Immersed finite element method and its applications to biological systems

This paper summarizes the newly developed immersed finite element method (IFEM) and its applications to the modeling of biological systems. This work was inspired by the pioneering work of Professor T.J.R. Hughes in solving fluid-structure interaction problems. In IFEM, a Lagrangian solid mesh moves on top of a background Eulerian fluid mesh which spans the entire computational domain. Hence, mesh generation is greatly simplified. Moreover, both fluid and solid domains are modeled with the finite element method and the continuity between the fluid and solid subdomains is enforced via the interpolation of the velocities and the distribution of the forces with the reproducing Kernel particle method (RKPM) delta function. The proposed method is used to study the fluid-structure interaction problems encountered in human cardiovascular systems. Currently, the heart modeling is being constructed and the deployment process of an angioplasty stent has been simulated. Some preliminary results on monocyte and platelet deposition are presented. Blood rheology, in particular, the shear-rate dependent de-aggregation of red blood cell (RBC) clusters and the transport of deformable cells, are modeled. Furthermore, IFEM is combined with electrokinetics to study the mechanisms of nano/bio filament assembly for the understanding of cell motility.

Experience with the Edwards MIRA mechanical bileaflet valve in the aortic and mitral positions

The Edwards MIRA bileaflet mechanical prosthesis, a heart valve not yet available in the United States, is designed with a unique hinge mechanism, curved leaflets, and thin titanium housing. We performed this study to investigate its clinical performance and postoperative hemodynamic results. We implanted 58 Edwards MIRA prostheses in 51 patients in the aortic (n = 18), mitral (n = 26), and aortic and mitral (n = 7) positions. Patients' ages ranged from 25 to 84 years (mean age, 53.7 +/- 13.6). Operative mortality was 2% (n = 1), and late mortality was 4% (n = 2). Thromboembolic events were observed in 2 patients (valve thrombosis in 1 and a cerebrovascular event in 1). There were no complications related to anticoagulation. No signs of valvular dysfunction or paravalvular leakage were observed. Peak transvalvular gradients of the aortic prostheses ranged from 24.25 +/- 5.32 mmHg for the 21-mm valve to 11 +/- 1.41 mmHg for the 25-mm valve. The effective orifice area ranged from 1.99 +/- 0.12 cm2 for the 21-mm valve to 2.44 +/- 0.17 cm2 for the 25-mm valve. The mean transvalvular gradients of the mitral prostheses ranged from 5.85 +/- 2.91 mmHg for the 27-mm valve to 4.5 +/- 0 mmHg for the 31-mm valve. The effective orifice area ranged from 2.31 +/- 0.03 cm2 for the 27-mm valve to 2.64 +/- 0.05 cm2 for the 33-mm valve. These preliminary data suggest good hemodynamic function and a low rate of valve-related complications in the use of the Edwards MIRA mechanical prosthesis.

Daughter, you broke my heart: accidental thrombosis at a muscular bridge

We report the case of a 59-year-old trained runner, who sustained an acute myocardial infarction, with residual effort angina, following extreme exertion while experiencing severe anxiety. Coronary angiography revealed that this patient had a myocardial bridge at the mid-left anterior descending artery, and an occlusive clot had developed at the proximal end of the muscular bridge. We discuss the possible relationships between the various circumstances of this sudden event. We argue that, under exceptional conditions, myocardial bridges can lead to myocardial infarction by clot formation.

Quantitative gene expression in Budd-Chiari syndrome: a molecular approach to the pathogenesis of the disease

BACKGROUND

Budd-Chiari syndrome (BCS) is associated with parenchymal changes leading to major architecture remodelling. In order to gain further insight into the pathogenesis of BCS, we investigated expression of a set of genes involved in the course of chronic liver diseases.

METHODS

Quantitative expression of 35 selected genes involved in extracellular matrix regulation, growth factors, and angiogenesis was investigated in 13 cases of BCS and compared with 10 normal livers and 13 cirrhosis cases by real time reverse transcription-polymerase chain reaction. Differential gene expression was considered significant for genes showing at least a twofold variation, with p < 0.05.

RESULTS

Expression of 14 genes was significantly increased in BCS versus normal liver, with the highest increase in superior cervical ganglion 10 (SCG10) gene. BCS cases were classified according to their evolution and morphological pattern as either acute or chronic in six and seven cases, respectively. Unsupervised hierarchical clustering of acute and chronic BCS cases on the basis of similarity in gene expression pattern led to distinction between the two groups. Expression of three genes was significantly different in acute versus chronic BCS (increase in matrix metalloproteinase 7 and SCG10, decrease in thrombospondin-1 for chronic BCS). Seventeen and 10 genes, mainly involved in extracellular matrix and vascular remodelling, were significantly deregulated in acute BCS versus normal liver and cirrhosis, respectively.

CONCLUSION

These results show that BCS cases display a specific gene expression profile that is different from that of normal liver and cirrhosis; the molecular configuration of BCS can be readily distinguished by its evolution and morphological pattern.

Cardiopulmonary bypass using argatroban as an anticoagulant for a 6.0-kg pediatric patient

A patient was born with transposition of the great arteries, double-outlet right ventricle, interrupted aortic arch, and a ventricular septal defect and underwent a Damus-Kaye-Stansel procedure with a modified Blalock-Taussig shunt at 14 days old. Three months later, this patient presented with hypoxia and bradycardia was found to have a thrombus present in the main pulmonary artery extending to right pulmonary artery. After initiation of thrombolytic therapy, the patient became severely hypoxic and required the institution of extracorporeal membrane oxygenation. As the result of unknown heparin resistance independent of adequate antithrombin III levels, argatroban therapy was used to achieve desired anticoagulation. The patient was taken to the operating room and converted to conventional cardiopulmonary bypass once adequate activated clotting times were achieved using argatroban. This case report summarizes the use of argatroban as an anticoagulant for a 6.0-kg pediatric patient undergoing cardiopulmonary bypass.

The emergency use of recombinant hirudin in cardiopulmonary bypass. 1999

The most common anticoagulant used for cardiopumonary bypass is heparin. An alternate form of anticoagulant therapy is needed for patients who have immune-mediated heparin-associated thrombocytopenia (HIT). Thrombocytopenia causes bleeding and may lead to serious arterial and venous thrombosis. HIT or heparin-induced thrombocytopenia with thrombosis type II (HITT) are both described as adverse reactions to heparin. They are diagnosed with a platelet count less than a 100,000/mcl for 2 consecutive days. HITT, the severe form, is characterized with the thrombocytopenia in combination with thromboembolic complications, such as strokes, myocardial infarctions, and limb ischemia. Two cases are presented in which r-hirudin was used for anticoagulation for aortocoronary bypass surgery and mitral valve replacement. The activated partial prothrombin time (aPTT) was used to monitor coagulation. In the first case, the aPTT was maintained greater than 100 seconds, and at the termination of cardiopulmonary bypass, some clot was noted in the cardiopulmonary bypass circuit. In the second case, a longer cardiopulmonary bypass run was anticipated, the hirudin bolus and infusion rate were increased, and the aPTT was maintained at greater than 200 sec. Adequate coagulation resulted, and, at the end of bypass, no clot was noted. These case studies seem to suggest a higher dosage of r-hirudin may be required for the use of cardiopulmonary bypass and a need to maintain aPTT values greater than 200 sec to help monitor anticoagulation.

