Trial protocol: a clustered, randomised, longitudinal, type 2 translational trial of alcohol consumption and alcohol-related harm among adolescents in Australia

Background

This cluster randomised control trial is designed to evaluate whether the Communities That Care intervention (CTC) is effective in reducing the proportion of secondary school age adolescents who use alcohol before the Australian legal purchasing age of 18 years. Secondary outcomes are other substance use and antisocial behaviours. Long term economic benefits of reduced alcohol use by adolescents for the community will also be assessed.

Methods

Fourteen communities and 14 other non-contiguous communities will be matched on socioeconomic status (SES), location, and size. One of each pair will be randomly allocated to the intervention in three Australian states (Victoria, Queensland and Western Australia). A longitudinal survey will recruit grade 8 and 10 students (M = 15 years old, N = 3500) in 2017 and conduct follow-up surveys in 2019 and 2021 (M = 19 years old). Municipal youth populations will also be monitored for trends in alcohol-harms using hospital and police administrative data.

Discussion

Community-led interventions that systematically and strategically implement evidence-based programs have been shown to be effective in producing population-level behaviour change, including reduced alcohol and drug use. We expect that the study will be associated with significant effects on alcohol use amongst adolescents because interventions adopted within communities will be based on evidence-based practices and target specific problems identified from surveys conducted within each community.

Trial registration

The trial was retrospectively registered in September, 2017 (ACTRN12616001276448), as communities were selected prior to trial registration; however, participants were recruited after registration. Findings will be disseminated in peer-review journals and community fora.

Production of transient ischaemic events by platelet emboli in baboons

To investigate the pathophysiological process of transient ischaemic events in a clinically relevant model, we produced transient focal cerebral ischaemia in five baboons using endogenously generated platelet microemboli. Thrombogenic segments of Dacron vascular graft were incorporated as unilateral carotid arterio-arterial shunts to produce endogenous platelet microemboli. The embolized microparticles were quantified by isotopic imaging using 111In-platelets and by transcranial Doppler ultrasonography. Platelet microemboli accumulated rapidly in the shunted carotid territory and reached a maximum value of 3.2 +/- 0.8 x 10(9) in the embolized hemisphere 20 min after initiating blood flow through the graft segment. Sixty min after removing the grafts 111In-platelets were largely cleared from hemispheric vasculature. Recovered animals exhibited mild contralateral hemiparesis which disappeared completely within 24 h. We conclude that endogenously generated platelet microemboli accumulate transiently in the dependent cerebral circulation and produce corresponding transient focal neurological dysfunction. This model may be useful in the evaluation of new therapeutic strategies in acute stroke.

Inhibition of acute vascular thrombosis in chimpanzees by an anti-human tissue factor antibody targeting the factor X binding site

Tissue factor (TF) antagonists targeting the factor VII (FVII) binding domain have been shown to interrupt acute vascular thrombus formation without impairing haemostasis in non-human primates. In this study, we evaluate whether a human/mouse chimeric monoclonal antibody (ALT-836, formerly known as Sunol-cH36) blocking the factor X/factor IX (FX/FIX) binding site of tissue factor could achieve similar clinical benefits in an arterial thrombosis model induced by surgical endarterectomy in chimpanzees. In this model, sequential surgical endarterectomies on right and left superficial femoral arteries were performed 30 days apart in five chimpanzees. A bolus (1 mg/kg) of ALT-836 was injected intravenously immediately preceding the restoration of flow in the endarterectomised femoral artery. Pre-surgical labelling of autologous platelets using (111)In-Oxine and post-surgical gamma camera imaging of (111)In-platelet deposition at endarterectomy sites was performed. The manipulated arterial segments were harvested for patency analysis 30 days following surgery. The results indicate that ALT-836 was highly effective at reducing acute vascular thrombosis, with no significant variations in surgical blood loss and template-bleeding time in the treated group compared to the control animals. These data suggest that ALT-836 is an effective and safe antithrombotic agent in preventing TF-initiated vascular thrombogenesis without compromising haemostasis.

Soluble thrombomodulin is antithrombotic in the presence of neutralising antibodies to protein C and reduces circulating activated protein C levels in primates

We studied whether there was a relationship between the anticoagulant effects of recombinant human soluble thrombomodulin (rhsTM) and activation of protein C in a primate model of acute vascular graft thrombosis in 11 baboons (Papio species). Baboons were pretreated with 0.1, 1 and 5 mg/kg of rhsTM, with or without co-injection of a neutralising monoclonal antibody to protein C (HPC4) in the 1 mg/kg rhsTM group. Subsequently, thrombogenic polyester grafts were deployed for 3 h into chronic exteriorised arteriovenous shunts. Thrombus growth in the graft, plasma-activated protein C (APC) levels, coagulation and thrombosis markers were determined. In untreated baboons, baseline circulating APC levels more than doubled and graft thrombi propagated until reaching equilibrium in about 1 h. Treatment with rhsTM reduced thrombus propagation rates, prolonged the clotting and bleeding times, decreased thrombin-antithrombin complex, beta-thromboglobulin and fibrinopeptide A levels, and, surprisingly, also decreased systemic APC levels, in a dose-dependent manner. In the presence of HPC4 antibody to inhibit APC generation, the acute antithrombotic activity of rhsTM on graft thromboses was not attenuated for up to 80 min, but sustained thrombus accumulation was observed over a 180-min period. These findings suggest that, in contrast to the prevailing hypotheses, the primary antithrombotic activity of rhsTM is independent of protein C, at least in this primate model. Direct inhibition of thrombin's prothrombotic activity upon complex formation with rhsTM might explain the molecular mechanism of the observed antithrombotic effect.

Clopidogrel (Plavix) and cardiac surgical patients: implications for platelet function monitoring and postoperative bleeding

The use of clopidogrel (Plavix), an inhibitor of adenosine diphosphate (ADP)-induced platelet aggregation, has been proven to reduce ischemic events in cardiovascular patients, but little information is available for optimal monitoring of platelet function in patients receiving the drug preoperatively. In the first part of the study we compared different testing modalities (thrombelastography (TEG), platelet aggregometry, and whole blood aggregation) to assess platelet ADP receptor inhibition. Because clopidogrel is a pro-drug, we used an in vitro model of ADP inhibition with 5'-p-fluorosulfonylbenzoyladenosine (FSBA). FSBA at final concentration of 80 microM completely inhibited platelet aggregation but had no effect on TEG maximum amplitude (MA). In the second part of the study, antiplatelet effects of clopidogrel were clinically assessed and correlated to postoperative bleeding in 18 coronary bypass surgery patients. Preoperative TEG results were normal or hypercoagulable in clopidogrel-treated patients, although platelet aggregation responses to ADP were inhibited. Clopidogrel-treated patients who underwent cardiopulmonary bypass had a high incidence (84.6%) of platelet transfusion therapy due to increased chest tube drainage. In conclusion, we have demonstrated that normal preoperative TEG-MA does not preclude clopidogrel-induced ADP receptor blockade; however, TEG can be a reliable monitor for CPB-induced platelet dysfunction related to GPIIb/IIIa. For monitoring clopidogrel, it is necessary to perform more specific platelet function tests (aggregometry or platelet count ratio) using ADP as an activator.

In vivo platelet redistribution and acute transient thrombocytopenia after eptifibatide injection in baboons

BACKGROUND

The occurrence of thrombocytopenia has been reported during clinical eptifibatide (Integrilin) therapy, but the exact mechanism is not yet established to explain the varied duration and severity of thrombocytopenia associated with glycoprotein (GP) IIb/IIIa inhibitors. We assessed the redistribution of platelets in juvenile baboons during acute transient thrombocytopenia that was observed after eptifibatide injection.

METHODS

Eptifibatide was administered intravenously to eight baboons by infusion at 20 microg/kg/min or a bolus injection of 10 mg. Platelet distribution was measured with a gamma scintillation camera using 111In-labeled autologous platelets. Platelet function and GP IIb/IIIa receptor inhibition were evaluated using the Plateletworks system. The effects of pretreatment with abciximab (0.4 mg/kg) or human immunoglobulin concentrate (0.75 g/kg) were also investigated.

RESULTS

Eptifibatide, administered as an infusion or a bolus, caused transient thrombocytopenia with uptake of platelets predominantly by the liver. The recovery of platelet aggregation was associated with the re-entry of platelets from the liver into the systemic circulation. Pretreatment with either abciximab (0.4 mg/kg) or human intravenous immunoglobulin (IVIG, 0.75 g/kg) attenuated eptifibatide-induced thrombocytopenia and the hepatic uptake of radiolabeled platelets.

CONCLUSION

Acute thrombocytopenia after eptifibatide injection was caused by the transient redistribution of platelets to the liver. Attenuation of the decrease in platelet count and hepatic sequestration by abciximab and IVIG suggests that thrombocytopenia may have been caused by ligand-induced binding site antigen induction and recognition by the reticuloendothelial system.

Effects of tirofiban on haemostatic activation in vitro

BACKGROUND

Thrombin plays a critical role in normal haemostasis and pathological thrombosis. Heparin has long been a mainstay choice of antithrombotic regimen in cardiac patients, but persistent thrombin generation seems to occur during heparin therapy. Because platelets are integral to primary haemostasis and clot formation, we evaluated the use of tirofiban (Aggrastat),a platelet inhibitor, as a therapy to improve heparin sensitivity and delay thrombin formation.

