipin antibodies or other immunoglobulins in concert with intravascular activation of the complement system may combine to elicit leukothrombosis in the brain. Therapies aimed at inhibiting leukocyte-endothelial cell interactions in the brain may be of use in CNS lupus.

CP-0597, a selective bradykinin B2 receptor antagonist, inhibits brain injury in a rat model of reversible middle cerebral artery occlusion

BACKGROUND AND PURPOSE

Recent studies demonstrated a significant neuroprotective action of the selective peptide-based bradykinin B2 receptor antagonist CP-0597 after permanent middle cerebral artery (MCA) occlusion (MCAO) in the rat. We therefore evaluated the efficacy of this compound after reversible MCAO in the rat.

METHODS

Male Wistar rats underwent reversible MCAO by insertion of a nylon monofilament to the origin of the MCA. After 1 hour the filament was retracted and the ischemic tissue reperfused. Immediately after MCAO, primed miniosmotic pumps containing either vehicle or CP-0597 (300 ng/kg per minute) were implanted into the subcutaneous space (n = 14 per group). Twenty-four hours after surgery, animals were killed and brains fixed, and 4-micron sections were taken from five sequential tissue blocks labeled A through E and stained with hematoxylin and eosin. Clinical evaluation of rats was performed by neurological scoring and change in body weight.

RESULTS

Treatment with CP-0597 significantly reduced percent increase in hemisphere size of the ischemic hemisphere in all brain sections (C section: vehicle, 40.6 +/- 4.3% versus CP-0597, 20.8 +/- 5.3%; P < 0.001), total infarct volume (vehicle, 206.5 +/- 7.7 mm3 versus CP-0597, 94.0 +/- 19.2 mm3; P < .001), cortical infarct volume (vehicle, 145.5 +/- 4.5 mm3 versus CP-0597, 64.0 +/- 15.1 mm3; P < .001), subcortical infarct volume (vehicle, 55.8 +/- 4.1 mm3 versus CP-0597, 27.5 +/- 4.5 mm3; P < .001), and the number of necrotic neurons (vehicle 42.9 +/- 3.8 versus CP-0597, 23.6 +/- 4.7 per field; P < .01). Neurological score (vehicle, 2.78 +/- 0.36 versus CP-0597, 6.29 +/- 0.87 P < .01) and change in body weight (vehicle, -28.7 +/- 2.0 g versus CP-0597, -18.2 +/- 2.8 g; P < .01) were also significantly improved.

CONCLUSIONS

The present data demonstrate the significant overall efficacy profile of CP-0597 in a rat model of reversible MCAO and provide strong rationale for the use of such bradykinin B2 receptor antagonist in the treatment of stroke.

New therapeutic possibility of blocking cytokine-induced neutrophil chemoattractant on transient ischemic brain damage in rats

Earlier we indicated that neutrophilic invasion into cerebral parenchyma is an important step in rat cerebral ischemia-reperfusion injury and the production of chemotactic factors, cytokine-induced neutrophil chemoattractant (CINC) precede the neutrophilic invasion. The aim of the present study was to evaluate the role of CINC production and the therapeutic possibility of blocking CINC activity in the transient ischemic brain damage in rats. Focal transient ischemia was produced by intraluminal occlusion of the right middle cerebral artery for 60 min. An enzyme immunoassay was used to measure the brain concentration of CINC and myeloperoxidase activity in ischemic areas was measured as a marker of neutrophilic accumulation. An immunohistochemical staining technique was used to detect the immunopositive cells for anti-CINC antibody. Further, application of anti-CINC antibody or anti-neutrophil antibody to rats was used to evaluate the role of CINC production. In ischemic areas, CINC production was detected and peaked 12 h after reperfusion, which followed 60 min of ischemia. Intraperitoneal injection of anti-neutrophil antibody 24 h before and immediately after reperfusion significantly reduced the brain water content and partially reduced the CINC production in ischemic areas. Further, immunohistochemical staining showed that anti-CINC antibody was found on the endothelial surface of venules and on parts of neutrophils that had invaded the ischemic area 6 to 24 h after reperfusion. Also, treatment with anti-CINC antibody reduced ischemic edema formation 24 h after reperfusion and the size of infarction areas 7 days after reperfusion. It thus appears that CINC, mainly produced by endothelium activated by factors released from neutrophils, plays an important role in ischemic brain damage. Furthermore, the blocking of CINC activity with antibody suggests an immuno-therapeutic approach to the treatment of stroke patients.

The role of neutrophils in the production of hypoxic-ischemic brain injury in the neonatal rat

Neutrophils contribute to ischemic brain injury in adult animals. The role of neutrophils in perinatal hypoxic-ischemic (HI) brain injury is unknown. Allopurinol reduces neutrophil accumulation after tissue ischemia and is protective against HI brain injury. This study was designed to investigate how neutrophils contribute to perinatal hypoxic ischemic brain injury and how neutropenia compared with allopurinol in its neuroprotective effects. A HI insult was produced in the right cerebral hemisphere of 7-d-old rats by right common carotid artery ligation and systemic hypoxia. Half the rats were rendered neutropenic with an anti-neutrophil serum (ANS). At 15 min of recovery from hypoxia, half the neutropenic and nonneutropenic rats received allopurinol (135 mg/kg, s.c.). The protective effect of the four treatment combinations was determined on brain swelling at 42 h of recovery. Neutropenia reduced brain swelling by about 70%, p < 0.01. Allopurinol alone produced similar protection so that the relatively small number of animals studied did not permit assessment of an additive effect. Neutrophil accumulation in cerebral hemispheres was measured by myeloperoxidase (MPO) activity assay and by neutrophil counts in 6-microm sections stained by MPO and ANS immunostaining. MPO activity peaked between 4 and 8 h of recovery in both hemispheres. Hemispheric neutrophil counts peaked at the end of the HI insult and again at 18 h of recovery. Neutrophils were stained within blood vessels and did not infiltrate the injured brain before infarction had occurred. We conclude that neutrophils contribute to HI brain injury in the neonate and that neutrophil depletion before the insult is neuroprotective.

