Heterologous cell-cell interactions: thromboregulation, cerebroprotection and cardioprotection by CD39 (NTPDase-1)

Blood platelets maintain vascular integrity and promote primary and secondary hemostasis following interruption of vessel continuity. Biochemical or physical damage to the coronary, carotid or peripheral arteries is followed by excessive platelet activation and recruitment culminating in vascular occlusion and tissue ischemia. Currently inadequate therapeutic approaches to stroke and coronary artery disease are a public health issue. Following our demonstration of neutrophil leukotriene production from arachidonate released from activated aspirin-treated platelets, we studied interactions between platelets and other blood cells, leading to concepts of transcellular metabolism and thromboregulation. Thrombosis has a proinflammatory component whereby biologically active substances are synthesized by interactions between different cell types that could not individually synthesize the product(s). Endothelial cells control platelet reactivity via three biochemical systems-autacoids leading to production of prostacyclin and nitric oxide, and endothelial ecto-ADPase/CD39/NTPDase-1. The autacoids are fluid-phase reactants, not produced by tissues in the basal state. They are only synthesized intracellularly and released upon interactions of cells with an agonist. When released, autacoids exert fleeting actions in the immediate milieu, and are rapidly inactivated. CD39 is an integral component of the endothelial cell surface and is substrate-activated. It maintains vascular fluidity in the complete absence of prostacyclin and nitric oxide, indicating that they are ancillary components of hemostasis. Therapeutic implications for the autacoids have not been compelling because of their transient, local and fleeting action, and limited potency. Conversely, CD39, acting solely on the platelet releasate, is efficacious in three different animal models. It metabolically neutralizes a prothrombotic platelet releasate via deletion of ADP--the major recruiting agent responsible for formation of an occlusive thrombus. In addition, solCD39 reduced ATP- and ischemia-induced norepinephrine release in the heart. This reduction can prevent fatal arrhythmia. Moreover, solCD39 ameliorated the sequelae of stroke in CD39 null mice. CD39 represents the next generation of cardioprotective and cerebroprotective molecules.

Intravenous allicin improves pulmonary blood flow after ischemia-reperfusion injury in rats

BACKGROUND

Allicin is a sulfur-containing compound extracted from garlic, with antiaggregatory, anti- migratory, anti-oxidant and pulmonary vasodilator actions. We hypothesized that allicin might be beneficial in lung ischemia-reperfusion.

METHODS

A non-nothermic rat lung ischemia-reperfusion model was established by clamping left pulmonary artery (PA) for 1 hr, followed by reperfusion for 2 hrs by clamping right PA to reflect solely the function of left lung. Groups were control (n=7), allicin 0.1 mg (n=8) and allicin 0.01 mg (n=4). In the beginning of reperfusion allicin/saline were injected. Pulmonary artery pressures (PAP), pulmonary artery flow (PAF), left atrial pressure (LAP) were monitored. At the end of reperfusion period arterial blood gas (ABG) analysis was done.

RESULTS

Six of 7 control and 3 of 8 group 2 animals died before completing the experiment. In group 1 all animals completed the experiment (p=0.015 vs control). PAF was significantly increased after 30, 60 and 120 min of reperfusion in group 1 (p=0.0028, 0.0009, 0.0003 respectively vs control) and after 60 and 120 minutes in group 2 (p=0.0453, 0.018 respectively vs control). Pulmonary vascular resistance was lower at 30 min in allicin 0.01 mg group (p=0.0017 vs control). PAP was increased after 60 and 120 min of reperfusion in group 1 (p=0.016, 0.0029 respectively vs control) and after 120 min in group 2 (p=0.0104 vs control).

CONCLUSIONS

This study shows that allicin improves postischemic PAF in this model. Allicin needs further investigation of potential utility and mechanism(s) of action.

Extinguishing Egr-1-dependent inflammatory and thrombotic cascades after lung transplantation

Hypoxic induction of the early growth response-1 (Egr-1) transcription factor initiates proinflammatory and procoagulant gene expression. Orthotopic/isogeneic rat lung transplantation triggers Egr-1 expression and nuclear DNA binding activity corresponding to Egr-1, which leads to increased expression of downstream target genes such as interleukin-1b, tissue factor, and plasminogen activator inhibitor-1. The devastating functional consequences of Egr-1 up-regulation in this setting are prevented by treating donor lungs with a phosphorothioate antisense oligodeoxyribonucleotide directed against the Egr-1 translation initiation site, which blocks expression of Egr-1 and its gene targets. Post-transplant graft leukostasis, inflammation, and thrombosis are consequently diminished, with marked improvement in graft function and recipient survival. Blocking expression of a proximal transcription factor, which activates deleterious inflammatory and coagulant effector mechanisms, is an effective molecular strategy to improve organ preservation.

Inhibition of platelet recruitment by endothelial cell CD39/ecto-ADPase: significance for occlusive vascular diseases

During their 7-9 day lifespan in the circulation platelets are mainly responsible for maintaining the integrity of the vasculature. In thrombocytopenic states, there is an increase in vascular permeability and fragility, presumably due to absence of this platelet function. In sharp contrast, biochemical or physical injury in the coronary, carotid or peripheral arteries induces platelet activation and platelet recruitment, which can culminate in thrombotic vascular occlusion. Since there is one death every 33 s from vascular occlusion in the United States, this situation constitutes a major public health issue. In the course of studying interactions between cells of the vascular wall and those in the circulation, we observed that platelets in close proximity to endothelial cells do not respond to agonists in vitro. Experiments initiated in the late 1980's cumulatively indicated that endothelial cell CD39--an ecto-ADPase--was mainly responsible for this phenomenon. CD39 rapidly and preferentially metabolizes ADP released from activated platelets. ADP is the final common pathway for platelet recruitment and thrombus formation, and platelet aggregation and recruitment are abolished by CD39. Our current hypothesis is that CD39 will be a novel antithrombotic agent for treating high risk patients who have activated platelets in their circulation--the identifying characteristic of coronary artery occlusion and thrombotic stroke. A recombinant, soluble form of human CD39 has been generated. This is solCD39, a glycosylated protein of 66 kDa whose enzymatic and biological properties are identical to the full-length form of the enzyme. In our in vitro experiments, solCD39 blocks ADP-induced human platelet aggregation, and inhibits collagen- and thrombin receptor agonist peptide-induced platelet reactivity. We studied solCD39 in vitro in a murine model of stroke, which was shown to be driven by excessive platelet recruitment. In studies with CD39 wild-type (CD39+/+) mice solCD39 completely abolished ADP-induced platelet aggregation, and strongly inhibited collagen- and arachidonate-induced platelet reactivity ex vivo. When solCD39 was administered prior to transient intraluminal middle cerebral artery occlusion, it reduced ipsilateral fibrin deposition, decreased (111)In-platelet deposition, and increased post-ischemic blood flow 2-fold at 24 hours. These results were superior to those we obtained with aspirin pre-treatment. CD39 null (CD39-/-) mice, which we generated by deletion of exons 4-6 (apyrase conserved regions 2-4), have a normal phenotype, normal hematologic profiles and bleeding times, but exhibit a decrease in post-ischemic perfusion and an increase in cerebral infarct volume when compared to genotypic CD39+/+ controls in our stroke model. "Reconstitution" of CD39 null mice with solCD39 reversed these pathologic changes. Thus, the CD39-/- mice were actually rescued from cerebral injury by solCD39, thereby fulfilling Koch's postulates. These experiments have led us to hypothesize that solCD39 has potential as a novel therapeutic agent for thrombotic stroke. In this review, we summarize our recent research results with CD39 and solCD39, and discuss our viewpoints on its present and future possibilities as a novel treatment for thrombosis.

Dehydroascorbic acid, a blood-brain barrier transportable form of vitamin C, mediates potent cerebroprotection in experimental stroke

Neuronal injury in ischemic stroke is partly mediated by cytotoxic reactive oxygen species. Although the antioxidant ascorbic acid (AA) or vitamin C does not penetrate the blood-brain barrier (BBB), its oxidized form, dehydroascorbic acid (DHA), enters the brain by means of facilitative transport. We hypothesized that i.v. DHA would improve outcome after stroke because of its ability to cross the BBB and augment brain antioxidant levels. Reversible or permanent focal cerebral ischemia was created by intraluminal middle cerebral artery occlusion in mice treated with vehicle, AA, or DHA (40, 250, or 500 mg/kg), either before or after ischemia. Given before ischemia, DHA caused dose-dependent increases in postreperfusion cerebral blood flow, with reductions in neurological deficit and mortality. In reperfused cerebral ischemia, mean infarct volume was reduced from 53% and 59% in vehicle- and AA-treated animals, respectively, to 15% in 250 mg/kg DHA-treated animals (P < 0.05). Similar significant reductions occurred in nonreperfused cerebral ischemia. Delayed postischemic DHA administration after 15 min or 3 h also mediated improved outcomes. DHA (250 mg/kg or 500 mg/kg) administered at 3 h postischemia reduced infarct volume by 6- to 9-fold, to only 5% with the highest DHA dose (P < 0.05). In contrast, AA had no effect on infarct volumes, mortality, or neurological deficits. No differences in the incidence of intracerebral hemorrhage occurred. Unlike exogenous AA, DHA confers in vivo, dose-dependent neuroprotection in reperfused and nonreperfused cerebral ischemia at clinically relevant times. As a naturally occurring interconvertible form of AA with BBB permeability, DHA represents a promising pharmacological therapy for stroke based on its effects in this model of cerebral ischemia.

The role of the complement cascade in ischemia/reperfusion injury: implications for neuroprotection

BACKGROUND

The complement cascade plays a deleterious role in multiple models of ischemia/reperfusion (I/R) injury, including stroke. Investigation of the complement cascade may provide a critical approach to identifying neuroprotective strategies that can be effective at clinically relevant time points in cerebral ischemia. This review of the literature describes the deleterious effects of complement activation in systemic I/R models and previous attempts at therapeutic complement inhibition, with a focus on the potential role of complement inhibition in ischemic neuroprotection. Translation of these concepts into ischemic stroke models and exploration of related neuroprotective strategies are also reviewed.

