Effects of Sulfated Polysaccharides on Inhibition of Thrombus Formation initiated by Different Stimuli

To test the possibility that different doses of heparin or other sulfated polysaccharides are required to inhibit thrombosis initiated by different stimuli, we compared the effects of heparin (HEP), pentosan polysulfate (SP54) and dermatan sulfate (DS) on the inhibition of thrombus formation induced by either I) tissue thromboplastin; II) thrombin; or III) factor Xa. Inhibition of thrombus formation induced by the stimuli was measured in a rabbit jugular vein hypercoagulation/stasis model. First, we determined the minimum dose of each sulfated polysaccharide which inhibited tissue thromboplastin-induced thrombus formation by ∼75%, and then compared the relative effectiveness of this dose to prevent thrombus formation initiated with the other two stimuli. HEP and SP54 were less effective when thrombin was the thrombogenic stimulus, while DS was more effective. HEP was the most effective agent when factor Xa was the stimulus. We conclude that the antithrombotic effectiveness of a given dose of a sulfated polysaccharide may vary depending on the stimulus which initiates thrombus formation.

A Low Molecular Weight Heparin Alters the Fetal Coagulation System in the Pregnant Sheep

Standard heparin and a LMWH, CY222 do not cross the placenta nor alter fetal coagulation when injected into the pregnant ewe. We found that another LMWH, Pharmuka-10169 (PK-10169) alters fetal coagulation without crossing the placenta in the pregnant sheep. To characterize this anticoagulant we measured the in vitro and in vivo effects of 125I-PK-10169 in maternal and fetal plasmas following administration of PK-10169 to the mother or fetus. The fetal anticoagulant activity was not neutralizable by protamine sulphate and was attributable to the inhibition of thrombin but not factor Xa. In vitro, the fetal anticoagulant activity had properties similar to dermatan sulphate : both catalyzed the inhibition of thrombin but not factor Xa by sheep plasma; and neither was neutralizable by protamine sulphate. These effects were due to the enhanced neutralization of thrombin by heparin cofactor II. We conclude that PK-10169 does not cross the placenta, but does induce the release of an endogenous dermatan sulphate-like substance which alters fetal coagulation.

Endothelial Cells Produce a Lipoxygenase Derived Chemo-Repellent which Influences Platelet/Endothelial Cell Interactions – Effect of Aspirin and Salicylate

We performed experiments to determine whether endothelial cells synthesize phospholipid metabolites via the lipoxygenase pathway and whether these metabolites influence platelet/vessel wall interactions. Monolayers of cultured human endothelial cells were incubated with 14C-arachidonic acid and their cyclo-oxygenase and lipoxygenase metabolites were extracted and identified by radioimmunoassay, thin layer chromatography and high performance liquid chromatography. We found that in addition to the membrane-associated production of PGI2, endothelial cells synthesized a cytosol-associated metabolite, LOX, which was presumably derived through the lipoxygenase pathway. Inhibition of LOX was associated with an increase in PGI2 production and inhibition of PGI2 with an increase in LOX production. Under either condition, platelet adhesion to cultured endothelial cells was significantly decreased. In contrast, when both PGI2 and LOX production were inhibited, platelet adhesion to endothelial cells was enhanced. Furthermore, when LOX was bound to a thrombogenic surface, platelet adhesion was significantly decreased whereas when arachidonic acid or 12-HETE was bound to the surface, platelet adhesion was increased. We conclude that endothelial cells produce not only a cyclo-oxygenase metabolite, but also a lipoxygenase metabolite, both of which influence platelet/endothelial cell interactions.

Catalysis of Thrombin Inhibition Provides an Index for Estimating the Antithrombotic Potential of Glycosaminoglycans in Rabbits

Previous studies have demonstrated that standard anticoagulant tests are poor indices of the antithrombotic potential of glycosaminoglycans which are weak catalysts of the thrombinantithrombin III reaction. In this study we investigated whether the catalysis of thrombin inhibition by plasma could serve as a reliable index for assessing the antithrombotic effectiveness of glycosaminoglycans. Equal volumes of 125I-thrombin and control or test plasma were incubated for up to 10 min at 37° C. Inactivation of thrombin was then determined after 7.9% SDS-polyacrylamide gel electrophoresis and subsequent autoradiography. Increasing concentrations of heparin (>0.066 μg/mL or 0.01 USP units/mL) and dermatan sulfate (>0.1 μg/mL) could be readily demonstrated in undiluted plasma by enhanced formation of complexes of thrombin with antithrombin III and heparin cofactor II respectively. However, the detection of any catalytic effect of the two glycosaminoglycans decreased significantly with increasing plasma dilutions. When ex vivo plasmas obtained from rabbits that had been injected with the minimum dose of any one of seven glycosaminoglycans required to achieve their optimal antithrombotic effect were assessed for their ability to catalyse thrombin inhibition, there was approximately a 2-fold increase in the amount of thrombin inactivated 30 s after the thrombin had been added to the plasma. The enhanced inhibition of thrombin was achieved by catalysis of antithrombin III and/or heparin cofactor II activities. These results suggest that measurement of the catalysis of thrombin inactivation in undiluted plasma is a sensitive and reliable index for estimating the antithrombotic potential of glycosaminoglycans in rabbits.

The Effects of Heparin and Annexin V on Fibrin Accretion after Injury in the Jugular Veins of Rabbits

We compared the relative abilities of unfractionated heparin and annexin V to prevent fibrin accretion onto injured jugular veins in vivo. Heparin was used to accelerate the inhibition of thrombin by antithrombin III, and annexin V was used to inhibit the assembly of the prothrombinase complex on phospholipid surfaces, thereby blocking thrombin generation. Rabbit jugular veins were isolated in situ, a 2 cm segment was injured by perfusing it with air, and then blood flow was re-established. Five minutes later, each rabbit was injected with heparin (20 U/kg) or annexin V (0.3 mg/kg) and then with 125I-fibrinogen. The amount of 125I-fibrin accumulation onto each injured vessel wall segment was measured 4 h later. Each injured vessel was completely deendothelialized as a result of the air perfusion as demonstrated by electron microscopy. 125I-fibrin accretion onto the injured jugular veins was enhanced 2.4-fold as compared to the uninjured veins in sham-operated animals. Heparin treatment did not reduce fibrin accretion, whereas, annexin V treatment decreased fibrin accretion by 60%, p <0.05. This latter effect was achieved without sustained circulating anticoagulation. Additional experiments confirmed that the inhibitory effect of annexin V on fibrin accretion was associated with a surface specific effect, since more annexin V bound to the injured jugular vein segments as compared to the non-injured jugular veins. We conclude that, i) mild vessel wall injury (selective de-endothelialization) in veins results in a thrombogenic vessel wall; ii) the thrombogenecity of which is not inhibited by prophylactic doses of heparin; but iii) is inhibited by annexin V, which binds to injured vessel wall surface, and inhibits thrombin generation independently of antithrombin III.

Thrombin Generation during Cardiac Surgery: Is Heparin the Ideal Anticoagulant?