Temporal impairment of microcirculatory perfusion following focal cerebral ischemia in the spontaneously hypertensive rat

Microcirculatory impairments have theoretically been proposed as a potential factor in the development of ischemic injury, but few attempts have been made to directly assess microvascular patency following stroke. To address this issue we investigated the temporal changes in microvascular perfusion induced by permanent focal ischemia. Halothane-anesthetized spontaneously hypertensive rats were subjected to middle cerebral artery occlusion (MCAO) of 5 min to 4 h duration. Two fluorescent tracers (FITC-dextran and Evans blue) were then sequentially administered i.v. and allowed to circulate for 10 and 5 s respectively. Tissue sections were examined by fluorescent microscopy, and the mean number of perfused microvessels/mm2 calculated for cortical areas representing non-ischemic (Region A), perifocal/penumbral (Region B) and core ischemic (Region C) regions. For sham-operated controls, virtually all microvessels perfused with tracer within 5 s. In contrast MCAO induced significant reductions in the number of perfused microvessels in Regions B and C. The most marked impairments in perfusion were observed in core MCA territory (e.g. 2-10% of control values for 5 s circulation period) while, initially, the deficit was less severe in penumbral cortex. However, a secondary perfusion impairment developed over time in the perifocal/penumbral region, so that the deficit was greater 4 h after MCAO than at earlier time points (e.g. 72%, 71% and 22% of control value for 0.5, 1 and 4 h MCAO respectively; 10 s circulation period). In conclusion, MCAO induced severe impairments in microcirculatory perfusion within the core ischemic region, and to a lesser extent in the penumbra. However, the development of a more severe perfusion deficit in the penumbra within 4 h of MCAO supports the hypothesis that microcirculatory failure in this region contributes to its recruitment to the ischemic infarct.

The rationale for new therapies in acute ischaemic stroke

Although stroke is a major cause of morbidity and mortality, it is only relatively recently that a concerted effort has been made to develop acute treatments. Thrombolytics, such as recombinant tissue plasminogen activator (rt-PA), may benefit selected patients within 3 h of cerebral infarction. CUrrently, rt-PA is only licensed for use in the United States. Many potential strategies for neuroprotection exist and are currently under investigation. Because the mechanisms of neurotoxicity involve numerous interdependent processes, it may be that the interpretation of a single site in the cascade of events is insufficient to provide effective neuroprotection. Drugs acting at several sites in the neurotoxic cascade may be more effective, and the results of Phase III studies with the novel neoroprotectant lubeluzole are anticipated.

Intraischemic hypothermia attenuates neutrophil infiltration in the rat neocortex after focal ischemia-reperfusion injury

OBJECTIVE

The mechanisms by which hypothermia influences postischemic outcome remain a matter of discussion. One mechanism thought to play an important role in neuronal damage after ischemia/reperfusion is the accumulation of polymorphonuclear leukocytes in compromised brain tissue. To better understand the potential impact of hypothermia on this injurious mechanism, the present study examined the effect of intraischemic hypothermia on polymorphonuclear leukocyte accumulation after transient focal ischemia.

METHODS

The effect of intraischemic hypothermia (30 degrees C) on the accumulation of polymorphonuclear leukocytes was quantified by measuring myeloperoxidase (MPO) activity in the neocortex of Sprague-Dawley rats. Reversible focal ischemia was created by subjecting rats to temporary occlusion of the left middle cerebral artery and both carotid arteries for 3 hours; animals were killed 24 hours after reperfusion.

RESULTS

Normothermic animals exhibited significantly greater MPO activity in the infarction core (P < 0.05) and the pericore areas (P < 0.05), compared with corresponding areas in sham-operated animals. Hypothermic animals exhibited significantly greater MPO activity in the core (P < 0.05) but not in the pericore region, compared with sham-operated animals. MPO activity in the pericore region of the hypothermic group was significantly less than that observed in the corresponding region of the normothermic group (P < 0.01). In addition, the total volume of cerebral infarction was reduced by 59% in the hypothermic group.

CONCLUSION

These findings demonstrate that intraischemic hypothermia attenuates the inflammatory response to transient focal ischemia in the pericore region, i.e., the region spared from infarction under hypothermic conditions. The findings raise the possibility that a reduction in the inflammatory response after ischemia/reperfusion contributes to the neuroprotective effects of hypothermia.

E-selectin in focal cerebral ischemia and reperfusion in the rat

The selectin family of glycoproteins facilitates the early phase of polymorphonuclear leukocyte adhesion to the endothelial cell and, thus, may promote ischemic cell damage. To evaluate E-selectin in the pathogenesis of focal cerebral ischemia and reperfusion injury, we cloned rat E-selectin cDNA and measured the temporal profiles E-selectin mRNA (Northern blot) and protein (immunohistochemistry) during (1 h of ischemia) and after (up to 1 week) transient (2 h) middle cerebral artery (MCA) occlusion in the male Wistar rat. We also tested the effect on these rats of administration of CY-1503, an analog of sialyl Lewis(x) (SLe(x)), on ischemia cell damage. mRNA for E-selectin was first detected in the ischemic hemisphere at 2 h of reperfusion and persisted to 46 h of reperfusion. E-selectin (protein) was localized to microvessels within the ischemic lesion at 0 h of reperfusion and persisted to 70 h of reperfusion. Treatment of the ischemic animals with CY-1503 (50 mg/kg) (n = 8) significantly reduced infarct volume by 42% (p < 0.05) and significantly reduced myeloperoxidase immunoreactive cells in the ischemic lesion by 60% (p < 0.05). These findings provide the first direct evidence for the involvement of E-selectin in transient MCA occlusion in rats and suggest that the E-selectin may facilitate neutrophil adhesion and subsequent cerebral ischemic cell damage.

