Platelet and fibrinogen consumption in man

BloodSurf 2017: News from the blood-biomaterial frontier

From stents and large-diameter vascular grafts, to mechanical heart valves and blood pumps, blood-contacting devices are enjoying significant clinical success owing to the application of systemic antiplatelet and anticoagulation therapies. On the contrary, research into material and device hemocompatibility aimed at alleviating the need for systemic therapies has suffered a decline. This research area is undergoing a renaissance fueled by recent fundamental insights into coagulation and inflammation that are offering new avenues of investigation, the growing recognition of the limitations facing existing therapeutic approaches, and the severity of the cardiovascular disorders epidemic. This Opinion article discusses clinical needs for hemocompatible materials and the emerging research directions for fulfilling those needs. Based on the 2017 BloodSurf conference that brought together clinicians, scientists, and engineers from academia, industry, and regulatory bodies, its purpose is to draw the attention of the wider clinical and scientific community to stimulate further growth. STATEMENT OF SIGNIFICANCE: The article highlights recent fundamental insights into coagulation, inflammation, and blood-biomaterial interactions that are fueling a renaissance in the field of material hemocompatibility. It will be useful for clinicians, scientists, engineers, representatives of industry and regulatory bodies working on the problem of developing hemocompatible materials and devices for treating cardiovascular disorders.

The platelet Fc receptor, FcγRIIa

Human platelets express FcγRIIa, the low-affinity receptor for the constant fragment (Fc) of immunoglobulin (Ig) G that is also found on neutrophils, monocytes, and macrophages. Engagement of this receptor on platelets by immune complexes triggers intracellular signaling events that lead to platelet activation and aggregation. Importantly these events occur in vivo, particularly in response to pathological immune complexes, and engagement of this receptor on platelets has been causally linked to disease pathology. In this review, we will highlight some of the key features of this receptor in the context of the platelet surface, and examine the functions of platelet FcγRIIa in normal hemostasis and in response to injury and infection. This review will also highlight pathological consequences of engagement of this receptor in platelet-based autoimmune disorders. Finally, we present some new data investigating whether levels of the extracellular ligand-binding region of platelet glycoprotein VI which is rapidly shed upon engagement of platelet FcγRIIa by autoantibodies, can report on the presence of pathological anti-heparin/platelet factor 4 immune complexes and thus identify patients with pathological autoantibodies who are at the greatest risk of developing life-threatening thrombosis in the setting of heparin-induced thrombocytopenia.

Thrombocytopenia in the Intensive Care Unit Setting

Thrombocytopenia is a commonly encountered labora tory abnormality in the intensive care unit setting. Al though moderate degrees of thrombocytopenia may be dismissed as clinically trivial, severe thrombocytopenia can have catastrophic consequences. This review di vides the potential pathogenesis of thrombocytopenia into three pathophysiological categories: (1) produc tive, (2) consumptive, and (3) distributional. The im portant etiologies and appropriate therapies for throm bocytopenia in each of these categories are discussed. We have attempted to emphasize the underlying patho genic mechanisms as well as highlight the diagnostic dilemmas likely to be faced by intensive care unit physi cians. Although this review stresses those thrombocyto penic disorders most likely to be encountered in the intensive care unit, chronic etiologies of thrombocy topenia are also discussed because preexistent throm bocytopenia will further complicate the care of any acutely ill intensive care unit patient.