Blood samples were collected from 43 patients undergoing elective cardiac surgery to determine the extent of thrombin generation and inhibition in patients when receiving heparin while undergoing cardiopulmonary bypass (CPB). Plasma prothrombin fragment F1 + 2 and thrombin-antithrombin III (TAT) levels were measured as markers of thrombin generation and inhibition, respectively. Both F1 + 2 and TAT levels increased significantly during the course of CPB despite the heparin causing significant systemic anticoagulation, i.e. the activated coagulation time (ACT) was prolonged to greater than 400 s throughout the entire surgical procedure. The extent of thrombin generation increased with time on CPB but did not differ between patients receiving normothermic and hypothermic cardioplegia during CPB. Furthermore, thrombin generation increased following the neutralization of the heparin with protamine sulphate, and continued to be elevated significantly 24 h post surgery. The observation that high dose heparin did not prevent thrombin generation during CPB, is consistent with previous experimental studies demonstrating that thrombin bound to fibrin or other surfaces (e.g. the CPB conduit) is resistant to antithrombin III/heparin inhibition, and thus able to facilitate further thrombin generation. The observation that thrombin generation continued to be elevated post surgery i.e. 24 h after neutralizing the heparin with protamine sulphate, suggests that the high dose heparin did not inhibit effectively all of the thrombin that had been generated. Thus, CPB patients may be at risk not only of bleeding and other side-effects associated with the acute use of high dose heparin, but may also be at risk of further thrombosis-related events either acutely or chronically.

Neutralization of Enoxaparine-lnduced Bleeding by Protamine Sulfate

It has been suggested that protamine sulfate is a poor antidote for the bleeding side-effeets of low molecular weight heparins (LMWHs) in vivo, since protamine sulfate does not completely neutralize the anti-factor Xa activity of LMWHs in vitro or ex vivo. Therefore, we performed experiments to compare directly the abilities of protamine sulfate to neutralize the anticoagulant activities of the LMWH, enoxaparine, and unfractionated heparin ex vivo, with its ability to neutralize the bleeding side-effeets of both compounds in vivo. Bleeding was measured as the amount of blood lost from 5 cuts made in rabbits ears before and after treatment with enoxaparine or unfractionated heparin ± protamine sulfate. Plasma anti-factor Xa and anti-thrombin activities ex vivo, were measured chromogenically. Doses of 400 and 1,500 anti-factor Xa U/kg of heparin and enoxaparine, respectively, were required to enhance blood loss to the same extent. Protamine sulfate completely neutralized blood loss induced by both compounds, but did not neutralize the anti-factor Xa nor antithrombin activities ex vivo. We conclude that protamine sulfate is an effective antidote for the bleeding side-effeets of enoxaparine and unfractionated heparin, despite its inability to completely neutralize their anticoagulant activities.

Antithrombotic Properties of Heparin in a Neonatal Piglet Model of Thrombin-Induced Thrombosis

The relative deficiency of antithrombin III (AT III) in neonatal plasma results in lower recovery of heparin in some assay systems. It is uncertain whether low AT III levels also limit the antithrombotic effects of heparin in this age group. We therefore compared the antithrombotic properties of heparin in mature pigs and newborn piglets, whose coagulation and inhibitor system closely resembles that of the human neonate. Animals were pretreated with saline, 10 or 25 U/kg heparin (n ≥16 per age group and dose). Following an injection of 100 U/kg thrombin, systemic 125I-fibrinogen consumption and local 125I-fibrinogen incorporation into jugular venous stasis thrombi were measured. Significantly more 125I-fibrinogen was consumed in piglets than in pigs systemically (p <0.0001), as well as within the occluded vein segment (p = 0.0112), largely because heparin was less effective in piglets than in pigs. This neonatal resistance to heparin could not be explained by lower heparin levels in the newborn animals. However, pretreatment with AT III concentrate significantly improved the antithrombotic properties of heparin in this age group (p <0.0001). We conclude that physiologically low AT III levels reduce the efficacy of heparin in neutralizing thrombin activity in newborn piglets. We speculate that AT III deficiency may also limit the antithrombotic properties of heparin in newborn infants with thrombotic disease.

The Basement Membrane Underlying the Vascular Endothelium Is Not Thrombogenic: In Vivo and In Vitro Studies with Rabbit and Human Tissue

Studies examining the interaction of platelets with exposed subendothelium in vivo have reported conflicting results, lo examine possible explanations for the apparently discrepant findings, we measured the platelet reactivity of subendothelium prepared by a number of methods both in vivo and in vitro. In addition, we examined the possibility that 13-hydroxyoc-tadecadinoic acid (13-HODE), an endothelial cell-derived chemorepellant, modulates the reactivity of the subendothelium to platelets. In vivo, the subendothelium of segments of rabbit carotid arteries was exposed by removing the endothelial cells by air perfusion or by balloon catheter stripping. Platelet accumulation onto the dc-cndothelialized segments was assessed by 3H-radioaclivily uptake, using 3H-adenine-labelled platelets, and by scanning electron microscopy. In vitro, 3H-adenine-labelled platelet adhesion was measured onto plain plastic discs and onto plastic discs coated with the following purified basement membrane components: collagens type I, III, IV, V, laminin, or fibronectin. In addition, 3H-adenine-labelled platelet adhesion was measured onto plastic discs coveredwith human endothelial cells or onto the basement membrane underlying the endothelial cells.

In vivo, there was marked 3H-platelet accumulation onto the ballon catheter carotid arteries one hour after injury. In contrast, there was no platelet accumulation onto the subendothelium of carotid arteries de-endothelialized by air perfusion. These differences were confirmed by scanning electron microscopy. Transmission electron microscopic examination demonstrated that the extracellular matrix was intact following the air perfusion injury whereas the majority of it was removed by the balloon catheter injury.

In vitro, the accumulation of 3H-platelets onto plain discs and onto discs coated with any of the four collagens, fibronectin or laminin was significantly greater than the adhesion of 3H-platelets onto intact endothelial cells or the basement membrane prepared by cellulose acetate stripping. In contrast, 3H-platelet adhesion onto the basement membrane prepared by ammonium hydroxide treatment was significantly increased. An HPLC analysis of methanol extracts obtained from the two basement membranes and the cultured endothelial in vitro demonstrated that there was significant amounts of 13-HODE present in the endothelial cells and in the basement membrane prepared by the mechanical stripping, but there was no detectable 13-HODE in the basement membrane prepared by ammonium hydroxide treatment.

We conclude that platelets do not adhere to subendothelium immediately beneath the endothelium and that this thromboresistance is contributed to by 13-HODE. We also suggest that the observed thrombogeneicity of subendothelium following balloon-induced injury is due to the mechanical removal of sub-endothelial structures including 13-HODE, exposing deeper more thrombogenic vascular wall structures.

Successful allogeneic stem cell transplant after invasive pulmonary zygomycosis

We report the successful outcome of allogeneic stem cell transplant (SCT) in a patient with acute lymphoblastic leukaemia (ALL) and pulmonary zygomycosis diagnosed prior to transplant. The lesion was surgically excised and SCT proceeded with antifungal therapy, granulocyte transfusions and G-CSF support during the period of neutropenia.