Cardiopulmonary bypass in patients with pre-existing coagulopathy

Patients with pre-existing coagulopathies who undergo surgical interventions are at increased risk for bleeding complications. This risk is especially true in cardiac surgical procedures with cardiopulmonary bypass (CPB) because of the necessity for heparinization and the use of the extracorporeal circuits, which have destructive effects on most of the blood components. In this review, cases of cardiac surgeries in patients with certain pre-existing coagulopathies are summarized, which could shed a light on future managements of such patients undergoing cardiac procedures with CPB. Pre-existing coagulopathies include antithrombin III deficiency, heparin-induced thrombocytopenia, cancer, factor XII deficiency, hemophilia, idiopathic thrombocytopenic purpura, protein S deficiency, and drug-induced platelet inhibition. In summary, pre-existing coagulopathy in patients undergoing open-heart surgeries, if not recognized and appropriately managed, can cause serious complications. Management of patients undergoing cardiac procedures should include a routine coagulation work-up and a thorough past medical history examination. If any of the foregoing is abnormal, further evaluation is warranted. Proper diagnosis and management of the pre-existing coagulopathy disorders is of crucial importance to the surgical outcome and long-term morbidity.

Prognostic factors for amputation or death in patients submitted to vascular surgery for acute limb ischemia

OBJECTIVE

To investigate the risk profile of patients with thrombosis and emboli, and prognostic factors for death or amputation in patients presenting with acute limb ischemia in a tertiary care regional hospital in Brazil.

METHODS

A prospectively planned cohort study was carried out in which 83 patients with acute limb ischemia, secondary to thrombosis, or embolism, classified in stages II and III of severity were evaluated. Univariate analysis and logistic regression models were used to explore the relationship between anthropometric and demographic characteristics, comorbidities, cardiovascular risk factors, duration of occlusion, and type of surgery with the incidence of amputation or death, which were evaluated in 30 days and 1 year thereafter.

RESULTS

Male gender, smoking, and comorbidities were more frequent among patients with thrombosis, and atrial fibrillation was more common among patients with embolism. Occlusion longer than 24 hours (odds ratio [OR] 2.6, 95% confidence interval [CI] 1.1-7.6) and a trend for diabetes (RR 2.6, 95% CI 0.9-7.5) were the characteristics associated with death or amputation in the multivariate analysis, which occurred in 15 (18.1%) and 24 (28.9%) of the participants, respectively. Reperfusion injury was a risk factor for death but not for amputation (OR 16.9, 95% CI 1.1-232.9) after adjustment for age, duration of occlusion, and diabetes.

CONCLUSIONS

Traditional and avoidable risk factors explain the occurrence of thrombosis and embolism in our region. Access to medical care is the most important and modifiable prognostic factor for death or amputation.

Genetic thrombophilia has pleiotropic effects in pregnancy

Genetic thrombophilia has been established as a risk factor for pregnancy-associated disorders, such as thrombosis, early and late miscarriage, and pre-eclampsia. Associations between the factor V (F5) Leiden G1691A and the prothrombin/factor II (F2) G20210A SNPs and pre-eclampsia have been evaluated in over 50 association studies. A pooled analysis of 23 and 11 studies demonstrates that carriage of the F5 Leiden G1691A (p < 0.001; odds ratio [OR] 2.0; 95% confidence interval [CI] 1.6-2.5) and the F2 G20210A (p < 0.001; OR 1.8; 95% CI 1.1-2.9) SNPs is significantly associated with pre-eclampsia. Besides pre-eclampsia, genotyping for the F5 Leiden G1691A and the F2 G20210A SNPs is also useful for individual risk assessment regarding pregnancy-associated thrombosis. Carriers of the F5 Leiden G1691A SNP will develop this condition in 6.4% of heterozygotes and in 8.9-16.7% of homozygotes. A total of 6.2% of women with the F2 G20210A SNP and 17.8% of women with simultaneous carriage of the F5 Leiden G1691A and F2 G20210A SNPs will develop pregnancy-associated thrombosis. Both the F5 Leiden G1691A and F2 G20210A SNPs are also risk factors of early recurrent, late recurrent and late spontaneous miscarriage based on a published meta-analysis of 31 studies. These women may benefit from prophylactic heparinization. Six case-control and cohort studies of 687 women with genetic thrombophilia document live birth rates of 82% (181/221) using low-molecular-weight heparin or fractionated heparin compared with 20% (95/466) without therapy (p < 0.001, OR 17.7; 95% CI 12.2-25.5). Based on the data in the literature, including association studies and meta-analyses of these association studies, it can be concluded that genetic thrombophilia due to carriage of the F5 Leiden G1691A and F2 G20210A SNPs is a significant and clinically relevant risk factor for pre-eclampsia, pregnancy-associated thrombosis, and early and late miscarriages.

Percutaneous management of thrombosed dialysis access grafts

This article reviews current concepts in the percutaneous management of thrombosed polytetrafluoroethylene (PTFE) dialysis access grafts. The maintenance of dialysis access grafts remains a challenging task. Graft surveillance is critical in the prevention of graft thrombosis to prolong graft survival. Once a graft is thrombosed, surgical and percutaneous options are available for restoration of flow. There has been an evolution in the percutaneous treatment of thrombosed dialysis access grafts during the last 20 years, with refinement of pharmacomechanical techniques, allowing for safe and efficacious restoration of flow in thrombosed grafts. There has been emergence of alternative thrombolytic agents to urokinase, which was withdrawn from the United States in late 1998 and recently reintroduced. These alternative thrombolytic agents have similar outcomes compared with urokinase, with the additional advantage of being less expensive. In addition, several mechanical devices, which were popular briefly when urokinase was unavailable, are available currently for use within grafts, with similar success, although their prices have limited widespread use.

MRI of coronary artery atherosclerosis in rabbits: Histopathology-MRI correlation and atheroma characterization

BACKGROUND AND OBJECTIVES: We report in vivo magnetic resonance imaging (MRI) characteristics and histopathology correlation of the thrombus formation in atherosclerosis the rabbit animal model. DESIGN AND METHODS: Atherosclerosis was induced in white male rabbits with vegetable ghee followed oxidized diet. Baseline MRI of atherosclerosis-recruited rabbits was done and later animals were used for atheroma histopathology characterization. Contiguous cross-sectional T2-weighted fast spin echo MRI images were compared by coronary histopathology. In all animals, coronary aortic wall thickening and atheroma size was measured using MRI. RESULTS: MRI images and digitized histological sections confirmed intraluminal thrombus in 6 (67%) of the 9 animals. MRI data showed correlation with the histopathology for aortic wall thickness (R2 = 0.82, P < 0.0001), lumen area (R2 = 0.88, P < 0.0001) and plaque size (R2 = 0.77, P < 0.0001). Optimized TE and TR parameters and multicontrast enhancement generated better MRI visibility of vulnerable plaque components. The MRI data evaluated % stenosis, plaque burden. Frequency of plaques, plaque height in aorta and coronary artery atheroma was also assessed by histology. In vivo, MRI determined the presence and size of the thrombus in this animal model of atherosclerosis and histopathology defined the plaque disruption. CONCLUSION: The combination of in vivo MRI and comparison with histopathology images of rabbit coronary thrombus may be a research tool for understanding of the pathogenesis of acute coronary plaques.