Thrombotic Thrombocytopenic Purpura

Thrombotic thrombocytopenic purpura (TTP) is classically highlighted by a pentad of features: fever, hemolytic anemia, thrombocytopenia purpura, transient or permanent central nervous system signs, and renal disease. The antemortem diagnosis is reliant upon the multisystem clinical signs and symptoms in conjunction with severe hemolytic anemia and thrombocytopenia. Relapse is common within the first six months after initial presentation. Laboratory findings have been generally nonspecific per se, and antemortem tissue biopsy findings are frequently unrewarding. Recently, however, unusually large multimers of the Factor VIII:Ag molecule (von Willebrand protein) have been identified in the plasma of patients with TTP who have recovered from an acute attack. This observation is very important because it may lead to essential information on the nature of the inciting event in this devastating illness. The differential diagnosis includes several multisystem disease processes such as the hemolytic uremic syndrome, toxemia of pregnancy, systemic lupus erythematosus, subacute bacterial endocarditis, nonbacterial thrombotic endocarditis, immune thrombocytopenic purpura, and the postpartum renal failure syndrome. The hemolytic uremic syndrome, toxemia of pregnancy, and TTP may resemble each other, exhibit many overlapping features, and are probably related. The cause of TTP remains unknown; the overwhelming majority of cases occur in otherwise healthy people without any recognizable underlying illness. Since 1965 45 to 70% of patients survive, a significant improvement in contrast to the early 1900s when the mortality rate was greater than 90%. The most dramatic advance has been observed in therapeutics, namely the utilization of some mode of plasma therapy (either infusion alone or plasmapheresis followed by plasma infusion). Corticosteroids remain very important in the management of patients with TTP. Vincristine may be very helpful, but additional studies are needed. The efficacy of vinca alkaloids, chronic immunosuppressive therapy, and sple. nectomy remains undefined. At present there is very little, if any, evidence that antiplatelet agents, aspirin, and prostacyclin are beneficial to patients with TTP. Prompt diagnosis and vigorous aggressive therapy is critical for successful management of TTP patients.

Endothelial cell dysfunction in viral hemorrhage and edema

The endothelium maintains a vascular barrier by controlling platelet and immune cell interactions, capillary tone and interendothelial cell (EC) adherence. Here we suggest common elements in play during viral infection of the endothelium that alter normal EC functions and contribute to lethal hemorrhagic or edematous diseases. In viral reservoir hosts, infection of capillaries and lymphatic vessels may direct immunotolerance without disease, but in the absence of these cognate interactions they direct the delayed onset of human disease characterized by thrombocytopenia and vascular leakage in a severe endothelial dysfunction syndrome. Here we present insight into EC controls of hemostasis, immune response and capillary permeability that are altered by viral infection of the endothelium.

Aspirin resistance: a clinical review focused on the most common cause, noncompliance

Aspirin is an inexpensive, readily available medication that reduces the risk of subsequent vascular disease by about 25% in patients with known occlusive vascular disease. Aspirin's beneficial effect is mediated via inhibition of arachidonic acid (AA) activation of platelets and is detected by demonstrating a decrease in platelet function and/or a decrease in prostaglandin metabolites. Patients who are assumed to be taking their aspirin, but who do not demonstrate an aspirin effect are labeled as, "aspirin resistant." This is an unfortunate designation as the vast majority of patients labeled as "aspirin resistant" are noncompliant. Noncompliance is demonstrated in multiple studies that use repeat testing for platelet inhibition in patients with an initial inadequate response to aspirin. When the test is repeated under condition where ingestion of the test aspirin is assured, the patients' platelets are inhibited. Instead of using the term "aspirin resistance," this review will use "inadequate response to aspirin." Patients with an inadequate aspirin response have an increased likelihood for subsequent vascular events. Detection and treatment of an inadequate aspirin response would be facilitated by the development of a bedside assay that uses whole blood, is technically simple, inexpensive, sensitive, specific, reproducible, and provides an answer in a few minutes. Future research in patients with an inadequate response to aspirin should focus on mechanisms to improve compliance, which should decrease their risk of future vascular events.

Glucocorticoid treatment increases density of serotonin 5-HT2A receptors in humans

BACKGROUND

Interactions between the serotonergic system and the hypothalamic-pituitary-adrenal axis have been suggested, albeit the details for such interactions have yet to be established. Animal studies have shown that the density of serotonin 5-HT2A receptors is increased after administration of exogenous glucocorticoids.

OBJECTIVE

The objective of this study was to explore possible changes in the pattern of density and affinity of 5-HT2A receptors in humans after treatment with glucocorticoids.

METHODS

Using a radioactive binding assay, the density and affinity (measured as Bmax and Kd) of 5-HT2A serotonin receptors were measured in blood samples drawn from 27 individuals diagnosed with polymyalgia rheumatica and/or giant cell arteritis before and after start of an oral treatment with prednisolone. For each patient Bmax and Kd at baseline before prednisolone treatment were compared with Bmax and Kd in samples drawn at a first and second follow-up clinic visit at an average of 8.8 (±2.5) days and 33.6 (±6.8) days, respectively.