Selective and sustained inhibition of surface-bound thrombin activity by intimatan/heparin cofactor II and its relevance to assessing systemic anticoagulation in vivo, ex vivo and in vitro

We compare the relative activities of surface-bound and fluid-phase thrombin and their inhibition by heparin and Intimatan, a novel heparin cofactor II (HCII) agonist. In vitro, we compared the observed amidolytic activities of fluid-phase and surface-bound thrombin with the expected activities based upon 125I-specific activity. In vivo, we compared the inhibitory effects of heparin and Intimatan on thrombin activity bound to injured vessel walls. In vitro, the correlations between observed and expected activities of fluid-phase and surface-bound thrombin, were: r = 0.9974, p < 0.001; and r = 0.9678, p < 0.001; respectively. In vivo, injured vessel wall surface-bound thrombin activity persisted for > 24 h. This activity was not inhibited by heparin, but was inhibited by Intimatan, p < 0.001. We conclude that surface-bound thrombin is as active as fluid-phase thrombin and remains protected from inhibition by heparin, thereby contributing to vessel wall thrombogenicity following injury. In contrast, surface-bound thrombin is inhibited by Intimatan, thereby effectively decreasing vessel wall thrombogenicity following injury in vivo.

Results of the BRAT study--a pilot study investigating the possible significance of ASA nonresponsiveness on the benefits and risks of ASA on thrombosis in patients undergoing coronary artery bypass surgery

BACKGROUND

Several studies suggest that acetylsalicylic acid (ASA) is less effective in preventing thrombotic events in ASA nonresponder patients. If so, the thrombotic event rate in ASA nonresponders should be higher than in ASA responders.

OBJECTIVE

To conduct a prospective, multicentre observational pilot study to determine the thrombotic event rates in ASA responders and nonresponders.

PATIENTS AND METHODS

Patients undergoing nonurgent coronary artery bypass grafting (CABG) who were prescribed 325 mg ASA/day were recruited. Patients were classified as an ASA responder or nonresponder based on the ASA effect (or lack thereof) on their bleeding times. All thrombotic events that occurred in the two years following CABG were recorded. These data were stored in a blinded fashion until the last patient follow-up, and then adjudicated by a validation committee.

RESULTS

A total of 289 patients recruited at three sites completed the two-year follow-up. Of these patients, 45.3% were classified as ASA responders and 54.7% were classified as ASA nonresponders. Of ASA responders, 6.9% had thrombotic events compared with 9.5% of the ASA nonresponders, but this difference was not significant (P=0.526).

CONCLUSIONS

While ASA responder or nonresponder status did not appear to affect the thrombotic event rate in patients undergoing nonurgent CABG, the possibility that ASA responder or nonresponder status affects the thrombotic event rate in more acutely ill CABG patients cannot be excluded.

Anticoagulant and antithrombin effects of intimatan, a heparin cofactor II agonist

Surface-bound thrombin, which is resistant to inhibition by heparin/antithrombin III (/AT), plays a key role in vessel wall disease. In contrast, surface-bound thrombin is not resistant to inhibition by heparin cofactor II (HCII) and its acceleration of its inhibitory effect by dermatan sulfate. However, the potential use of dermatan sulfate to prevent thrombus formation in vivo is limited by its low specific activity, which in turn, necessitates excessively high doses when given on a gravimetric basis. Recently, a novel HCII agonist, Intimatan, has been synthesized by site-specific sulphation of highly purified dermatan sulfate comprising primarily of L-iduronic acid-4-O-sulphated N-acetyl-D-galactosamine, yielding a 4, 6-O-disulphate compound on the galactopyranose ring with a lower molecular weight, higher solubility, and specific activity than its parent, dermatan sulfate. In this study, we compared the abilities of Intimatan with its parent compound, dermatan sulfate, and with heparin to affect coagulation and to inhibit surface-bound thrombin both in vitro and in vivo, to determine if Intimatan demonstrates a better potential than either other compound in preventing thrombus formation in vivo. Intimatan prolonged the activated partial thromboplastin time (APTT) more effectively than either dermatan sulfate or heparin at comparable antithrombin concentrations. This activity was attributed to the more selective action of Intimatan against surface-bound thrombin in vitro. Intimatan also inhibited thrombin bound to an injured vessel wall surface in vivo more effectively than heparin, i.e., when measured in injured carotid arteries of rabbits injected with Intimatan or with heparin at the time of injury. We conclude that Intimatan effectively inhibits surface-bound thrombin, thereby exhibiting better anticoagulant and antithrombin properties than heparin and dermatan sulfate.

A rationale for targeting antithrombotic therapy at the vessel wall: improved antithrombotic effect and decreased risk of bleeding

Intimal hyperplasia after percutaneous transluminal coronary angioplasty (PTCA) or vascular surgical procedures remains a significant problem despite current antithrombotic therapy. The use of the current antithrombotic drugs, namely heparin + chronic aspirin (ASA) +/- oral anticoagulants, is based upon the assumptions that: i) heparin blocks thrombin generation and/or accelerates thrombin inhibition by antithrombin III (ATIII); ii) aspirin acetylates platelet cyclooxygenase, thereby preventing thromboxane A2 (TxA2) synthesis; and iii) oral anticoagulants reduce the availability of vitamin K-dependent procoagulants, thereby reducing the risk of thrombus formation. Albeit beneficial, this approach has a number of shortcomings and limitations: i) when thrombin binds to an injured vessel wall, it becomes resistant to inhibition by heparin/ATIII; thus, surface-bound thrombin remains active, stimulating further thrombus formation, smooth muscle cell proliferation and subsequent hyperplasia; ii) while TxA2 inhibition reduces platelet reactivity, platelets are able to respond to multiple stimuli generated at the time of, or after, vessel wall injury; and iii) heparin, aspirin and the oral anticoagulants all render the patient hemostatically defective and at risk of bleeding. Recent studies suggest that alternate therapeutic approaches can inhibit thrombogenesis more effectively at the time of injury, thereby not only inhibiting hyperplasia more effectively than the currently used drugs, but also reducing (or eliminating) the need for long-term therapy. For example, we suggest that the heparin cofactor II (HCII) catalysts, dermatan sulfate and Intimatan, inhibit surface-bound thrombin more effectively than heparin/ATIII, thereby inhibiting intimal hyperplasia effectively. Their effects are achieved when the drug is given only at the time of injury; i.e. with no further antithrombotic therapy. Other studies indicate that injured vessel wall thrombogenicity can be reduced by pretreatment with Persantine (dipyridamole) or with certain fatty acid supplements which either increase vessel wall cAMP and/or 13HODE synthesis. These increases are associated with decreased vessel wall thrombogenicity, which, in turn, is associated with decreased intimal hyperplasia. Such results suggest that vessel wall repair is achieved more effectively by targeting antithrombotic drugs directly at the vessel wall thrombogenicity per se rather than indirectly by altering the circulating blood cells and systemic coagulant system.

Cardiopulmonary bypass pumps and thrombin generation: what goes around comes around

Thrombin generation and subsequent fibrin deposition occur during cardiopulmonary bypass (CPB) using roller pumps (RPs) despite the administration of high dose heparin. The authors attempted to determine if less thrombin is generated and less fibrin is deposited during CPB using a centrifugal pump (CP). In Part 1 of the experiment, 12 pigs receiving 400 U/kg heparin underwent CPB, including hypothermia, cardioplegia, and aortic cross-clamping, using a CP or RP. Blood samples were collected throughout CPB to measure thrombin generation. At the end of CPB, the amount of fibrin deposited onto each filter was assessed spectrophotometrically. In Part 2, blood samples and arterial in-line filters were obtained from 20 patients undergoing CPB, using either RP or CP, and studied as described previously. The Part 1 results showed that thrombin generation and fibrin deposition in CP pigs were <50% of those seen in the RP pigs (p < 0.01 and p < 0.01, respectively). In Part 2, thrombin generation was significantly attenuated both during and after CPB in the CP patients (p < 0.01 and p < 0.01, respectively). However, there was no significant difference in fibrin deposition between the two types of pumps after their use in the patients undergoing cardiopulmonary bypass. It is concluded that there is less thrombin generation and subsequent fibrin deposition during CPB when using a CP instead of RP in a defined experimental in vivo situation, suggesting that there is less hypercoagulability during CPB when using a CP instead of an RP. However, a large study in more patients undergoing CPB for longer pump runs is required to determine the relevance of these observations on subsequent clinical endpoints.