Experimental antileukocyte interventions in cerebral ischemia

White blood cells (WBCs) play vital roles in host defense. Recently, increasing interest has been directed toward the question of whether WBCs, particularly polymorphonuclear leukocytes, could also act as mediators of secondary brain damage in the setting of focal and global cerebral ischemia with and without reperfusion. Considerable insight into the importance of WBC-mediated tissue injury has been gained from studies employing antileukocyte interventions in experimental cerebral ischemia. The purpose of this article is to survey the different approaches taken to interfere with WBC inflammatory function. Emphasis is laid on a discussion of the efficacy of these interventions, their effects and side effects on cerebral and systemic parameters, and the power of evidence they provide for identification of WBCs as important factors in cerebral ischemia. The role of WBCs has been investigated in a great variety of global and focal cerebral ischemia models with and without reperfusion, leading to sometimes contradictory results. In the light of currently available data, it seems likely that WBCs contribute to secondary brain damage in the scenario of experimental transient focal cerebral ischemia, if the insult is not too severe.

Inducible nitric oxide synthase gene expression in vascular cells after transient focal cerebral ischemia

BACKGROUND AND PURPOSE

We investigated whether inducible nitric oxide synthase (iNOS) is expressed after transient cerebral ischemia and, if so, we sought to define the temporal profile and cellular localization of the expression and the role of iNOS in the mechanism of ischemic brain injury.

METHODS

The middle cerebral artery in rats was occluded for 2 hours by an intraluminal filament. The occurrence of transient ischemia and reperfusion was confirmed by laser-Doppler flowmetry (n = 5). iNOS message in the ischemic neocortex was determined by reverse-transcription polymerase chain reaction. iNOS enzymatic activity was assessed by citrulline assay. The cellular localization of iNOS expression was determined by immunohistochemistry.

RESULTS

iNOS mRNA was maximally expressed in postischemic brain at 12 hours and was not present at 4 days (n = 3 per time point). iNOS mRNA was not observed in the contralateral cerebral cortex. iNOS enzymatic activity developed in the postischemic brain between 12 and 24 hours (P < .05) and subsided at 4 days (n = 4 to 8 per time point). iNOS immunoreactivity in the ischemic region was restricted to the wall of capillaries and of larger blood vessels at 12 to 24 hours. In regions of early necrosis, inflammatory cells were iNOS positive. Treatment with the iNOS inhibitor aminoguanidine (n = 5; 100 mg/kg IP, BID for 4 days), starting 6 hours after ischemia, reduced infarct size in neocortex by 36 +/- 7% in comparison with vehicle-treated controls (n = 5) (P < .05).

CONCLUSIONS

Transient focal ischemia leads to iNOS expression in postischemic brain. However, the spatial and temporal patterns of expression differ from those occurring in permanent ischemia: iNOS is induced earlier and predominantly in vascular cells rather than in neutrophils. Thus, the temporal profile and localization of postischemic iNOS expression depend on the nature of the ischemic insult. The finding that aminoguanidine reduces infarct size adds further support to the hypothesis that postischemic iNOS expression contributes to ischemic brain damage.

E-selectin expression on human brain microvascular endothelial cells

E-Selectin is an endothelial adhesion molecule involved in binding and targeting of neutrophils. Little is known of its expression in the brain. We examined the expression of E-selectin on cultured human brain microvascular endothelial cells (HBMEC). There was no basal expression of E-selectin on HBMEC but with I1-1b, tumor necrosis factor (TNF), or lipopolysaccharide (LPS) stimulation there was surface expression at 4 h. The expression was quantitatively less than on cultured human umbilical vein endothelial cells (HUVEC). The cytokine-induced upregulation was partially inhibited with the glutathione donor, N-acetylcysteine (NAC), the free radical scavenger, dimethylthiourea (DMTU; 15 mM) and dexamethasone (1 microM). Allopurinol (100 microM) had no effect. TNF activated nuclear factor kappa B (NF kappa B) in HBMEC. This activation could be attenuated by prior treatment with NAC and dexamethasone. Thiol donors and corticosteroids could play a role in inhibiting potentially deleterious neutrophil-endothelial interactions in inflammatory conditions involving the brain.

Antibodies against adhesion molecules reduce apoptosis after transient middle cerebral artery occlusion in rat brain

We tested the hypothesis that treatment of transient focal cerebral ischemia in rat with antibodies directed against adhesion molecules reduces apoptosis. Rats (n = 31) were subjected to 2 h of middle cerebral artery (MCA) occlusion induced by intraluminal insertion of a nylon monofilament into the internal carotid artery. Upon reperfusion, animals were treated with monoclonal antibodies directed against intercellular adhesion molecule (ICAM)-1) (n = 8) or integrin CD11b/CD18 (n = 10), or administered IgG1 as a control (n = 13). At 48 h after ischemia, animals were killed and the brains analyzed for ischemic cell damage, using hematoxylin and eosin (H/E); apoptosis, using the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) method; and inflammatory cells, using immunohistochemistry with an anti-myeloperoxidase (MPO) antibody. Data revealed a significant reduction in the volume of infarction (p < 0.01) and a decline in the absolute (p < 0.001), and normalized (to the ischemic areas, p < 0.05) numbers of apoptotic cells in both animals treated with anti-ICAM-1 and anti-CD11b antibodies compared to control animals. The numbers of immunoreactive MPO cells were also reduced in the treatment groups compared to those in the control group (p < 0.05). These data suggest that treatment with anti-adhesion molecule antibodies selectively reduce apoptosis, and that a contributing factor to the beneficial effect of antibody treatment for reducing ischemic cell damage may be a reduction in numbers of apoptotic cells.