METHODS

Blood samples were obtained from healthy subjects (n=8) and cardiac surgical patients (n=34). Thrombin formation was measured in platelet-rich plasma with a Thrombogram-Ascent fluorescent plate reader system. Platelet inhibition by tirofiban was evaluated with Plateletworks, and the interaction of tirofiban and heparin (>1.5 U ml(-1)) on clot formation was evaluated with Sonoclot Analyzer or kaolin activated clotting times (ACTs).

RESULTS

Addition of tirofiban (70-280 ng ml(-1)) progressively delayed onset of thrombin generation triggered by adenosine diphosphate (ADP). Plateletworks showed platelet inhibition with tirofiban (>35 ng ml(-1)), whereas heparin per se failed to produce platelet inhibition at 7 U ml(-1). Heparin (1.5 U ml(-1)) slowed the onset and rate of fibrin formation on Sonoclot analyses, and this was further slowed after addition of tirofiban (70 ng ml(-1)) to heparin-containing blood samples. Significant increases in ACT at all heparin concentrations were observed with the addition of tirofiban (70 ng ml(-1)). The addition of antithrombin (0.2 units/ml) to heparinized blood samples further prolonged ACTs, but the difference was not statistically significant when compared with heparin alone.

CONCLUSION

Tirofiban delays platelet activation-mediated thrombin generation and prolongs ACT in heparinized blood.

Helping the female partners of men abusing alcohol: a comparison of three treatments

AIM

To evaluate the effectiveness of three approaches to assisting the female partners of male problem drinkers with the stress imposed by the male's drinking.

DESIGN

Participants were assigned randomly via random number tables to one of three treatment conditions: supportive counselling, stress management or alcohol-focused couples therapy.

SETTING

The intervention took place at the Behaviour Research and Therapy Centre (BRTC), The University of Queensland. This research and training centre offers outpatient psychology services to the community.

PARTICIPANTS

Sixty-one married women whose husbands drank heavily. Participants reported protracted alcohol problems, severe impact of alcohol on social functioning and severe marital distress.

MEASUREMENT

The women's stress, alcohol consumption by the male, and relationship functioning were assessed at pre- and post-treatment and at 6-month follow-up.

INTERVENTIONS

All three treatments involved 15 1-hour sessions with the woman. In the alcohol-focused couple therapy, attempts were made to engage the man in these sessions.

RESULTS

Contrary to our predictions, there were few differences between the treatments. All three treatments were associated with reductions in the women's reported stress, with trends for somewhat greater reduction in the women's stress in the stress management and alcohol-focused couples therapy conditions than for supportive counselling. None of the treatments produced clinically significant reductions in men's drinking or relationship distress.

CONCLUSION

The treatments ease stresses and burden but do not improve drinking or relationships. Limited power in the design restricted the capacity to detect differential treatment effects.

Helping the female partners of men abusing alcohol: a comparison of three treatments

AIM

To evaluate the effectiveness of three approaches to assisting the female partners of male problem drinkers with the stress imposed by the male's drinking.

DESIGN

Participants were assigned randomly via random number tables to one of three treatment conditions: supportive counselling, stress management or alcohol-focused couples therapy.

SETTING

The intervention took place at the Behaviour Research and Therapy Centre (BRTC), The University of Queensland. This research and training centre offers outpatient psychology services to the community.

PARTICIPANTS

Sixty-one married women whose husbands drank heavily. Participants reported protracted alcohol problems, severe impact of alcohol on social functioning and severe marital distress.

MEASUREMENT

The women's stress, alcohol consumption by the male, and relationship functioning were assessed at pre- and post-treatment and at 6-month follow-up.

INTERVENTIONS

All three treatments involved 15 1-hour sessions with the woman. In the alcohol-focused couple therapy, attempts were made to engage the man in these sessions.

RESULTS

Contrary to our predictions, there were few differences between the treatments. All three treatments were associated with reductions in the women's reported stress, with trends for somewhat greater reduction in the women's stress in the stress management and alcohol-focused couples therapy conditions than for supportive counselling. None of the treatments produced clinically significant reductions in men's drinking or relationship distress.

CONCLUSION

The treatments ease stresses and burden but do not improve drinking or relationships. Limited power in the design restricted the capacity to detect differential treatment effects.

Effects of Mpl ligands on platelet production and function in nonhuman primates

Endogenous thrombopoietin (TPO) stimulates platelet production in nonhuman primates dose-dependentbyinducing megakaryocyte development from early marrow hematopoietic progenitors and subsequent proliferation and endoreduplication. Recombinant human TPO, nonpegylated or pegylated recombinant human megakaryocyte growth and development factor produce log-linear responses in peak peripheral platelet counts (or peripheral platelet mass turnover), platelet TPO receptor density, and marrow megakaryocyte volume, ploidy, number and mass. Mpl ligand therapy sustains normal peripheral platelet concentrations following myelosuppressive chemotherapy in baboons and corrects peripheral platelet counts in HIV-infected chimpanzees with severe thrombocytopenia. Whereas Mpl ligands do not directly induce platelet aggregation in vitro, they enhance aggregatory responsiveness of platelets to physiologic agonists both in vitro and transiently ex vivo following treatment with Mpl ligands. However, platelet recruitment into forming thrombus is not augmented by these agents when evaluated in quantitative rabbit or baboon models of platelet-dependent thrombus formation, except for the direct effect of platelet concentration per se. These findings indicate that appropriate dosing of these agents prevents thrombocytopenia without increasing the risk of platelet-dependent thrombo-occlusive complications.

Maritally distressed women with alcohol problems: the impact of a short-term alcohol-focused intervention on drinking behaviour and marital satisfaction

AIM

To evaluate the efficacy of a short-term alcohol-focused intervention for maritally distressed women, and to explore changes in relationship functioning.

DESIGN

Participants were assigned randomly to an alcohol-focused treatment or to a waiting-list control group. The waiting-list control group began the intervention at 1-month follow-up.

SETTING

The intervention took place at a research and training centre offering outpatient psychology services to the community.

PARTICIPANTS

A sample of 32 women with alcohol and marital problems were recruited through the media. Participants reported protracted alcohol problems, moderate to severe impact of alcohol on social and occupational functioning, and moderate to severe marital distress.

MEASUREMENTS

Measures of average alcohol consumption, marital distress, relational efficacy and depression were administered at pre- and post-therapy, and at 1, 6 and 12-month follow-up.

INTERVENTION

The intervention involved six 1-hour sessions, consisting of clinical assessment, motivational interviewing, cognitive-behavioural strategies and relapse prevention.

RESULTS

At 1-month follow-up, the intervention was associated with statistically significant improvements in alcohol consumption, marital satisfaction, relational efficacy and depression, and these effects were sustained at 12-month follow-up.

CONCLUSIONS

At 1-month follow-up the intervention was associated with decreased alcohol consumption and depression, and increased marital satisfaction and relational efficacy, with evidence of maintained effects at 12-month follow-up. However, it is unlikely that reduced problem drinking and improved confidence in resolving problems were the only factors producing low marital quality in these couples. Further research is needed to identify those individuals who might benefit from marital interventions.

Reduction in vascular lesion formation by hirudin secreted from retrovirus-transduced confluent endothelial cells on vascular grafts in baboons

BACKGROUND

The hypothesis that thrombin mediates the formation of neointimal vascular lesions at sites of mechanical vascular injury has been tested in baboons by measurement of the effects of hirudin delivered by retrovirus-transduced hirudin-secreting vascular endothelial cells (ECs) lining surgically implanted arterial vascular grafts (AVGs).

METHODS AND RESULTS

The antithrombotic efficacy of baboon ECs transduced with cDNA encoding hirudin was assessed in vitro and in vivo on thrombogenic segments in chronically exteriorized femoral arteriovenous (AV) shunts. Bilateral brachial AVGs lined with hirudin-transduced versus nonhirudin control ECs at confluent density were surgically implanted, and vascular lesion formations at distal graft-vessel anastomoses were compared after 30 days. Hirudin-transduced ECs secreted 20+/-6 ng x 10(6) cells(-1) x 24 h(-1) (range, 14 to 24 ng x 10(6) cells(-1) x 24 h(-1)) hirudin in supernatants of static cultures. Hirudin-secreting ECs on segments of collagen-coated graft interposed in chronic AV shunts decreased the accumulation of (111)In-labeled platelets to 0.52+/-0.34 x 10(9) platelets, compared with 0.82+/-0.49 x 10(9) platelets in controls (P = 0.03) and reduced platelet deposition in propagated thrombotic tails extending downstream from segments of vascular graft from 1.38+/-0.41 x 10(9) platelets in controls to 0.59+/-0.22 x 10(9) platelets (P = 0.04). ECs recovered from 30-day AVG implants generated 17+/-9 ng x 10(6) cells(-1) x 24 h(-1) (range, 9 to 25 ng x 10(6) cells(-1) x 24 h(-1)) hirudin. Hirudin-secreting ECs reduced neointimal lesion formation at distal graft-vessel anastomoses, ie, 1.02 mm(2) (range, 0.88 to 1.95 mm(2)) versus 1.82 mm(2) (range, 0.88 to 2.56 mm(2)) in contralateral AVGs bearing nonhirudin control ECs (P<0.01).

CONCLUSIONS

Viral vector-directed secretion of hirudin from ECs lining implanted AVGs significantly reduces the formation of thrombus and neointimal vascular lesions.