Is inflammatory bowel disease an independent and disease specific risk factor for thromboembolism?

BACKGROUND

Patients with inflammatory bowel disease (IBD) are thought to be at increased risk of venous thromboembolism (TE). However, the extent of this risk is not known. Furthermore, it is not known if this risk is specific for IBD or if it is shared by other chronic inflammatory diseases or other chronic bowel diseases.

AIMS

To compare the risk of TE in patients with IBD, rheumatoid arthritis, and coeliac disease with matched control subjects.

PATIENTS AND METHODS

Study subjects answered a questionnaire assessing the history of TE, any cases of which had to be confirmed radiologically. A total of 618 patients with IBD, 243 with rheumatoid arthritis, 207 with coeliac disease, and 707 control subjects were consecutively included. All three patient groups were compared with control subjects matched to the respective group by age and sex.

RESULTS

Thirty eight IBD patients (6.2%) had suffered TE. This was significantly higher compared with the matched control population with only 10 cases reported (1.6%) (p<0.001; odds ratio (OR) 3.6 (95% confidence interval (CI) 1.7-7.8)). Five patients with rheumatoid arthritis (2.1%) had suffered TE compared with six subjects (2.5%) in the control population matched to patients with rheumatoid arthritis (NS; OR 0.7 (95% CI 0.2-2.9)). TE had occurred in two patients with coeliac disease (1%) compared with four subjects (1.9%) in the control population matched to the coeliac disease group (NS; OR 0.4 (95% CI 0.1-2.5)). In 60% of TE cases in the IBD group, at least one IBD specific factor (active disease, stenosis, fistula, abscess) was present at the time TE occurred.

CONCLUSIONS

IBD is a risk factor for TE. It seems that TE is a specific feature of IBD as neither rheumatoid arthritis, another chronic inflammatory disease, nor coeliac disease, another chronic bowel disease, had an increased risk of TE.

Postoperative nadroparin administration for prophylaxis of thromboembolic events is not associated with an increased risk of hemorrhage after spinal surgery

AIM

To determine the risk of postoperative hemorrhage during a 3-year period of early postoperative administration of nadroparin (Fraxiparin) plus compression stockings in a large cohort of patients who underwent spinal surgery.

METHODS

A total of 1,954 spinal procedures at different levels (503 cervical, 152 thoracic and 1,299 lumbar), performed between June 1999 and 2002 at the Department of Neurosurgery, Johann-Wolfgang-Goethe University Frankfurt, were included in this study. To prevent venous thromboembolic events (VTE), all patients were routinely treated subcutaneously with 0.3 ml of early (less than 24 h) postoperative nadroparin calcium (Fraxiparin) (2850 IU anti-Xa, Sanofi Winthrop Industrie, France) plus intra- and postoperative compression stockings until discharge. The occurrence of a postoperative hematoma (defined as a hematoma requiring surgical evacuation because of space occupation and/or neurological deterioration) and a deep venous thrombosis (DVT) were recorded in a database and analyzed retrospectively.

RESULTS

13 (0.7%) of the 1,954 spinal operations were complicated by major postoperative hemorrhages. In 5 of the 13 patients (38.5%) the hemorrhage occurred on the day of surgery before the administration of nadroparin. Thus, the hemorrhage rate of patients receiving nadroparin was 0.4% (8/1,949). Ten (77%) of the 13 patients with major postoperative hematoma showed a progressive neurological deficit, which resolved in 6 patients and resulted in a hematoma-related morbidity of 31% (4/13). Only 1 patient (0.05%) in this series developed a clinically evident DVT, and none of the patients suffered from pulmonary embolus during the hospital stay.

CONCLUSION

Although retrospective, this is to date the largest study providing information about the hemorrhage rate associated with early postoperative anticoagulation following spinal surgery. The results confirm that early postoperative pharmacological thromboembolic prophylaxis using nadroparin in patients with spinal surgery is not associated with an increased risk of postoperative hemorrhage.

The presence of multiple prothrombotic risk factors is associated with a higher risk of thrombosis in individuals with anticardiolipin antibodies

OBJECTIVE

To explore the effect of multiple prothrombotic risk factors in individuals with anticardiolipin antibodies (aCL), we evaluated immunologic, coagulation, and genetic prothrombotic abnormalities in a cohort of individuals with different aCL titers.

METHODS

We recruited 87 individuals into 4 categories (normal, low, intermediate, or high) based on their baseline IgG aCL (aCL-IgG) titers. We measured at followup: repeat aCL-IgG, IgM aCL (aCL-IgM), antibodies to beta2-glycoprotein I (anti-beta2-GPI), lupus anticoagulant (LAC) antibodies, protein C, protein S, activated protein C resistance, factor V506 Leiden mutation, methyl tetrahydrofolate reductase (MTHFR) C677T genotype, and prothrombin 20210A gene mutation. Thrombotic events were confirmed.

RESULTS

At recruitment, 20 individuals were negative for aCL-IgG and 67 were positive (22 low, 20 intermediate, and 25 high titer). Twenty of the 87 participants had experienced a previous thrombotic event: 4 in the aCL-IgG negative group and 16 in the aCL-IgG positive group. Among the 87 individuals, the number of those with concomitant prothrombotic risk factors was as follows: 5 had no other prothrombotic risk factors, 32 had 1 risk factor, 24 had 2 risk factors, 10 had 3 risk factors, 10 had 4 risk factors, and 6 had 5 risk factors. Thrombotic events were observed in 20%, 13%, 33%, 10%, 30%, and 50% of these groups, respectively, and the odds ratio associated with a previous thrombotic event was 1.46 per each additional prothrombotic risk factor (95% confidence interval: 1.003-2.134).

CONCLUSION

In individuals with positive aCL-IgG, we observed an association between the number of prothrombotic risk factors and history of thrombotic events.

Thrombotic occlusion of Bjork-Shiley prosthetic aortic valve

Thrombotic occlusion of a prosthetic Bjork-Shiley valve is a potentially fatal complication. We present the case of a male, 62 years of age, diagnosed with thrombotic occlusion of prosthetic Bjork-Shiley aortic valve approximately 17 years post implantation. A brief review of the literature focusing on potential risk factors associated with the development of this condition and currently available diagnostic modalities used for evaluation and treatment are presented.

Between the devil and the deep blue sea: an unusual kind of late cardiac tamponade with a therapeutic dilemma

A 67-year-old patient underwent a left pneumectomy because of a moderately differentiated squamous cell carcinoma. Two weeks later, while still in hospital, he suddenly experienced an acute increase in dyspnoea. Pulmonary embolism was considered. However, echocardiography showed compression of the right ventricle and right atrium by an intrapericardial mass, confirmed by computed tomography. Following signs of a large thrombus in the inferior vena cava, pericardiocentesis was considered undesirable due to possible dislocation resulting from the sudden changes in intrapericardial pressure. Re-thoracotomy was equally undesirable because of the recent operation and status of the patient. After stabilisation and extensive consulting the patient was referred for pericardiocentesis by sternotomy. Huge blood clots were removed from the pericardial space. No thrombus mass was found in the inferior vena cava. The patient recovered uneventfully.

