Jozef Vermylen

Diesel Exhaust Particles in Lung Acutely Enhance Experimental Peripheral Thrombosis

Background—Pollution by particulates has consistently been associated with increased cardiovascular morbidity and mortality, but a plausible biological basis for this association is lacking. Methods and Results—Diesel exhaust particles (DEPs) were instilled into the trachea of hamsters, and blood platelet activation, experimental thrombosis, and lung inflammation were studied. Doses of 5 to 500 &mgr;g of DEPs per animal induced neutrophil influx into the bronchoalveolar lavage fluid with elevation of protein and histamine but without lactate dehydrogenase release. The same doses enhanced experimental arterial and venous platelet rich-thrombus formation in vivo. Blood samples taken from hamsters 30 and 60 minutes after instillation of 50 &mgr;g of DEPs yielded accelerated aperture closure (ie, platelet activation) ex vivo, when analyzed in the Platelet Function Analyser (PFA-100). The direct addition of as little as 0.5 &mgr;g/mL DEPs to untreated hamster blood significantly shortened closure time in vitro. Conclusions—The intratracheal instillation of DEPs leads to lung inflammation as well as a rapid activation of circulating blood platelets. The kinetics of platelet activation are consistent with the reported clinical occurrence of thrombotic complications after exposure to pollutants. Our findings, therefore, provide a plausible explanation for the increase in cardiovascular morbidity and mortality accompanying urban air pollution.

Size effect of intratracheally instilled particles on pulmonary inflammation and vascular thrombosis

Particulate air pollution is associated with cardiorespiratory effects and ultrafine particles (UFPs, diameter < 100 nm) are believed to play an important role. We studied the acute (1 h) effect of intratracheally instilled unmodified (60 nm), negatively charged carboxylate-modified (60 nm), or positively charged amine-modified (60 or 400 nm) polystyrene particles on bronchoalveolar lavage (BAL) indices and on peripheral thrombosis in hamster. The latter was assessed by measuring the extent of photochemically induced thrombosis in a femoral vein via transillumination. Unmodified and negative UFPs did not modify thrombosis and BAL indices. Positive UFPs increased thrombosis at 500 microg per animal (+ 341 +/- 96%) and at 50 microg per animal (+ 533 +/- 122%), but not at 5 microg per animal. Neutrophils, lactate dehydrogenase, and histamine were increased in BAL at all these doses but protein concentration was increased only at 500 microg per animal. Positive 400-nm particles (500 microg per animal) did not affect thrombosis, although they led to a neutrophil influx and an increase in BAL proteins and histamine. Using the Platelet Function Analyser (PFA-100), the platelets of hamsters were activated by the in vitro addition of positive UFPs and 400-nm particles to blood. We conclude that intratracheally administered positive ultrafine and 400-nm particles induce pulmonary inflammation within 1 h. Positive UFPs, but not the 400-nm particles enhance thrombosis. Hence, particle-induced lung inflammation and thrombogenesis can be partially uncoupled.

Inhibition of integrin function by a cyclic RGD-containing peptide prevents neointima formation.

BACKGROUND RGD-containing peptides are able to prevent binding of ligands to certain integrins such as alpha IIb beta 3 (glycoprotein IIb/IIIa) and alpha v beta 3 and as such are inhibitors for platelet aggregation and smooth muscle cell migration, both of which are involved in neointima formation. METHODS AND RESULTS Hamster carotid arteries were damaged, and neointima formation was determined at different time points. G4120, a cyclic RGD-containing peptide, was administered continuously intravenously by an implanted osmotic pump. Neointima formation was inhibited dose dependently. The inhibition was strongest when treatment was started before the vascular injury and continued for the full observation period. Treatment started after the damage and maintained until neointima assessment or started before and stopped earlier was less effective. CONCLUSIONS Inhibition of integrin function by an RGD-containing peptide results in reduction of the development of a neointima. This effect is due both to an early event, which could be due to inhibition of secretion of PDGF by the platelets with blocked alpha IIb beta 3, and to a late event, possibly by interference with smooth muscle cell alpha v beta 3.