Distinct patterns of neuropeptide gene expression in the lateral hypothalamic area and arcuate nucleus are associated with dehydration-induced anorexia

We have investigated the hormonal and hypothalamic neuropeptidergic substrates of dehydration-associated anorexia. In situ hybridization and hormone analyses of anorexic and paired food-restricted rats revealed two distinct profiles. First, both groups had the characteristic gene expression and endocrine signatures usually associated with starvation: increased neuropeptide Y and decreased proopiomelanocortin and neurotensin mRNAs in the arcuate nucleus (ARH); increased circulating glucocorticoid but reduced leptin and insulin. Dehydrated animals are strongly anorexic despite these attributes, showing that the output of leptin- and insulin-sensitive ARH neurons that ordinarily stimulate eating must be inhibited. The second pattern occurred only in anorexic animals and had two components: (1) reduced corticotropin-releasing hormone (CRH) mRNA in the neuroendocrine paraventricular nucleus (PVH) and (2) increased CRH and neurotensin mRNAs in the lateral hypothalamic (LHA) and retrochiasmatic areas. However, neither corticosterone nor suppressed PVH CRH gene expression is required for anorexia after dehydration because PVH CRH mRNA in dehydrated adrenalectomized animals is unchanged from euhydrated adrenalectomized controls. We also showed that LHA CRH mRNA was strongly correlated with the intensity of anorexia, increased LHA CRH gene expression preceded the onset of anorexia, and dehydrated adrenalectomized animals (which also develop anorexia) had elevated LHA CRH gene expression with a distribution pattern similar to intact animals. Finally, we identified specific efferents from the CRH-containing region of the LHA to the PVH, thereby providing a neuroanatomical framework for the integration by the PVH of neuropeptidergic signals from the ARH and the LHA. Together, these observations suggest that CRH and neurotensin neurons in the LHA constitute a novel anatomical substrate for their well known anorexic effects.

The progression of thrombus in an ex-vivo shunt model evaluated by intravascular ultrasound radiofrequency analysis

We tested the ability of ultrasound radiofrequency (RF) signal analysis to characterize thrombus accumulation in a Dacron graft incorporated into the exteriorized arteriovenous shunt in 3 baboons with constant blood flow for 60 min. Thrombus formation was quantified by sequential measurements of 111Indium-labeled platelet deposition. RF signals were acquired every 15 min at 2 sites in the graft, using a 2.9 Fr intravascular ultrasound catheter-based transducer (30 MHz) and digitized at 250 MHz in 8-bit resolution. Regions of interest were placed within a 0.5-mm perimeter adjacent to the graft wall. Integrated backscatter increased significantly (p < 0.001) with increasing platelet deposition. However, mean-to-standard deviation ratio of the RF envelope showed no significant change and the distribution pattern of the RF probability function remained constant and consistent with a Rayleigh scattering process. These results provide a basis for using RF analysis to monitor the time-course of thrombus formation.

The role of alpha and beta platelet-derived growth factor receptor in the vascular response to injury in nonhuman primates

Restenosis remains a significant clinical problem associated with mechanical interventional procedures for arterial revascularization or repair, including coronary angioplasty and stenting. Studies with rodents have established that platelet-derived growth factor (PDGF), a potent chemotactic and mitogenic agent for vascular smooth muscle cells, is a key mediator of lesion formation after vascular injury. To further explore this hypothesis in a more clinically relevant model, neutralizing monoclonal antibodies (mAbs) were used to examine the effect of selective inhibition of alpha or beta PDGF receptor (PDGFR) on neointima formation in nonhuman primates. Carotid arteries were injured by surgical endarterectomy and femoral arteries by balloon catheter dilatation. Immunostaining revealed that both injuries induced cell proliferation and the upregulation of beta PDGFR but not alpha PDGFR. By 7 days after injury, beta PDGFR staining was limited to the luminal region of the media, the small areas of neointima, and the adventitia. Nearly all bromodeoxyuridine-positive cells were found in these regions as well. After 30 days, a concentric neointima that stained strongly for beta PDGFR had formed in the carotid and femoral arteries. Treatment of baboons with anti-beta PDGFR mAb 2A1E2 for 6 days after injury reduced the carotid artery and femoral artery lesion sizes by 37% (P<0.05) and 48% (P<0.005), respectively, when measured at 30 days. Under the same conditions, treatment with anti-alpha PDGFR mAb 2H7C5 had no effect. These findings suggest that PDGF mediates neointima formation through the beta PDGFR, and that antagonism of this pathway may be a promising therapeutic strategy for reducing clinical restenosis.

Clopidogrel inhibition of stent, graft, and vascular thrombogenesis with antithrombotic enhancement by aspirin in nonhuman primates

BACKGROUND

A recent study showed that clopidogrel reduces thrombo-occlusive complications in patients with symptomatic atherosclerosis more effectively than aspirin.

METHODS AND RESULTS

The effects of clopidogrel and aspirin have been compared, singly and in combination, for measurements of 111In-labeled platelets and 125I-labeled fibrin deposition in baboon models of arterial thrombosis and related to platelet aggregation and expression of activation epitopes induced by ADP, collagen, and thrombin receptor agonist peptide (TRAP) and to template bleeding times (BTs). Low-dose oral clopidogrel (0.2 mg. kg-1. d-1) produced cumulative (1) intermediate decreases in 111In-platelet and 125I-fibrin deposition for segments of prosthetic vascular graft, deployed endovascular metallic stents, and endarterectomized aorta (P<0.009 in all cases); (2) elimination of ADP-induced platelet aggregation (P<0.001); (3) modest inhibition of collagen-induced platelet aggregation (P<0.01); (4) no reduction in TRAP-induced platelet aggregation; and (5) minimal prolongation of BTs (P=0.03). High-dose oral clopidogrel (>/=2 mg/kg) produced the same effects within 3 hours. The effects of clopidogrel dissipated over 5 to 6 days. Aspirin 10 mg. kg-1. d-1 alone did not decrease 111In-platelet and 125I-fibrin deposition on segments of vascular graft but detectably decreased 111In-platelet and 125I-fibrin accumulation on stents (P<0.01), minimally inhibited ADP- and collagen-induced platelet aggregation (P<0.05 in both cases), and minimally prolonged BTs (P=0.004). Within 3 hours of aspirin administration, the antithrombotic effects of acute high-dose or chronic low-dose clopidogrel were substantially enhanced, and BTs were modestly prolonged without inhibiting platelet aggregation induced by TRAP (P<0.001 in all cases compared with clopidogrel alone).

CONCLUSIONS

Clopidogrel produces irreversible, dose-dependent, intermediate reduction in thrombosis that is substantially enhanced by the addition of aspirin. The effects of combining aspirin and clopidogrel need to be evaluated in patients at risk of vascular thrombosis.

Treatment of thrombocytopenia in chimpanzees infected with human immunodeficiency virus by pegylated recombinant human megakaryocyte growth and development factor

Three chimpanzees experimentally infected with human immunodeficiency virus (HIV) developed significant chronic thrombocytopenia after 5, 4, and 2 years, with peripheral platelet counts averaging 64 +/- 19 x 10(3)/microL (P = .004 compared with 228 +/- 92 x 10(3)/microL in 44 normal control animals), mean platelet volumes of 11.2 +/- 1.8 fL (P > .5 compared with 10.9 +/- 0. 7 fL in normal controls), endogenous thrombopoietin (TPO) levels of 926 +/- 364 pg/mL (P < .001 compared with 324 +/- 256 pg/mL in normal controls), uniformly elevated platelet anti-glycoprotein (GP) IIIa49-66 antibodies, and corresponding viral loads of 534, 260, and 15 x 10(3) RNA viral copies/mL. Pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) was administered subcutaneously (25 microg/kg twice weekly for 3 doses) to determine the effects of stimulating platelet production on peripheral platelet concentrations in this cohort of thrombocytopenic HIV-infected chimpanzees. PEG-rHuMGDF therapy increased (1) peripheral platelet counts 10-fold (from 64 +/- 19 to 599 +/- 260 x 10(3) platelets/microL; P = .02); (2) marrow megakaryocyte numbers 30-fold (from 11.7 +/- 6.5 x 10(6)/kg to 353 +/- 255 x 10(6)/kg; P = .04); (3) marrow megakaryocyte progenitor cells fourfold (from a mean of 3.6 +/- 0.6 to 14.1 x 10(3) CFU-Meg/1, 000 CD34(+) marrow cells); and (4) serum levels of Mpl ligand from 926 +/- 364 pg/mL (endogenous TPO) to predosing trough levels of 1, 840 +/- 353 pg/mL PEG-rHuMGDF (P = .02). The peripheral neutrophil counts were also transiently increased from 5.2 +/- 2.6 x 10(3)/microL to 9.9 +/- 5.0 x 10(3)/microL (P = .01), but neither the erythrocyte counts nor the reticulocyte counts were altered significantly (P > .1). The serum levels of antiplatelet GPIIIa49-66 antibodies exhibited reciprocal reductions during periods of thrombocytosis (P < .07). PEG-rHuMGDF therapy did not increase viral loads significantly (395, 189, and 53 x 10(3) RNA viral copies/mL; P > .5 compared with baseline values). The striking increase in peripheral platelet counts produced by PEG-rHuMGDF therapy implies that thrombocytopenia in HIV-infected chimpanzees is attributable to insufficient compensatory expansion in platelet production resulting from HIV-impaired delivery of platelets despite stimulated megakaryocytopoiesis. These data suggest that PEG-rHuMGDF therapy may similarly correct peripheral platelet counts in thrombocytopenic HIV-infected patients.