Inflammatory and thrombotic mechanisms in coronary atherosclerosis

Many molecular and cellular mechanisms link inflammation and haemostatic mechanisms. Inflammation, and perhaps chronic infection, may play important roles in the initiation and progression of atherosclerosis. Atherosclerotic lesions are heavily infiltrated by cellular components associated with inflammation (macrophages and T lymphocytes), and acute plaque rupture is also associated with inflammatory components. Several markers of systemic inflammation may predict future cardiovascular events in apparently healthy subjects as well as in patients with chronic and acute syndromes. There may thus be therapeutic potential in modifying the atherosclerotic, vasomotor, and thrombotic components of ischaemic heart disease.

Chronic venous disease in an ethnically diverse population: the San Diego Population Study

In a 1994-1998 cross-sectional study of a multiethnic sample of 2,211 men and women in San Diego, California, the authors estimated prevalence of the major manifestations of chronic venous disease: spider veins, varicose veins, trophic changes, and edema by visual inspection; superficial and deep functional disease (reflux or obstruction) by duplex ultrasonography; and venous thrombotic events based on history. Venous disease increased with age, and, compared with Hispanics, African Americans, and Asians, non-Hispanic Whites had more disease. Spider veins, varicose veins, superficial functional disease, and superficial thrombotic events were more common in women than men (odds ratio (OR) = 5.4, OR = 2.2, OR = 1.9, and OR = 1.9, respectively; p < 0.05), but trophic changes and deep functional disease were less common in women (OR = 0.7 for both; p < 0.05). Visible (varicose veins or trophic changes) and functional (superficial or deep) disease were closely linked; 92.0% of legs were concordant and 8.0% discordant. For legs evidencing both trophic changes and deep functional disease, the age-adjusted prevalences of edema, superficial events, and deep events were 48.2%, 11.3%, and 24.6%, respectively, compared with 1.7%, 0.6%, and 1.3% for legs visibly and functionally normal. However, visible disease did not invariably predict functional disease, or vice versa, and venous thrombotic events occurred in the absence of either.

Thromboembolic risk in patients with high titre anticardiolipin and multiple antiphospholipid antibodies

Asymptomatic antiphospholipid antibody (aPL) carriers with high risk for thrombosis may benefit from preventive anticoagulation. It was our objective to test whether the risk of thrombosis increases with: 1). increasing titres of anticardiolipin antibodies (aCL) after adjustment for other cardiovascular risk factors and 2). the number of aPL detected. In a cross-sectional study, blood was collected from clinics in two teaching hospitals. The study included 208 individuals suspected of having an aPL and 208 age- and sex-matched controls having blood drawn for a complete blood count. Clinical variables included history of previous arterial (ATE) or venous (VTE) thrombotic events, traditional risk factors for cardiovascular disease, and systemic lupus erythematosus (SLE). Laboratory variables included IgG/IgM aCL, lupus anticoagulant, and IgG/IgM anti-beta2-glycoprotein I. Mean age was 46.5 years and 83% were female. Seventy-five of the 416 participants had >or= 1 aPL, and 69 had confirmed >or= 1 ATE or VTE. Family history was positive in 48% of participants, smoking in 28%, hypertension in 16%, diabetes in 6%, and SLE in 20%. A 10-unit increase in aCL IgG titre was associated with an odds ratio (OR) [95% CI] of 1.07 [1.01-1.13] for ATE and 1.06 [1.02-1.11] for VTE. The odds of a previous thrombosis increased with each additional aPL detected: 1.5 [0.93-2.3] for ATE and 1.7 [1.1-2.5] for VTE. These results indicate that increased titres of aCL and multiple aPL were associated with an increased risk of a previous thrombotic event.

Accumulation of tissue factor into developing thrombi in vivo is dependent upon microparticle P-selectin glycoprotein ligand 1 and platelet P-selectin

Using a laser-induced endothelial injury model, we examined thrombus formation in the microcirculation of wild-type and genetically altered mice by real-time in vivo microscopy to analyze this complex physiologic process in a system that includes the vessel wall, the presence of flowing blood, and the absence of anticoagulants. We observe P-selectin expression, tissue factor accumulation, and fibrin generation after platelet localization in the developing thrombus in arterioles of wild-type mice. However, mice lacking P-selectin glycoprotein ligand 1 (PSGL-1) or P-selectin, or wild-type mice infused with blocking P-selectin antibodies, developed platelet thrombi containing minimal tissue factor and fibrin. To explore the delivery of tissue factor into a developing thrombus, we identified monocyte-derived microparticles in human platelet-poor plasma that express tissue factor, PSGL-1, and CD14. Fluorescently labeled mouse microparticles infused into a recipient mouse localized within the developing thrombus, indicating that one pathway for the initiation of blood coagulation in vivo involves the accumulation of tissue factor- and PSGL-1-containing microparticles in the platelet thrombus expressing P-selectin. These monocyte-derived microparticles bind to activated platelets in an interaction mediated by platelet P-selectin and microparticle PSGL-1. We propose that PSGL-1 plays a role in blood coagulation in addition to its known role in leukocyte trafficking.

Transverse sinus thrombosis and IVIg treatment: a case report and discussion of risk-benefit assessment for immunoglobulin treatment

A 54 year old woman presented with symptoms resulting from a thrombosis of the lateral transverse and sagittal sinuses the day after an infusion of intravenous immunoglobulin (IVIg) replacement treatment. She had previously suffered a milder episode after IVIg. Following recurrent bacterial chest infections and sinusitis for more than 40 years, a diagnosis of IgG1 deficiency had been made two years earlier, after exclusion of other causes. She made a good recovery from the thrombosis but high platelet counts were investigated and primary thrombocythaemia was diagnosed. Investigation of humoral immunity revealed protective amounts of IgG antibodies to pathogens, and because the previous IgG1 deficiency had resolved IVIg infusions were not restarted. She made a good response to treatment with hydroxyurea, with improvement of the headaches and lowering of the platelet counts. Prophylactic antibiotics reduced the number of bacterial chest infections and nasal corticosteroids improved the chronic sinusitis. This case is presented to highlight the need to look for other contributing factors for severe recurrent headaches after IVIg treatment, and to consider the risk of thrombosis even when replacement doses of IVIg are used. It is also important to emphasise the need to ensure that an isolated IgG subclass deficiency is not transient; that failure to produce specific IgG antibodies to immunisation and/or exposure antigens is confirmed, thus meeting the criteria for the diagnosis of primary antibody deficiency. A thorough risk-benefit assessment is essential before blood product treatment is started.

An unusual complication of prostatic bony metastases

Carcinoma of the prostate is a common condition and often spreads to bone. We describe the imaging findings in two patients with known carcinoma of the prostate who presented with visual disturbance (both had papilloedema on examination). MRI showed occipital bone metastases and superior sagittal sinus thrombosis. We suggest that MRI is the imaging modality of choice in patients suffering from prostate cancer who have visual disturbance and that MRV sequences should be included to detect venous sinus thrombosis.