SUMMARY OF REVIEW

We performed a MEDLINE search to identify any studies published between 1966 and 2001 dealing with complement activation in the setting of I/R injury. We also searched for studies demonstrating up-regulation of any complement components within the central nervous system during inflammation and/or ischemia.

CONCLUSIONS

The temporal and mechanistic overlap of the complement cascade with other biochemical events occurring in cerebral I/R injury is quite complex and is only beginning to be understood. However, there is compelling evidence that complement is quite active in the setting of acute stroke, suggesting that anticomplement strategies should be further investigated through genetic analysis, nonhuman primate models, and clinical investigations.

Paradoxical rescue from ischemic lung injury by inhaled carbon monoxide driven by derepression of fibrinolysis

Carbon monoxide (CO) can arrest cellular respiration, but paradoxically, it is synthesized endogenously by heme oxygenase type 1 (Ho-1) in response to ischemic stress. Ho-1-deficient (Hmox1-/-) mice exhibited lethal ischemic lung injury, but were rescued from death by inhaled CO. CO drove ischemic protection by activating soluble guanylate cyclase and thereby suppressed hypoxic induction of the gene encoding plasminogen activator inhibitor-1 (PAI-1) in mononuclear phagocytes, which reduced accrual of microvascular fibrin. CO-mediated ischemic protection observed in wild-type mice was lost in mice null for the gene encoding PAI-1 (Serpine1). These data establish a fundamental link between CO and prevention of ischemic injury based on the ability of CO to derepress the fibrinolytic axis. These data also point to a potential therapeutic use for inhaled CO.

A pathway leading to hypoxia-induced vascular fibrin deposition

Hypoxemia has long been associated with vascular fibrin formation leading to thrombosis. This review describes a pathway through which mononuclear phagocytes and vascular smooth muscle cells upregulate tissue factor under hypoxic conditions. Increased expression of tissue factor triggers events leading to vascular fibrin deposition, providing insight into a novel mechanism potentially underlying thrombosis in ischemic vasculature.

The endothelial response to oxygen deprivation: biology and clinical implications

This review provides the theoretical background of phenotypic and gene-based changes in the vessel wall triggered by acute hypoxia. Only in the last few decades has the endothelium been ascribed a prominent role as a modulator of vascular homeostasis under both physiological and pathological conditions. Molecular mechanisms leading to endothelial activation are being rapidly elucidated and their contribution to vascular dysfunction during hypoxia becoming better understood. New insights gained from hypoxic cell culture and ischaemic organ models may ultimately lead to new treatment strategies. If nothing else, insights gained from vascular research will lead to a more complete understanding of the inflammatory processes in blood vessels and how they impact on human disease.

Egr-1, a master switch coordinating upregulation of divergent gene families underlying ischemic stress

Activation of the zinc-finger transcription factor early growth response (Egr)-1, initially linked to developmental processes, is shown here to function as a master switch activated by ischemia to trigger expression of pivotal regulators of inflammation, coagulation and vascular hyperpermeability. Chemokine, adhesion receptor, procoagulant and permeability-related genes are coordinately upregulated by rapid ischemia-mediated activation of Egr-1. Deletion of the gene encoding Egr-1 strikingly diminished expression of these mediators of vascular injury in a murine model of lung ischemia/reperfusion, and enhanced animal survival and organ function. Rapid activation of Egr-1 in response to oxygen deprivation primes the vasculature for dysfunction manifest during reperfusion. These studies define a central and unifying role for Egr-1 activation in the pathogenesis of ischemic tissue damage.

A modified transorbital baboon model of reperfused stroke

BACKGROUND AND PURPOSE

Although pathophysiological studies of focal cerebral ischemia in nonhuman primates can provide important information not obtainable in rodent models, primate experimentation is limited by considerations of cost, availability, effort, and ethics. A reproducible and quantitative model that minimizes the number of animals necessary to detect differences between treatment groups is therefore crucial.

METHODS

Eight male baboons (weight, 22+/-2 kg) underwent left transorbital craniectomy followed by 1 hour of temporary ipsilateral internal carotid artery occlusion at the level of the anterior choroidal artery together with bilateral temporary occlusion of both anterior cerebral arteries (A1) proximal to the anterior communicating artery. A tightly controlled nitrous oxide-narcotic anesthetic allowed for intraoperative motor evoked potential confirmation of middle cerebral artery (MCA) territory ischemia. Animals survived to 72 hours or 10 days if successfully self-caring. Outcomes were assessed with a 100-point neurological grading system, and infarct volume was quantified by planimetric analysis of both MRI and triphenyltetrazolium chloride-stained sections.

RESULTS

Infarction volumes (on T2-weighted images) were 32+/-7% (mean+/-SEM) of the ipsilateral hemisphere, and neurological scores averaged 29+/-9. All animals demonstrated evidence of hemispheric infarction, with damage evident in both cortical and subcortical regions in the MCA vascular territory. Histologically determined infarction volumes differed by <3% and correlated with absolute neurological scores (r=0.9, P:=0.003).

CONCLUSIONS

Transorbital temporary occlusion of the entire anterior cerebral circulation with strict control of physiological parameters can reliably produce reperfused MCA territory infarction. The magnitude of the resultant infarct with little interanimal variability diminishes the potential number of animals required to distinguish between 2 treatment regimens. The anatomic distribution of the infarct and associated functional deficits offer comparability to human hemispheric strokes.

Postischemic cerebrovascular E-selectin expression mediates tissue injury in murine stroke

BACKGROUND AND PURPOSE

Although the deleterious role of several proinflammatory mediators, including P-selectin, in reperfused stroke is well established, the role of E-selectin has not been fully characterized.

METHODS

E-selectin mRNA expression was studied at 4, 10, and 24 hours after reperfusion with reverse transcription and polymerase chain reaction in mice (n=18) subjected to transient intraluminal middle cerebral artery occlusion (MCAO). Mice received intravenous injection with anti-E-selectin monoclonal antibody (10, 35, or 50 microg), nonimmune IgG, or vehicle immediately before MCAO and 90 minutes later (n=85). Others received anti-E-selectin antibody 3 or 6 hours after MCAO (n=32). Myeloperoxidase activity was measured in sham-operated mice and after 10 hours of reperfusion in saline-, nonimmune IgG-, or anti-E-selectin IgG-treated cohorts (n=17). Serial cerebral blood flow was measured with laser-Doppler flowmetry, and outcomes were assessed by neurological deficits and infarct volumes with the use of planimetric analysis of triphenyltetrazolium chloride-stained sections.

RESULTS

Upregulated E-selectin expression occurred in the ischemic cerebral vasculature within 4 hours of reperfusion and persisted for 24 hours. Anti-E-selectin antibody increased ischemic cortical cerebral blood flow up to 2.6-fold (P:<0.05). In addition to dose-dependent reductions in neurological deficits (P:<0.05), mortality, and infarct volumes (P:<0.01 for 35 and 50 microg), anti-E-selectin treatment reduced cerebral neutrophil accumulation (P:<0.05) and was neuroprotective even if delayed until 3 hours after ischemia (P:<0. 05).

CONCLUSIONS

These findings establish a functional role for E-selectin in the pathogenesis of tissue injury after cerebral ischemia and reperfusion and suggest that E-selectin blockade may be clinically useful in the treatment of reperfused stroke.

Amyloid beta -peptide-binding alcohol dehydrogenase is a component of the cellular response to nutritional stress

Amyloid beta-peptide-binding alcohol dehydrogenase (ABAD) is a member of the family of short chain dehydrogenase/reductases whose distinctive properties include the capacity to bind amyloid beta-peptide and enzymatic activity toward a broad array of substrates including n-isopropanol and beta-estradiol. In view of the wide substrate specificity of ABAD and its high activity on l-beta-hydroxyacyl-CoA derivatives, we asked whether it might also catalyze the oxidation of the ketone body d-3-hydroxybutyrate. This was indeed the case, and oxidation proceeded with K(m) of approximately 4.5 mm and V(max) of approximately 4 nmol/min/mg protein. When placed in medium with d-beta-hydroxybutyrate as the principal energy substrate, COS cells stably transfected to overexpress wild-type ABAD (COS/wtABAD) better maintained 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide reduction, cellular energy charge, and morphologic phenotype compared with COS/vector cells. Using a severe model of metabolic perturbation, transgenic mice with targeted neuronal expression of ABAD subjected to transient middle cerebral artery occlusion showed strokes of smaller volume and lower neurologic deficit scores in parallel with increased brain ATP and decreased lactate, compared with nontransgenic controls. These data suggest that ABAD contributes to the protective response to metabolic stress, especially in the setting of ischemia.

Potentiation of endogenous fibrinolysis and rescue from lung ischemia/reperfusion injury in interleukin (IL)-10-reconstituted IL-10 null mice

Little is known about interactions between endogenous anti-inflammatory paradigms and microvascular thrombosis in lung ischemia/reperfusion (I/R) injury. Interleukin (IL)-10 suppresses macrophage activation and down-regulates proinflammatory cytokine production, but there are no available data to suggest a link between IL-10, thrombosis, and fibrinolysis in the setting of I/R. We hypothesized that hypoxia/ischemia triggers IL-10 production, to dampen proinflammatory cytokine and adhesion receptor cascades and to restore vascular patency by fibrinolytic potentiation. Studies were performed in a mouse lung I/R model. IL-10 mRNA levels in lung were increased 43-fold over base line by 1 h of ischemia/2 h of reperfusion, with a corresponding increase in plasma IL-10. Expression was prominently localized in bronchial epithelial cells and mononuclear phagocytes. To study the link between IL-10 and fibrinolysis in vivo, the induction of plasminogen activator inhibitor-1 (PAI-1) was evaluated. Northern analysis demonstrated exaggerated pulmonary PAI-1 expression in IL-10 (-/-) mice after I/R, with a corresponding increase in plasma PAI/tissue-type plasminogen activator activity. In vivo, IL-10 (-/-) mice showed poor postischemic lung function and survival after I/R compared with IL-10 (+/+) mice. Despite a decrease in infiltration of mononuclear phagocytes in I/R lungs of IL-10 (-/-) mice, an increased intravascular pulmonary fibrin deposition was observed by immunohistochemistry and Western blotting, along with increased IL-1 expression. Recombinant IL-10 given to IL-10 (-/-) mice normalized the PAI/tissue-type plasminogen activator ratio, reduced pulmonary vascular fibrin deposition, and rescued mice from lung injury. Since recombinant hirudin (direct thrombin inhibitor) also sufficed to rescue IL-10 (-/-) mice, these data suggest a preeminent role for microvascular thrombosis in I/R lung injury. Ischemia-driven IL-10 expression confers postischemic pulmonary protection by augmenting endogenous fibrinolytic mechanisms.