The region of the pontine parabrachial nucleus is a major target of dehydration-sensitive CRH neurons in the rat lateral hypothalamic area

Neurons in a restricted part of the lateral hypothalamic area (LHA) show increased expression of corticotropin-releasing hormone (CRH) mRNA as a consequence of cellular dehydration. In the present study, we have investigated the organization of their efferent projections by using anterograde and retrograde tracing techniques. Additionally, we have compared the distribution of CRH mRNA-containing neurons after cellular dehydration and intraventricular (i.c.v.) colchicine injections. Our results show that cellular dehydration activates a more restricted neuronal population than does i.c.v. colchicine. Iontophoretic injections of Phaseolus vulgaris leucoagglutinin (PHAL) were placed in the LHA of animals drinking hypertonic saline and their proximity to activated CRH neurons determined by in situ hybridization for CRH mRNA. Although labelled fibers from these injections were seen throughout the brain, the region of the parabrachial nucleus and nucleus of the solitary tract (NTS) were most conspicuous in also having CRH immunoreactive fibers. Injections of Fluoro-Gold placed in these two structures were used to confirm these findings in dehydrated animals. Significant numbers of neurons containing both Fluoro-Gold and CRH mRNA were seen in the lateral hypothalamus after injections in the lateral and medial parts of the parabrachial nucleus; far fewer were seen after injections in the NTS. These results strongly suggest that the CRH neurons in the LHA activated by cellular dehydration provide an input to the region of the parabrachial nucleus. The altered biochemical composition of this pathway may well be able to modify sensory and motor patterns both during and after dehydration.

Reduction in stent and vascular graft thrombosis and enhancement of thrombolysis by recombinant Lys-plasminogen in nonhuman primates

BACKGROUND

To enhance thrombolytic responses without increasing hemorrhagic risks, the antithrombotic effects of recombinant Lys-plasminogen (r-LysPgn), a prothrombolytic plasminogen intermediate, were examined in baboon models of thrombus formation and dissolution.

METHODS AND RESULTS

The dose-response effects of r-LysPgn, alone or in combination with subthreshold dosing of tissue plasminogen activator (TPA), were measured with respect to the accumulation of (111)In-labeled platelets and (125)I-fibrin in thrombus forming on endovascular metallic stents or thrombogenic segments of vascular graft interposed in exteriorized long-term arteriovenous (AV) femoral shunts. Thrombolytic losses have also been determined for preformed, stable, (111)In-platelet- and (125)I-fibrin-labeled graft thrombus and corresponding propagated thrombotic tails, together with changes in blood tests of thrombosis, thrombolysis, and hemostasis. Bolus intravenous r-LysPgn in escalating doses (2, 4, or 8 mg/kg) increased circulating plasminogen levels in a dose-dependent manner, was removed by log-linear clearance with a T50 of 120 minutes, and reciprocally decreased the accumulating thrombus on metallic stents and segments of vascular graft (P<.001 in all cases for 8-mg/kg doses). r-LysPgn also impaired platelet aggregatory responses to physiological agonists in vitro but not ex vivo. Prethrombosis administration of low-dose r-LysPgn (2 mg/kg) greatly enhanced the lysis of radiolabeled nonoccluding thrombus by a subthreshold dose of TPA (0.1 mg/kg) compared with TPA-only controls (P=.03).

CONCLUSIONS

Elective bolus injections of r-LysPgn before stent deployment decrease the amount of thrombus formed without compromising hemostasis by facilitating endogenous TPA thrombolysis. r-LysPgn may provide effective and safe antithrombotic therapy for interventional vascular procedures.

Antithrombotic strategies targeting thrombin activities, thrombin receptors and thrombin generation

Thrombin mediates acute vascular thrombosis and subsequent vascular lesion formation following mechanical denuding injury or spontaneous atherosclerotic plaque rupture. In the process of generating thrombin Factor VII/VIIa binds avidly with tissue factor (TF) exposed on cellular membranes, and coagulation serine proteases are sequentially cleaved via macromolecular catalytic complexes on phospholipid surfaces. Thrombin activates platelets, blood leukocytes, endothelium and vascular smooth muscle cells (SMCs) by cleaving G protein-coupled thrombin receptors (TRs), leading to SMC intimal proliferation and synthesis of extracellular matrix in the local formation of stenosing neointimal vascular lesions. Therapeutic strategies include inactivation of bound thrombin, inhibition of TR activation by thrombin, and interruption of thrombin generation. In patients having orthopedic surgery, inactivating bound thrombin with direct antithrombins markedly reduces venous thromboembolic events, compared with heparin or its derivatives, without significant impairment of hemostasis. However, acute coronary syndrome patients are not benefitted when given systemic direct antithrombins at safe levels, because interrupting TR-dependent platelet thrombosis demands systemic levels of direct antithrombins that concurrently compromise hemostatic function. Local drug delivery strategies have yet to be explored. In preclinical studies: a) enhancing the formation of endogenous activated Protein C (APC) by Protein C-selective thrombin mutants produces antithrombotic levels of APC; b) inhibiting thrombin activation of TRs abolishes platelet recruitment in arterial thrombogenesis in nonhuman primates, while sparing fibrin formation in hemostatic plugs; and c) preventing thrombin generation by inhibiting precursor serine protease function interrupts the formation of both acute thrombosis and chronic stenotic lesions after denuding vascular damage without significant hemostatic compromise. TF antagonists appear to have a highly favorable efficacy:safety therapeutic relationship for preventing the formation of thrombosis and vascular lesions.

Induction of vascular endothelial growth factor in balloon-injured baboon arteries. A novel role for reactive oxygen species in atherosclerosis

Neovascularization is a hallmark of neointimal formation in atherosclerotic plaques and restenotic lesions. Vascular endothelial growth factor (VEGF) promotes neovascular growth, whereas oxidative stress is a potent factor in vascular cell proliferation. To investigate the mechanisms of neovascular formation, we treated human and rat vascular smooth muscle cells (VSMCs) with H2O2. Northern blot analysis demonstrated a dose- and time-dependent increase in VEGF mRNA, with a maximum of 4-fold at 3 hours (200 mumol/L). As determined by immunoblotting and enzyme-linked immunosorbent assay, VEGF protein expression and secretion were similarly increased. Human umbilical vein endothelial cells were treated with conditioned medium from VSMCs incubated with 200 mumol/L H2O2. DNA synthesis, measured by thymidine incorporation, was increased 4-fold compared with control, an effect that was blocked by a neutralizing anti-VEGF antibody. The lipid peroxidation product 4-hydroxynonenal (1 mumol/L), an endogenous reactive oxygen species present in human atherosclerotic lesions, also increased VEGF secretion in VSMCs in a similar time-dependent fashion. Immunohistochemical staining and in situ hybridization of aortic sections from balloon-injured baboons demonstrated increased VEGF expression in discrete areas of the neointima and media compared with control sections, and expression correlated with the generation of 4-hydroxynonenal. Regulators of VEGF expression, such as reactive oxygen species, may enhance neovascularization of atherosclerotic and restenotic arteries.

Anti-VLA-4 antibody reduces intimal hyperplasia in the endarterectomized carotid artery in nonhuman primates

PURPOSE

Recently, very late antigen-4 (VLA-4) has been shown to mediate initial monocyte adhesion and migration to the injured artery. We hypothesized that blocking monocyte adhesion using a specific monoclonal antibody against VLA-4 may reduce intimal hyperplasia.

METHODS

Bilateral carotid endarterectomies were performed in eight adult baboons. Among them, five animals received an intravenous bolus injection of anti-VLA-4 antibody (3 mg/kg) during surgery and again after 2 weeks. Three animals underwent bilateral carotid endarterectomies and served as untreated control subjects. Specimens were harvested at 4 weeks and subjected to morphometric analysis, cell proliferation assay, and immunostaining for macrophages.

RESULTS

All of the endarterectomized arteries were patent except for one in the treated group. The number of macrophages in the intimal tissues was significantly reduced in the treated arteries compared with that in the control vessels (15.78 +/- 3.05 cells/section versus 33.50 +/- 6.13 cells/section; p < 0.001). The cell proliferation rate was significantly lower (p < 0.001) in the treated vessels (2.88% +/- 1.07%) compared with the control vessels (4.89% +/- 0.77%). The intimal area at the endarterectomized sites of carotid arteries was significantly less (p < 0.05) in the group treated with the anti-VLA-4 antibody (1.10 +/- 0.68 mm2) than in the control group (2.00 +/- 0.52 mm2).

CONCLUSION

These data show that blocking monocyte adhesion by use of an anti-VLA-4 antibody significantly reduces the number of intimal macrophages, intimal cell proliferation, and intimal hyperplasia in injured carotid arteries in baboons. This study supports a central role for macrophages in the development of intimal hyperplasia and may suggest a new therapeutic strategy to prevent clinical restenosis.

Antithrombotic potency of hirudin is increased in nonhuman primates by fibrin targeting

BACKGROUND

Inhibition of thrombin by either the indirect thrombin inhibitor heparin or by more potent direct thrombin inhibitors such as hirudin reduces thrombus formation after arterial injury. The present study was designed to determine if a fibrin-specific thrombin inhibitor could, by local thrombin inhibition, prevent thrombosis more effectively.

METHODS AND RESULTS

We first studied antithrombotic potency in vitro, comparing fibrin-targeted hirudin (recombinant hirudin covalently linked to the Fab' fragment of the anti-fibrin monoclonal antibody 59D8) to recombinant hirudin in baboon plasma. Fibrin-targeted hirudin was nine times more effective than recombinant hirudin in inhibiting fibrin deposition on experimental clot surfaces in baboon plasma (P < .01). The potency of fibrin-targeted hirudin was then compared with that of recombinant hirudin in a baboon model of thrombus formation. 111In-labeled platelet deposition was measured in a synthetic graft segment of an extracorporeal arteriovenous shunt in control animals and in animals receiving either fibrin-targeted hirudin or hirudin. In these experiments, fibrin-targeted hirudin was 10-fold more potent than hirudin in inhibiting platelet deposition and thrombus formation (P < .05).