RESULTS

The density of 5-HT2A receptors increased after treatment in 23 individuals. The mean Bmax value at baseline for all patients was 45.2 fmol/mg protein compared with 64.9 fmol/mg protein in the corresponding samples drawn at the second follow-up visit (p=0.001). There also was an association between individuals accumulated prednisolone dose and the magnitude of change in Bmax between baseline and the first follow-up visit. Erythrocyte sedimentation rate, platelet count or gender had no influence on the results. There were no significant differences in Kd during the treatment period. However, a low Kd value at baseline was a predictor for an increase in Bmax following treatment.

CONCLUSIONS

The results of this study showed that the density of 5-HT2A serotonin receptors in man is increased after a subchronic treatment with glucocorticoids. The magnitude of the increase appears to be associated with the affinity of 5-HT2A receptors before treatment and the accumulated dose of glucocorticoid early in the treatment period.

Thrombotic microangiopathy: current knowledge and outcomes with plasma exchange

The classification of thrombotic microangiopathy has evolved and expanded due to treatment and mechanistic advances. The two basic clinical forms of thrombotic microangiopathy (excluding disseminated intravascular coagulation [DIC]), thrombotic thrombocytopenic purpura (TTP), and hemolytic uremic syndrome (HUS) encompass a wide range of primary and secondary forms. The advent of plasma therapy and the identification of an inhibitor to ADAMTS13 in the idiopathic or acute forms of TTP and its absence in diarrheal HUS have had a major impact on our current classification of thrombotic microangiopathy. In adults, the difficulty of differentiating TTP, which is much more common than HUS and the need for a speedy diagnosis to provide life-saving plasma therapy has resulted in the term TTP/HUS for adult forms of thrombotic microangiopathy that present with unexplained thrombocytopenia and microangiopathic hemolytic anemia without a DIC. In this adult population a primary idiopathic and hereditary form as well as eight known secondary categories or clinical forms of TTP/HUS have been identified. HUS also embraces a primary (atypical HUS) and secondary forms (majority, diarrheal HUS secondary to Escherichia coli 0157:H7). In children, who present with HUS with no preceding history of diarrhea, plasma therapy is also offered on an urgent basis and studies are carried out to determine if they are suffering an abnormality in complement activation that may require eculizumab therapy. The advent of plasma therapy in the treatment of thrombotic microangiopathy has led to a clearer understanding of the role of ADAMTS13, both short- and long-term outcomes and the need for future surveillance and intervention.

Polymorphisms of platelet ADP receptor P2RY12 in the risk of venous thromboembolism in the Korean population

Although it was thought that platelets did not play a significant role in the pathogenesis of venous thromboembolism (VTE), several studies demonstrated that a marked activation of platelets occurs in patients with VTE. We carried out a case-control study to investigate the effect of the T744C P2RY12 polymorphism on the risk of VTE in the Korean population. We enrolled 154 consecutive patients with VTE and 415 healthy controls. Genotype frequencies for patients with TT, TC, and CC were 71.4%, 24.7%, and 3.9% and in the controls, 68.2%, 30.1%, and 1.7%, respectively. T744C P2RY12 polymorphism did not significantly affect the risk of VTE. Our study shows that T744C P2RY12 polymorphism did not significantly affect the risk of VTE in the Korean population.

ADP-induced platelet aggregation in vitro in patients with ischemic heart disease and peripheral thromboatherosclerosis

ADP-induced platelet aggregation in vitro has been studied in 90 normal controls and in 30 patients with ischemic heart disease (IHD) and 22 with peripheral thromboatherosclerosis (PTA). The sensitivity to ADP was defined by the threshold concentration which produced secondary aggregation with an amplitude corresponding to not less than 80% of the transmission obtained by platelet-poor plasma. In the normal controls the threshold concentration was significantly lower in women aged 50 or more than in women under that age. The geometric means were lower in the patients than in the controls. Significantly lower threshold concentrations than in the corresponding age groups of controls were found in the following age groups of patients: Men and women greater than or equal to 50 years with IHD (p less than 0.005 and p less than 0.001, respectively), men and women under 50 with IHD (p less than 0.05). Men and women greater than or equal to 50 years with PTA (p less than 0.002 and p less than 0.01, respectively), men and women under 50 with PTA (p less than 0.005).