Improvement of rejection-induced diastolic abnormalities in rat cardiac allografts with inducible nitric oxide synthase inhibition

OBJECTIVE

Inhibition of inducible nitric oxide synthase (nitric oxide II) activity has been proposed as a method to attenuate capillary leak and edema during rejection of heterotopically transplanted rat hearts. Myocardial edema has previously been implicated in diastolic dysfunction during allograft rejection. Accordingly, we tested the hypothesis that inducible nitric oxide synthase inhibition with aminoguanidine would alleviate left ventricular stiffening and myocardial edema formation in 4-day heterotopic rat heart allografts.

METHODS

Passive left ventricular filling was studied in American Cancer Institute Lewis rats receiving heterotopic heart transplants receiving either aminoguanidine, a selective nitric oxide synthase inhibitor (n = 6); dexamethasone (1 mg. kg(-1). d(-1) administered subcutaneously) for 4 days after transplantation (n = 6); or intravenous saline solution (n = 6). American Cancer Institute-to-American Cancer Institute isografts (n = 6) were used as controls.

RESULTS

Serum nitrite/nitrate levels in the aminoguanidine group (18 +/- 3 mmol/L) and dexamethasone group (22 +/- 4 mmol/L) were reduced versus the intravenous saline group (144 +/- 36 mmol/L [SEM]) to levels seen in controls (25 +/- 9 mmol/L). Left ventricular volume at 15 mm Hg for the aminoguanidine group was increased versus that for the intravenous saline solution group, similar to that for controls, and reduced versus dexamethasone-treated animals. Myocardial water content for the aminoguanidine-treated animals (78.3% +/- 0.4%) was similar to those of intravenous saline-treated animals (78.0% +/- 0. 3%) but greater than those of controls (77.1% +/- 0.2%) and dexamethasone-treated animals (76.7% +/- 0.3%).

CONCLUSIONS

Nitric oxide II inhibition with aminoguanidine minimizes the reduction in left ventricular filling that is seen with allograft rejection through a mechanism that is not associated with attenuation of myocardial edema.

Pulmonary expression of early growth response-1: biphasic time course and effect of oxygen concentration

Hypoxia induces complex adaptive responses. In this report, induction of early growth response-1 (Egr-1) transcripts in lungs of mice subjected to hypoxia is shown to be dose and time dependent. Within 30 min of hypoxia, Egr-1 transcripts were approximately 20-fold elevated in 6% oxygen, approximately 5.2-fold increased by 10% oxygen, and returned to the normoxic baseline by 12% oxygen. Time course studies up to 48 h showed a biphasic profile with an initial steep rise in Egr-1 transcripts after 0.5 h of hypoxia and a second elevation beginning after 20-24 h. Hypoxic induction of Egr-1 was paralleled by enhanced expression of the downstream target gene tissue factor. Egr-1 and tissue factor antigen were visualized in bronchial and vascular smooth muscle and in alveolar macrophages. Egr-1 has the capacity to modulate expression of genes involved in the remodeling of the extracellular matrix and properties of smooth muscle, thus possibly contributing to the pulmonary response to chronic hypoxia.

Noninvasive assessment and necropsy validation of changes in left ventricular mass in ascending aortic banded mice

Although left ventricular (LV) hypertrophy can be induced by aortic banding, noninvasive assessment of changes in LV mass in mice with a banded ascending aorta by using 2-dimensional (2D) images has not been previously performed. In this study we serially assessed changes in LV mass by 2D echocardiography with a newly available 12-MHz transducer in mice with a banded ascending aorta and validated measurements at necropsy. Estimated by echocardiography, LV mass increased from 74+/- 17 mg before banding to 191.08+/-54 mg at 8 weeks after banding (P <.0001), and excellent correlation was shown with postmortem measurements (r = 0.97). Furthermore, with the use of pulsed Doppler 2-dimensionally guided echocardiography, noninvasive measurement of flow velocities in the ascending aorta before and after the band at the various time points was possible. We propose that 2D echocardiography with a 12-MHz transducer is a powerful tool for serial noninvasive evaluations as an adjunct to the study of cardiac hypertrophy in the murine model.

cAMP pulse during preservation inhibits the late development of cardiac isograft and allograft vasculopathy

The causes of transplant-associated coronary artery disease remain obscure, and there is no known treatment. Preservation injury of murine heterotopic vascularized cardiac isografts caused a small, albeit significant, increase in neointimal formation; preservation injury of allografts markedly increased both the incidence and severity of transplant-associated coronary artery disease. As cAMP is an important vascular homeostatic mediator the levels of which decline during organ preservation, buttressing cAMP levels solely during initial preservation both improved acute allograft function and reduced the severity of transplant-associated coronary artery disease in grafts examined 2 months later. Inhibiting the cAMP-dependent protein kinase abrogated these beneficial effects. cAMP treatment was associated with an early reduction in leukocyte infiltration and a reciprocal decrease in superoxide and increase in NO levels. These data indicate that alloantigen-independent injury to the graft, which occurs at the time of cardiac preservation, can set in motion pathological vascular events that are manifest months later. Furthermore, a cAMP pulse during cardiac preservation reduces the incidence and severity of transplant-associated coronary artery disease.

Contribution of inflammation to reperfusion injury

Interrupting the flow of blood to an organ for even a relatively brief period disrupts multiple essential vascular homeostatic mechanisms. This results in the cardinal manifestations of reperfusion injury, which, at the tissue level, are comprised of leukocyte infiltration, thrombosis, edema, and vasoconstriction. Molecular mechanisms that are particularly relevant to postischemic inflammation and reperfusion injury include induction of adhesion receptor expression at the endothelial surface, alterations in the procoagulant/anticoagulant balance to promote accumulation of intravascular thrombus, oxidant stress that directly injures cells and indirectly promotes inflammatory upregulation, loss of protective second messenger cyclic nucleotide systems, and activation of the complement cascade that causes vascular injury as well as collateral damage to innocent bystander cells with the reperfused tissue. Understanding the inflammatory mechanisms that participate in reperfusion injury may lead to reperfusion therapies designed to improve postischemic organ function.

Antisense intercellular adhesion molecule-1 (ICAM-1) oligodeoxyribonucleotide delivered during organ preservation inhibits posttransplant ICAM-1 expression and reduces primary lung isograft failure

Transiently increased expression of leukocyte adhesion receptors after lung preservation contributes to early graft demise by recruiting leukocytes, activating complement, and causing microcirculatory stasis. We hypothesized that inhibiting intercellular adhesion molecule-1 (ICAM-1) expression even briefly may significantly improve lung graft function and that the preservation period might provide a unique window to deliver a therapeutic pulse of antisense oligonucleotide ICAM-1 to inhibit ICAM-1 expression after transplantation. Interleukin-1beta-treated rat pulmonary endothelial cells given a 20-mer phosphorothioate oligonucleotide comprising an antisense span targeted to the 3'-untranslated region of rat ICAM-1 demonstrated an oligonucleotide dose-dependent reduction in ICAM-1 expression. Using a cationic liposomal carrier, this same antisense oligonucleotide (but not the sense control) instilled into the pulmonary vasculature at the time of preservation reduced subsequent graft ICAM-1 expression and graft leukostasis and markedly improved oxygenation, pulmonary blood flow, and graft survival. These experiments demonstrate that the preservation period presents a window during which to target an anti-ICAM-1 expression strategy to inhibit early adhesion receptor expression and improve functional outcome after lung transplantation.

Effects of mast cell membrane stabilizing agents in a rat lung ischemia-reperfusion model

BACKGROUND

The aim of this study was to test the hypothesis that agents which stabilize the mast cell membrane may modulate the phenotype of the vascular wall in a lung ischemia-reperfusion model, including altering expression of endothelial and leukocyte adhesion receptors and the inducible nitric oxide synthase (NOS-2).

METHODS

Three sets of rats were given either intravenous saline (group A), ketotifen (group B), or cromolyn (group C), respectively. The left pulmonary artery was ligated temporarily and reopened after 2 hours of ischemia. Then, after a 2-hour period of reperfusion, the left lung was excised. ICAM-1 and NOS-2 were measured at the protein level by Western blotting, and cGMP levels were measured by enzyme-linked immunosorbent assay in the lung tissue specimens for each drug group.

RESULTS

ICAM-1 expressions, determined as the intensity of a given band on the Western blot, were 197+/-59 in group B and 195+/-83 in group C versus 369+/-114 in group A (p = 0.002 for analysis of variance). In contrast with ICAM-1, NOS-2 expression was increased by ketotifen or cromolyn treatment (464+/-82 in group B and 507+/-93 in group C, compared with 377+/-44 for group A, p = 0.007). The finding of increased NOS-2 expression in groups B and C is consistent with the observed increase in tissue cGMP levels in the same groups (1.92+/-0.9 pmol/mL for group A versus 7.8+/-3.5 pmol/mL for group B, and 12.4+/-5.8 pmol/mL for group C, p = 0.0004).