CONCLUSIONS

These data indicate that targeting a thrombin inhibitors such as hirudin to an epitope present in thrombi results in increased antithrombotic potency.

Prevention of thrombocytopenia and neutropenia in a nonhuman primate model of marrow suppressive chemotherapy by combining pegylated recombinant human megakaryocyte growth and development factor and recombinant human granulocyte colony-stimulating factor

This report examines the effects on hematopoietic regeneration of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) (2.5 micrograms/ kg/d) alone and in combination with recombinant human granulocyte colony stimulating factor (rHu-GCSF) (10 micrograms/ kg/d) for 21 days in rhesus macaques receiving intense marrow suppression produced by single bolus injections of hepsulfam (1.5 g/m2). In six hepsulfam-only control animals thrombocytopenia (platelet count < 100 x 10(9)/L) was observed between days 12 and 25 (nadir 39 +/- 20 x 10(9)/L on day 17), and neutropenia (absolute neutrophil count < 1 x 10(9)/L) occurred between days 8 and 30 (nadir 0.167 +/- 0.120 x 10(9)/L on day 15). PEG-rHuMGDF (2.5 micrograms/kg/d) injected subcutaneously into four animals from day 1 to day 22 following hepsulfam administration produced trough serum concentrations of 1.9 +/- 0.2 ng/mL and increased the platelet count twofold over basal prechemotherapy levels (856 +/- 594 x 10(9)/L v baseline of 416 +/- 88 x 10(9)/L; P = .01). PEG-rHuMGDF alone also shortened the period of posthepsulfam neutropenia from 22 days to 12 days (P = .01), although the neutropenic nadir was not significantly altered (neutrophil count 0.224 +/- 0.112 x 10(9)/L v 0.167 +/- 0.120 x 10(9)/L; P > .3). rHu-GCSF (10 micrograms/kg/d) injected subcutaneously into four animals from day 1 to day 22 following hepsulfam administration produced trough serum concentrations of 1.4 +/- 1.1 ng/mL, and reduced the time for the postchemotherapy neutrophil count to attain 1 x 10(9)/L from 22 days to 4 days (P = .005). The postchemotherapy neutropenic nadir was 0.554 +/- 0.490 x 10(9)neutrophils/L (P = .3 v hepsulfam-only control of 0.167 +/- 0.120 x 10(9)/L). However, thrombocytopenia of < 100 x 10(9) platelets/L was not shortened (persisted from day 12 to day 25), or less severe (nadir of 56 +/- 32 x 10(9) platelets/L on day 14; P = .7 compared with untreated hepsulfam animals). The concurrent administration of rHu-GCSF (10 micrograms/kg/d) and PEG-rHuMGDF (2.5 micrograms/kg/d) in four animals resulted in postchemotherapy peripheral platelet counts of 127 +/- 85 x 10(9)/L (P = .03 compared with 39 +/- 20 x 10(9)/L for untreated hepsulfam alone, and P = .02 compared with 856 +/- 594 x 10(9)/L for PEG-rHuMGDF alone), and shortened the period of neutropenia < 1 x 10(9)/L from 22 days to 4 days (P = .8 compared with rHu-GCSF alone). Increasing PEG-rHuMGDF to 10 micrograms/kg/d and maintaining the 21-day schedule of coadministration with rHu-GCSF (10 micrograms/kg/d) in another four animals produced postchemotherapy platelet counts of 509 +/- 459 x 10(9)/L (P < 10(-4) compared with untreated hepsulfam alone, and P = .04 compared with 2.5 micrograms/kg/d PEG-rHuMGDF alone), and 4 days of neutropenia. Coadministration of rHu-GCSF and PEG-rHuMGDF did not significantly alter the pharmacokinetics of either agent. The administration of PEG-rHuMGDF (2.5 micrograms/kg/d) from day 1 through day 22 and rHu-GCSF (10 micrograms/kg/d) from day 8 through day 22 in six animals produced peak postchemotherapy platelet counts of 747 +/- 317 x 10(9)/L(P < 10(-4) compared with untreated hepsulfam alone, and P = .7 compared with PEG-rHuMGDF alone), and maintained the neutrophil count > 3.5 x 10(9)/L (P = .008 v rHu-GCSF therapy alone). Thus, both thrombocytopenia and neutropenia are eliminated by initiating daily PEG-rHuMGDF therapy on day 1 and subsequently adding daily rHu-GCSF after 1 week in the rhesus model of hepsulfam marrow suppression. This improvement in platelet and neutrophil responses by delaying the addition of rHu-GCSF to PEG-rHuMGDF therapy demonstrates the importance of optimizing the dose and schedule of cytokine combinations after severe myelosuppressive chemotherap

Neuropeptides and thirst: the temporal response of corticotropin-releasing hormone and neurotensin/neuromedin N gene expression in rat limbic forebrain neurons to drinking hypertonic saline

The authors have demonstrated in rats that the ingestion of hypertonic saline for 5 days provides an increasingly complex dehydrating stimulus to the rats. Initially, the stimulus leads to cellular dehydration, but extracellular dehydration develops as ingestion continues beyond 3 days. The initial cellular dehydration provokes modifications to corticotropin-releasing hormone and neurotensin/neuromedin N messenger RNAs (mRNAs) in some neurons of the limbic forebrain, changes that are either maintained or are modified as extracellular dehydration develops. These changes in mRNA content occur in neurosecretory neurons as well as in neurons in hypothalamic and telencephalic regions associated with behavior and autonomic regulation. The authors propose that alterations in peptide mRNAs are allied to altered neuronal signaling processes that direct the different components of the homeostatic response to dehydration.

Enhanced thrombolytic and antithrombotic potency of a fibrin-targeted plasminogen activator in baboons

BACKGROUND

Thrombolytic therapy reduces mortality in patients with acute myocardial infarction, but significant limitations exist with the use of currently available agents. In the present report, we describe the thrombolytic and antithrombotic potencies of a hybrid recombinant plasminogen activator consisting of an antifibrin antibody 59D8 (AFA) and low-molecular-weight single-chain urokinase-type plasminogen activator (scuPA).

METHODS AND RESULTS

A thrombolysis model in which thrombi are preformed in vivo in juvenile baboons was developed to compare the potencies of AFA-scuPA, recombinant tissue plasminogen activator (rTPA), and recombinant scuPA (rscuPA) in lysing nonocclusive 111In-labeled platelet-rich arterial-type thrombi and 125I-labeled fibrin-rich venous-type thrombi. Systemic infusion of 1.89 nmol/kg AFA-scuPA produced thrombolysis that was comparable to that obtained with much higher doses of TPA (14.2 nmol/kg) and rscuPA (28.5 nmol/kg). When steady-state plasma concentrations are normalized, AFA-scuPA lyses thrombi sixfold more rapidly than scuPA and TPA (P < .001) and reduces the rate of formation more than comparable doses of rscuPA (P < .0001). At equivalent thrombolytic doses, AFA-scuPA produced fewer antihemostatic effects than either rTPA or rscuPA. Template bleeding time measurements were shorter (3.5 +/- 0.12 minutes for AFA-scuPA versus 5.3 +/- 0.36 and 5.2 +/- 0.04 minutes for rTPA and rscuPA, respectively; P < .05), alpha 2-antiplasmin consumption was less (P < .05), and D-dimer generation was lower (P < .05).

CONCLUSIONS

We conclude that antibody targeting of scuPA to fibrin increases thrombolytic and antithrombotic potencies with less impairment of hemostasis compared with rTPA and rscuPA.

Dose-response effects of pegylated human megakaryocyte growth and development factor on platelet production and function in nonhuman primates

Thrombopoietin (TPO) is the physiologic Mpl-ligand regulating platelet production. Pegylated human recombinant megakaryocyte growth and development factor (PEG-rHuMGDF), a truncated polypeptide Mpl-ligand derivitized with poly-(ethylene glycol), induces megakaryocyte endoreduplication and proliferation in vitro and in vivo. In the present study, the dose-response effects of PEG-rHuMGDF on pharmacokinetics, megakaryocytopoiesis, platelet production, and platelet function were characterized for dosing 0.05, 0.10, 0.50, or 2.5 micrograms/kg/d in 22 baboons for 28 days. Daily subcutaneous injections of PEG-rHuMGDF produced linear log-dose responses in (1) steady-state trough plasma levels of PEG-HuMGDF (P < 10(-3)); (2) marrow megakaryocyte volume (P < 10(-3)), ploidy (P < 10(-4)), and number (P < .01); and (3) peripheral platelet concentrations (P < 10(-4)) and platelet mass turnover (P < 10(-3)). Platelet morphology, life span, and recovery were normal, and peripheral leukocyte, neutrophil, and erythrocyte counts were not significantly affected by PEG-rHuMGDF (P > .1 in all cases). PEG-rHuMGDF at 0.5 micrograms/kg/d produced similar blood concentrations of Mpl-ligand and platelets as 10 times the dose of rHu-MGDF (5.0 micrograms/kg/d), reflecting the extended plasma half-life achieved through pegylation. Whereas PEG-rHuMGDF did not induce platelet aggregation in vitro, platelet aggregatory responsiveness induced by thrombin receptor agonist peptide (TRAP1-6) and collagen was transiently enhanced ex vivo during the initial few days of PEG-rHuMGDF administration. However, adenosine diphosphate (ADP)-induced platelet aggregation was not enhanced ex vivo by PEG-rHuMGDF therapy. 111In-platelet deposition on segments of homologous endarterectomized aorta (EA) and vascular graft (VG) interposed in arteriovenous femoral shunts increased in direct proportion to the circulating platelet concentration (P < 10(-4) for both EA and VG); 125l-fibrin accumulation was not affected by PEG-rHuMGDF-induced increases in peripheral platelet counts. Changes in platelet production and function produced by PEG-rHuMGDF returned to baseline within 2 weeks after discontinuing treatment. Thus, in nonhuman primates, PEG-rHuMGDF increases platelet production in a linear log-dose-dependent manner by stimulating megakaryocyte endoreduplication and new megakaryocyte formation from marrow hematopoietic progenitors. These findings suggest that appropriate dosing of PEG-rHuMGDF therapy during periods of chemotherapy-induced marrow suppression may maintain hemostatic concentrations of peripheral platelets without increasing the risk of thrombosis.