Emerging treatments for stroke in humans

Ischaemic stroke causes loss of brain function in millions of people worldwide each year. Despite the enormity of the problem, no currently approved therapy reduces stroke size or neurological disability. This contrasts with a number of recently developed agents, reviewed here by Walter Koroshetz and Michael Moskowitz, which limit infarct size in animal stroke models. Therapies that dissolve clot and restore blood flow, block excitatory neurotransmission, prevent the ischaemic inflammatory response or scavange free radicals have the potential to revolutionize stroke treatment if proven beneficial in ongoing, placebo-controlled clinical trials. Developments in the experimental arena continue to reinforce the need to characterize the pathophysiological stages leading to brain infarction and recovery.

Intercellular adhesion molecule-1-deficient mice are less susceptible to cerebral ischemia-reperfusion injury

Neutrophil emigration is mediated by adhesion proteins that are highly expressed on the endothelial surface during inflammatory processes in the brain. Intercellular adhesion molecule-1 (ICAM-1) is an inducible adhesion molecule that binds to leukocyte integrins and facilitates neutrophil adhesion and transendothelial migration. To study the role of ICAM-1 during ischemia and reperfusion in the brain, we analyzed the effect of transient focal cerebral ischemia in ICAM-1-deficient mice generated by gene targeting in embryonic stem cells. Transient focal ischemia was induced by occluding the left middle cerebral artery for 3 hours followed by a 21- or 45-hour reperfusion period. When compared with their wild-type littermates, ICAM-1-deficient mice were less susceptible to cerebral injury as demonstrated by a 5.6- or 7.8-fold reduction in infarction volume, respectively. These data support the premise that neutrophil adhesion in ischemic areas may be deleterious and that ICAM-1 deficiency reduces neurological damage after transient focal cerebral ischemia.

Treatment of focal cerebral ischemia with synthetic oligopeptide corresponding to lectin domain of selectin

BACKGROUND AND PURPOSE

Synthetic oligopeptides with amino acid sequences of the lectin domain of selectin block selectin-mediated cell adhesion in vitro, which may be applied to a therapeutic intervention to attenuate acute inflammatory reactions. To evaluate the efficacy of such treatment against ischemic brain injury, the effects of administering a selectin oligopeptide that selectively blocks selectin-mediated cell adhesion on histological outcome and on cerebral blood flow (CBF) were studied in models of rodent focal cerebral ischemia.

METHODS

Spontaneously hypertensive rats were anesthetized with halothane. Permanent focal cerebral ischemia was induced by tandem left middle cerebral artery (MCA) and common carotid artery (CCA) occlusion. Focal cerebral ischemia with partial reperfusion was introduced by reperfusing the CCA after 2 hours of tandem MCA/CCA occlusion. A synthetic oligopeptide (amino acid residues 23-30 from N terminal) of E-selectin was dissolved in physiological saline and was injected intravenously at a dosage of 2 mg/kg or 10 mg/kg before artery occlusion. Control animals received equivalent volumes of physiological saline or 10 mg/kg of synthetic oligopeptide with a scrambled amino acid sequence. Twenty-four hours after the occlusion, seven coronal brain slices were stained with 2,3,5-triphenyltetrazolium chloride, and the volume of ischemic injury was calculated. In a separate set of animals, regional CBF was monitored with laser-Doppler flowmetry at the dorsolateral cerebral cortex during 2-hour ischemia and 30 minutes after partial reperfusion.

RESULTS

The volume of ischemic injury did not differ among groups in permanent ischemia. In ischemia with partial reperfusion, 10 mg/kg selectin oligopeptide, but not the same dosage of scrambled oligopeptide, significantly reduced the volume of ischemic injury (95 +/- 13, 73 +/- 11, 55 +/- 6, and 111 +/- 14 mm3 for saline [n = 11]; 2 mg/kg [n = 10] and 10 mg/kg [n = 16] selectin oligopeptide and 10 mg/kg scrambled oligopeptide [n = 6], respectively; P < .01 by one-way ANOVA followed by the Tukey test). Laser-Doppler flowmetry demonstrated a larger increase in CBF after reperfusion of the CCA in the 10-mg/kg selectin oligopeptide group.

CONCLUSIONS

Our data demonstrate that administration of a synthetic oligopeptide corresponding to the lectin domain of selectin decreases the size of ischemic injury after transient, but not after permanent, focal cerebral ischemia as evaluated at 24 hours after onset of ischemia. These effects were associated with an improved CBF at the dorsolateral cerebral cortex after partial reperfusion.