Inhibition of chronic vessel wall intimal hyperplasia following acute anticoagulant treatment: relative effects of heparin and dermatan sulphate

Surface-bound thrombin which contributes to vessel wall hyperplasia, is resistant to inhibition by heparin/antithrombin III (/ATIII) but not to inhibition by dermatan sulphate/heparin cofactor II (/HCII). To determine the effects of heparin and dermatan sulphate on vessel wall hyperplasia after a first or second injury, rabbit carotid arteries first were injured, using a standard procedure (first injury). Half of the first-injury rabbits were given heparin, dermatan sulphate, or saline, 5 minutes before and at 30-minute intervals over 2 hours post-injury, and then allowed to recover. Four weeks later, the first-injury treated animals were killed and their injured carotid arteries were processed histologically. The remaining untreated first-injury rabbits were also allowed to recover. At 4 weeks, those rabbits were re-anesthetized and their first-injury arteries (which were occluded >75%), were isolated, and vessel wall lumen patency was re-established by endarterectomy (second injury). During this second injury, the animals were treated with heparin, dermatan sulphate, or saline as described above. Four weeks after this second injury, these rabbits were killed and their second injury arteries were processed histologically. Intimal hyperplasia determined histologically, was expressed as an x-fold increase in vessel wall cross-sectional area (i.e., [(media+intima area) media area]). Vessel wall lumen occlusion was expressed as [1-(lumen area/internal elastic lamina area) x 100; % occlusion]. Vessel wall area in the saline-treated animals, increased 2.6+/-1.2 and 2.4+/-1.0 fold respectively, means+/-SD, n = 12, within 4 weeks of the first and second injuries. These increases were due to intimal hyperplasia and associated with 75+/-19% and 79+/-21% occlusion of the vessel wall lumen, respectively. Heparin had little effect, whereas dermatan sulphate (1) decreased hyperplasia by 45% after the first injury and by 47% after the second injury, p<0.008 and <0.03, respectively, and (2) decreased vessel wall occlusion 47+/-12% and 33+/-5% after the first and second injury, respectively. We conclude that (1) dermatan sulphate/HCII may be a useful inhibitor of vessel wall hyperplasia following vessel wall injury, and (2) this effect can be achieved by an acute anticoagulant treatment at the time of injury, unlike heparin/ATIII.

Regulation of endothelial cell and platelet receptor-ligand binding by the 12- and 15-lipoxygenase monohydroxides, 12-, 15-HETE and 13-HODE

In previous studies, we reported that vascular wall cells such as endothelial cells metabolize linoleic acid to 13-hydroxyoctadecadienoic acid (13-HODE) via the 15-lipoxygenase pathway. Endothelial cell 13-HODE levels vary inversely with endothelial cell reactivity to platelets, which, in turn, varies directly with the expression of the vitronectin receptor (VnR) on the apical surface of endothelial cells. We and others have also found that tumour cell adhesivity is dependent, in part, upon the relative amounts of intracellular 13-HODE and the arachidonic acid monohydroxide(s), 12- and/or 15-hydroxyeicosatetraenoic acids (12-, 15-HETE). In addition, we and others have found that platelet adhesivity is dependent upon the intraplatelet level of its major lipoxygenase metabolite, 12-HETE. Finally, we have demonstrated that 13-HODE and VnR co-localize in nonadhesive endothelial cells but dissociate following endothelial cell injury, at which time, the VnR relocates on the endothelial cell apical surface. These data suggest to us that lipoxygenase-derived monohydroxides regulate the ability of various receptors to recognize their specific ligands. The latter data also suggest that these monohydroxides act directly by a physiochemical mechanism. The present study supports this possibility. Thus, we demonstrate that 13-HODE downregulates VnR binding with vitronectin (Vn) > fibronectin (Fn) > fibrinogen (Fgn), whereas 12- and 15-HETE upregulate specific VnR/ligand binding, using purified VnR/liposomes and purified ligands in an adhesion assay; and that 12- and 15-HETE upregulate GPIIb/IIIa:liposome binding of Fgn > Fn > Vn. We conclude that cell-specific monohydroxides influence cell-specific receptor-ligand binding directly through a physiochemical mechanism.

Aspirin increases the bleeding side effects in essential thrombocythemia independent of the cyclooxygenase pathway: role of the lipoxygenase pathway

Acetylsalicylic acid (ASA) is currently recommended as an antithrombotic for patients with essential thrombocythemia (ET) who are at an increased risk of thrombotic events. However, ASA is also associated with an increased risk of bleeding in these patients as compared to the risk of bleeding in other patients treated with ASA. Recent data suggest that while ASA inhibits platelet thromboxane A2 (TxA2) synthesis in all individuals, ASA has little effect or inhibits the lipoxygenase pathway (i.e., 12-hydroxyeicosatetranoic acid or 12-HETE synthesis) in some individuals, and enhances 12-HETE synthesis in others. These differential effects are associated with a pronounced prolongation of the bleeding time vs. no prolongation of the bleeding time, respectively, i.e., in ASA responders and ASA nonresponders, respectively. To determine if the increased risk of ASA-induced bleeding seen in ET patients is associated with an effect on 12-HETE synthesis, we compared the relative effects of ASA on the bleeding time, platelet TxA2 and 12-HETE synthesis, and platelet aggregation and adhesion in ET patients and healthy volunteers. ASA (300 mg, taken orally) prolonged the bleeding time in 82% of the ET patients but only 27% of the healthy volunteers although platelet TxA2 synthesis and ADP- and collagen-induced aggregation were inhibited significantly in both groups. In contrast, platelet 12-HETE synthesis was unchanged and platelet adhesion was decreased in those patients and volunteers whose bleeding times were prolonged by ASA, whereas platelet 12-HETE synthesis was increased significantly and platelet adhesion was unaffected in those patients and volunteers whose bleeding times were not prolonged, and in some cases shortened by ASA. These results confirm previous data that demonstrate that ASA has different effects on platelet 12-HETE synthesis and platelet adhesion in different individuals, i.e., inhibitory or no effect in ASA responders (in whom ASA prolonged bleeding) vs. enhancing effects in ASA nonresponders (in whom ASA did not prolong bleeding). These results also indicate that there is a greater percentage of ASA responders in patients with ET than that seen in the general population, a difference that is associated with an effect of ASA on the lipoxygenase pathway. This may explain the increased bleeding side effects seen in the ET patient population.