Mediation of dehydration-induced peptidergic gene expression in the rat lateral hypothalamic area by forebrain afferent projections

We have previously shown in dehydrated rats that cellular levels of the mRNAs encoding the precursor peptides for corticotropin-releasing hormone and neurotensin/neuromedin N significantly increase in a restricted region of the lateral hypothalamic area (Watts, 1992, Brain Res. 581:208-216). The experiments reported here address the role that forebrain osmosensitive cells groups or regions associated with autonomic regulation play in developing this mRNA response. The first experiment showed that unilateral knife cuts placed between the rostral forebrain and the lateral hypothalamic area (LHA) will unilaterally attenuate the mRNA response in the LHA to dehydration. In a second experiment, small injections of the retrograde tracer Fluorogold into the region of the LHA containing these mRNAs revealed a direct input from the osmosensitive median preoptic nucleus and subfornical organ and from the fusiform nucleus of the bed nuclei of the stria terminalis, which is part of a complex of cell groups associated with autonomic regulation. We found that at least 30% of the neurons in the median preoptic nucleus and subfornical organ and 14% of the neurons in the fusiform nucleus of the bed nuclei of the stria terminalis that project to the LHA responded to a rapid increase in plasma osmolality with increased c-fos mRNA levels. In the final experiment, injections of Fluorogold into the LHA were made simultaneously with ipsilateral rostral knife cuts. Here the numbers of neurons accumulating Fluorogold in the median preoptic nucleus, subfornical organ, and the fusiform nucleus were all significantly decreased concomitantly with attenuated mRNA responses in the LHA to dehydration. We conclude that the LHA receives direct and functional projections from the median preoptic nucleus, subfornical organ, and the fusiform nucleus. These projections appear capable of mediating a substantial part of the response of peptidergic mRNAs in the LHA to dehydration.

Regulation of platelet production and function by megakaryocyte growth and development factor in nonhuman primates

The primary physiologic regulator of platelet production, Mpl ligand, has recently been cloned and characterized. To define the regulatory role of Mpl ligand on platelet production and function we measured the effects of a recombinant truncated human Mpl ligand, megakaryocyte growth and development factor (rHu-MGDF) on megakaryocytopoiesis, platelet function, and thrombogenesis in nonhuman primates. rHu-MGDF was administered to 10 baboons for 28 days while performing pharmacokinetics and repeated measurements of the following: (1) platelet count, volume, turnover, and function ex vivo and in vitro; (2) marrow megakaryocyte number, volume, and ploidy; and (3) platelet deposition and fibrin accumulation on segments of vascular graft and endarterectomized aorta in vivo. Daily subcutaneous injections of rHu-MGDF (5 microgram/kg/d) attained plasma concentrations averaging 1,300 +/- 300 pg/mL 2 hours after injection with trough levels of 300 +/- 65 pg/mL before the next dose. These levels of rHu-MGDF incrementally increased the peripheral platelet concentration threefold by day 7 and fivefold by day 28 (P < 10(-4)) associated with a reciprocal decrease of 25% in mean platelet volumes (P < 10(-3)). Platelet mass turnover, a steady-state measure of platelet production, increased fivefold (P < 10(-4)). Platelet morphology, life span, and recovery were normal. No significant change occurred in peripheral leukocyte, neutrophil, or erythrocyte counts (P > .1 in all cases). The platelet count gradually returned to baseline within 2 weeks after discontinuing rHu-MGDF infections. Marrow megakaryocyte volume doubled (P < 10(-3)) three days after initiating rHu-MGDF therapy and the modal ploidy shifted from 16N to 64N (P < 10(-4)). Marrow megakaryocyte number increased twofold by day 7, and nearly fourfold by day 28 (P < 10(-4)), resulting in a 6.5-fold increase in marrow megakaryocyte mass (P < 10(-3)). The effects of rHu-MGDF on thrombosis were determined by comparing baseline, day 5, and day 28 rHu-MGDF-treatment measurements of 111In-platelet deposition and 125I-fibrin accumulation on segments of homologous endarterectomized aorta (EA) and vascular graft (VG) interposed in arteriovenous femoral shunts. rHu-MGDF increased 111In-platelet deposition in direct proportion to the circulating concentration of platelets for both EA and VG (r=.98 in both cases), without significant changes in fibrin accumulation (P > .5 in both cases). During the first week of rHu-MGDF treatment ex vivo platelet aggregatory responsiveness was enhanced to physiologic agonists (adenosine diphosphate, collagen, and thrombin receptor agonist peptide, TRAP1-6) (P < .05 in all cases). Although in vitro platelet aggregation was not induced by any concentration of rHu-MGDF tested (P > .5), rHu-MGDF enhanced aggregatory responses to low doses of physiologic agonists, effects that were maximal at 10 ng/mL for baboon platelets and 100 ng/mL for human platelets, and were blocked by excess soluble c-Mpl receptor. Flow cytometric expression of platelet activation epitopes was not increased on resting platelets (ligand-induced binding sites, P-selectin, or Annexin V binding sites; P > .1 in all cases). Megakaryocyte growth and development factor regulates platelet production and function by stimulating endoreduplication and megakaryocyte formation from marrow progenitor cells, and transiently enhancing platelet functional responses ex vivo. rHu-MGDF has the potential for achieving platelet hemostatic protection with minimal thrombo-occlusive risk.

Enhanced in vivo antithrombotic effects of endothelial cells expressing recombinant plasminogen activators transduced with retroviral vectors

BACKGROUND

The effects of regulating endothelial cell (EC) plasminogen activator production on thrombus accumulation in vivo are incompletely understood. By overexpressing plasminogen activators in ECs via gene transfer, the hypothesis was tested that increased levels of plasminogen activators inhibit the accumulation of thrombus in vivo.

METHODS AND RESULTS

Cultured baboon ECs transduced with human cDNAs for wild-type tissue plasminogen activator (TPA) or for glycosylphosphatidylinositol-anchored urokinase-type plasminogen activator (a-UPA) were seeded onto collagen-coated segments of vascular graft (collagen segments) and exposed overnight to flow using an in vitro perfusion circuit. The antigenic levels of TPA and UPA each increased 10-fold in the media perfusing the corresponding transduced ECs compared with untransduced ECs (P < or = .05 in both cases). In baboons the antithrombotic effects of TPA-transduced or a-UPA-transduced ECs were measured as 111In-platelet deposition and 125I-fibrin accumulation on collagen segments bearing sparsely attached ECs (tarnsduced versus untransduced) interposed in exteriorized arteriovenous femoral shunts. Platelet-rich thrombus formed on the collagen segments with fibrin-rich thrombus propagated distally. The presence of TPA-transduced or a-UPA-transduced ECs on collagen segments at a density of 25,000 ECs/cm2 decreased 111AIn-platelet deposition and 125I-fibrin accumulation on collagen surfaces compared with untransduced ECs present at equivalent density (P < .05 for platelet deposition with TPA-transduced ECs and P < .05 for platelet deposition on the propagated tail, as well as fibrin accumulation on the graft with a-UPA-transduced ECs). The systemic levels of fibrinopeptide A, thrombin-antithrombin complex, D-dimer, and both local and systemic levels of TPA and UPA were not increased by transduced ECs compared with untransduced ECs. The focal antithrombotic effects of transduced ECs appear to be due to local enhancement of thrombolysis.

CONCLUSIONS

ECs transduced with recombinant TPA and a-UPA enhance local antithrombotic activity in vivo. This strategy of attaching transduced ECs overexpressing plasminogen activators may be therapeutically useful by preventing thrombo-occlusive failure of implanted cardiovascular devices or mechanically denuded vessels.

Antithrombotic and antilesion benefits without hemorrhagic risks by inhibiting tissue factor pathway

The effects of inhibiting tissue factor-dependent thrombus formation on vascular neointimal lesion formation have been evaluated by inhibiting tissue factor activity using intravenous injections of active-site inactivated recombinant factor VIIa (FVIIai) administered to baboons immediately prior to initiating bilateral femoral balloon artery angioplasty and surgical carotid endarterectomy. FVIIai abolished thrombus formation at sites of vascular injury and decreased vascular lesion formation by approximately 50 percent at 30 days. We conclude that thrombus formation at sites of vascular injury is predominately tissue factor-dependent and that transient inhibition of tissue factor activity prevents both vascular thrombosis and vascular lesion formation, which implies that transiently inhibiting tissue factor at the time of elective mechanical vascular procedures may be useful in reducing clinical restenosis.