CONCLUSIONS

These data establish that mast cell stabilizing agents modulate the vascular phenotype in the setting of pulmonary ischemia and reperfusion by decreasing ICAM-1 expression, augmenting expression of NOS-2, and increasing tissue cGMP levels. As decreasing ICAM-1 expression and increasing cGMP levels have proven useful to limit proinflammatory mechanisms of tissue injury, mast cell stabilizing agents may provide a new therapeutic option to improve organ function in the setting of reperfusion.

Identification of optimal conditions for lung graft storage with Euro-Collins solution by use of a rat orthotopic lung transplant model

BACKGROUND

Lung preservation disrupts normal vascular homeostasis, resulting in increased permeability, vasoconstriction, and endothelial cell adhesion for neutrophils. We hypothesized that a storage strategy that best preserves post-lung transplantation (LTX) vascular homeostasis might be organ and species specific. Because of the potential utility of a rat LTX model for developing improved lung preservation strategies, we have attempted to identify the optimal physical conditions for rat lung graft storage.

METHODS AND RESULTS

Conditions that were tested included harvest inflation pressure (0, 10, or 20 mm Hg), inflation gas composition (100% N(2), room air, or 100% O(2)), and storage temperature (4 degrees, 10 degrees, or 15 degrees C). Modified Euro-Collins solution served as the base preservation solution for all experiments, with a preservation duration of 4 to 6 hours. Arterial oxygenation (PaO(2), mm Hg), pulmonary vascular resistance (mm Hg/mL per minute), recipient survival (%), and graft neutrophil infiltration (DeltaAbs(460 nm)/min) were measured 30 minutes after transplantation of the left lung and exclusion of the right lung from the circulation. All tested conditions significantly affect post-LTX vascular homeostasis. Inflation at 10 mm Hg pressure preserved lungs significantly better than did other pressures. There was a tendency for room air to improve all measured variables compared with 100% N(2) or 100% O(2) and a significant improvement in recipient survival with room air storage. Of the 3 storage temperatures investigated, 10 degrees C storage provided the best preservation in terms of PaO(2), graft neutrophil infiltration, and survival.

CONCLUSIONS

We conclude that storage at 10 degrees C, 10 mm Hg inflation pressure, with room air establishes optimal lung storage conditions with Euro-Collins solution in this rat LTX model. These data suggest that these conditions should be used to evaluate new and potentially improved preservation strategies.

Nitric oxide triggers programmed cell death (apoptosis) of adult rat ventricular myocytes in culture

Excessive nitric oxide (NO) production within the heart is implicated in the pathogenesis of myocyte death, but the mechanism whereby NO kills cardiac myocytes is not known. To determine whether NO may trigger programmed cell death (apoptosis) of adult rat ventricular myocytes in culture, the NO donor S-nitroso-N-acetylpenicillamine (SNAP) was shown to kill purified cardiac myocytes in a dose-dependent fashion. In situ analysis of ventricular myocytes plated on chamber slides using nick-end labeling of DNA demonstrated that SNAP induces cardiac myocyte apoptosis, which was confirmed by the identification of oligonucleosomal DNA fragmentation on agarose gel electrophoresis. Similarly, treatment of cardiac myocytes with cytokines that induce inducible NO synthase was shown to cause an NO-dependent induction of apoptosis. Addition of reduced hemoglobin to scavenge NO liberated by SNAP extinguished both the increase in percentage of apoptotic cells and the appearance of DNA ladders. Treatment with SNAP (but not with N-acetylpenicillamine or SNAP + hemoglobin) not only induced apoptosis but resulted in a marked increase in p53 expression in cardiac myocytes detected by Western blotting and immunohistochemistry. These data indicate that NO has the capacity to kill cardiac myocytes by triggering apoptosis and suggest the involvement of p53 in this process.

Hypoxia/Hypoxemia-Induced activation of the procoagulant pathways and the pathogenesis of ischemia-associated thrombosis

Although oxygen deprivation has long been associated with triggering of the procoagulant pathway and venous thrombosis, blood hypoxemia and stasis by themselves do not lead to fibrin formation. A pathway is outlined through which diminished levels of oxygen activate the transcription factor early growth response-1 (Egr-1) leading to de novo transcription/translation of tissue factor in mononuclear phagocytes and smooth muscle cells, which eventuates in vascular fibrin deposition. The procoagulant response is magnified by concomitant suppression of fibrinolysis by hypoxia-mediated upregulation of plasminogen activator inhibitor-1. These data add a new facet to the biology of thrombosis associated with hypoxemia/stasis and imply that interference with mechanisms causing Egr-1 activation in response to oxygen deprivation might prevent vascular fibrin deposition occurring in ischemia without directly interfering with other pro/anticoagulant pathways.

Titration of postischemic cerebral hypoperfusion by variation of ischemic severity in a murine model of stroke

OBJECTIVE

Murine models using intraluminal occluding sutures to establish transient focal cerebral ischemia are becoming increasingly widespread, because of advances in transgenic technology and the advent of cerebroprotective strategies to ameliorate postischemic cerebrovascular no-reflow. We hypothesize that the degree of postischemic hypoperfusion is directly related to the severity of the initial ischemic insult.

METHODS

Transient ischemia of 45-minute duration was produced using middle cerebral artery occlusion with 10-0 (n = 5), 9-0 (n = 5), 8-0 (n = 6), 7-0 (n = 8), 6-0 (n = 30), or 5-0 (n = 5) sutures. In separate experiments, transient vessel occlusion with 6-0 sutures was performed for 15 (n = 17), 30 (n = 16), or 45 (n = 30) minutes. Sequential laser Doppler measurements of relative cerebral blood flow were obtained, and stroke severity was assessed using neurological deficit scores and infarction volumes.

RESULTS

Although relative cerebral blood flow at the time of occlusion and 24 hours thereafter was diminished in parallel with increasing suture diameters, only the use of larger sutures resulted in postischemic no-reflow. As the suture diameter was increased, the resultant reflow was decreased and the stroke outcome worsened. A more than twofold increase in infarction volume (8.0 +/- 3 versus 19.7 +/- 3%, P < 0.05) resulted when ischemia duration was increased from 30 to 45 minutes.

CONCLUSION

Titration of the initial ischemic insult leads to corresponding variations in the magnitude of postischemic no-reflow and tissue damage. Therefore, critical control of the severity of the initial injury in studies using intraluminal suture occlusion is warranted.

Membrane stabilization in harvested vein graft storage: effects on adhesion molecule expression and nitric oxide synthesis

OBJECTIVE

Expression of cellular adhesion molecules in human saphenous vein grafts may occur even during harvesting and storage, before the grafts have been implanted as bypass conduits. This may play a role in graft adaptation to arterial flow conditions, which may play an important role in late graft patency. In this study, ketotifen, a mast cell membrane stabilizing agent was studied for its effects on reducing endothelial reactivity during storage of harvested vein graft segments.

METHODS

Human saphenous vein grafts, obtained from seven patients and then divided into two equal parts of control and study specimens, were stored in either heparinized blood (Group A) or heparinized blood containing 100 microg/ml ketotifen (Group B) for 1 h at room temperature. Specimens were analyzed by Western blotting to quantify ICAM-1, E-selectin, P-selectin, VCAM-1, and inducible nitric oxide synthase (NOS-2) expression, as well as tissue cGMP levels in response to topical application of an endothelium-independent vasodilator.

RESULTS

ICAM-1, E-selectin and P-selectin expression did not differ between the groups. However, VCAM-1 expression was significantly lower in Group B (460 +/- 29 vs. 289 +/- 50, P = 0.01). NOS-2 expression (488 +/- 64 vs. 577 +/- 38, P = 0.02) and tissue cGMP levels (2.2 +/- 0.6 pmol/ml vs. 5.7 +/- 1.7 pmol/ml, P = 0.01) in response to nitroglycerin (24 +/- 10% vs. 11 +/- 5%, P = 0.02) were higher in Group B.

CONCLUSIONS

Of all of the adhesion receptors studied, only VCAM-1 expression was reduced by a mast cell membrane-stabilizing agent, perhaps because of activation of the venous endothelium during harvest prior to ketotifen exposure. However, ketotifen also augmented NOS-2 expression, increased tissue cGMP levels in response to nitroglycerin. These actions may improve vascular homeostasis in the venous graft, suggesting the possibility that this strategy may improve long-term graft patency.

Neuronal protection in stroke by an sLex-glycosylated complement inhibitory protein

Glycoprotein adhesion receptors such as selectins contribute to tissue injury in stroke. Ischemic neurons strongly expressed C1q, which may target them for complement-mediated attack or C1qRp-mediated clearance. A hybrid molecule was used to simultaneously inhibit both complement activation and selectin-mediated adhesion. The extracellular domain of soluble complement receptor-1 (sCR1) was sialyl Lewis x glycosylated (sCR1sLex) to inhibit complement activation and endothelial-platelet-leukocyte interactions. sCR1 and sCR1sLex colocalized to ischemic cerebral microvessels and C1q-expressing neurons, inhibited neutrophil and platelet accumulation, and reduced cerebral infarct volumes. Additional benefit was conferred by sialyl Lewis x glycosylation of the unmodified parent sCR1 molecule.