Plant alkaloids, tetrandrine and hernandezine, inhibit calcium-depletion stimulated calcium entry in human and bovine endothelial cells

Depletion of internal Ca2+ stores causes capacitative Ca2+ entry which occurs through non-selective cation channels sensitive to blockade by SK&F 96365. Recently, alkaloids of Chinese herbal medicinal origin, tetrandrine and hernandezine, have been shown to possess actions including inhibition of Ca2+ channels in non-excitable cell types. In this study, we compared the actions of these novel inhibitors to those of SK&F 96365 in fura-2-loaded endothelial cells from human umbilical vein and bovine pulmonary artery. Depletion of Ca2+ from the internal stores was accomplished in Ca(2+)-free medium using an endoplasmic reticulum Ca2+ pump inhibitor, cyclopiazonic acid (CPA) or receptor agonists, histamine and bradykinin. Stimulation with histamine or bradykinin caused a marked and rapid transient increase in Ca2+ signal whereas CPA caused a smaller amplitude increase of longer duration. Restoring Ca2+ to the medium caused marked and sustained increases in the fluorescence indicating movement of Ca2+ into the cytosol presumably stimulated by the emptied Ca2+ stores. SK&F 96365 as well as tetrandrine and hernandezine antagonized depletion-induced Ca2+ entry. The results suggest that these putative inhibitors interact with Ca2+ entry triggered by depletion of the internal Ca2+ stores and their action is presumed to be on the non-selective cation channels. Their effectiveness may be enhanced by the mechanisms which lead to the opening of the Ca2+ influx channel.

Individual variation in the effects of ASA on platelet function: implications for the use of ASA clinically

OBJECTIVE

To determine whether acetylsalicylic acid (ASA) inhibits hemostasis and platelet function in some individuals (ASA responders) but not in others (ASA nonresponders).

DESIGN

In this two-part study, part 1 was a randomized, double-blind crossover study of the effects of various single doses of ASA (80 to 1300 mg) on primary hemostasis and platelet function. Part 2 was a prospective cohort study of the effects of a chronic dose of ASA (325 mg) on primary hemostasis and platelet function.

SETTING

A hospital research laboratory and a cardiac care ward.

SUBJECTS

Part 1: 10 healthy volunteers (five male, five female). Part 2: 40 consecutive patients undergoing elective coronary artery bypass grafting (CABG).

RESULTS

Part 1: ASA, in a dose-related manner, prolonged the bleeding time in 60% of volunteers (ASA responders), which was associated with decreases in platelet thromboxane (Tx) A2 and 12-hydroxyeicosatetraenoic acid (12-HETE) synthesis and in platelet aggregation and adhesion. However, in volunteers whose bleeding time was not prolonged (ASA nonresponders), platelet 12-HETE synthesis and platelet adhesion were unchanged or increased (P < 0.001), despite platelet TxA2 and platelet aggregation being inhibited. Part 2: similarly, 58% of the CABG patients were ASA responders and all of their platelet biochemistry and function tests were inhibited, while in the CABG patient ASA nonresponders (no prolongation of bleeding time), platelet 12-HETE and platelet adhesion were increased (P < 0.001).

Thrombin generation in patients undergoing carotid endarterectomy: implications in acute vessel wall closure and antithrombotic therapy

We determined the extent and duration of activation of coagulation during the first 24 hours after carotid endarterectomy. Serial blood samples were collected before, during and after surgery from 10 patients with severe stenosis (> 70%) undergoing carotid endarterectomy with heparinization. Platelet poor plasmas prepared from these samples, were analysed for activated prothrombin fragment F1 + 2 and thrombin-antithrombin III (TAT) levels, using commercially available ELISA kits. F1 + 2 and TATs were measured as indices of thrombin generation and inhibition respectively. Baseline F1 + 2 and TAT levels were 1.19 +/- 0.27 nMol/ml and 17 +/- 10 pMol/ml, respectively. Neither the F1 + 2 nor TAT level increased during surgery at a time when the patients were heparinized. However, both the F1 + 2 and TAT levels increased significantly within 3 hours after surgery and after the heparin had been neutralized with protamine, (p < 0.01). Moreover, both the F1 + 2 and TAT levels remained elevated in 75% of the patients for at least 24 hours, p < 0.01. We conclude that i) thrombin generation is significant post surgery in patients undergoing carotid endarterectomy despite their receiving heparin during surgery; ii) heparin may not be the ideal anticoagulant for carotid endarterectomy; and iii) persistent thrombin generation may contribute to early post-endarterectomy ischemic events.

Prevention of thrombus formation and growth by antithrombin III and heparin cofactor II-dependent thrombin inhibitors: importance of heparin cofactor II

Heparin (HEP) prevents thrombus formation (TF) and thrombus growth (TG), by accelerating thrombin (THR) inhibition by antithrombin III (ATIII). Recent studies suggest that dermatan sulphate which catalyzes thrombin inhibition by heparin cofactor II (HCII), can inhibit TF and TG as effectively as HEP. This study compared the antithrombotic effects of HEP and another agent, Sulodexide (SLX) which catalyzes thrombin inhibition by ATIII and HCII simultaneously. TF was induced in rabbit jugular veins, using the stasis/hypercoagulation model. TG was measured as the accretion of 125I-fibrin onto existing thrombi in rabbit jugular veins. HEP and SLX inhibited TF when given in doses of 10 and 5 anti-thrombin U/kg, respectively. SLX (16 anti-thrombin U/kg or 260 micrograms/kg) was more effective than HEP (120 anti-thrombin U/kg or 800 micrograms/kg) in preventing TG when administered either as a bolus or by continuous infusion. These data suggest that agents which accelerate THR inhibition by both ATIII and HCII simultaneously, can inhibit TF and TG with less systemic anticoagulation than comparable antithrombotic doses of HEP.

Is heparin the ideal anticoagulant for cardiopulmonary bypass? Dermatan sulphate may be an alternate choice

Performance of cardiopulmonary bypass (CPB) during cardiac surgery requires the administration of high dose heparin to prevent CPB pump occlusion. However, this heparin use is associated with bleeding side-effects. Moreover, at the end of CPB, the heparin must be neutralized with protamine sulphate, which is also associated with adverse side-effects. A number of recent studies suggest that dermatan sulphate may be useful as an alternate anticoagulant to heparin. We determined whether CPB could be performed using dermatan sulphate instead of heparin, in an adult pig CPB model. When heparin was used, a high dose (> 200 U/kg, which generated > 3 anti-thrombin U/ml of plasma), was required to perform successful CPB and to maintain CPB pump patency. This dose was associated with a post CPB bleeding of approximately 600 ml/2 h. In contrast, successful CPB could be achieved when the pigs were given lower doses of dermatan sulphate than heparin, which in turn, were associated with less bleeding. We conclude that dermatan sulphate may be an alternate anticoagulant for cardiac surgery.

Influence of endothelium-derived relaxing factor on platelet function and hemostasis in vivo

Endothelium-derived relaxing factor (EDRF) is a potent vasodilator, and is also, in vitro, a platelet-inhibitor. Experiments were performed to determine whether systemically released EDRF inhibits platelet-dependent hemostasis in vivo. Rabbits were treated with agents to release or block EDRF, and 5 standardized incisions were made in the ear. Carbachol, infused to stimulate EDRF release, abruptly lowered the blood pressure and caused increased bleeding. Neither effect was attributable to prostacyclin since neither was blocked by treatment of the rabbits with acetylsalicylic acid. In contrast, both the hypotension and bleeding were attenuated by the selective antagonist of EDRF synthesis, NG-nitro-L-arginine. However, neither the hypotension nor the bleeding associated with carbachol was inhibited by an infusion of free hemoglobin, used to scavenge intraluminally-released EDRF. We conclude that in this model endogenously-released EDRF increases bleeding indirectly by provoking vasodilatation, rather than directly by inhibiting platelet function.