Neuropeptides and thirst: the temporal response of corticotropin-releasing hormone and neurotensin/neuromedin N gene expression in rat limbic forebrain neurons to drinking hypertonic saline

The authors have demonstrated in rats that the ingestion of hypertonic saline for 5 days provides an increasingly complex dehydrating stimulus to the rats. Initially, the stimulus leads to cellular dehydration, but extracellular dehydration develops as ingestion continues beyond 3 days. The initial cellular dehydration provokes modifications to corticotropin-releasing hormone and neurotensin/neuromedin N messenger RNAs (mRNAs) in some neurons of the limbic forebrain, changes that are either maintained or are modified as extracellular dehydration develops. These changes in mRNA content occur in neurosecretory neurons as well as in neurons in hypothalamic and telencephalic regions associated with behavior and autonomic regulation. The authors propose that alterations in peptide mRNAs are allied to altered neuronal signaling processes that direct the different components of the homeostatic response to dehydration.

Antithrombotic effects of orally active synthetic antagonist of activated factor X in nonhuman primates

BACKGROUND

Since activated factor X (FXa) has a central role in hemostasis and thrombosis, it is an attractive target for antithrombotic strategies. Accordingly, we evaluated the relative antihemostatic and antithrombotic effects of an orally active amidinoaryl propanoic acid inhibitor of FXa, APAP, in baboons.

METHODS AND RESULTS

With a two-component thrombogenic device that induced the concurrent formation of both arterial-type platelet-rich and venous-type fibrin-rich thrombus when interposed in chronic exteriorized arteriovenous (AV) femoral shunts flowing at 40 mL/min, thrombus formation was compared for oral versus parenteral APAP by measurement of 111In-platelet deposition, 125I-fibrin accumulation, thrombotic obstruction of flow, and circulating levels of blood biochemical markers of thrombosis. The direct infusion of APAP (120 micrograms/min) into AV shunts proximal to thrombogenic devices for 1 hour achieved local drug levels of 4.3 +/- 0.4 mg/L and substantially reduced the accumulation of platelets and fibrin in the formation of venous-type fibrin-rich thrombus (P < .01) but not in the formation of platelet-rich arterial-type thrombus (P > .1). APAP was subsequently removed from plasma with plasma clearance rates of T50 alpha of 6.3 minutes and T50 beta of 99 minutes. The oral administration of APAP (50 mg/kg) produced peak plasma levels of 3.7 +/- 1.4 micrograms/mL at 30 minutes and gradually declining plasma levels over about 6 to 8 hours, with bioavailability estimated to be approximately 5% to 12%. Oral APAP decreased platelet deposition (P < .01) and fibrin accumulation (P < .05) in venous-type thrombus but failed to decrease platelet or fibrin accumulation in arterial-type thrombus (P > .1 in both cases). Oral and infused APAP prolonged the activated partial thromboplastin time and prevented thrombus-dependent elevations in plasma fibrinopeptide A, thrombin-antithrombin III complex, beta-thromboglobulin, and platelet factor 4 levels. Additionally, APAP produced dose-dependent inhibition of FXa bound to thrombus on segments of vascular graft interposed in exteriorized AV shunts for 15 minutes.

CONCLUSIONS

An oral synthetic antagonist of FXa, APAP, inhibits the formation of venous-type fibrin-rich thrombus by inactivating bound and soluble FXa without impairing platelet hemostatic function.

Relative antithrombotic effects of monoclonal antibodies targeting different platelet glycoprotein-adhesive molecule interactions in nonhuman primates

The relative antithrombotic effectiveness of targeting glycoprotein (GP) Ib-dependent versus GPIIb-IIIa-dependent platelet interactions has been determined in baboons by measuring thrombus formation after infusing comparable antihemostatic doses of anti-von Willebrand factor (vWF) monoclonal antibody (MoAb) BB3-BD5, anti-GPIb MoAb AP1, and anti-GPIIb-IIIa MoAb LJ-CP8 under conditions of arterial and venous flow (shear rates of 750 to 1,000 seconds-1 and 100 seconds-1, respectively). Thrombus formation was quantified as 111In-platelet deposition and 125I-fibrin accumulation on segments of collagen-coated tubing interposed in chronic exteriorized arteriovenous (AV) shunts for 40 minutes. In vitro, anti-vWF MoAb BB3 BD5 (IgG) and anti-GPIb MoAb AP1 [IgG or F(ab)2 fragments] inhibited ristocetin-induced platelet aggregation (IC50 50 nmol/L and 1 mumol/L, respectively), but neither of these MoAbs blocked platelet aggregation induced by adenosine diphosphate (ADP) (P > .5). Conversely, anti-GPIIb-IIIa MoAb LJ-CP8 inhibited platelet aggregation induced by ADP (IC50 1 mumol/L, but failed to block ristocetin-induced platelet aggregation (P > .5). In vivo, the intravenous infusion of anti-vWF MoAb BB3 BD5 or anti-GPIIb-IIIa MoAb LJ-CP8 into baboons at doses that abolished corresponding agonist-induced aggregation ex vivo (bolus injections of 0.5 mg/kg and 10 mg/kg, respectively) prolonged template bleeding times from baseline values of 4.0 +/- 0.3 minutes to > 27 +/- 4 minutes, and to > 26 +/- 4 minutes, respectively (P < .001 in both cases), without affecting the peripheral platelet count (P > .5). However, injection of anti-GPIb MoAb AP1 [10 mg/kg as IgG or 1 mg/kg as F(ab)2 fragments] produced immediate irreversible thrombocytopenia (< 40,000 platelets/microL). Anti-GPIIb-IIIa MoAb LJ-CP8 abolished platelet deposition and fibrin accumulation on collagen segments under both arterial and venous flow conditions (P < .01 in all cases), whereas MoAb BB3 BD5 produced minimal inhibition of platelet deposition and no decrease in fibrin accumulation at arterial shear rates and undetectable antithrombotic outcomes at low shear. Thus, inhibiting GPIIb-IIIa-dependent platelet recruitment abrogates both thrombus formation and platelet hemostatic function at both venous and arterial shear rates. By contrast, interfering with GPIb-vWF-dependent platelet interactions abolishes platelet hemostatic function without producing corresponding antithrombotic effects.

Antithrombotic effects of thrombin-induced activation of endogenous protein C in primates

The effects on thrombosis and hemostasis of thrombin-induced activation of endogenous protein C (PC) were evaluated in baboons. Thrombosis was induced by placing into arteriovenous shunts a segment of Dacron vascular graft, which generated arterial platelet-rich thrombus, followed by an expansion region of low-shear blood flow, which in turn accumulated fibrin-rich venous-type thrombus. Thrombosis was quantified by 111In-platelet imaging and 125I-fibrinogen accumulation. Intravenous infusion of alpha-thrombin, 1-2 U/kg-min for 1 h, increased baseline activated PC levels (approximately 5 ng/ml) to 250-500 ng/ml (P < 0.01). The lower thrombin dose, which did not deplete circulating platelets, fibrinogen, or PC, reduced arterial graft platelet deposition by 48% (P < 0.05), and platelet and fibrin incorporation into venous-type thrombus by > 85% (P < 0.01). Thrombin infusion prolonged the activated partial thromboplastin clotting time, elevated fibrinopeptide A (FPA), thrombin-antithrombin III complex (T:AT III), and fibrin D-dimer plasma levels (P < 0.01), but did not affect bleeding times. Thrombin's antithrombotic effects were blocked by infusing a monoclonal antibody (HPC-4) which prevented PC activation in vivo, caused shunt occlusion, increased the consumption of platelets and fibrinogen, elevated plasma FPA and T:AT III levels, and reduced factor VIII (but not factor V) procoagulant activity (P < 0.05). We conclude that activated PC is a physiologic inhibitor of thrombosis, and that activation of endogenous PC may represent a novel and effective antithrombotic strategy.

Exteriorized chronic aorto-caval arteriovenous access shunts in the baboon (Papio cynocephalus)

A chronic arteriovenous (AV) blood access shunt has been developed in baboons. It is composed of silicone rubber tubing extensions bonded to vascular graft polytetrafluoroethylene (ePTFE) cuffs, for creating anastomoses with the distal aorta and inferior vena cava. Following surgical implantation, shunts remain patent for months (X = 9 +/- 2.5 months) and provides long-term ex vivo access to non-anticoagulated blood (Mean Blood Flow = 312 +/- 69 mL/min).