Targeted inhibition of intrinsic coagulation limits cerebral injury in stroke without increasing intracerebral hemorrhage

Agents that restore vascular patency in stroke also increase the risk of intracerebral hemorrhage (ICH). As Factor IXa is a key intermediary in the intrinsic pathway of coagulation, targeted inhibition of Factor IXa-dependent coagulation might inhibit microvascular thrombosis in stroke without impairing extrinsic hemostatic mechanisms that limit ICH. A competitive inhibitor of native Factor IXa for assembly into the intrinsic Factor X activation complex, Factor IXai, was prepared by covalent modification of the Factor IXa active site. In a modified cephalin clotting time assay, in vivo administration of Factor IXai caused a dose-dependent increase in time to clot formation (3.6-fold increase at the 300 micrograms/kg dose compared with vehicle-treated control animals, P < 0.05). Mice given Factor IXai and subjected to middle cerebral artery occlusion and reperfusion demonstrated reduced microvascular fibrin accumulation by immunoblotting and immunostaining, reduced 111In-labeled platelet deposition (42% decrease, P < 0.05), increased cerebral perfusion (2.6-fold increase in ipsilateral blood flow by laser doppler, P < 0.05), and smaller cerebral infarcts than vehicle-treated controls (70% reduction, P < 0.05) based on triphenyl tetrazolium chloride staining of serial cerebral sections. At therapeutically effective doses, Factor IXai was not associated with increased ICH, as opposed to tissue plasminogen activator (tPA) or heparin, both of which significantly increased ICH. Factor IXai was cerebroprotective even when given after the onset of stroke, indicating that microvascular thrombosis continues to evolve (and may be inhibited) even after primary occlusion of a major cerebrovascular tributary.

Superior protection in orthotopic rat lung transplantation with cyclic adenosine monophosphate and nitroglycerin-containing preservation solution

BACKGROUND

Primary lung graft failure is common, and current lung preservation strategies are suboptimal. Because the decline in lung levels of cyclic adenosine monophosphate and cyclic guanosine monophosphate during preservation could enhance adhesiveness of endothelial cells for leukocytes as well as increase vascular permeability and vasoconstriction, we hypothesized that buttressing these levels by means of a preservation solution would significantly improve lung preservation.

METHODS

An orthotopic rat left lung transplantation model was used. Lungs were harvested from male Lewis rats and preserved for 6 hours at 4 degrees C with (1) Euro-Collins solution (n = 8); (2) University of Wisconsin solution (n = 8); (3) low-potassium dextran glucose solution (n = 8); (4) Columbia University solution (n = 8), which contains a cyclic adenosine monophosphate analog (dibutyryl cyclic adenosine monophosphate) and a nitric oxide donor (nitroglycerin) to buttress cyclic guanosine monophosphate levels; or (5) Columbia University solution without cyclic adenosine monophosphate or nitroglycerin (n = 8). PaO2, pulmonary vascular resistance, and recipient survival were evaluated 30 minutes after left lung transplantation and removal of the nontransplanted right lung from the pulmonary circulation.

RESULTS

Among all groups studied, grafts stored with Columbia University solution demonstrated the highest Pa O2 (355 +/- 25 mm Hg for Columbia University solution versus 95 +/- 22 mm Hg for Euro-Collins solution, P <.01, 172 +/- 55 mm Hg for University of Wisconsin solution, P <.05, 76 +/- 15 mm Hg for low-potassium dextran glucose solution, P <.01, and 82 +/- 25 mm Hg for Columbia University solution without cyclic adenosine monophosphate or nitroglycerin, P <.01) and the lowest pulmonary vascular resistances (1 +/- 0.2 mm Hg * mL-1 * min-1 for Columbia University solution versus 12 +/- 4 mm Hg * mL-1 * min-1 for Euro-Collins solution, P <.01, 9 +/- 2 mm Hg * mL-1 * min-1 for University of Wisconsin solution, 14 +/- 6 mm Hg * mL-1 * min-1 for low-potassium dextran glucose solution, P <.01, and 8 +/- 2 mm Hg * mL-1 * min-1 for Columbia University solution without cyclic adenosine monophosphate and nitroglycerin). These functional and hemodynamic improvements provided by Columbia University solution were accompanied by decreased graft leukostasis and decreased recipient tumor necrosis factor alpha and interleukin 1alpha levels compared with the other groups. In toto, these improvements translated into superior survival among recipients of Columbia University solution-preserved grafts (100% for Columbia University solution, 37% for Euro-Collins solution, P <.01, 50% for University of Wisconsin solution, P <.05, 50% for low-potassium dextran glucose solution, P <.05, and 13% for Columbia University solution without cyclic adenosine monophosphate and nitroglycerin, P <.01).

CONCLUSION

Nitroglycerin and cyclic adenosine monophosphate confer beneficial vascular effects that make Columbia University solution a superior lung preservation solution in a stringent rat lung transplantation model.

Hypoxia-associated induction of early growth response-1 gene expression

The paradigm for the response to hypoxia is erythropoietin gene expression; activation of hypoxia-inducible factor-1 (HIF-1) results in erythropoietin production. Previously, we found that oxygen deprivation induced tissue factor, especially in mononuclear phagocytes, by an early growth response (Egr-1)-dependent pathway without involvement of HIF-1 (Yan, S.-F., Zou, Y.-S., Gao, Y., Zhai, C., Mackman, N., Lee, S., Milbrandt, J., Pinsky, D., Kisiel, W., and Stern, D. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 8298-8303). Now, we show that cultured monocytes subjected to hypoxia (pO2 approximately 12 torr) displayed increased Egr-1 expression because of de novo biosynthesis, with a approximately 10-fold increased rate of transcription. Transfection of monocytes with Egr-1 promoter-luciferase constructs localized elements responsible for hypoxia-enhanced expression to -424/-65, a region including EBS (ets binding site)-SRE (serum response element)-EBS and SRE-EBS-SRE sites. Further studies with each of these regions ligated to the basal thymidine kinase promoter and luciferase demonstrated that EBS sites in the element spanning -424/-375 were critical for hypoxia-enhanceable gene expression. These data suggested that an activated ets factor, such as Elk-1, in complex with serum response factor, was the likely proximal trigger of Egr-1 transcription. Indeed, hypoxia induced activation of Elk-1, and suppression of Elk-1 blocked up-regulation of Egr-1 transcription. The signaling cascade preceding Elk-1 activation in response to oxygen deprivation was traced to activation of protein kinase C-betaII, Raf, mitogen-activated protein kinase/extracellular signal-regulated protein kinase kinase and mitogen-activated protein kinases. Comparable hypoxia-mediated Egr-1 induction and activation were observed in cultured hepatoma-derived cells deficient in HIF-1beta and wild-type hepatoma cells, indicating that the HIF-1 and Egr-1 pathways are initiated independently in response to oxygen deprivation. We propose that activation of Egr-1 in response to hypoxia induces a different facet of the adaptive response than HIF-1, one component of which causes expression of tissue factor, resulting in fibrin deposition.

CD18-mediated neutrophil recruitment contributes to the pathogenesis of reperfused but not nonreperfused stroke

BACKGROUND AND PURPOSE

Neutrophil (PMN) recruitment mediated by increased expression of intercellular adhesion molecule-1 expression (ICAM-1, CD54) in the cerebral microvasculature contributes to the pathogenesis of tissue injury in stroke. However, studies using blocking antibodies against the common beta2-integrin subunit on the PMN, the counterligand for ICAM-1 (CD18), have demonstrated equivocal efficacy. The current study tested the hypothesis that mice deficient in CD18 would be protected in the setting of reperfused but not nonreperfused stroke.

METHODS

Two groups of mice were studied, those whose PMNs could express CD18 (CD18 +/+) and those mice hypomorphic for the CD-18 gene (CD18 -/-). PMNs obtained from CD18 -/- or CD18 +/+ mice were fluorescently labeled and tested for binding to murine brain endothelial monolayers. Using a murine model of focal cerebral ischemia in which an occluding suture placed in the middle cerebral artery (MCA) is removed after 45 minutes (transient ischemia, reperfused stroke) or left in place (permanent ischemia, nonreperfused stroke), cerebral infarct volumes (% ipsilateral hemisphere by TTC staining), cerebral blood flow (CBF, % contralateral hemisphere by laser-Doppler flowmetry), and survival (%) were examined 24 hours after the initial ischemic event. Adoptive transfer studies used 111In-labeled PMNs (from either CD18 +/+ or CD18 -/- mice) to examine the relative accumulation of PMNs in the ischemic region.

RESULTS

PMNs obtained from CD18 -/- mice exhibit reduced adhesivity (compared with CD18 +/+ PMNs) for both quiescent and cytokine-activated endothelial monolayers. CD18 -/- mice (n=14) subjected to transient focal cerebral ischemia demonstrated a 53% decrease in infarct volumes versus CD18 +/+ mice (n=26, P<0.05), improved penumbral CBF at 24 hours (1.8-fold, P=0.02), and a 3.7-fold decrease in mortality (P=0.02). However, when CD18 -/- mice (n=12) were subjected to permanent focal cerebral ischemia, no differences were noted in infarct volume, mortality, or CBF versus similarly treated CD18 +/+ mice (n=10). There was a greater accumulation of CD18 +/+ PMNs in the ischemic zone of CD18 +/+ animals than CD18 -/- animals subjected to reperfused stroke (82% increase, P=0.02), although there was no difference between groups when subjected to permanent MCA occlusion.

CONCLUSIONS

Deficiency for the CD18 gene confers cerebral protection in a murine model of reperfused stroke, but this benefit does not extend to CD18-deficient animals subjected to permanent MCA occlusion. These data suggest that anti-PMN strategies should be targeted to reperfused stroke and may perhaps be used in conjunction with thrombolytic therapy that establishes reperfusion.