Platelet survival and platelet production in acute myocardial infarction

Thrombokinetic studies were carried out on 26 consecutive patients with myocardial infarction (MI) admitted to a coronary care unit in the acute stage during a two-month period. The results were compared with those of an age-matched control group. In the MI patients, platelet mean life-span was 5.0 +/- 0.3 days and significantly shorter (p greater than 0.01) than in the controls (6.4 +/- 0.4 days). The mean platelet production rate for the patients with MI was significantly higher (p greater than 0.005) than for the controls. On the basis of results reported by others as well as the present data, it is suggested that during the acute phase of MI there is no additional measurable reduction in platelet survival above that observed in chronic coronary artery disease.

Splenic platelet kinetics and platelet production after major reconstructive vascular surgery

By using 111In-labelled platelets and dynamic gamma camera scintigraphy, platelet production rate and intrasplenic platelet kinetics were determined in 13 patients at 1 and 4 months after aortic reconstructive vascular surgery with implantation of dacron prostheses. A significant decrease in platelet production rate and venous platelet count was recorded over time after surgery. Irrespective of whether the exchangeable splenic platelet pool was estimated from initial recovery of platelet-bound radioactivity or from compartmental analysis, the size of this pool was significantly lower at the first study; a change in intrasplenic platelet transit time accounted for the observed difference. Platelet mean life-span increased over time after surgery but the difference between the duplicate studies was not statistically significant. It can be concluded that there is a reduction of platelet production rate and venous platelet count over time after major reconstructive vascular surgery. The early postoperative elevation in the platelet count is mainly the result of an increased platelet production and to a lesser degree due to redistribution of platelets between the splenic platelet pool and general circulation.

The role of platelet activation in tumor metastasis

Platelets are highly reactive components of the circulatory system, which exert not only haemostatic activity but also contribute to the modulation of various pathological conditions including inflammation, atherosclerosis and cancer metastasis through the release of cytokines, chemokines and the presentation of several adhesion molecules. During cancer metastasis, the formation of platelet-tumor cell aggregates in the circulation facilitates immune evasion and the microvascular arrest of tumor cells at distant sites. Several adhesion molecules, such as integrins and glycoproteins, were shown to be involved in this process. Recent findings indicate that P-selectin is another main mediator of platelet-tumor cell interactions. Other effects of activated platelets on cancer progression are associated with a release of platelet-derived factors stimulating tumor growth and angiogenesis. Any interference in platelet-tumor cell interactions resulted in attenuation of cancer metastasis. The well recognized, albeit not fully characterized function of platelets during cancer progression defines platelets as potential targets for cancer therapy. Specifically, the rapid expression of P-selectin on the cell surface of activated platelets and its strong association with metastasis provide a rationale for P-selectin inhibition as an antimetastatic treatment.

Prognostic importance of serum vascular endothelial growth factor in relation to platelet and leukocyte counts in human renal cell carcinoma

It has been shown that both serum vascular endothelial growth factor (VEGF) and also platelet counts are associated with survival in renal cell carcinoma (RCC). It is not known, however, whether VEGF in serum relates to the angiogenic activity of the tumour or is derived from circulating blood components. Therefore, the interrelation between serum VEGF, platelet and leukocyte counts compared with health history, clinicopathological findings and outcome was evaluated in patients with RCC. Blood samples were collected before nephrectomy in 161 patients. Serum VEGF165 was assessed by a quantitative ELISA method. Platelet and leukocyte counts were analysed routinely and obtained from medical records. The variables were compared using univariate and multivariate analysis. There were significant correlations between VEGF levels, and platelet (P < 0.001) and leukocyte counts (P < 0.001). Serum VEGF levels, platelet counts, as well as leukocyte counts correlated significantly to stage and grade. Platelet counts were significantly lower in men with medication (P = 0.042), and decreased with age particularly in women (P = 0.001). Age or medication did not affect VEGF levels or leukocyte counts. Both VEGF and platelets gave significant prognostic information in univariate analysis. Using Cox multivariate analysis, VEGF was the last variable to be excluded. Only stage and grade remained as independent prognostic factors. Both VEGF levels and platelet counts gave prognostic information but VEGF was more reliable as predictor of survival in patients with RCC.