Cytokines and adhesion molecules in stroke and related diseases

Once thought as immunologically naive, cells from the central nervous system have been shown to become immunologically reactive and produce various substances including cytokines and adhesion molecules. Recent investigations have revealed that mRNAs of certain cytokines such as tumor necrosis factor, interleukin-1, and interleukin-6 are expressed in the ischemic brain of the animals. Chemokines including CINC, MCP-1, and MIP-1, as well as adhesion molecules such as ICAM-1. ELAM and P-selectin were also found to be expressed. Although identification of the cells producing these cytokines were often difficult, neurons, endothelia, activated astrocytes and microglia/macrophages were the likely sources. The induction of these molecules in ischemic brain is time-locked and appears to be controlled in a highly regulated manner during the process of ischemic cascade. The functional role, interrelationship, and basic mechanism of action of these molecules are being increasingly recognized, while trials such as antiadhesion antibody molecules, growth factors, and anticytokine antibodies have been successful in reducing the neuronal damage in animals subjected to ischemic injury. Furthermore, changes of certain cytokines or adhesion molecules have been detected in the serum or cerebrospinal fluid of patients with stroke and related diseases suggesting that these molecules play a role in the pathogenesis of human stroke. Understanding of these cytokine-adhesion molecule cascades in the ischemic brain may allow us to develop new strategies for the treatment of stroke.

Cyclophosphamide is neuroprotective in a gerbil model of transient severe focal cerebral ischemia: correlation with effects of tirilazad mesylate (U-74006F)

Using a gerbil model of severe, temporary focal ischemia (3 h unilateral carotid occlusion), preliminary experiments identified an involvement of neutrophils in the reperfusion injury to the ischemic hemisphere. The present experiments were designed to (1) quantitate the temporal accumulation of neutrophils in the gerbil model, (2) determine if cyclophosphamide-induced neutropenia provided cytoprotection to the ischemic hemisphere, and (3) attempt to correlate the cytoprotective efficacy of tirilazad mesylate with possible effects on postischemic neutrophil accumulation. Following 3 h of unilateral carotid occlusion, animals were collected at increasing times of reperfusion and the CA1 region of the hippocampus and the lateral cortex were assessed for postischemic neuronal damage using a semiquantitative index (N.D.I.) of 0 (no damage) to 4 (>75% neuronal loss). The extent of neutrophil accumulation was determined by counting intensely cytochrome oxidase-positive cells. Minimal neuronal death was evident after 2 h of reperfusion, mean N.D.I. = 0.36. However, between 2 and 4 h of reperfusion, neuronal death did not increase. By 6 h of reperfusion, the neuronal death began to proceed at an accelerated rate, N.D.I. = 0.78. By 12 h, the N.D.I. reached 3.20. The accelerated neuronal death coincided with parenchymal invasion of neutrophils. Cyclophosphamide administration delayed neuronal death in the hippocampus, but exhibited a more sustained protective effect in the lateral cortex. Administration of tirilazad mesylate also resulted in a significant reduction in neutrophil accumulation and significant neuronal protection in both brain areas. Thus, in this gerbil model of transient, but prolonged focal cerebral ischemia, neutrophils appear to play an active role in the reperfusion injury to brain tissue. Our experiments confirm the previously demonstrated neuroprotective efficacy of tirilazad mesylate in this model and provide evidence for a similar protective effect of cyclophosphamide. Although other effects of this antioxidant are also thought to contribute to the overall efficacy, the data are consistent with the hypothesis that one mechanism by which tirilazad acts involves limiting the ability of neutrophils to participate in the reperfusion phase of ischemic cerebral injury.

The role of inflammation and cytokines in brain injury

The original notion that the brain represented an "immune-privileged" organ lacking the capability to produce an inflammatory response to an injury, would appear no longer tenable. Indeed, accumulating evidence during the last decade has shown that the CNS can mount a well-defined inflammatory response to a variety of insults including trauma, ischemia, transplantation, viral infections, toxins as well as neurodegenerative processes. Many aspects of this centrally-derived inflammatory response parallel, to some extent, the nature of such a reaction in the periphery. Through the recent application of molecular biological techniques, new concepts are rapidly emerging as to the molecular mechanisms associated with the development of brain injury. In particular, the importance of cytokines, especially TNF alpha and IL-1 beta, as well as adhesion molecules, has been emphasized in the propagation and maintenance of a CNS inflammatory response. This review will summarize recent observations as to the involvement of these inflammatory mediators in CNS injury and lay claim to the possibility that inhibitors of peripheral inflammation may also be of benefit in treating CNS injuries such as stroke, head trauma, Alzheimer's disease and multiple sclerosis.

Time course of ICAM-1 expression and leukocyte subset infiltration in rat forebrain ischemia

The time course of ICAM-1 expression and leukocyte subset infiltration was studied in a model of CNS reperfusion injury in adult rats. Leukocyte adhesion and infiltration, mediated in part by intercellular adhesion molecule-1 (ICAM-1), appears to potentiate CNS reperfusion injury. The timing and relationship between ICAM-1 staining and leukocyte infiltration postglobal CNS ischemia is unknown. Reversible forebrain ischemia was produced in 32 adult Sprague-Dawley rats using the two-vessel occlusion model with histologic analysis performed at specific intervals postischemia: 1, 3, 6, 12, and 24 h, 4 and 7 d, or sham-operated controls (n = 4 each group). Monoclonal antibodies against ICAM-1 (1A29 and TM8), a specific granulocyte (PMN) (HIS48), and a specific monocyte/macrophage (M phi) (ED1) were used. No specific leukocyte and only rare ICAM-1 vessel immunoreactivity was observed in sham controls. ICAM-1: Significant expression in microvessels beginning at 1 h with additional diffuse CA1 pyramidal layer staining beginning at 4 d. Leukocytes: No PMN cells and rare M phi identified at 6 and 12 h. By 24 h: moderate infiltrate in areas of ICAM-1 expression of PMN and M phi. At 4 and 7 d: only M phi accumulation, cellular morphology now similar to microglia. The results of this study indicate that early and persistent ICAM-1 expression occurs following CNS ischemia with associated leukocyte infiltration.