Reduced microvascular thrombosis and improved outcome in acute murine stroke by inhibiting GP IIb/IIIa receptor-mediated platelet aggregation

Treatment options in acute stroke are limited by a dearth of safe and effective regimens for recanalization of an occluded cerebrovascular tributary, as well as by the fact that patients present only after the occlusive event is established. We hypothesized that even if the site of major arterial occlusion is recanalized after stroke, microvascular thrombosis continues to occur at distal sites, reducing postischemic flow and contributing to ongoing neuronal death. To test this hypothesis, and to show that microvascular thrombosis occurs as an ongoing, dynamic process after the onset of stroke, we tested the effects of a potent antiplatelet agent given both before and after the onset of middle cerebral arterial (MCA) occlusion in a murine model of stroke. After 45 min of MCA occlusion and 23 h of reperfusion, fibrin accumulates in the ipsilateral cerebral hemisphere, based upon immunoblotting, and localizes to microvascular lumena, based upon immunostaining. In concordance with these data, there is a nearly threefold increase in the ipsilateral accumulation of 111In-labeled platelets in mice subjected to stroke compared with mice not subjected to stroke. When a novel inhibitor of the glycoprotein IIb/IIIa receptor (SDZ GPI 562) was administered immediately before MCA occlusion, platelet accumulation was reduced 48%, and fibrin accumulation was reduced by 47% by immunoblot densitometry. GPI 562 exhibited a dose-dependent reduction of cerebral infarct volumes measured by triphenyltetrazolium chloride staining, as well as improvement in postischemic cerebral blood flow, measured by laser doppler. GPI 562 caused a dose-dependent increase in tail vein bleeding time, but intracerebral hemorrhage (ICH) was not significantly increased at therapeutic doses; however, there was an increase in ICH at the highest doses tested. When given immediately after withdrawal of the MCA occluding suture, GPI 562 was shown to reduce cerebral infarct volumes by 70%. These data support the hypothesis that in ischemic regions of brain, microvascular thrombi continue to accumulate even after recanalization of the MCA, contributing to postischemic hypoperfusion and ongoing neuronal damage.

Coordinated induction of plasminogen activator inhibitor-1 (PAI-1) and inhibition of plasminogen activator gene expression by hypoxia promotes pulmonary vascular fibrin deposition

Oxygen deprivation, as occurs during tissue ischemia, tips the natural anticoagulant/procoagulant balance of the endovascular wall to favor activation of coagulation. To investigate the effects of low ambient oxygen tension on the fibrinolytic system, mice were placed in a hypoxic environment with pO2 < 40 Torr. Plasma levels of plasminogen activator inhibitor-1 (PAI-1) antigen, detected by ELISA, increased in a time-dependent fashion after hypoxic exposure (increased as early as 4 h, P < 0.05 vs. normoxic controls), and were accompanied by an increase in plasma PAI-1 activity by 4 h (P < 0.05 vs. normoxic controls). Northern analysis of hypoxic murine lung demonstrated an increase in PAI-1 mRNA compared with normoxic controls; in contrast, transcripts for both tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) decreased under hypoxic conditions. Immunocolocalization studies identified macrophages as the predominant source of increased PAI-1 within hypoxic lung. Using a transformed murine macrophage line, striking induction of PAI-1 transcripts occurred under hypoxic conditions, due to both increased de novo transcription as well as increased mRNA stability. Consistent with an important role of the fibrinolytic system in hypoxia-induced fibrin accumulation, PAI-1 +/+ mice exposed to hypoxia exhibited increased pulmonary fibrin deposition based upon a fibrin immunoblot, intravascular fibrin identified by immunostaining, and increased accumulation of 125I-fibrinogen/fibrin in hypoxic tissue. In contrast, mice deficient for the PAI-1 gene (PAI-1 -/-) similarly exposed to hypoxic conditions did not display increased fibrin accumulation compared with normoxic PAI-1 +/+ controls. Furthermore, homozygous null uPA (uPA -/-) and tPA (tPA -/-) mice subjected to oxygen deprivation showed increased fibrin deposition compared with wild-type controls. These studies identify enhanced expression of PAI-1 as an important mechanism suppressing fibrinolysis under conditions of low oxygen tension, a response which may be further amplified by decreased expression of plasminogen activators. Taken together, these data provide insight into an important potential role of macrophages and the fibrinolytic system in ischemia-induced thrombosis.

Does poly-L-lysine coating of the middle cerebral artery occlusion suture improve infarct consistency in a murine model?

BACKGROUND AND PURPOSE

Rodent models of stroke that employ an intraluminal suture to cause focal cerebral ischemia are associated with some variability of resultant infarct volumes, thus requiring increased numbers of animals to determine significant differences between experimental groups. A recent modification of the occluding suture by coating with poly-L-lysine has been shown to create more uniform infarct volumes in rats.

METHODS

To evaluate the utility of this modification in murine models of both transient and permanent focal cerebral ischemia, male C57B16J mice were subjected to reversible middle cerebral artery occlusion (MCAo) for 45 minutes (n=42), or to permanent MCAo (n=25), with an intraluminal monofilament suture. Three types of sutures were used: untreated, partially coated, and completely coated with poly-L-lysine. Relative changes in regional cerebral blood flow, severity of neurological deficits, and infarct volumes were measured 24 hours after the ischemic injury.

RESULTS

Animals subjected to 45 minutes of temporary occlusion with completely coated poly-L-lysine sutures had infarct volumes of 13.8%+/-5% compared with infarct volumes of 7.2%+/-4% in those subjected to partially coated sutures and 22.4%+/-6% in the group occluded with untreated sutures (P=ns). Use of completely coated sutures resulted in significantly less reperfusion following suture removal. Control animals undergoing permanent occlusion with untreated sutures had infarct volumes of 17%+/-7% compared with 14.1%+/-5% using completely coated sutures and 6.5%+/-3% in animals with partially coated sutures (P=ns). There were no significant differences in cerebral blood flow between the experimental groups undergoing permanent MCAo.

CONCLUSIONS

Poly-L-lysine coating of intraluminal sutures does not increase the consistency of infarct volumes in a murine model of temporary/permanent MCAo. These findings are in marked contrast to findings in rats.

Cardiac graft intercellular adhesion molecule-1 (ICAM-1) and interleukin-1 expression mediate primary isograft failure and induction of ICAM-1 in organs remote from the site of transplantation

During the first few hours after heart transplantation, the occurrence of graft failure is unpredictable and devastating. An explosive cascade of inflammatory events within the reperfused graft vasculature is likely to be mediated, at least in part, by the local expression of the leukocyte adhesion receptor intercellular adhesion molecule-1 (ICAM-1, CD54). Furthermore, although proinflammatory cytokines such as interleukin-1 (IL-1) are known to autoinduce their own (and ICAM-1) expression in vitro, there are no data to identify their functional in vivo cross talk in the setting of isograft transplantation. To determine the role of ICAM-1 in primary graft failure, we used an isogeneic vascularized model of heterotopic cardiac transplantation. ICAM-1 mRNA and protein increased in grafts during the early posttransplant period and were predominantly localized in the endothelium. The functional significance of this was established using donor hearts obtained from either ICAM-1-deficient (ICAM-1 -/-) or control (ICAM-1 +/+) mice. ICAM-1 +/+ grafts exhibited increased neutrophil infiltration, reduced left ventricular compliance, and poorer survival than did ICAM-1 -/- grafts. Increased ICAM-1 expression was not limited to ICAM-1 +/+ grafts but also occurred in unmanipulated recipient organs located remote from the site of surgery (but only after transplantation of ICAM-1 +/+, not ICAM-1 -/-, cardiac grafts). This expression of ICAM-1 in remote organs appeared to be triggered by IL-1alpha released from the graft, because (1) in situ hybridization revealed increased IL-1 mRNA within cells of the reperfused graft, including myocytes and endothelial cells; (2) ICAM-1 expression in remote organs coincided with a significant increase in serum levels of IL-1alpha after transplantation of ICAM-1 +/+ grafts; both remote organ ICAM-1 expression and IL-1alpha levels were blunted by implantation of ICAM-1 -/- grafts; and (3) remote organ ICAM-1 expression and neutrophil infiltration and IL-1 levels could be blocked by the administration of an IL-1 receptor antagonist. These data demonstrate an apparent positive-feedback loop in which local ICAM-1 and IL-1 expression leads to a mutual amplification of each other's expression within the reperfused graft, promulgating inflammatory events that are likely to be an important cause of primary cardiac graft failure. Because IL-1 receptor blockade reduces the IL-1-mediated autoinduction of IL-1, reduces the expression of ICAM-1 in both the graft and remote organs, and improves graft survival, it may provide a new and effective strategy to prevent the occurrence of primary cardiac graft failure.

Complement activation as a cause for primary graft failure in an isogeneic rat model of hypothermic lung preservation and transplantation

Although agents that inhibit complement activation may be beneficial in discordant xenotransplantation, it is not known whether local complement activation occurs and is deleterious after isogeneic lung transplantation. Lungs were harvested from Lewis rats subjected to 4 degrees C 6-hr preservation followed by transplantation into strain-, gender-, and weight-matched recipients. Transplanted lungs demonstrated increased immunostaining for C5b-9 compared with nontransplanted controls, confirming local complement activation in this isograft model. To investigate the physiologic relevance of complement activation in the transplanted lung, the native pulmonary artery was ligated after transplantation, and pulmonary vascular resistance (mmHg/ml/min), arterial oxygenation (mmHg), graft neutrophil infiltration (myeloperoxidase activity, deltaAbs 460 nm/min), and recipient survival were measured at 30 min. Animals received either saline (control; n=22) or soluble complement receptor type-1 (sCR1, 15 mg/kg; n=19) 2 min before reperfusion. Animals treated with sCR1 showed a marked reduction in serum complement hemolytic activity (CH50; 90% lower than that of control animals, P<0.001). Compared with controls, sCR1-treated animals showed reduced pulmonary vascular resistance (2.9+/-1.1 vs. 8.5+/-1.5 mmHg/ml/min, P<0.05), improved arterial oxygenation (194+/-34 vs. 91+/-17 mmHg, P<0.05), decreased neutrophil infiltration (35% decrease, P<0.005), and improved recipient survival (74% vs. 23%, P<0.005). In parallel with the reduction in complement hemolytic activity in sCR1-treated animals, immunohistology of the transplanted lung revealed decreased C5b-9 deposition compared with controls. Taken together, these data indicate that complement activation occurs after lung preservation and transplantation in an isograft model, and that inhibiting complement activation improves outcome after transplantation.