The effects of heparin and oral anticoagulants on thrombus propagation and prevention of the postphlebitic syndrome: a critical review of the literature

Based on a comprehensive literature search, this report aims to examine the effects of heparin and oral anticoagulants on thrombus propagation and prevention of the postphlebitic syndrome. The effects on recurrence of thromboembolic disease have not been addressed. It is concluded that published reports of serial venograms and ultrasound examinations of patients treated with conventional anticoagulant therapy for deep venous thrombosis show either no change or thrombus extension in the first few months in approximately 50% of cases. Approximately two thirds of patients will have damage to the venous valves, leading to incompetence or other hemodynamic changes. More than one third of patients so treated may have oedema, leg pain, or other severe symptoms on long-term follow-up. The consistency with which these outcomes have been observed, particularly in many large, recent, prospective trials, adds to the credibility of these figures. The results of prospective controlled trials have failed uniformly to show any significant local benefits of anticoagulant therapy for deep vein thrombosis compared with other treatments or placebo. There does not seem to be any convincing evidence that heparin exerts a favorable influence on pulmonary embolism in situ or on portal vein thrombosis. Use of anticoagulant therapy to limit thrombus propagation therefore cannot be said to be "evidence based." These generally poor outcomes with regard to postphlebitic complications should lead to an active exploration of alternative methods of management. Substantial uncertainties surrounding many fundamental aspects of the treatment of this disease remain, and further placebo-controlled trials are needed.

Vascular endothelial growth factor–stimulated endothelial cells promote adhesion and activation of platelets

Coagulation abnormalities, including an increased platelet turnover, are frequently found in patients with cancer. Because platelets secrete angiogenic factors on activation, this study tested the hypothesis that platelets contribute to angiogenesis. Stimulation with vascular endothelial growth factor (VEGF, 25 ng/mL) of human umbilical vein endothelial cells (HUVECs) promoted adhesion of nonactivated platelets 2.5-fold. In contrast, stimulation of HUVECs with basic fibroblast growth factor (bFGF) did not promote platelet adhesion. By blocking tissue factor (TF) activity, platelet adhesion was prevented and antibodies against fibrin(ogen) and the platelet-specific integrin, αIIbβ3, inhibited platelet adhesion for 70% to 90%. These results indicate that VEGF-induced platelet adhesion to endothelial cells is dependent on activation of TF. The involvement of fibrin(ogen) and the αIIbβ3 integrin, which exposes a high-affinity binding site for fibrin(ogen) on platelet activation, indicates that these adhering platelets are activated. This was supported by the finding that the activity of thrombin, a product of TF-activated coagulation and a potent platelet activator, was required for platelet adhesion. Finally, platelets at physiologic concentrations stimulated proliferation of HUVECs, indicative of proangiogenic activity in vivo. These results support the hypothesis that platelets contribute to tumor-induced angiogenesis. In addition, they may explain the clinical observation of an increased platelet turnover in cancer patients. Platelets may also play an important role in other angiogenesis-dependent diseases in which VEGF is involved, such as diabetes and autoimmune diseases.

Vascular endothelial growth factor–stimulated endothelial cells promote adhesion and activation of platelets

Coagulation abnormalities, including an increased platelet turnover, are frequently found in patients with cancer. Because platelets secrete angiogenic factors on activation, this study tested the hypothesis that platelets contribute to angiogenesis. Stimulation with vascular endothelial growth factor (VEGF, 25 ng/mL) of human umbilical vein endothelial cells (HUVECs) promoted adhesion of nonactivated platelets 2.5-fold. In contrast, stimulation of HUVECs with basic fibroblast growth factor (bFGF) did not promote platelet adhesion. By blocking tissue factor (TF) activity, platelet adhesion was prevented and antibodies against fibrin(ogen) and the platelet-specific integrin, αIIbβ3, inhibited platelet adhesion for 70% to 90%. These results indicate that VEGF-induced platelet adhesion to endothelial cells is dependent on activation of TF. The involvement of fibrin(ogen) and the αIIbβ3 integrin, which exposes a high-affinity binding site for fibrin(ogen) on platelet activation, indicates that these adhering platelets are activated. This was supported by the finding that the activity of thrombin, a product of TF-activated coagulation and a potent platelet activator, was required for platelet adhesion. Finally, platelets at physiologic concentrations stimulated proliferation of HUVECs, indicative of proangiogenic activity in vivo. These results support the hypothesis that platelets contribute to tumor-induced angiogenesis. In addition, they may explain the clinical observation of an increased platelet turnover in cancer patients. Platelets may also play an important role in other angiogenesis-dependent diseases in which VEGF is involved, such as diabetes and autoimmune diseases.