Neutrophil inhibitory factor is neuroprotective after focal ischemia in rats

We tested the neuroprotective potential of neutrophil inhibitory factor (rNIF), a novel 41-kd recombinant glycoprotein derived from a hookworm, in a model of focal cerebral ischemia in the rat. Male Wistar rats were assigned to treatment with rNIF and vehicle. Middle cerebral artery occlusion (MCAO) for 2 hours was induced by insertion of an intraluminal suture. Infusion of the drug was initiated at the onset of reperfusion. Infarct volume was determined 48 hours after reperfusion. Neutrophils were measured within the ischemic tissue by myeloperoxidase (MPO) staining. Treatment with rNIF resulted in a 48% reduction in cerebral infarction compared with control animals (p < 0.01). Neutrophil accumulation in the ischemic brains of rNIF-treated rats was reduced significantly (p < 0.01) compared with control animals. The number of neutrophils within the infarcted tissue correlated positively with the size of the area of infarction (p < 0.001, r = 0.6) within representative cerebral coronal sections. We demonstrated a significant neuroprotective effect of rNIF with continuous treatment for 48 hours following 2 hours of MCAO. The neuroprotective effect was correlated with a reduced number of neutrophils within the ischemic tissue. These results demonstrate potential therapeutic properties of rNIF in the management of stroke.

Postischemic treatment (2-4 h) with anti-CD11b and anti-CD18 monoclonal antibodies are neuroprotective after transient (2 h) focal cerebral ischemia in the rat

We investigated the effects of F(ab')2 fragments of anti-CD11b and anti-CD18 monoclonal antibodies on ischemic cell damage in the rat when administered upon reperfusion and at 2 h of reperfusion after transient (2 h) middle cerebral artery (MCA) occlusion. 2 h of MCA occlusion was induced by intraluminal insertion of a monofilament. The following groups of animals were investigated. Anti-CD11b groups (n = 15): an intact anti-CD11b antibody (1B6c) and an anti-CD11b F(ab')2 fragment of 1B6c were infused upon reperfusion (4 mg/kg i.v.). Anti-CD18 group (n = 8): an anti-CD18 F(ab')2 fragment of CL26 was infused upon reperfusion (2 mg/kg i.v.), and at 22 h of reperfusion (1 mg/kg i.v.). Anti-CD11b delayed group (n = 9): an anti-CD11b F(ab')2 fragment of 1B6c was infused at 2 h of reperfusion (4 mg/kg i.v.), and at 22 h after reperfusion (2 mg/kg i.v.). Control groups (n = 18): an isotype-matched control antibody (mouse IgG1) was administered: (a) upon reperfusion (n = 13), and (b) at 2 h and 22 h of reperfusion (n = 5). Rats were sacrificed at 7 days of reperfusion. In a separate population of rats subjected to 2 h of MCA occlusion (n = 9), brain myeloperoxidase (MPO) activity was measured at 46 h of reperfusion. The vehicle groups had infarct volumes of 35.21 +/- 2.82% to 41.39 +/- 2.73% of the contralateral hemisphere, respectively. Infarct volume was significantly reduced after treatment with: the intact anti-CD11b antibody upon reperfusion (19.0 +/- 6.6%) (P < 0.05), the fragments of mAbs of anti-CD11b administered upon reperfusion (19.7 +/- 2.7%) (P < 0.05), and at 2 h of reperfusion (22.2 +/- 4.8%) (P < 0.05), and anti-CD18 administered upon reperfusion (20.4 +/- 4.8%) (P < 0.05). Anti-CD11b treatment significantly (P < 0.05) inhibited the increase of MPO activity in the ischemic hemisphere. Our data demonstrate that anti-CD11b and anti-CD18 mAb fragments significantly reduce infarct volume and inhibit the increase of MPO activity in the ischemic lesion; administration of anti-CD11b mAb fragment even at 2 h of reperfusion significantly reduces infarct volume. These data support importance of the beta 2 integrin CD11b/CD18 in ischemia/reperfusion injury and indicate that the therapeutic window for intervention to reduce ischemic cell damage in this model is at least 4 h from the onset of MCA occlusion.

Induced expression of adhesion molecules following focal brain ischemia

Central nervous system injuries such as focal brain ischemia and trauma are known to initiate inflammatory reactions. To demonstrate the involvement of adhesion molecules in these inflammatory responses, we have observed significant increases of ICAM-1 and ELAM-1 mRNA expression in the ischemic cortex of rats by means of Northern blot analysis and/or semiquantitative reverse transcription and polymerase chain reaction (RT-PCR). In the ischemic cortex, levels of ICAM-1 mRNA increased significantly at 3 h (2.6-fold, p < 0.05), peaked at 6 to 12 h (6.0-fold, p < 0.01), and remained elevated for up to 5 days (2.5-fold, p < 0.05) after permanent occlusion of the middle cerebral artery (PMCAO). The basal expression of ELAM-1 mRNA was extremely low (undetectable by Northern analysis). Following focal ischemia, however, ELAM-1 mRNA was markedly increased at 6 h in the ischemic cortex, peaked at 12 h (6.4-fold increase compared to sham samples, p < 0.01), and then returned to almost basal levels by 5 days post-PMCAO. Immunohistochemical stainings using anti-ICAM-1 antibodies demonstrated a marked increase of ICAM-1 in the ischemic cortex over the nonischemic cortex or the sham-operated samples. The immunoreactive ICAM-1 signal was localized to endothelial cells of intraparenchymal blood vessels in the ischemic cortex. Furthermore, time-course analysis demonstrated that the increased expression of ICAM-1 and ELAM-1 parallel those of chemokines such as KC and MCP-1, but are more delayed than those of inflammatory cytokines including TNF-alpha and IL-1 beta, which are known to induce expression of ICAM-1 and ELAM-1 on endothelial cells. The upregulation of the inflammatory genes and their products precedes leukocytes' adhesion to endothelial cells and their migration into the ischemic tissue, suggesting that these upregulated adhesion molecules on brain capillary endothelium play an important role in leukocyte migration into ischemic brain tissue.