Use of a spectrophotometric hemoglobin assay to objectively quantify intracerebral hemorrhage in mice

BACKGROUND AND PURPOSE

There is great interest in developing novel anticoagulant or thrombolytic strategies to treat ischemic stroke. However, at present there are limited means to accurately assess the hemorrhagic potential of these agents. The present studies were designed to develop and validate a method to accurately quantify the degree of intracerebral hemorrhage (ICH) in murine models.

METHODS

In a murine model, ICH was induced by stereotaxic intraparenchymal infusion of collagenase B alone (6 x 10(-6) U; n = 5) or collagenase B followed by intravenous recombinant tissue plasminogen activator (rt-PA) (0.1 mg/kg; n = 6). Controls consisted of either sham surgery with stereotaxic infusion of saline (n = 5) or untreated animals (n = 5). ICH was (1) graded by a scale based on maximal hemorrhage diameter on coronal sections and (2) quantified by a spectrophotometric assay measuring cyanomethemoglobin in chemically reduced extracts of homogenized murine brain. This spectrophotometric assay was validated with the use of known quantities of hemoglobin or autologous blood added to a separate cohort of homogenized brains. With this assay, the degree of hemorrhage after focal middle cerebral artery occlusion/reperfusion was quantified in mice treated with postocclusion high-dose intravenous rt-PA (10 mg/kg; n = 11) and control mice subjected to stroke but treated with physiological saline solution (n = 9).

RESULTS

Known quantities of hemoglobin or autologous blood added to fresh whole brain tissue homogenates showed a linear relationship between the amount added and optical density (OD) at the absorbance peak of cyanomethemoglobin (r = 1.00 and .98, respectively). When in vivo studies were performed to quantify experimentally induced ICH, animals receiving intracerebral infusion of collagenase B had significantly higher ODs than saline-infused controls (2.1-fold, increase; P = .05). In a middle cerebral artery occlusion and reperfusion model of stroke, administration of rt-PA after reperfusion increased the OD by 1.8-fold compared with animals that received physiological saline solution (P < .001). When the two methods of measuring ICH (visual score and OD) were compared, there was a linear correlation (r = .88). Additional experiments demonstrated that triphenyltetrazolium staining, which is commonly used to stain viable brain tissue, does not interfere with the spectrophotometric quantification of ICH.

CONCLUSIONS

These data demonstrate that the spectrophotometric assay accurately and reliably quantifies murine ICH. This new method should aid objective assessment of the hemorrhagic risks of novel anticoagulant or thrombolytic strategies to treat stroke and can facilitate quantification of other forms of ICH.

Mechanical transduction of nitric oxide synthesis in the beating heart

NO alters contractile and relaxant properties of the heart. However, it is not known whether changes in ventricular loading conditions affect cardiac NO synthesis. To understand this potential contractile-relaxant autoregulatory mechanism, production of cardiac NO in response to mechanical stimuli was measured in vivo using a porphyrinic sensor placed in the left ventricular myocardium. The beating rabbit heart exhibited cyclic changes in [NO], peaking at 2.7+/-0.1 micromol/L near the endocardium and 0.93+/-0.20 micromol/L in the midventricular myocardium (concentrations were 15+/-4% lower in the rat heart). In the present study, we demonstrate for the first time that increasing or decreasing ventricular preload in vivo is followed by parallel changes in [NO], which may represent a novel autoregulatory mechanism to adjust cardiac performance or perfusion on a beat-to-beat basis. To quantify the relationship between applied force and NO synthesis, intermittent compressive or distending forces applied to ex vivo nonbeating hearts were shown to cause bursts of NO synthesis, with peak [NO] linearly related to ventricular transmural pressure. Experiments in which denuding cardiac endothelial and endocardial cells abrogated the NO signal indicate that these cells transduce mechanical stimulation into NO production in the heart. Taken together, these studies may help explain load-dependent relaxation, cardiac memory for mechanical events of preceding beats, diseases associated with myocardial distension, autoregulation of myocardial perfusion, and protection from thrombosis in the turbulent flow environment within the beating heart.

Exacerbation of cerebral injury in mice that express the P-selectin gene: identification of P-selectin blockade as a new target for the treatment of stroke

There is currently a stark therapeutic void in the treatment of evolving stroke. Although P-selectin is rapidly expressed by hypoxic endothelial cells in vitro, the functional significance of P-selectin expression in stroke remains unexplored. In order to identify the pathophysiological consequences of P-selectin expression and to identify P-selectin blockade as a potential new approach for the treatment of stroke, experiments were performed using a murine model of focal cerebral ischemia and reperfusion. Early P-selectin expression in the postischemic cerebral cortex was demonstrated by the specific accumulation of radiolabeled anti-murine P-selectin IgG, with the increased P-selectin expression localized to the ipsilateral cerebral microvascular endothelial cells by immunohistochemistry. In experiments designed to test the functional significance of increased P-selectin expression in stroke, neutrophil accumulation in the ischemic cortex of mice expressing the P-selectin gene (PS +/+) was demonstrated to be significantly greater than that in homozygous P-selectin-null mice (PS -/-). Reduced neutrophil influx was accompanied by greater postischemic cerebral reflow (measured by laser Doppler) in the PS -/- mice. In addition, PS -/- mice demonstrated smaller infarct volumes (5-fold reduction, P<.05) and improved survival compared with PS +/+ mice (88% versus 44%, P<.05). Functional blockade of P-selectin in PS +/+ mice using a monoclonal antibody directed against murine P-selectin also improved early reflow and stroke outcome compared with control mice, with reduced cerebral infarction volumes noted even when the blocking antibody was administered after occlusion of the middle cerebral artery. These data are the first to demonstrate a pathophysiological role for P-selectin in stroke and suggest that P-selectin blockade may represent a new therapeutic target in the treatment of stroke.

Cloning of a putative vesicle transport-related protein, RA410, from cultured rat astrocytes and its expression in ischemic rat brain

To elucidate the role of astrocytes in the stress response of the central nervous system to ischemia, early gene expression was evaluated in cultured rat astrocytes subjected to hypoxia/reoxygenation. Using differential display, a novel putative vesicle transport-related factor (RA410) was cloned from reoxygenated astrocytes. Analysis of the deduced amino acid sequence showed RA410 to be composed of domains common to vesicle transport-related proteins of the Sec1/Unc18 family, including Sly1p and Sec1p (yeast), Rop (Drosophila), Unc18 (Caenorhabditis elegans), and Munc18 (mammalian), suggesting its possible role in vesicular transport. Northern analysis of normal rat tissues showed the highest expression of RA410 transcripts in testis. When astrocyte cultures were subjected to a period of hypoxia followed by reoxygenation, induction of RA410 mRNA was observed within 15 min of reoxygenation, reaching a maximum by 60 min. At the start of reoxygenation, the addition of diphenyl iodonium, an NADPH oxidase inhibitor, blocked in parallel astrocyte generation of reactive oxygen intermediates and expression of RA410 message. In contrast, cycloheximide did not affect RA410 mRNA levels, indicating that RA410 is an immediate-early gene in the setting of reoxygenation. Using polyclonal antibody raised against an RA410-derived synthetic peptide, Western blotting of lysates from reoxygenated astrocytes displayed an immunoreactive band of approximately 70 kDa, the expression of which followed induction of the mRNA. Fractionation of astrocyte lysates on sucrose gradients showed RA410 antigen to be predominantly in the plasma membrane. Immunoelectron microscopic analysis demonstrated RA410 in large vesicles associated with the Golgi, but not in the Golgi apparatus itself, consistent with its participation in post-Golgi transport. Consistent with these in vitro data, RA410 expression was observed in rat brain astrocytes following transient occlusion of the middle cerebral artery. These data provide insight into a new protein (RA410) that participates in the ischemia-related stress response in astrocytes.

QT dispersion as a marker of risk in patients awaiting heart transplantation

OBJECTIVES

The objectives of this study were to determine whether a signal-averaged electrocardiogram (SAECG) or measurement of interlead variability of QT intervals on an electrocardiogram (ECG) obtained at the time of wait-listing could provide prognostic value with respect to cardiac death during the waiting period.

BACKGROUND

Because heart transplantation is a life-saving but limited resource, there remains an urgent need to identify those patients at greatest risk of dying while awaiting heart transplantation as part of the strategy to optimize the allocation of donor organs to those in greatest need. This study was undertaken to prospectively identify clinical, ECG or SAECG variables that might predict mortality during the waiting period.

METHODS

Of 108 consecutive patients referred for heart transplant evaluation, 80 were placed on a waiting list, at which time a standard 12-lead ECG and a SAECG were recorded. In this cohort of 80 patients, QT dispersion was characterized from the 12-lead ECG as either the maximal-minimal QT interval (QTDISP) or as the coefficient of variation of all QT intervals (QTCV).

RESULTS

During the 25-month follow-up period (mean time on waiting list, 201 days), the mortality rate was 27%/year, divided equally between heart failure and sudden deaths. No clinical variable identified at entry predicted mortality. QTDISP and QTCV were strong mortality predictors, with a 4.1-fold increase in mortality in patients with QTDISP > 140 ms compared with those patients with QTDISP < or = 140 ms (95% CI 1.1 to 14.9), whereas a QTCV > or = 9% also predicted a 4.1-fold increased risk of death (95% CI 1.4 to 11.8). Although 88% of all SAECGs were abnormal, no patient with a normal SAECG died suddenly during the waiting period.

CONCLUSIONS

Indexes of QT dispersion provide a means of stratifying a patient's risk of dying while awaiting heart transplantation and may help to establish priority on a heart transplant waiting list.

Circulatory resuscitation with left ventricular assist device support reduces interleukins 6 and 8 levels

BACKGROUND

Elevated tumor necrosis factor serum levels have been reported in patients with severe congestive heart failure. This study was designed to characterize the cytokine profile in patients with acute circulatory collapse.

METHODS

Blood drawn from 14 consecutive patients within 24 hours before undergoing left ventricular assist device placement and after at least 30 days of mechanical assistance or before transplantation was assayed for levels of interleukin 6, interleukin 8, and tumor necrosis factor-alpha.