Diagnostic value of D-dimer and antithrombin-III levels in predicting prosthetic heart valve thrombosis

The aim of this prospective study was to investigate the diagnostic value of plasma D-dimer levels and antithrombin-III activity in predicting prosthetic valve thrombus. The study group comprised 97 consecutive patients with prosthetic heart valves (59 with mitral, 21 with aortic, and 17 with both mitral and aortic prostheses) and 35 healthy control subjects. Six patients presented with symptoms of obstruction; the remaining 91 were asymptomatic. Patients were evaluated by both transthoracic and transesophageal echocardiography. Asymptomatic nonobstructive thrombus was detected in 13 patients (13%), whereas obstructive thrombus was demonstrated in all symptomatic patients. Plasma antithrombin-III levels of patients with prosthetic valve thrombi were slightly lower than those of patients without thrombus and of the control group, but the difference was not statistically significant. However, significantly higher plasma D-dimer levels were observed in patients with prosthetic valve thrombi, compared with patients without thrombus and the control group (735 +/- 633 microg/L, 372 +/- 342 microg/L, and 228 +/- 219 microg/L, respectively). Valve thrombus, the prosthetic heart valve itself, and INR levels were identified as major determinants of plasma D-dimer levels. A plasma D-dimer level of >445 microg/L predicted the presence of a prosthetic valve thrombus with 57.8% sensitivity and 83.3% specificity (positive predictive value, 47.8%; negative predictive value, 87.8%). Current data suggest that increased plasma D-dimer levels can be clinically helpful in predicting the presence of prosthetic valve thrombus. Plasma antithrombin-III activity does not seem to have a diagnostic value in predicting prosthetic valve thrombi.

COX-2: where are we in 2003?--distinction from NSAIDs becoming blurred

The distinction between cyclooxygenase-2-selective inhibitors (CSIs) and nonsteroidal anti-inflammatory drugs ultimately must be clinical and must be clinically and economically relevant. This distinction needs to be demonstrated in a substantial and clinically relevant difference in the respective rates of serious adverse reactions of the upper gastrointestinal tract. Event-driven, randomized, blinded, controlled trials with sufficient power are required to resolve uncertainties concerning the relative risk of thrombotic cardiovascular events in patients taking CSIs who have risk factors for these events. Patients and situations more representative of those in primary-care practice - elderly, comorbidities, comedication - need to be included in larger studies to provide a better understanding of the risks and benefits of CSIs.

The hypercoagulable state of malignancy: pathogenesis and current debate

A hypercoagulable or prothrombotic state of malignancy occurs due to the ability of tumor cells to activate the coagulation system. It has been estimated that hypercoagulation accounts for a significant percentage of mortality and morbidity in cancer patients. Prothrombotic factors in cancer include the ability of tumor cells to produce and secrete procoagulant/fibrinolytic substances and inflammatory cytokines, and the physical interaction between tumor cell and blood (monocytes, platelets, neutrophils) or vascular cells. Other mechanisms of thrombus promotion in malignancy include nonspecific factors such as the generation of acute phase reactants and necrosis (i.e., inflammation), abnormal protein metabolism (i.e., paraproteinemia), and hemodynamic compromise (i.e., stasis). In addition, anticancer therapy (i.e., surgery/chemotherapy/hormone therapy) may significantly increase the risk of thromboembolic events by similar mechanisms, e.g., procoagulant release, endothelial damage, or stimulation of tissue factor production by host cells. However, not all of the mechanisms for the production of a hypercoagulable state of cancer are entirely understood. In this review, we attempt to describe what is currently accepted about the pathophysiology of the hypercoagulable state of cancer. We also discuss whether or not to screen patients with idiopathic deep venous thrombosis for an underlying malignancy, and whether this would be beneficial to patients. It is hoped that a better understanding of these mechanisms will ultimately lead to the development of more targeted treatment to prevent thromboembolic complications in cancer patients. It is also hoped that antithrombotic strategies may also have a positive effect on the process of tumor growth and dissemination.

Plaque composition in plexogenic and thromboembolic pulmonary hypertension: the critical role of thrombotic material in pultaceous core formation

BACKGROUND

Patients with pulmonary hypertension develop intimal plaques in large pulmonary arteries.

OBJECTIVE

To test the hypothesis that the composition of such plaques differs depending on whether the aetiology of the disease is thromboembolic or hypertensive.

DESIGN

Chronic thromboembolic and plexogenic pulmonary hypertension (primary and secondary (Eisenmenger syndrome)) were investigated. These are spontaneous human models and were used to examine the independent role of thrombus and hypertension in plaque composition.

SETTING

A national tertiary referral centre for lung transplantation and pulmonary thromboendoarterectomy.

PATIENTS

Thirty nine patients with chronic thromboembolic pulmonary hypertension who had undergone thromboendoarterectomy (n = 32) or lung transplantation (n = 7), 28 with plexogenic diseases (nine primary and 19 Eisenmenger), and three with Eisenmenger syndrome complicated by thromboembolic events.

INTERVENTIONS

The lung and thromboendoarterectomy samples were sectioned, stained with Movat pentachrome, and immunostained with antibodies for fibrin, platelets, inflammatory cells, smooth muscle cells, and erythrocyte membrane glycophorin A.

MAIN OUTCOME MEASURE

Composition of the plaques affecting large pulmonary arteries.

RESULTS

Two types of intimal lesion were distinguished in chronic thromboembolic pulmonary hypertension: fibrous plaques with angioneogenesis; and core-rich atherosclerotic plaques with pultaceous cores largely consisting of glycophorin immunoreactive material, with cholesterol clefts (61.5%), CD68 positive macrophages (84.6%), T lymphocytes (87%), and calcification (46.1%). The samples from the patients with Eisenmenger syndrome and thromboembolic complications had similar characteristics, whereas those from patients with uncomplicated primary pulmonary hypertension had core-free fibrous plaques, spotted with macrophages and T lymphocytes.

CONCLUSIONS

Chronic thromboembolic pulmonary hypertension is associated with atherosclerotic plaques with glycophorin-rich pultaceous cores, and plexogenic pulmonary hypertension with fibrous plaques. Thromboembolic material thus plays a critical role in the formation of pultaceous cores, of which erythrocyte membrane derived glycophorin is a major component.

Relation between early mitral regurgitation and left ventricular thrombus formation after acute myocardial infarction: results of the GISSI-3 echo substudy

OBJECTIVE

To evaluate the prevalence and correlates of left ventricular thrombosis in patients with acute myocardial infarction, and whether the occurrence of early mitral regurgitation has a protective effect against the formation of left ventricular thrombus.

DESIGN AND SETTING

Multicentre clinical trial carried out in 47 Italian coronary care units.

PATIENTS AND METHODS

757 patients from the GISSI-3 echo substudy population with their first acute myocardial infarct were studied by echocardiography at 24-48 hours from symptom onset (S1), at discharge (S2), at six weeks (S3), and at six months (S4). The diagnosis of left ventricular thrombosis was based on the detection of an echo dense mass with defined margins visible throughout the cardiac cycle in at least two orthogonal views.

RESULTS

In 64 patients (8%), left ventricular thrombosis was detected in one or more examinations. Compared with the remaining 693 patients, subjects with left ventricular thrombosis were older (mean (SD) age: 64.6 (13.0) v 59.8 (11.7) years, p < 0.005), and had larger infarcts (extent of wall motion asynergy: 40.9 (11.5)% v 24.9 (14)%, p < 0.001), greater depression of left ventricular ejection fraction at S1 (43.3 (6.9)% v 48.1 (6.8)%, p < 0.001), and greater left ventricular volumes at S1 (end diastolic volume: 87 (22) v 78 (18) ml/m(2), p < 0.001; end systolic volume: 50 (17) v 41 (14) ml/m(2), p < 0.001). The prevalence of moderate to severe mitral regurgitation on colour Doppler at S1 was greater in patients who had left ventricular thrombosis at any time (10.2% v 4.2%, p < 0.05). On stepwise multiple logistic regression analysis the only independent variables related to the presence of left ventricular thrombosis were the extent of wall motion asynergy and anterior site of infarction.