Demonstration of increased endothelial-leukocyte adhesion molecule-1 mRNA expression in rat ischemic cortex

BACKGROUND AND PURPOSE

Leukocyte infiltration from circulating blood into ischemic brain tissue contributes significantly to ischemic injury. The role of adhesion molecules in leukocyte attachment and infiltration in ischemic tissue has been emphasized. The aim of the present study was to evaluate whether endothelial-leukocyte adhesion molecule-1 (ELAM-1 or E-selectin) mRNA expression is upregulated in focal brain ischemia.

METHODS

Northern blot analysis with the use of poly(A) RNA isolated from the ischemic and nonischemic rat cortex at 2 and 12 hours after permanent occlusion of the middle cerebral artery (PMCAO) was used to examine ELAM-1 mRNA expression. The temporal expression profile of ELAM-1 mRNA in the ischemic cortex was further evaluated with the use of a quantitative reverse transcription and polymerase chain reaction technique.

RESULTS

A very low level of ELAM-1 mRNA was detected in the sham-operated cortex or in the nonischemic cortex. The expression of ELAM-1 mRNA in the focal ischemic cortex was significantly induced by PMCAO, reaching a peak level at 12 hours (6.9-fold increase compared with sham surgery cortical samples, P < .01) and remained elevated for up to 2 days (3.3-fold increase, P < .01) after PMCAO.

CONCLUSIONS

The demonstration of upregulated ELAM-1 mRNA expression after focal stroke suggests that ELAM-1 may play an important role in leukocyte infiltration into the ischemic brain and that ELAM-1 may provide a potential therapeutic target in ischemic stroke. However, the demonstration of translated ELAM-1 and its cellular localization in the ischemic tissue is required when specific antibodies become available.

Anti-intercellular adhesion molecule-1 antibody reduces ischemic cell damage after transient but not permanent middle cerebral artery occlusion in the Wistar rat

BACKGROUND AND PURPOSE

Postischemic cerebral inflammation may contribute to ischemic cell damage. Intercellular adhesion molecule-1 (ICAM-1) is a glycoprotein expressed on endothelial cells that facilitates leukocyte adhesion. We investigated the effect of administration of an anti-ICAM-1 antibody (1A29) on ischemic cell damage after transient (2-hour) or permanent middle cerebral artery (MCA) occlusion in the Wistar rat.

METHODS

Groups studied were as follows: (1) transient MCA occlusion: rats were subjected to 2 hours of MCA occlusion, and after 1 hour of reperfusion they were treated with 1A29 (n = 11) or an isotype control antibody (n = 9); and (2) permanent MCA occlusion: rats were treated with 1A29 (n = 9) or an isotype control antibody (n = 7) 2 hours after onset of MCA occlusion. All animals were killed 1 week after onset of ischemia. Brain sections were stained with hematoxylin and eosin for histological evaluation.

RESULTS

Significant reductions (P < .05) in both volume (44%) of the ischemic lesion and weight loss were found in animals subjected to transient MCA occlusion and treated with 1A29 compared with vehicle-treated animals. In contrast, in animals subjected to permanent MCA occlusion the lesion and the temporal profile of body weight were not altered by 1A29 administration.

CONCLUSIONS

Ischemic cell damage is promoted by postischemic inflammatory response after 2 hours of transient MCA occlusion, and ischemic cell damage is reduced by administration of an anti-ICAM-1 antibody during reperfusion.

Transition from ischemic neuronal necrosis to infarction in repeated ischemia

To study morphological changes in the cortex that follow repeated ischemia, one, two, and three 7-min unilateral occlusions of the carotid artery at 6-h intervals, and three, four, and five 7-min similar occlusions at 12-h intervals were produced in gerbils. Animals with one and two 7-min occlusions at 6-h intervals showed selective neuronal necrosis in the cortex; those with three 7-min occlusions at 6-h intervals showed focal infarction in the third layer of the cortex. Animals with three 7-min occlusions at 12-h intervals showed selective neuronal necrosis; those with four 7-min occlusions at 12-h intervals showed focal infarction in the third layer. In animals with five 7-min occlusions at 12 h intervals, infarction affecting all layers of the cortex was seen. Results of the present study indicate that cortical infarction occurred when a brief ischemic insult that does not cause any visible morphological damage in cortical neurons was inflicted repeatedly, and that development of infarction in the cortex following repeated episodes of ischemia depended on both the number of insults and the time intervals between them. This finding suggests that there is a threshold of infarction in repeated ischemia. In our model, various stages of ischemic brain injury could be achieved more easily than in transient ischemia by altering the number of insults or the intervals between them. This model is suitable for studying the pathophysiology on transition from ischemic neuronal necrosis to infarction.

The temporal profiles of ICAM-1 protein and mRNA expression after transient MCA occlusion in the rat

Leukocytes may contribute to ischemic cell damage. ICAM-1 expression on endothelial cells facilitates the migration of leukocytes into tissue. Therefore, we measured the temporal profiles of ICAM-1 mRNA and protein in rat brain after transient (1 or 2 h) of middle cerebral artery (MCA) occlusion. Male Wistar rats (n = 86) were subjected to 1 or 2 h MCA of occlusion, or 2 h of MCA occlusion followed by reperfusion for a variety of durations ranging from 1 h to 1 week. 10 additional control animals were employed. ICAM-1 mRNA and protein were measured during ischemia and reperfusion, and immunohistochemical methods were used to identify specific cell types expressing ICAM-1. ICAM-1 mRNA was detected 1 h after the onset of ischemia. mRNA maximized at 10 h of reperfusion and persisted out to 1 week of reperfusion. ICAM-1 significantly increased in microvascular endothelial cells at 2 h of reperfusion, maximized at 46 h and persisted out to 1 week of reperfusion (P < 0.05). ICAM-1 mRNA and protein are present in ischemic brain early after the onset of ischemia and reperfusion, respectively. These data provide support for the role of ICAM-1 in mediating leukocyte-endothelial adhesion after transient MCA occlusion in the rat.