RESULTS

Interleukin 6 level was elevated in 11 (79%), interleukin 8 in 10 (71%), and tumor necrosis factor in 2 (14%) of the 14 patients. After hemodynamic recovery, interleukin 6 levels decreased from 33.6 +/- 9 pg/mL to 11.3 +/- 4 pg/mL (p = 0.05) and interleukin 8 levels decreased from 122 +/- 34 pg/mL to 19.7 +/- 8 pg/mL (p = 0.005). Tumor necrosis factor-alpha levels did not vary significantly; they were associated with infection in 2 left ventricular assist device recipients and normalized after left ventricular assist device support. All patients had resolution of circulatory shock after mechanical support and had improvement in parameters of end-organ function.

CONCLUSIONS

Circulatory shock treated with left ventricular assist device placement is associated with a proinflammatory response similar to that seen in septic shock. The decrease in cytokine serum levels that follows hemodynamic recovery suggests that these cytokines may be markers of tissue damage and may modulate cardiac dysfunction.

Monocytes and tissue factor promote thrombosis in a murine model of oxygen deprivation

Clinical conditions associated with local or systemic hypoxemia can lead to prothrombotic diatheses. This study was undertaken to establish a model of whole-animal hypoxia wherein oxygen deprivation by itself would be sufficient to trigger tissue thrombosis. Furthermore, this model was used to test the hypothesis that hypoxia-induced mononuclear phagocyte (MP) recruitment and tissue factor (TF) expression may trigger the local deposition of fibrin which occurs in response to oxygen deprivation. Using an environmental chamber in which inhaled oxygen tension was lowered to 6%, hypoxic induction of thrombosis was demonstrated in murine pulmonary vasculature by 8 h based upon: (a) immunohistologic evidence of fibrin formation in hypoxic lung tissue using an antifibrin antibody, confirmed by 22.5-nm strand periodicity by electron microscopy; (b) immunoblots revealing fibrin gamma-gamma chain dimers in lungs from hypoxic but not normoxic mice or hypoxic mice treated with hirudin; (c) accelerated deposition of 125I-fibrin/fibrinogen and 111In-labeled platelets in the lung tissue of hypoxic compared with normoxic animals; (d) reduction of tissue 125I-fibrin/fibrinogen accumulation in animals which had either been treated with hirudin or depleted of platelets before hypoxic exposure. Because immunohistochemical analysis of hypoxic pulmonary tissue revealed strong MP staining for TF, confirmed by increased TF RNA in hypoxic lungs, and because 111In-labeled murine MPs accumulated in hypoxic pulmonary tissue, we evaluated whether recruited MPs might be responsible for initiation of hypoxia-induced thrombosis. This hypothesis was supported by several lines of evidence: (a) MP depletion before hypoxia reduced thrombosis, as measured by reduced 125I-fibrin/fibrinogen deposition and reduced accumulation of cross-linked fibrin by immunoblot; (b) isolated murine MPs demonstrated increased TF immunostaining when exposed to hypoxia; and (c) administration of an anti-rabbit TF antibody that cross-reacts with murine TF decreased 125I-fibrin/fibrinogen accumulation and cross-linked fibrin accumulation in response to hypoxia in vivo. In summary, these studies using a novel in vivo model suggest that MP accumulation and TF expression may promote hypoxia-induced thrombosis.

Hypoxia-induced modulation of endothelial cell properties: regulation of barrier function and expression of interleukin-6

The endothelial cell response to hypoxia involves a range of adaptive mechanisms that reflect an active response of the cell's biosynthetic and metabolic apparatus. Hypoxia-mediated suppression of endothelial barrier function, resulting in increased vascular leakage, is likely to contribute to pulmonary and cerebral edema associated with high altitude and is closely associated with a fall in intracellular cyclic AMP levels. Buttressing of this second messenger pathway in the endothelium using membrane permeant cyclic AMP analogs prevents increased vascular leakage due to hypoxia. Application of this principle to organ preservation has shown that supplementation with cyclic AMP analogs or inhibition of endogenous cAMP metabolism enables extension of the time a harvested organ can remain extracorporeally, after which transplantation is successful. The underlying mechanism through which cyclic AMP exerts its effects appears to be maintenance of vascular homeostasis in the graft. A distinct adaptive mechanism triggered in the endothelium by hypoxia is expression of the cytokine interleukin-6 (IL-6) by a novel mechanism involving transcription driven by the nuclear factor IL-6 (NF-IL-6) DNA binding site in the promoter. IL-6 may exert protective effects on vascular function, thereby limiting vascular injury by a different mechanism than those recruited by elevated cAMP levels. These studies provide insights into tow independent mechanisms through which endothelium responds to oxygen deprivation, and suggest possible new approaches to attentuate vascular injury associated with ischemia.

Failure to express the P-selectin gene or P-selectin blockade confers early pulmonary protection after lung ischemia or transplantation

Endothelial P-selectin expression contributes to the first wave of neutrophil (polymorphonuclear leukocyte: PMN) influx in several inflammatory conditions. Although remote tissue ischemia, such as a crush injury to the hindlimb, may result in P-selectin-mediated pulmonary leukosequestration, it is not known whether the lungs exhibit a similar response after hypothermic preservation or when subjected to a direct ischemic insult. To determine if P-selectin may mediate early primary graft failure, left lungs harvested from male Lewis rats were preserved for 6 hr at 4 degrees C and transplanted orthotopically into isogeneic recipients. Recipients immunodepleted of PMNs before transplantation demonstrated improved graft function; pulmonary vascular resistance was reduced approximately 6-fold, arterial oxygenation was increased approximately 3-fold, and recipient survival was increased approximately 4-fold (P < 0.05, 0.05, and 0.005, respectively). Administration of a blocking anti-P-selectin IgG 10 min before reperfusion diminished graft PMN infiltration and resulted in improved graft function and recipient survival compared with controls. To establish the role of P-selectin in normothermic pulmonary ischemia, mice were subjected to temporary left pulmonary artery ligation. After functional removal of the nonischemic right lung, mice deletionally mutant for the P-selectin gene (P-selectin-/-) exhibited reduced PMN infiltration (approximately 2-fold), improved arterial oxygenation (approximately 2-fold), and improved survival (approximately 3-fold) compared with P-selectin +/+ control mice (P < 0.05, 0.01, and 0.05, respectively). These studies isolate and identify the central role of a single gene product (P-selectin) in early PMN recruitment and tissue injury after frank pulmonary ischemia and in the setting of lung transplantation after hypothermic preservation.

cAMP-mediated vascular protection in an orthotopic rat lung transplant model. Insights into the mechanism of action of prostaglandin E1 to improve lung preservation

Prostaglandin E1 (PGE1) is often added to the donor pulmonary flush solution to enhance clinical lung preservation for transplantation. Although PGE1 is thought to act as a pulmonary vasodilator during the harvest period, the precise mechanism(s) of action whereby PGE1 enhances lung preservation is unknown. Because cAMP levels decline in endothelial and vascular smooth muscle cells exposed to hypoxia, we hypothesized that a PGE1-mediated increase in cAMP levels within the preserved lungs might improve pulmonary vascular homeostasis following lung transplantation. Rat lungs demonstrated a time-dependent decline in cAMP levels during hypothermic storage, with cAMP levels significantly increased by PGE1 supplementation (approximately 2-fold by 6 hours, P < .0005). To test whether augmenting cAMP levels may enhance lung preservation, experiments were performed using an orthotopic rat left lung transplant model. Compared with controls, supplementing the preservation solution with the membrane-permeable cAMP analogue dibutyryl-cAMP resulted in dose-dependent preservation enhancement, marked by reduced pulmonary vascular resistance (6.0-fold, P < .01), improved arterial oxygenation (3.0-fold, P < .01), reduced graft neutrophil infiltration (1.5-fold, P < .05), and improved recipient survival (7.0-fold, P < .005). Similar preservation enhancement was observed with another cAMP analogue (8-bromo-cAMP) or the phosphodiesterase inhibitor indolidan. Stimulating the cAMP second messenger system by PGE1 supplementation resulted in marked hemodynamic benefits and improved recipient survival, in parallel with reduced graft neutrophil infiltration, vascular permeability, and platelet deposition. These beneficial effects of PGE1 were abrogated by simultaneous administration of the cAMP-dependent protein kinase antagonist Rp-cAMPS. Although an arterial vasodilator (minoxidil) resulted in significant pulmonary vasodilation during harvest, it lacked other nonvasodilating effects of PGE1 and resulted in poor preservation. These data show that harvest vasodilation by itself is insufficient to enhance lung preservation and that PGE1 enhances lung preservation by stimulating the cAMP-dependent protein kinase and promoting non-vasodilatory mechanisms of pulmonary protection.

Procedural and strain-related variables significantly affect outcome in a murine model of focal cerebral ischemia

The recent availability of transgenic mice has led to a burgeoning number of reports describing the effects of specific gene products on the pathophysiology of stroke. Although focal cerebral ischemia models in rats have been well described, descriptions of a murine model of middle cerebral artery occlusion are scant and sources of potential experimental variability remain undefined. We hypothesized that slight technical modifications would produce widely discrepant results in a murine model of stroke and that controlling surgical and procedural conditions could lead to reproducible physiological and anatomic stroke outcomes. To test this hypothesis, we established a murine model that would permit either permanent or transient focal cerebral ischemia by intraluminal occlusion of the middle cerebral artery. This study provides a detailed description of the surgical technique and reveals important differences among strains commonly used in the production of transgenic mice. In addition to strain-related differences, infarct volume, neurological outcome, and cerebral blood flow appear to be importantly affected by temperature during the ischemic and postischemic periods, mouse size, and the size of the suture that obstructs the vascular lumen. When these variables were kept constant, there was remarkable uniformity of stroke outcome. These data emphasize the protective effects of hypothermia in stroke and might help to standardize techniques among different laboratories to provide a cohesive framework for evaluating the results of future studies in transgenic animals.