CONCLUSIONS

Left ventricular thrombosis is not reduced, and may even be increased, by early moderate to severe mitral regurgitation after acute myocardial infarction. The only independent determinant of left ventricular thrombosis is the extent of the akinetic-dyskinetic area detected on echocardiography between 24-48 hours from symptom onset.

Fibrinogen E fragment selectively disrupts the vasculature and inhibits the growth of tumours in a syngeneic murine model

We recently demonstrated that a fragment of human fibrinogen, fibrinogen E fragment, inhibits the migration and differentiation of human endothelial cells in vitro. Here we show that it exerts similar effects on murine endothelial cells in vitro, and selectively disrupts tumour endothelium in vivo, causing widespread intravascular thrombosis and retarding the growth of CT26 tumours in a syngeneic murine model.

Polyethylene glycol diisocyanate decreases platelet deposition after balloon injury of rabbit femoral arteries

BACKGROUND

Platelet deposition after angioplasty remains problematic and may contribute to intimal hyperplasia and restenosis. We proposed that polyethylene glycol diisocyanate (PEG-DISO), a polymer that rapidly forms covalent linkages with amine residues on proteins, could mask thrombogenic vascular wall proteins from platelets, thereby abrogating acute platelet deposition.

METHODS AND RESULTS

To test this hypothesis, we isolated the femoral arteries of 10 New Zealand White rabbits and injured them with 3 passes of a 2F Fogarty catheter which was inserted through a distal arteriotomy. Immediately after balloon injury, (111)indium-labeled autologous platelets were infused peripherally and the injured femoral arteries were randomly treated for 1 minute with a PEG-DISO solution in one artery and a control solution of the phosphate buffered saline vehicle in the contralateral artery. Following treatment, reflow was initiated. The vessels were harvested after 1 hour and radioactivity was quantified in a gamma counter. Platelet counts were standardized by weight and expressed as platelets/mg (mean +/- SEM). Platelet deposition onto arteries treated with PEG-DISO was (1.2 +/- 0.5) x 10(6) platelets/mg compared to (5.6 +/- 4.2) x 10(6) platelets/mg onto the contralateral control arteries treated with vehicle (P < 0.005). Scanning electron micrographs of the injured vessel segment confirmed qualitatively less platelet deposition on the treated segments than on the control segments.

CONCLUSION

Treatment with PEG-DISO significantly inhibited platelet deposition after vascular injury. These data support the hypothesis that treatment with PEG-DISO masks surface adhesive proteins from platelet receptors in vivo and that the resulting molecular barrier significantly reduces platelet deposition onto the damaged vessel wall for at least one hour. The formation of a molecularly thin barrier to platelet deposition may thus be a novel and effective treatment to abrogate acute intravascular thrombosis and may have value in the treatment of restenosis.

Complement C3 activation is required for antiphospholipid antibody-induced fetal loss

The antiphospholipid syndrome (APS) is characterized by recurrent fetal loss, vascular thrombosis, and thrombocytopenia occurring in the presence of antiphospholipid (aPL) antibodies. The pathogenesis of fetal loss and tissue injury in APS is incompletely understood, but is thought to involve platelet and endothelial cell activation as well as procoagulant effects of aPL antibodies acting directly on clotting pathway components. Recent studies have shown that uncontrolled complement activation in the placenta leads to fetal death in utero. We hypothesized that aPL antibodies activate complement in the placenta, generating split products that mediate placental injury and lead to fetal loss and growth retardation. To test this hypothesis, we used a murine model of APS in which pregnant mice are injected with human IgG containing aPL antibodies. We found that inhibition of the complement cascade in vivo, using the C3 convertase inhibitor complement receptor 1-related gene/protein y (Crry)-Ig, blocks fetal loss and growth retardation. Furthermore, mice deficient in complement C3 were resistant to fetal injury induced by aPL antibodies. While antigenic epitopes recognized by aPL antibodies are important in the pathogenesis of APS, our data show that in vivo complement activation is required for aPL antibody-induced fetal loss and growth retardation.

The role of high density lipoproteins in thrombosis

Lipids and lipoproteins, as well as factors involved in hemostasis and thrombosis, play a central role in the pathogenesis of cardio- and cerebrovascular disease. In recent years it has become clear that a strong association exists between coagulation factors and plasma lipoproteins. Anionic phospholipids are necessary for the optimal activity of both pro- and anticoagulant enzymatic complexes. Cell membranes have traditionally been considered to provide the essential lipid-containing surfaces. However, in light of recent studies, plasma lipoproteins are also believed to provide appropriate surfaces to support coagulation. While triglyceride-rich lipoproteins and oxidized low-density lipoproteins are associated with a procoagulant profile, high-density lipoproteins (HDL) may have an anticoagulant effect. This paper reviews scientific data on the potential role of HDL as modulator of thrombotic processes.

HMG CoA reductase inhibitors affect the fibrinolytic system of human vascular cells in vitro: a comparative study using different statins

1. The results of several clinical studies investigating the effect of statin therapy on the fibrinolytic system in vivo are inconclusive. We compared the effect of six different statins (atorvastatin, cerivastatin, fluvastatin, lovastatin, pravastatin, simvastatin) on components of the fibrinolytic system expressed by human vascular endothelial cells and smooth muscle cells and by the human hepatoma cell line HepG2. 2. All statins used except pravastatin significantly decreased PAI-1 production in human endothelial and smooth muscle cells. This effect was also seen in the presence of IL-1 alpha and TNF-alpha. All statins except pravastatin increased t-PA production in human smooth muscle cells. On a molar basis cerivastatin was the most effective HMG CoA reductase inhibitor used. Only simvastatin and lovastatin increased t-PA production in endothelial cells. The effects on the fibrinolytic system were reversed by mevalonate. Statins decreased mRNA levels for PAI-1 in endothelial and smooth muscle cells and increased mRNA levels for t-PA in smooth muscle cells. Statins did not affect PAI-1 expression in HepG2 cells. Cell viability was not influenced by statins in endothelial cells and HepG2 cells whereas in smooth muscle cells a cytotoxic effect was seen at high concentrations. 3. If the effects on the fibrinolytic system of vascular cells in vitro shown in this study are also operative in vivo one could speculate that by increasing t-PA and decreasing PAI-1 at sites of vascular lesions statins might reduce fibrin formation and thrombus development. Such an effect might contribute to the clinically proven benefits of statin therapy.