Lasting safe interruption of endarterectomy thrombosis by transiently infused antithrombin peptide D-Phe-Pro-ArgCH2Cl in baboons

To evaluate the relative antithrombotic efficacy and hemostatic safety of antithrombin therapy for vascular thrombus formation at sites of mechanical vascular injury, we administered the potent and specific irreversible synthetic antithrombin D-PHE-PRO-ARG chloromethyl ketone (D-FPRCH2Cl) after performing carotid endarterectomies in baboons. The continuous intravenous infusion of D-FPRCH2Cl, 100 nmol/kg per minute for 1 hour, abolished acute carotid endarterectomy thrombosis for at least 48 hours. The plasma level of D-FPRCH2Cl during the infusion was maintained steady at 7.2 +/- 0.9 mumol/L, but decreased rapidly after discontinuing its infusion (T50 17 minutes). Platelet deposition, measured in real time using autologous 111In-platelet scintillation camera imaging, was 1.51 +/- 0.40 x 10(8) platelet/cm in the 14 treated animals 90 minutes postoperatively, compared with 11.7 +/- 1.16 x 10(8) platelet/cm in 14 heparin-treated controls (P < .002). The antithrombotic benefit was equivalent for treatment begun either 5 minutes before (nine animals) or 15 minutes after (five animals) reestablishing flow in the operated vessel, ie, 1.59 +/- 0.36 x 10(8) platelet/cm versus 1.35 +/- 0.51 x 10(8) platelet/min, respectively; P > .5. Endarterectomy thrombosis remained decreased for at least 48 hours postoperatively, as determined by the ratio between net 111In-platelet radioactivity at the endarterectomized site versus whole blood (ratio 0.82 +/- 0.25 in the treatment group v 3.03 +/- 0.51 in heparin controls at 90 minutes, P < .005; and 0.85 +/- 0.23 v 3.25 +/- 0.48 at 48 hours, P < .002). The marked reduction in endarterectomy thrombosis in treated animals at 48 hours was confirmed by scanning electron microscopy. Thrombin activity formed rapidly and became immediately bound to thrombus on thrombogenic segments in untreated control studies; treatment with D-FPRCH2Cl irreversibly inactivated the thrombus-bound thrombin. Hemostatic function, as measured by bleeding time (BT), activated partial thromboplastin time (APTT), and prothrombin time (PT) was impaired throughout the intravenous administration of D-FPRCH2Cl (BT > 30 minutes, APTT > 150 seconds, PT > 50 seconds); BT, APTT, and PT values were normal 30 minutes after discontinuing the infusions. As expected, blood loss into the surgical wound was substantial in nine animals receiving therapy initiated before restoring flow in the operated vessel (mean 95 mL, range 45 to 130 mL). By contrast, beginning D-FPRCH2Cl therapy in five animals 15 minutes after restoring arterial flow, a time when surgical hemostasis had been achieved, prevented excessive blood loss (mean 15 mL, range 10 to 35 mL; P < .01 compared with earlier treatment) without compromising the antithrombotic effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Interruption of vascular thrombus formation and vascular lesion formation by dietary n-3 fatty acids in fish oil in nonhuman primates

BACKGROUND

Because of discrepant claims regarding the relative biological effects of n-3 fatty acids (n-3FAs), we have concurrently measured the effects of dietary n-3FAs on blood and vascular lipid composition, hemostatic function, blood thrombotic responses, vascular thrombus formation, and vascular lesion formation in baboons.

METHODS AND RESULTS

Dietary n-3FAs displaced n-6FAs in plasma, platelets, blood vessels, and corresponding urinary eicosanoid metabolites (p < 0.01 in all cases) within weeks after initiation of a semipurified diet containing 1 g/kg per day n-3FA-ethyl ester concentrate (composed of two thirds eicosapentanoic acid and one third docosahexanoic acid). Coincidentally, platelet hemostatic function became minimally impaired (template bleeding times prolonged from 4.3 +/- 0.5 minutes to 7.6 +/- 1.3 minutes, p = 0.039); concentrations of collagen producing half-maximal platelet aggregation increased (from 6.4 +/- 2.1 to 8.5 +/- 2.5 micrograms/mL, p = 0.045); and tissue factor expression by endotoxin-stimulated blood monocytes fell (from 6.5 +/- 1.2 to 1.7 +/- 0.14 mU/10(6) cells, p < 0.005). Dietary n-3FAs decreased deposition of platelets onto thrombogenic segments of Dacron vascular graft incorporated into chronic exteriorized femoral arteriovenous (AV) shunts, a thrombotic process resistant to the effects of both aspirin and heparin (111In-labeled platelet deposition decreased from 14.1 +/- 1.4 x 10(9) platelets/5-cm segment at 40-60 minutes with occlusion to 7.5 +/- 0.8 x 10(9) platelets/5-cm segment without occlusion; p < 0.001). Platelet deposition onto segments of endarterectomized homologous normal aorta in the AV shunts of n-3FA-treated animals was similarly reduced (from 4.4 +/- 0.9 to 1.8 +/- 0.4 x 10(9) platelets; p < 0.01). Dietary n-3FAs interrupted vascular thrombus formation at sites of surgical carotid endarterectomy (platelet deposition, 1.5 +/- 0.4 versus 4.4 +/- 1.0 x 10(9) platelets in untreated controls; p < 0.001). Moreover, endarterectomized aortic segments (EASs) from n-3FA-treated donors exhibited little capacity to induce thrombus formation when tested in the AV shunts of control recipient animals (0.24 +/- 0.10 versus 4.4 +/- 0.90 x 10(9) platelets). However, in the converse crossover experiments, EASs from control animals actively accumulated platelets when studied in the AV shunts of n-3FA-treated animals (1.8 +/- 0.4 x 10(9) platelets; p < 0.01 versus n-3FA-treated EASs in shunts of normal animals). Dietary n-3FAs also abolished vascular lesion formation at sites of carotid endarterectomy 6 weeks after surgery (cross-sectional area of neointima 0.048 +/- 0.031 mm2 compared with 0.428 +/- 0.104 mm2 in control arteries; p = 0.010).

CONCLUSIONS

In nonhuman primates, dietary n-3FAs in high doses eliminate both vascular thrombus formation and vascular lesion formation after mechanical vascular injury while largely sparing hemostatic function and modestly reducing blood thrombotic responses. These effects are attributed to selective n-3FA-dependent alterations in cellular membrane functions.

Interruption of vascular thrombosis by bolus anti-platelet glycoprotein IIb/IIIa monoclonal antibodies in baboons

PURPOSE

Because the platelet membrane receptor glycoprotein IIb/IIIa plays a central role in the recruitment of platelets into forming thrombus, therapeutic inhibition of this receptor complex may be particularly useful to prevent thrombosis after small vessel arterial manipulation.

METHODS

The relative hemostatic safety and antithrombotic efficacy for thrombus formation at sites of endarterectomy and implanted prosthetic vascular graft of a murine monoclonal antibody (LJ-CP8) against platelet glycoprotein IIb/IIIa have been determined in baboons after bolus injections in doses (10 mg/kg) that block platelet receptor function for fibrinogen and other adhesive glycoproteins (absent platelet aggregation and bleeding times > 30 minutes without affecting circulating platelet counts).

RESULTS

Thrombus formation was eliminated by LJ-CP8 at sites of surgical endarterectomy in fresh segments of homologous aorta incorporated into chronic exteriorized arteriovenous femoral shunts (accumulation of indium 111-labeled platelets fell from 4.40 +/- 0.89 x 10(9) platelets/cm in control animals [n = 6] to 0.23 +/- 0.01 x 10(9) platelets/cm in treated animals [n = 4]; p < 0.005). The formation of thrombus was also abolished by LJ-CP8 at sites of 1 cm prosthetic vascular grafts (4 mm inner diameter polytetrafluoroethylene grafts) interposed into common carotid arteries (deposition of indium 111-labeled platelets decreased from 2.57 +/- 0.43 x 10(9) platelets/cm [n = 5] to 0.16 +/- 0.06 x 10(9) platelets/cm, [n = 4]; p = 0.004). However, LJ-CP8 injections produced substantial bleeding in the surgical wound during the first few hours after operation. Thirty days after operation all four graft implants were patent in JJ-CP8-treated animals compared with two of five in control animals (p = 0.06).

CONCLUSIONS

We conclude that profound inhibition of platelet glycoprotein IIb/IIIa receptor function by single bolus injection of LJ-CP8 monoclonal antibody transiently abolishes platelet hemostatic function, eliminates acute thrombus formation at sites of endarterectomy and prosthetic vascular graft implants, and may improve vascular patency.

Antihemostatic and antithrombotic effects of monoclonal antibodies against von Willebrand factor in nonhuman primates

BACKGROUND

Because the adhesive glycoprotein von Willebrand Factor (vWF) mediates initial platelet attachment at sites of vascular injury and may also contribute to shear-dependent platelet thrombus formation, we have determined in vivo the relative antithrombotic efficacy and hemostatic safety of infusing murine monoclonal antibodies against vWF.

METHODS

In baboons with chronic arteriovenous shunts, thrombus formation was initiated by interposition of thrombogenic Dacron vascular grafts (VG) and endarterectomized baboon aortic segments (EAS). Thrombus formation on VG and EAS was assessed by use of real-time scintillation camera imaging of indium 111-labeled platelet deposition. In control and treated animals (anti-vWF antibody) platelet hemostatic competence was evaluated by means of serial measurements of platelet count, bleeding time, and ex vivo platelet aggregation in response to adenosine diphosphate and ristocetin.

RESULTS

Although bolus antibody infusions did not affect circulating platelet counts, bleeding times were immediately prolonged to 28 +/- 4 minutes (vs 4.7 +/- 0.4 minutes before treatment, p = 0.01). Bleeding times normalized within 24 hours after antibody administration. Platelet aggregation in response to adenosine diphosphate was unchanged by antibody therapy, whereas ristocetin-induced platelet aggregation was abolished acutely and remained impaired for 24 hours. Platelet deposition on VG after 60 minutes of exposure to flowing blood was 2.95 +/- 0.74 x 10(9) platelets/cm in six control animals as compared to 1.86 +/- 0.16 x 10(9) platelets/cm in five treated animals (p = 0.04). Similarly, platelet deposition on EAS averaged 4.40 +/- 0.89 x 10(9) platelets/cm in control studies and was reduced significantly by antibody therapy (1.52 +/- 0.50 x 10(9) platelets/cm, p = 0.02).

CONCLUSIONS

Despite profound interruption of platelet hemostatic functions, therapeutic targeting of vWF modestly inhibits platelet-dependent thrombosis.