The relative roles of vitronectin receptor, E-selectin and alpha 4 beta 1 in cancer cell adhesion to interleukin-1-treated endothelial cells

Adhesion of cancer cells to endothelium is thought to be a prerequisite to extravasation during the haematogenous phase of metastasis, and is enhanced after perturbation of the endothelium by interleukin-1 (IL-1). The inducible endothelial adhesion molecules, E-selectin, VCAM-1/alpha 4 beta 1 and vitronectin receptor have been reported to mediate attachment of cancer cells to IL-1-treated endothelial cells. We have examined the relative contribution of these molecules by quantifying the adhesion of a panel of 22 human, 125I-labelled cancer cells and the rat W256 tumour to untreated and IL-1-treated endothelial monolayers in the presence of relevant neutralising antibodies. Antibodies against E-selectin inhibited the adhesion of HL-60 leukaemia cells and two colon carcinomas. Anti-alpha 4 beta 1 antibodies blocked adhesion of four melanomas, five sarcomas and one lung carcinoma. Anti-vitronectin receptor antibodies inhibited adhesion of 14 of the 22 human cell lines to IL-1-treated endothelial cells. Adhesion of seven cell lines was inhibited by more than a single antibody. In contrast, adhesion of one of the cancer cell lines was unaffected by any of the antibodies, suggesting involvement of other IL-1-inducible endothelial adhesion molecules. Moreover, none of the antibodies altered the attachment of cancer cells to unstimulated endothelial monolayers. We conclude that the mechanisms of cancer cell adhesion to the endothelium are influenced by endothelial activation and by the adhesive repertoire of the cancer cell.

Thrombin generation during cardiac surgery: is heparin the ideal anticoagulant?

Blood samples were collected from 43 patients undergoing elective cardiac surgery to determine the extent of thrombin generation and inhibition in patients when receiving heparin while undergoing cardiopulmonary bypass (CPB). Plasma prothrombin fragment F1 + 2 and thrombin-antithrombin III (TAT) levels were measured as markers of thrombin generation and inhibition, respectively. Both F1 + 2 and TAT levels increased significantly during the course of CPB despite the heparin causing significant systemic anticoagulation, i.e. the activated coagulation time (ACT) was prolonged to greater than 400 s throughout the entire surgical procedure. The extent of thrombin generation increased with time on CPB but did not differ between patients receiving normothermic and hypothermic cardioplegia during CPB. Furthermore, thrombin generation increased following the neutralization of the heparin with protamine sulphate, and continued to be elevated significantly 24 h post surgery. The observation that high dose heparin did not prevent thrombin generation during CPB, is consistent with previous experimental studies demonstrating that thrombin bound to fibrin or other surfaces (e.g. the CPB conduit) is resistant to antithrombin III/heparin inhibition, and thus able to facilitate further thrombin generation. The observation that thrombin generation continued to be elevated post surgery i.e. 24 h after neutralizing the heparin with protamine sulphate, suggests that the high dose heparin did not inhibit effectively all of the thrombin that had been generated. Thus, CPB patients may be at risk not only of bleeding and other side-effects associated with the acute use of high dose heparin, but may also be at risk of further thrombosis-related events either acutely or chronically.

Adhesion molecules and their role in cancer metastasis

This article describes various adhesion molecules and reviews evidence to support a mechanistic role for adhesion molecules in the process of cancer metastasis. A variety of evidence supports the involvement of specific adhesion molecules in metastasis. 1. For example, some cancer cells metastasize to specific organs, irrespective of the first organ encountered by the circulating cancer cells. This ability to colonize a specific organ has been correlated with the preferential adhesion of the cancer cells to endothelial cells derived from the target organ. This suggests that cancer cell/endothelial cell adhesion is involved in cancer cell metastasis and that adhesion molecules are expressed on the endothelium in an organ-specific manner. 2. Further, inclusion of peptides that inhibit cell adhesion, such as the YIGSR- or RGD-containing peptides, is capable of inhibiting experimental metastasis. 3. Metastasis can be enhanced by acute or chronic inflammation of target vessels, or by treatment of animals with inflammatory cytokines, such as interleukin-1. In vitro, cancer cell/endothelial cell adhesion can be enhanced by pretreating the endothelial cell monolayer with cytokines, such as interleukin-1 or tumor necrosis factor-alpha. This suggests that, in addition to organ-specific adhesion molecules, a population of inducible endothelial adhesion molecules is involved and is relevant to metastasis. 4. Further support for this model is found in the comparison to leukocyte/endothelial adhesion during leukocyte trafficking. Convincing evidence exists, both in vivo and in vitro, to demonstrate an absolute requirement for leukocyte/endothelial adhesion before leukocyte extravasation can occur. The relevance of this comparison to metastasis is reinforced by the observation that some of the adhesion molecules involved in leukocyte/endothelial adhesion are also implicated in cancer cell/endothelial adhesion. The involvement of adhesion molecules suggests a potential therapy for metastasis based on interrupting adhesive interactions that would augment other treatments for primary tumors.

Localization of 13-hydroxyoctadecadienoic acid and the vitronectin receptor in human endothelial cells and endothelial cell/platelet interactions in vitro

Blood/vessel wall cell interactions depend, in part, on the expression of adhesion receptors on cell surfaces, such as expression of the vitronectin receptor (VnR) on the apical surface of endothelial cells (ECs) for platelet/EC adhesion. However, it is unclear how receptor expression is regulated from within cells. In previous studies, we found that ECs metabolize linoleic acid into the lipoxygenase monohydroxide, 13-hydroxyoctadecadienoic acid (13-HODE), and that the intracellular level of 13-HODE correlates inversely with VnR expression and platelet adhesion to the EC apical surface. In this study, we determined the physical associations of 13-HODE and VnR in unstimulated and stimulated ECs, ie, at times when ECs were and were not adhesive for specific ligands and platelets, using double antibody immunofluorescent staining techniques and binding assays. 13-HODE and the VnR were colocalized within unstimulated ECs. When ECs were stimulated, 13-HODE was no longer detectable, either in or outside the ECs, and the VnR was detected on the apical surface of the ECs. These changes were paralleled by increased vitronectin binding and increased platelet adhesion to the ECs. We suggest that colocalization of 13-HODE with VnR reflects a 13-HODE/VnR interaction, confining the VnR in a nonadhesive form inside unstimulated ECs, and, as a result, the ECs are nonadhesive. When the ECs are stimulated, 13-HODE and VnR dissociate, allowing the VnR to relocate on the EC surface, where the VnR undergoes a conformational change resulting in increased EC adhesivity.

Interleukin 1-induced cancer cell/endothelial cell adhesion in vitro and its relationship to metastasis in vivo: role of vessel wall 13-HODE synthesis and integrin expression

Previously, we have demonstrated that stimulation of endothelial cells (ECs) with interleukin-1 alpha (IL-1 alpha) enhances the synthesis and expression of the vitronectin receptor (VnR), promotes VnR-dependent adhesion of human A549 adenocarcinoma cells to ECs, and is associated with decreased EC 13-hydroxyoctadecadienoic acid (13-HODE) synthesis in vitro. To determine whether these observations are relevant in vivo, we examined the acute retention and subsequent metastasis of intravenously-injected B16F10 melanoma cells in murine lungs, in relation to vessel wall 13-HODE. In C57BL/6 mice pretreated with IL-1 alpha, vessel wall 13-HODE was decreased and B16F10 lung entrapment and metastasis were increased. The latter two events were blocked by pretreating the animals with the GRGDS peptide. These data suggest a relationship between vessel wall 13-HODE synthesis, adhesion molecule expression, and adhesion of B16F10 cells to the endothelium.