Potential therapeutic targets in the rapidly expanding field of purinergic signalling

The concept of a purinergic signalling system, using purine nucleotides and nucleosides as extracellular messengers, was first proposed over 30 years ago. After a brief historical review and update of purinoceptor subtypes, this article focuses on the diverse physiological roles of adenosine triphosphate, adenosine diphosphate, uridine triphosphate and adenosine. These molecules mediate short-term (acute) signalling functions in neurotransmission, secretion and vasodilation, and long-term (chronic) signalling functions in development, regeneration, proliferation and cell death. Plasticity of purinoceptor expression in pathological conditions is frequently observed, including an increase in the purinergic component of parasympathetic nervous control of the human bladder in interstitial cystitis and outflow obstruction, and in sympathetic cotransmitter control of blood vessels in hypertensive rats. The antithrombotic action of clopidogrel (Plavix), a P2Y12 receptor antagonist, has been shown to be particularly promising in the prevention of recurrent strokes and heart attacks in recent clinical trials (CAPRIE and CURE). The role of P2X3 receptors in nociception and a new hypothesis concerning purinergic mechanosensory transduction in visceral pain will be considered, as will the therapeutic potential of purinergic agonists or antagonists for the treatment of supraventricular tachycardia, cancer, dry eye, bladder hyperactivity, erectile dysfunction, osteoporosis, diabetes, gut motility and vascular disorders.

[Cellular pathophysiology of pulmonary hypertension]

Pulmonary hypertension comprises a group of diseases with heterogeneous etiology characterized by an increase of hydrostatic pressure in the pulmonary vascular bed. While secondary pulmonary hypertension predominantly results from acute or chronic left ventricular failure, characteristic gene defects or predisposing risk factors lead to various forms of primary pulmonary hypertension. Despite its diverse pathogenesis, pulmonary hypertension exhibits a uniform cellular pathophysiology in the pulmonary microcirculation.    The dysfunction of lung vascular endothelial cells, which are the front line in response to hemodynamic changes in the pulmonary circulation, is the pathophysiological driving force of pulmonary hypertension. Endothelial dysfunction is characterized by a reduced production of vasodilative, anti-proliferative mediators and an increased release of vasoconstrictive, proliferative factors. This apparent imbalance not only enhances pulmonary vasoconstriction, but supports pathologic remodeling processes in the vascular intima and media. In addition, the pulmonary endothelium recruits platelets and leukocytes, thus, contributing to further release of vasoconstrictive and proliferative mediators and characteristic thrombus formation. These endothelium-derived pathomechanisms amplify each other, further enhance pulmonary vascular resistance, and finally result in fixation of the hypertensive state.    Hence, pulmonary hypertension not only describes an alteration of lung hemodynamics, but comprises a complex set of pathophysiological events in both lung parenchymal cells and circulating blood cells. For development of new therapeutical strategies, the multifactorial character of the disease should be considered.

Pitfalls in the Use of Anticoagulants

Anticoagulants are in widespread use for the management of a variety of conditions, ranging from thrombus prevention to the treatment of arterial and venous occlusion. As with any effective therapy, recognition of adverse effects is critically important for the safe use of these drugs. Pitfalls in the use of heparins include dosing in close proximity to invasive procedures; not closely monitoring patients in whom dose adjustments may be required, such as the very obese, the elderly, and patients with renal or hepatic failure; failing to make dose adjustments during pregnancy; and not recognizing when patients are developing heparin-induced thrombocytopenia or osteoporosis. Pitfalls in the use of unfractionated heparin include delays in achieving a therapeutic activated partial thromboplastin time (aPTT) and failure to consider the effects of protein binding in acutely ill patients. A pitfall in the use of low molecular weight heparin is giving prophylactic doses when therapeutic doses are indicated. Pitfalls in the use of warfarin are stopping heparin before the warfarin is fully effective; failing to maintain the International Normalized Ratio within the therapeutic range; failing to adjust the dose of warfarin because of changes in diet, renal or hepatic failure, and exposure to new drugs; failing to stop warfarin at an appropriate interval before an invasive procedure; and giving warfarin during pregnancy. Pitfalls in the use of thrombin inhibitors include using them with thrombolytic agents; giving them in proximity to invasive procedures; not adjusting the dose for renal or hepatic failure; and failing to consider the effect of these agents on the prothrombin time when initiating warfarin therapy.

In vivo magnetic resonance imaging of experimental thrombosis in a rabbit model

The process of atherosclerotic plaque disruption has been difficult to monitor because of the lack of an animal model and the limited ability to directly visualize the plaque and overlying thrombus in vivo. Our aim was to validate in vivo magnetic resonance imaging (MRI) of the thrombus formation after pharmacological triggering of plaque disruption in the modified Constantinides animal model of plaque disruption. Atherosclerosis was induced in 9 New Zealand White male rabbits (3 kg) with aortic balloon endothelial injury followed by a high cholesterol (1%) diet for 8 weeks. After baseline (pretrigger) MRI, the rabbits underwent pharmacological triggering with Russell's viper venom and histamine, followed by another MRI 48 hours later. Contiguous cross-sectional T2-weighted fast spin echo images of the abdominal aorta were compared by histopathology. In all animals, aortic wall thickening was present on the pretrigger MRI. On MRIs performed 48 hours after triggering, a histologically confirmed intraluminal thrombus was visualized in 6 (67%) of the 9 animals. MRI data correlated with the histopathology regarding aortic wall thickness (R=0.77, P<0.0005), thrombus size (R=0.82, P<0.0001), thrombus length (R=0.86, P<0.005), and anatomic location (R=0.98, P<0.0001). In vivo, MRI reliably determines the presence, location, and size of the thrombus in this animal model of atherosclerosis and plaque disruption. The combination of in vivo MRI and the modified Constantinides animal model could be an important research tool for our understanding of the pathogenesis of acute coronary syndromes.

Lupus anticoagulant and history of thrombosis are not associated with persistent endothelial cell activation in systemic lupus erythematosus

Antiphospholipid antibodies (aPL), especially lupus anticoagulant (LAC), characterize systemic lupus erythematosus (SLE) patients at increased risk for arterial and venous thromboembolic complications. It has been reported that purified human anti-phospholipid antibodies cause endothelial cell activation in in vitro experiments. In order to investigate whether increased endothelial cell activation is associated with thromboembolic events in SLE patients with LAC, we measured plasma levels of thrombomodulin (TM), von Willebrand factor (vWf), sP-selectin, vascular cell adhesion molecule-1 (sVCAM-1) and ED1-fibronectin in a study of 76 patients with SLE. Patients were subdivided on the basis of: no history of thrombosis and LAC-negative (n = 22) or LAC-positive (n = 17); positive history of thrombosis and LAC-negative (n = 16) or LAC-positive (n = 21). The median SLE disease activity index (SLEDAI) was 4. Although concentrations of sTM, vWf, sP-selectin and sVCAM-1 were significantly elevated in SLE compared with values in healthy controls, they did not differ between the four groups, between patients with or without history of thrombosis, and between patients with or without LAC. Presence of anticardiolipin antibodies could not explain these negative findings. Adjustment of the concentrations for significantly associated variables, such as age, hypertension, smoking, immunosuppressive treatment and concentrations of creatinine, cholesterol and homocysteine, did not change the main results of the study. Only sTM was significantly lower in patients with both LAC and thrombosis than in patients without both these features after adjustment for serum creatinine concentrations. In conclusion, we did not find an association between endothelial cell activation and presence of LAC or history of thrombosis in SLE.