MK-383 (L-700,462), a selective nonpeptide platelet glycoprotein IIb/IIIa antagonist, is active in man

BackgroundFibrinogen-dependent cross-linking of glycoprotein (GP) lIb/IIIa on activated platelets is the final mechanism leading to platelet aggregation. Inhibition of this mechanism may result in a novel antithrombotic agent. We studied the activity of MK-383 (L-700,462), a new, nonpeptide GPIIb/IIIa antagonist, in vitro and in vivo, in man. Methods and ResultsMK-383, a nonpeptide trosine derivative, dose-dependently inhibited fibrinogendependent platelet aggregation, in vitro. Binding of 125I-labeled fibrinogen to activated platelets was prevented in a competitive manner with an IC50 of 10±4.2 nmol/L. The activity and tolerability of MK-383 were evaluated in a two-part double-blind, placebo-controlled, dose-escalation study in healthy male subjects using 1- and 4-hour intravenous infusions. Effects on ADP- and collagen-induced ex vivo platelet aggregation (APA or CPA) and template bleeding time (TBT) were evaluated. Twenty-four subjects participated in the 1-hour part. Six received placebo and 18 MK-383 in doses ranging from 0.05 to 0.40 μg · kg-1 · min-1. MK-383 inhibited platelet aggregation and prolonged bleeding time in a dose-dependent manner. APA and CPA were totally inhibited at the end of infusion of 0.4 μg · kg-1 · min-1 and returned to 55% and 89% of baseline, respectively, at 3 hours after infusion. TBT was prolonged at this dose from 5.0±1.3 minutes predose to 22.7±6 minutes at the end of the infusion (P<.01) and was normalized by 3 hours after infusion. In the 4-hour infusion part, 15 subjects received MK-383 (0.1 to 0.2 μg · kg-1 · min-1), and five received placebo. Complete inhibition of ex vivo platelet aggregation was seen at 0.15 and 0.2 μg · kg-1 · min-1. At 0.2 μg · kg-1 · min-1, TBT was prolonged from 4.4±1.2 to 23.9±4.3 minutes at the end of infusion (P<.01) and remained slightly prolonged 3 hours after infusion (7.2±1.8 minutes). No adverse effects were observed in any of the 33 subjects receiving MK-383. ConclusionsThe results from this study indicate that MK-383 appears to be well tolerated and active in man. It is the first nonpeptide GPIIb/IIMa antagonist that can be used to investigate the antithrombotic potential of this new class of antiplatelet agents.

A THROMBOXANE SYNTHETASE INHIBITOR REORIENTS ENDOPEROXIDE METABOLISM IN WHOLE BLOOD TOWARDS PROSTACYCLIN AND PROSTAGLANDIN E2

During incubation of citrated blood at 37 degrees C the levels of 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha) and prostaglandin E2 (PGE2) remain constant, but rise markedly within one minute after the addition of collagen, particularly when thromboxane synthetase is blocked. The amount of 6-keto PGF1 alpha formed is dose-dependent for both collagen and the thromboxane synthetase inhibitor (UK-37,248). Moreover, the number of platelets will determine the extent of the 6-keto PGF1 alpha jump, that does not occur when blood is drawn after aspirin ingestion. The production of 6-keto PGF1 alpha in function of time is composed of a fast platelet-related (intercept) and a slower probably leukocyte-dependent contribution (slope). In the absence of UK-37,248 the intercept is 115 +/- 85 pg/ml, the slope is 12.9 +/- 7.7 pg/min/ml whereas in the presence of the thromboxane synthetase inhibitor they are 411 +/- 177 pg/ml and 56.2 +/- 25 pg/min/ml respectively. The present findings indicate that a thromboxane synthetase inhibitor, by not only reducing thromboxane A2 production but also enhancing prostacyclin generation with blood is exposed to thrombogenic stimuli such as collagen, should be superior to aspirin as an antithrombotic agent, although possible interference by enhanced PGE2 production should be taken into account.

Ambient air pollution and acute myocardial infarction

Summary.  This review summarizes the nature of ambient air pollutants, which are either gaseous or particulate of various sizes, the latter determining their penetration into the body, the smallest even translocating from the lung into the systemic circulation. It presents the epidemiological evidence linking air pollution to overall mortality, cardiovascular mortality and myocardial infarction, making the distinction between acute and chronic exposure to the pollutants. It reviews mechanistic investigations that have evaluated the links among exposure to pollutants, thrombosis, pulmonary inflammation, arterial vasoconstriction and heart rate variability. It concludes by attempting to integrate current epidemiological and mechanistic observations into a pathophysiological framework that links ambient air pollution to acute myocardial infarction and cardiovascular mortality.