The effects of heparin and annexin V on fibrin accretion after injury in the jugular veins of rabbits

We compared the relative abilities of unfractionated heparin and annexin V to prevent fibrin accretion onto injured jugular veins in vivo. Heparin was used to accelerate the inhibition of thrombin by antithrombin III, and annexin V was used to inhibit the assembly of the prothrombinase complex on phospholipid surfaces, thereby blocking thrombin generation. Rabbit jugular veins were isolated in situ, a 2 cm segment was injured by perfusing it with air, and then blood flow was re-established. Five minutes later, each rabbit was injected with heparin (20 U/kg) or annexin V (0.3 mg/kg) and then with 125I-fibrinogen. The amount of 125I-fibrin accumulation onto each injured vessel wall segment was measured 4 h later. Each injured vessel was completely de-endothelialized as a result of the air perfusion as demonstrated by electron microscopy. 125I-fibrin accretion onto the injured jugular veins was enhanced 2.4-fold as compared to the uninjured veins in sham-operated animals. Heparin treatment did not reduce fibrin accretion, whereas, annexin V treatment decreased fibrin accretion by 60%, p < 0.05. This latter effect was achieved without sustained circulating anticoagulation. Additional experiments confirmed that the inhibitory effect of annexin V on fibrin accretion was associated with a surface specific effect, since more annexin V bound to the injured jugular vein segments as compared to the non-injured jugular veins.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet adhesivity to subendothelium is influenced by polymorphonuclear leukocytes: studies with aspirin and salicylate

Interactions between blood platelets and polymorphonuclear leukocytes (PMN) influence cell reactivity. We have examined the effects of inhibiting platelet and PMN cyclooxygenase and lipoxygenase pathways, by treatment with aspirin (ASA) and salicylate (SAL) on platelet-vessel wall interaction studied under flow conditions by means of an annular chamber perfusion system. We have also measured the levels of cyclooxygenase-derived metabolites during perfusion. Perfusates were prepared with untreated and ASA- or SAL-treated PMN or platelets. Our results demonstrated that blockage of the lipoxygenase pathway in PMN significantly increased platelet thrombus formation and favored the production of thromboxane B2 (TxB2) during perfusion, whereas inhibition of cyclooxygenase pathway in PMN had no effect either on platelet deposition or on TxB2 levels. In contrast, blockage of platelet cyclooxygenase, which caused almost total inhibition of TxB2, enhanced platelet adhesion and did not modify platelet thrombus formation. These results suggest that under dynamic conditions cooperative metabolic mechanisms between platelets and PMN directly influence platelet interaction with vascular subendothelium.

Prevention of thrombus growth by antithrombin III-dependent and two direct thrombin inhibitors in rabbits: implications for antithrombotic therapy

We compared the abilities of heparin and two direct thrombin inhibitors to prevent fibrin accretion onto pre-existing thrombi in rabbits. Inhibition of thrombus growth was measured as the ability of each test compound to inhibit the accretion of 125I-fibrin onto thrombi pre-formed in jugular veins of rabbits. When administered as a continuous infusion, the two direct (i.e. antithrombin III-independent) thrombin inhibitors, r-hirudin and a tripeptide, Ac(D)-Phe-Pro-bor-Arg (P-8714) inhibited fibrin accretion as effectively as heparin, but did so in doses which generated little systemic anticoagulation, as compared to the marked anticoagulation associated with the heparin effect. However, both r-hirudin and P-8714 were more effective when they were administered as a single bolus injection than as a continuous infusion. Under the former conditions, there was only a transient systemic anticoagulant effect. We conclude that direct or antithrombin III-independent thrombin inhibitors are more effective than heparin in preventing thrombus growth. The limited effect of heparin is likely due to fibrin impairing the ability of heparin/antithrombin III to inactivate thrombin.

Inhibition of the amplification reactions of blood coagulation by site-specific inhibitors of alpha-thrombin

Hirudin and hirulog-1 [D-Phe-Pro-Arg-Pro-[Gly]4-desulphohirudin-(54-65)] abrogate the enzyme activities of alpha-thrombin by binding the enzyme simultaneously at its catalytic centre and fibrin(ogen)-recognition exosite. In contrast, hirugen [hirudin-(54-65)] binds alpha-thrombin solely at the fibrin(ogen)-recognition exosite, and competitively inhibits fibrinopeptide A release. To investigate the extent to which the fibrin(ogen)-recognition exosite is involved when alpha-thrombin catalyses the amplification reactions of coagulation, we compared the abilities of hirudin, hirulog-1 and hirugen to inhibit simultaneously Factor X, Factor V and prothrombin activation. Whereas 0.1 microM-hirudin and 0.1 microM-hirulog-1 (i.e. less than 10% of the concentration of prothrombin in plasma) inhibited Factor X, Factor V and prothrombin activation, 10 microM was the minimum concentration of hirugen to achieve a similar anticoagulant action. Concentrations of hirudin and hirulog-1 equimolar to and 5 times greater than those of alpha-thrombin respectively abrogated Factor V activation by exogenous alpha-thrombin. In contrast, a 500-fold molar excess of hirugen could not. The inability of hirugen to inhibit the activation of the three clotting factors effectively suggests that the fibrin(ogen)-recognition exosite does not play a mandatory role when thrombin activates Factor V.

Up-regulated biosynthesis and expression of endothelial cell vitronectin receptor enhances cancer cell adhesion

Extravasation of circulating cancer cells during metastasis is thought to involve adhesion to the vascular endothelium. To characterize this process, we measured the attachment of A549 human lung carcinoma cells to monolayers of cultured human umbilical vein endothelial cells. Pretreatment of the endothelial cells with 10 ng/ml interleukin 1 alpha (IL-1) for 4 h increased cancer cell attachment 2-5-fold. This increase was blocked by 100 microM glycyl-arginyl-glycyl-aspartyl-serine peptide and was decreased 60 +/- 10% (SD) by a vitronectin receptor polyclonal antiserum or 56 +/- 8% by a vitronectin receptor monoclonal antibody, LM609. Glycyl-arginyl-glycyl-aspartyl-serine or the vitronectin receptor antibodies did not inhibit cancer cell attachment to untreated endothelial cells. A fibronectin receptor antiserum had no effect on attachment to untreated or IL-1-treated endothelial cells. Pretreatment of endothelial cells with IL-1 increased their adhesion to fibronectin and vitronectin and increased the expression of vitronectin receptor and fibronectin receptor as detected by immunofluorescence flow cytometry, quantitative antibody binding, and immunoprecipitation of [35S]methionine-labeled cell extracts. IL-1 pretreatment also increased beta 1, beta 3, and alpha, integrin mRNA. The A549 cells did not express vitronectin receptor, since LM609 did not inhibit A549 adhesion to vitronectin or bind to A549 cells in flow cytometry, and vitronectin receptor antisera failed to immunoprecipitate vitronectin receptor from A549 cells. Furthermore, the beta 3 complementary DNA probe failed to hybridize to A549 RNA. A549 cells did express fibronectin receptor, which was increased by IL-1 treatment. We conclude that IL-1 induces the expression of both vitronectin receptor and fibronectin receptor on endothelial cells and that vitronectin receptor, in turn, facilitates A549 cell adhesion to endothelial cells.