Control of von Willebrand factor multimer size by thrombospondin-1

Plasma von Willebrand factor (vWF) is a multimeric protein that mediates adhesion of platelets to sites of vascular injury. Only the very large vWF multimers are effective in promoting platelet adhesion in flowing blood. A protein disulfide bond reductase in plasma reduces the average multimer size of vWF secreted by endothelial cells. This activity has been isolated from human endothelial cell conditioned medium and shown to be the trimeric glycoprotein, thrombospondin-1 (TSP-1). Incubation of purified TSP-1 with vWF resulted in formation of thiol-dependent complexes of TSP-1 and vWF, generation of new thiols in vWF, and reduction in the average multimer size of vWF. The ratio of the concentrations of TSP-1 and vWF in plasma reflected with average multimer size of vWF. The higher the plasma TSP-1/vWF molar ratio, the smaller the average vWF multimer size. In addition, administration of TSP-1 to mice resulted in reduction in the average multimer size of plasma vWF. Interaction of TSP-1 with vWF is mediated by TSP-1 type 1 properdin domains and the vWF A3 domain. These results indicate that TSP-1 regulates the multimeric size and therefore hemostatic activity of vWF.

Fast detection and characterization of vessels in very large 3-D data sets using geometrical moments

An improved and very fast algorithm dealing with the extraction of vessels in three-dimensional imaging is described. The approach is based on geometrical moments and a local cylindrical approximation. A robust estimation of vessel and background intensity levels, position, orientation, and diameter of the vessels with adaptive control of key parameters, is provided during vessel tracking. Experimental results are presented for lower limb arteries in multidetector computed tomography scanner.

Local gene transfer of tissue factor pathway inhibitor regulates intimal hyperplasia in atherosclerotic arteries

Tissue factor (TF), the initiator of blood coagulation and thrombosis, is up-regulated after vascular injury and in atherosclerotic states. Systemic administration of recombinant TF pathway inhibitor (TFPI) has been reported to decrease intimal hyperplasia after vascular injury and also to suppress systemic mechanisms of blood coagulation and thrombosis. Here we report that, in heritable hyperlipidemic Watanabe rabbits, adenoviral gene transfer of TFPI to balloon-injured atherosclerotic arteries reduced the extent of intimal hyperplasia by 43% (P < 0.05) compared with a control vector used at identical titer (1 x 10(10) plaque-forming units/ml). Platelet aggregation and coagulation studies performed 7 days after local gene transfer of TFPI failed to show any impairment in systemic hemostasis. At time of sacrifice, 4 weeks after vascular injury, the 10 Ad-TFPI treated carotid arteries were free of thrombi, whereas two control-treated arteries were occluded (P, not significant). These findings suggest that TFPI overexpressed in atherosclerotic arteries can regulate hyperplastic response to injury in the absence of changes in the hemostatic system, establishing a role for local TF regulation as target for gene transfer-based antirestenosis therapies.

Long-term antithrombotic protection by in vivo depletion of platelet glycoprotein VI in mice

Coronary artery thrombosis is often initiated by abrupt disruption of the atherosclerotic plaque and activation of platelets on the subendothelial layers in the disrupted plaque. The extracellular matrix protein collagen is the most thrombogenic constituent of the subendothelial layer; therefore, a selective inhibition of the collagen activation pathway in platelets may provide strong antithrombotic protection while preserving other platelet functions. Here we demonstrate that treatment of mice with a monoclonal antibody against the activating platelet collagen receptor glycoprotein VI (GPVI; JAQ1) results in specific depletion of the receptor from circulating platelets and abolished responses of these cells to collagen and collagen-related peptides (CRPs). JAQ1-treated mice were completely protected for at least 2 wk against lethal thromboembolism induced by infusion of a mixture of collagen (0.8 mg/kg) and epinephrine (60 microg/ml). The tail bleeding times in JAQ1-treated mice were only moderately increased compared with control mice probably because the treatment did not affect platelet activation by other agonists such as adenosine diphosphate or phorbol myristate acetate. These results suggest that GPVI might become a target for long-term prophylaxis of ischemic cardiovascular diseases and provide the first evidence that it is possible to specifically deplete an activating glycoprotein receptor from circulating platelets in vivo.

Skeletal muscle necrosis and regeneration after injection of Thalassophryne nattereri (niquim) fish venom in mice

Stings by Thalassophryne nattereri are responsible for envenomation of fishermen in north-eastern Brazil. Its venom induces prominent local tissue damage, characterized by pain, oedema and necrosis. The pathogenesis of acute muscle damage induced by T. nattereri venom was studied in mice. Intramuscular injection induced myonecrosis within the first hours. Some muscle cells presented a hypercontracted morphology, but most necrotic fibres were not hypercontracted, being instead characterized by a disorganization of myofibrils, with Z line loss, mitochondrial swelling and sarcolemmal disruption. In addition, thrombosis was observed histologically in venules and veins, together with vascular congestion and stasis, evidenced by intravital microscopy. Venom induced a rapid increment in serum creatine kinase (CK) levels, concomitant with a reduction in gastrocnemius muscle CK activity, whereas no increments in muscle lactic acid were detected. A rapid cytolytic effect was induced by the venom on C2C12 murine myoblasts in culture. The inflammatory reaction in affected muscle was characterized by oedema and scarce cellular infiltrate of polymorphonuclear leucocytes and macrophages, with a consequent delay in the removal of necrotic material. Skeletal muscle regeneration was partially impaired, as evidenced by the presence of regenerating fibres of variable size and by the increase of fibrotic tissue in endomysium and perimysium. It is suggested that T. nattereri venom affects muscle fibres by a direct cytotoxic effect, and that the vascular alterations described preclude a successful regenerative process.

Abnormalities of platelet aggregation in chronic myeloproliferative disorders

A large variety of platelet dysfunctions has been described in chronic myeloproliferative disorders. These abnormalities may be due to deficiency of platelet granules, arachidonic acid metabolism defects or platelet membrane glycoproteins abnormalities. In this study we intend to detect the incidence of platelet function defects in 76 patients with various types of chronic myeloproliferative disorders. The platelet activity was studied in vitro by measuring platelet aggregation in response to ADP, epinephrine, collagen, arachidonic acid and ristocetin. These results were subsequently correlated with bleeding time and clinical aspects (bleeding or thrombosis). We found complex changes in platelet response with all agonists, in varied proportions. These abnormalities include absent, decreased or abnormal platelet aggregation response. In a few cases we found a markedly decreased, almost absent platelet response to all agonists while in some patients a normal platelet aggregation was noted. The correlation between these results and template bleeding time, thrombotic or hemorrhagic events and the type of diseases was difficult to establish and sometimes conflictual. Despite this fact, we consider that investigating platelet aggregation may be useful not only for the assessment of the hemostatic balance in chronic myeloproliferative disorders but also for a better insight into cell abnormalities occurring in these pathologic conditions.

Thrombophilia, polymorphisms, and vascular disease

Thrombophilia traditionally refers to rare inherited defects leading to enhanced coagulation, especially of the venous system. In recent years, a broader search for genetic polymorphisms of prothrombotic genes has been carried out to determine the relative impact on venous and arterial thrombosis. The bulk of evidence is drawn from numerous, often small, heterogeneous, case control association studies, with a variety of end points (deep venous thrombosis, myocardial infarction, or stroke). The data are often conflicting and inconclusive with only factor V Leiden and prothrombin polymorphisms having clear associations with venous thrombosis. Many of the polymorphisms interact with established cardiovascular risk factors, in particular smoking, to increase greatly the risk of a thrombotic episode. Future studies will need to consider the confounding factors of sample size, race, and clinical end points as well gene-environment interactions.