Inhibition of platelet aggregation by putrescine, spermidine, and spermine in hypercholesterolemic rabbits

BACKGROUND

Hypercholesterolemia causes alterations in platelet function. Platelet hyperaggregation is considered a predisposing factor for atherosclerosis. In this paper, the antiaggregating effect of the polyamines putrescine, spermidine, and spermine was studied on platelets of normal and hypercholesterolemic rabbits.

METHODS

New Zealand rabbits were fed with a cholesterol-enriched diet for 10 weeks. Lipids and glucose were determined in serum. The assays of platelet aggregation were carried out using platelet-rich plasma (PRP) obtained from both control and cholesterol-fed rabbits. We used 2.5 micromol /mL ADP and 2 microg/mL collagen as inductors of platelet aggregation. In addition, arginase activity and L-arginine content were determined in PRP.

RESULTS

Serum total cholesterol and LDL-cholesterol concentrations were increased from 26.3 +/- 8.1 to 1,485.0 +/- 26.8 mg/dL and from 15.9 +/- 5.9 to 1,383.8 +/- 58.9 mg/dL, respectively, whereas triglyceride concentration increased from 88.3 +/- 35.6 to 411.0 +/- 154.5 mg/dL upon cholesterol feeding. Seventy-five percent of platelet aggregation inhibition was observed with 10 microM of polyamines in PRP of normal rabbits. Spermine inhibited platelet aggregation by 54% in PRP of hypercholesterolemic rabbits when ADP was used as agonist. The order of polyamine action was spermine > spermidine > putrescine. In addition, we found that platelet arginase activity and L-arginine content were unaltered upon hypercholesterolemia.

CONCLUSIONS

These results show that the polyamines putrescine, spermidine, and spermine have antagonist action in platelet aggregation and suggest a key role of polyamines in platelet aggregation under normal and hypercholesterolemic conditions.

Antiplatelet and antithrombotic effects of a novel selective phosphodiesterase 3 inhibitor, NSP-513, in mice and rats

We investigated the effects of NSP-513, (R)-4,5-dihydro-5-methyl-6-[4-(2-propyl-3-oxo-1-cyclohexenyl)amino] phenyl-3(2H)-pyridazinone, on phosphodiesterase (PDE) isozyme activities, in vitro platelet aggregation and in vivo thrombus formation. NSP-513 selectively inhibited human platelet PDE 3 isozyme with an IC50 value of 0.039 microM. In an in vitro human platelet aggregation assay, the IC50 values (microM) of NSP-513 for platelet aggregation induced by collagen, U-46619, arachidonic acid, adenosine diphosphate (ADP), epinephrine and thrombin were 0.31, 0.25, 0.082, 0.66, 0.23 and 0.73, respectively. In a mouse pulmonary thromboembolism model, orally administered NSP-513 showed in vivo antithrombotic effects that were 320 to 470 times more potent than those of cilostazol. In a rat carotid arterial thrombosis model, intraduodenally administered NSP-513 (0.1 mg/kg), cilostazol (30 mg/kg) and aspirin (30 mg/kg) reduced thrombus formation by 75%, 66% and 48%, respectively. However, intravenously administered dipyridamole (10 mg/kg) did not significantly prevent thrombus formation. These results demonstrate that NSP-513 has the potential to prevent not only in vitro platelet aggregation but also in vivo thrombus formation and indicate that the highly selective PDE 3 inhibitory effect of NSP-513 may make this compound useful for assessing the physiological role of PDE 3.