Current status and implications of autoimmune antiphospholipid antibodies in relation to thrombotic disease

Summary.  This review briefly describes the development of the concepts of antiphospholipid antibody and of antiphospholipid syndrome. It focuses on the two main antigenic targets, β2 glycoprotein I and prothrombin. An excessive production of natural antibodies rather than an immune response to exogenous antigen is proposed as pathogenetic for the development of these antibodies. The review attempts to explain how some of these antibodies are anticoagulant in vitro yet prothrombotic in vivo. The final section discusses when to test for such antibodies, how to test and how to consider treatment of patients with the antiphospholipid syndrome.

Catheter-directed lysis of iliofemoral vein thrombosis with use of rt-PA

Abstract The aim of our study was to evaluate the results of catheter-directed thrombolysis and complementary procedures to treat acute iliofemoral deep vein thrombosis (DVT). A total of 24 consecutive patients with acute iliofemoral DVT underwent intrathrombus drip infusion of alteplase (3 mg/h; mean dosage 86 mg, range 45–174 mg), while intravenous heparin (1000 U/h) was continued. Complementary procedures were hydrodynamic thrombectomy in 3 and primary insertion of a Wallstent in 9 patients. Patency of 19 thrombosed veins (79 %) was restored with prompt symptomatic relief. An underlying anatomical anomaly or lesion was present in 13 patients: iliac vein compression syndrome (n = 8), absent (n = 2) or obstructed (n = 1) vena cava or venous stenosis (n = 2). Ten of the abnormalities were unknown before lysis and eight were relieved by stent deployment. Puncture site bleeding was the only complication but led to transfusion in 6 patients (25 %). Symptomatic reocclusion occurred in 4 patients. Catheter thrombolysis of iliofemoral vein thrombosis revealed many anatomical abnormalities which may predispose to thrombosis and are often amenable to stenting.

Role of proaggregatory and antiaggregatory prostaglandins in hemostasis. Studies with combined thromboxane synthase inhibition and thromboxane receptor antagonism.

Thromboxane synthase inhibition can lead to two opposing effects: accumulation of proaggregatory cyclic endoperoxides and increased formation of antiaggregatory PGI2 and PGD2. The elimination of the effects of the cyclic endoperoxides by an endoperoxide-thromboxane A2 receptor antagonist should enhance the inhibition of hemostasis by thromboxane synthase blockers. We have carried out a series of double-blind, placebo-controlled, crossover studies in healthy volunteers to check if this hypothesis may be operative in vivo in man. In a first study, in 10 healthy male volunteers, the combined administration of the thromboxane receptor antagonist BM 13.177 and the thromboxane synthase inhibitor dazoxiben gave stronger inhibition of platelet aggregation and prolonged the bleeding time more than either drug alone. In a second study, in 10 different healthy male volunteers, complete inhibition of cyclooxygenase with indomethacin reduced the prolongation of the bleeding time by the combination BM 13.177 plus dazoxiben. In a third study, in five volunteers, selective cumulative inhibition of platelet TXA2 synthesis by low-dose aspirin inhibited platelet aggregation and prolonged the bleeding time less than the combination BM 13.177 plus dazoxiben. In vitro, in human platelet-rich plasma stimulated with arachidonic acid, the combination of BM 13.177 and dazoxiben increased intraplatelet cAMP while the single drugs did not affect it. Our results indicate that prostaglandin endoperoxides can partly substitute for the activity of TXA2 in vivo in man and that an increased formation of endogenous antiaggregatory and vasodilatory prostaglandins, as obtained with selective thromboxane synthase inhibitors, may contribute to the impairment of hemostasis.

Percutaneous transluminal renal angioplasty: initial results and long-term follow-up in 202 patients.

Percutaneous transluminal renal angioplasty was performed in 202 patients with 250 stenoses. The procedure was successful in 201 of 250 (83%). Results were better for postostial atherosclerotic lesions (94%), fibromuscular lesions (83%), and transplant kidneys (71%) than for ostial atherosclerotic lesions (29%). Of all the patients, 61% had reduced blood pressures following the procedure, with cure (diastolic blood pressure ≤90 mm Hg) in 31% of the patients. Cure rate with a mean follow-up of 25.8±19.4 months was 21% in bilateral atheromatous lesions, 30% in unilateral atheromatosis, 65% in unilateral fibromuscular disease, and 40% in bilateral fibromuscular dysplasia. Of the transplanted patients, 60% were cured. Complications occurred in 23 (11%) of the patients. Recurrence of stenoses occurred in 16 lesions (8%). 80% within the first year after the procedure.