The influence of antiadhesion therapies on leukocyte subset accumulation in central nervous system ischemia in rats

Although treatment with agents that block leukocyte function, including anti-ICAM-1 and doxycycline, reduces experimental central nervous system (CNS) ischemic injury, it is not known how leukocyte subset accumulation is affected by these agents. Using the rat two-vessel occlusion model and immunohistochemistry, we investigated granulocyte (PMN) and monocyte/macrophage (M phi) accumulation at 1 and 4 d postischemia. A total of 24 animals were randomized to sham surgery, or to ischemia with saline, anti-ICAM-1, or doxycycline treatments. No leukocytes were observed in sham animals. At 24 h postischemia, there was a moderate infiltration of PMN and M phi in untreated animals that was significantly decreased with either treatment. At 4 d after ischemia no PMN were identified, with extensive M phi accumulation occurring in untreated animals that was only partially reduced with doxycycline treatment. These results confirm that both anti-ICAM-1 and doxycycline treatments reduce PMN and M phi infiltration at 24 h. Delayed M phi accumulation occurs despite treatment, suggesting that some of these cells represent transformed resident microglia.

Neuroprotective effect of human osteogenic protein-1 in a rat model of cerebral hypoxia/ischemia

Possible neuroprotective actions of osteogenic protein-1 (OP-1) were evaluated in a rat model of cerebral hypoxia/ischemia. Intraperitoneal injection of 50 micrograms of OP-1 prior to bilateral carotid ligation and transient hypoxia in 12-day-old rats reduced cerebral infarct area from 44.8 +/- 3.3% in vehicle-injected controls to 29 +/- 4.9%. Treatment of 14-day-old rats with 20 micrograms of OP-1 1 h after hypoxia reduced mortality from 45% to 13%. OP-1 may represent a novel class of neuroprotective agents.

Adhesive glycoproteins CD11a and CD18 are upregulated in the leukocytes from patients with ischemic stroke and transient ischemic attacks

Leukocytes may have an important role in the pathogenesis of brain injury after ischemia. Expression of adhesion molecules on leukocytes and/or endothelia is needed for leukocytes to adhere to endothelia and infiltrate into the injured brain. The purpose of the present pilot study is to delineate whether the expression of leukocyte adhesion molecules, CD11a and CD18, are upregulated in patients with ischemic stroke and transient ischemic attack. Ten patients with ischemic stroke, 6 with transient ischemic attack (TIA), and 11 age and risk factor matched controls were studied. Using immunofluorescence phenotyping and flow cytometry, leukocyte membrane expression of CD11a and CD18 were measured within 72 h after onset of ischemia. Follow-up measurements were performed at 5-7 days after ictus in 6 patients with stroke, and at 3-5 days after ictus in 3 patients with TIA. CD11a immunofluorescence (IF) was significantly increased within 72 h after onset of symptoms in patients with stroke as well as TIA compared with the control group (p < 0.017). IF of CD18 also increased in both patient groups, but significance was reached only in the TIA group (p < 0.05). No difference of CD11a and CD18 IF was detected between stroke and TIA groups. Follow-up measurement of CD11a and CD18 showed a trend of decrease, but CD11a IF remained significantly elevated compared with the control group (p < 0.017). Expression of leukocyte adhesion molecules CD11a, and CD18 are upregulated in patients with ischemic stroke and TIA. Although these data are preliminary, our data suggest that these molecules are associated with cerebrovascular disorders including ischemic stroke and TIA.

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)

Upregulation of intercellular adhesion molecule 1 (ICAM-1) on brain microvascular endothelial cells in rat ischemic cortex

The expression of intercellular adhesion molecule 1 (ICAM-1) was studied in rat focal ischemic cortex. A significant increase in ICAM-1 mRNA expression in the ischemic cortex over levels in contralateral (nonischemic) site was observed by means of Northern blot analysis following either permanent or temporary occlusion with reperfusion of the middle cerebral artery (PMCAO or MCAO with reperfusion) in spontaneously hypertensive rats. In the ischemic cortex, levels of ICAM-1 mRNA increased significantly at 3 h (2.6-fold, n = 3, P < 0.05), peaked at 6 to 12 h (6.0-fold, P < 0.01) and remained elevated up to 5 days (2.5-fold, P < 0.05) after PMCAO. The profile of ICAM-1 mRNA expression in the ischemic cortex following MCAO with reperfusion was similar to that following PMCAO, except that ICAM-1 mRNA was significantly increased as early as 1 h (6.3-fold, n = 3, P < 0.05) and then gradually reached a peak at 12 h (12-fold, P < 0.01) after reperfusion. ICAM-1 mRNA expression in ischemic cortex following PMCAO was significantly greater in hypertensive rats than in two normotensive rat strains. Immunostaining using anti-ICAM-1 antibodies indicated that upregulated ICAM-1 expression was localized to endothelial cells of intraparenchymal blood vessels in the ischemic but not contralateral cortex. The data suggest that an upregulation of ICAM-1 mRNA and protein on brain capillary endothelium may play an important role in leukocyte migration into ischemic brain tissue.

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)