Eicosanoids, other fatty acid metabolites and the cardiovascular system: are the present antithrombotic approaches rational?

Antiplatelet +/- anticoagulant drugs are currently used as the standard treatment to prevent and treat thrombosis. While this approach is beneficial, it is not optimal. Recent evidence suggests that constituents of the vascular endothelium play an important role in regulating vessel wall thrombogenecity, thereby inhibiting thrombogenesis. These include constituents such as PGI2, tissue plasminogen activator, thrombomodulin and the lipoxygenase fatty acid metabolite derived from linoleic acid, 13-hydroxyoctadecadienoic acid (13-HODE). Consequently, new strategies have been developed to maximize the use of these agents for antithrombotic therapy. We will review these different approaches, discuss their rationale, and based upon recent experimental data, introduce an alternative approach for antithrombotic therapy which may circumvent a number of limitations and side-effect of the currently used drugs.

Endothelial cell damage by Walker carcinosarcoma cells is dependent on vitronectin receptor-mediated tumor cell adhesion

The transport of cancer cells from blood vessels to extravascular tissue is a critical step in metastasis, where endothelial cells and the vascular basement membrane act as barriers to cell traffic. Because endothelial injury can facilitate the metastasis of intravascular cancer cells in vivo, the authors have studied in vitro the free-radical-mediated endothelial damage caused by the rat Walker 256 carcinosarcoma (W256) cell after stimulation with 10(-6) mol/l (molar) phorbol ester. Here the authors have examined the hypothesis that W256 cell-mediated endothelial injury is dependent on adhesion between the effector and target cells. Attachment of phorbol 12-myristate, 13-acetate (PMA)-stimulated W256 cells to endothelial monolayers was increased 1.8 +/- 0.1-fold and damage (3H-2-deoxyglucose release from labeled endothelium) 1.4 +/- 0.1-fold after 4-hour pretreatment of the endothelium with 10 ng/ml recombinant human interleukin-1 alpha (rIL-1 alpha). Under various assay conditions, the release of 3H-2-deoxyglucose correlated directly with tumor cell adhesion (r = 0.98, P less than 0.005). In the presence of a polyclonal anti-vitronectin receptor antiserum, adhesion of stimulated W256 cells to rIL-1 alpha-treated monolayers was inhibited by 39% +/- 2%, and 3H-2-deoxyglucose release was inhibited by 53% +/- 13%. Immunoblot analysis and immunofluorescence flow cytometry demonstrated that the endothelial cells but not the W256 cells expressed vitronectin receptor (VnR) on their cell surface. The surface expression of VnR by endothelial cells was increased 1.9 +/- 0.1-fold after 4 hours' incubation with rIL-1 alpha. The authors conclude that W256 cell-mediated endothelial damage is dependent on cell adhesion, which, in turn, is partly regulated by the expression of VnR on the endothelial cell surface.

Fibrin moderates the catalytic action of heparin but not that of dermatan sulfate on thrombin inhibition in human plasma

Three recent studies have reported that fibrin in solution significantly inhibits the ability of heparin to catalyze the inhibition of thrombin by antithrombin III. In addition, heparin inhibits the release of fibrinopeptide A by clot-bound thrombin less effectively than it inhibits the release of fibrinopeptide A by thrombin in solution. We have also reported that dermatan sulfate, which catalyzes thrombin inhibition by heparin cofactor II, inhibits thrombus growth in rabbits more effectively than heparin. Because the results of these studies suggest that fibrin inhibits the reactivity of thrombin with antithrombin III-heparin but not with heparin cofactor II-dermatan sulfate, we compared the relative catalytic effects of heparin and dermatan sulfate on thrombin inhibition in plasma, both in the presence and absence of fibrin. We quantitated the rates of thrombin inhibition by antithrombin III and heparin cofactor II by specific enzyme-linked immunosorbent assays. When it was generated, fibrin was kept in solution by adding 2 mmol/L Gly-Pro-Arg-Pro to plasma. Fibrinogen-fibrin reduced the reactivity of thrombin with plasma antithrombin III, both in the presence of and in the absence of heparin. In contrast, the catalytic action of dermatan sulfate on thrombin inhibition by plasma heparin cofactor II was unimpaired by fibrinogen-fibrin. Based on the ability of dermatan sulfate to inhibit thrombus growth in rabbits, failure of fibrinogen-fibrin to moderate the catalytic action of dermatan sulfate may account for its greater antithrombotic effectiveness relative to that of heparin.

Platelet adhesion to exposed endothelial cell extracellular matrixes is influenced by the method of preparation

The relative thrombogenicity of extracellular matrixes (ECMs) produced by cultured human umbilical endothelial cells (ECs) was studied under flow conditions. ECMs were prepared using a number of physical and chemical methods, and their reactivity toward platelets was morphometrically evaluated. von Willebrand factor (vWF), fibronectin (FN), and 13-hydroxy-9-cis,11-trans-octadecadienoic acid (13-HODE) were also determined. We found that platelet adhesion to ECMs differed significantly, both quantitatively and qualitatively, with the method of ECM preparation. Mechanically prepared ECM exposed a less thrombogenic surface compared with ECM prepared by chemical methods (platelet-covered surface of 20% and 50%, respectively). Evaluation of the ECM components vWF, FN, and 13-HODE showed significant changes, both in their concentrations and distribution patterns, depending on the method of ECM preparation. The decrease measured in the levels of ECM-associated vWF (from 108 to 9.2 ng/10(4) cells) and the minor changes observed in the distribution pattern of subendothelial FN did not appear to be sufficient to explain the altered platelet adhesion observed in our model. This suggests that the amount of 13-HODE probably associated to the remaining ECs present in the mechanically exposed ECM could be one factor that specifically contributed to the nonthrombogenic state of these preparations. We conclude that the degree of ECM reactivity toward platelets is dependent on the method of ECM preparation and that this is related to the removal of specific EC/ECM components that modulate their thromboresistant/thrombogenic properties. This fact should be taken into account when ECMs produced by cultured ECs are used in platelet adhesion studies.

Comparative effects of heparin and LMW heparin on hemostasis

We performed studies to investigate the effect of protamine sulfate neutralization on both the anticoagulant and hemostatic effects of enoxaparin and heparin. Although the anti-Factor Xa effect of enoxaparin was incompletely neutralized by protamine sulfate in an experimental animal model, protamine sulfate reversed bleeding induced by hemorrhagic doses of enoxaparin.

Wound healing in the media of the normolipemic rabbit carotid artery injured by air drying or by balloon catheter de-endothelialization

The response to air-dry injury to the carotid artery of the normolipemic rabbit was compared with the response to de-endothelialization with a balloon catheter. Air drying induced an inflammatory response that resembled arteritis rather than atherosclerosis. There was medial damage, neutrophil but not macrophage infiltration, and fibrin formation, limited smooth muscle proliferation, which regressed after 3 months, and no lipid deposition. Within 1 week the smooth muscle cells were mainly of the secretory phenotype, and a neointima had formed. At 4 weeks the neointimal proliferation continued, but most cells showed a contractile phenotype. By 3 months, the lesion consisted of fibromuscular thickening with few small smooth muscle cells. Balloon injury induced minimal medial damage and continuing intimal proliferation with no evidence of regression by 3 months. It is concluded that air drying the carotid artery induces smooth muscle damage as well as endothelial cell loss, and this stimulates a wound-healing mechanism that is different from the response to selective intimal injury.