Lipoproteins and the haemostatic system in atherothrombotic disorders

The remarkable extent to which interactions between the plasma lipoproteins, inflammatory factors and the haemostatic system contribute to the response to injury and growth of the plaque in atherosclerosis is being increasingly documented. High plasma concentrations of very-low density (VLDL) and low-density lipoproteins (LDL), together with oxidatively modified LDL and lipoprotein (a), can induce responses in vascular endothelial cells, smooth muscle cells, monocytes/macrophages, platelets, neutrophils and humoral factors that are in a variety of ways both procoagulant and antifibrinolytic. Plasma high-density lipoproteins appear to promote anticoagulant mechanisms. Post-prandial lipaemia is associated with transient changes in factor VII which may be indicative of temporary hypercoagulability. The cellular and humoral effects of LDL and VLDL on the haemostatic system appear to be largely reversible, which may help to explain the prompt improvement in the atherothrombotic state gained by correction of hyperlipidaemia.

Assessment of bovine platelet life span with biotinylation and flow cytometry

Reduced platelet life span is associated with the implantation of a variety of cardiovascular devices and may be used as a gauge of device biocompatibility. In the bovine model, platelet life span has previously been assessed with radioisotope labeling of removed platelets followed by reinjection and periodic gamma counting of blood samples. We report here the use of protein-reactive biotin (sulfo-N-hydroxysuccinimido [NHS]-biotin) as an alternative to radioisotope techniques whereby reinjected biotinylated platelets are subsequently detected in blood samples using phycoerythrin-streptavidin and flow cytometric techniques. Platelet life span was quantified in a normal calf (4.9 days) and in a calf prior to (6.1 days) and following (3.1 days) implantation of a Nimbus Axial Flow Pump ventricular assist device. The assessment of bovine platelet life span with biotinylation and flow cytometry avoids the technical, regulatory, and safety considerations associated with radioisotope usage and appears readily amenable to application in cardiovascular device testing.

Anticoagulation with prostaglandin E1 and unfractionated heparin during continuous venovenous hemofiltration

OBJECTIVE

To determine the effect of two doses of prostaglandin E1 (PGE1, alprostadil) combined with unfractionated heparin on the hemofilter life-span and the coagulation profile during continuous venovenous hemofiltration.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Intensive care unit at a university-affiliated hospital.

PATIENTS

Twenty-four critically ill, mechanically ventilated patients with postoperative acute renal failure who require continuous venovenous hemofiltration.

INTERVENTIONS

The patients were anticoagulated with 5 ng/kg/min PGE1 and 6 IU/kg/hr heparin or 20 ng/kg/min PGE1 and 6 IU/kg/hr heparin, injected into the extracorporeal circuit before the hemofilter.

MEASUREMENTS AND MAIN RESULTS

The life-span of 43 hemofilters was evaluated. They were used until extracorporeal line pressure exceeded 250 mm Hg, ultrafiltration rate decreased to 16 mL/min, or grossly visible extracorporeal clotting occurred. Blood was sampled from the afferent (prefilter) and efferent (postfilter) lines of the extracorporeal circuit. Platelet counts, in vitro platelet function, plasma concentrations of platelet factor 4, prothrombin fragment F1+2, thrombin-antithrombin complex, routine plasma coagulation tests, and hemodynamic profile were determined before and during hemofiltration. Hemofilter usage was significantly longer in patients anticoagulated with 20 ng/kg/min PGE1 (32 +/- 3 [SEM] hrs) than with 5 ng/kg/min PGE1 (22 +/- 3 hrs). In vitro bleeding parameters were significantly prolonged in postfilter blood in patients receiving 20 ng/kg/min PGE1. Prefilter, there was no antiplatelet activity in either group and platelet counts remained stable. No intra- or intergroup differences in plasma coagulation profile or hemodynamic parameters were detected.

CONCLUSION

Extracorporeal administration of PGE1, combined with low-dose heparinization, inhibits platelet reactivity and preserves hemofilter life dose-dependently.

Do we still need dipyridamole?

There is limited evidence that dipyridamole is generally an effective antithrombotic agent when used alone, nor is there convincing evidence that the combination of aspirin and dipyridamole is more effective than aspirin alone, except perhaps in cerebrovascular disease. There is no consistent evidence to support the routine use of dipyridamole after coronary artery bypass grafting and in patients with occlusive peripheral vascular disease, although these remain common reasons for its use. Dipyridamole is a useful agent in 'pharmacological stress' testing in nuclear cardiology imaging and may be valuable when combined with warfarin in certain patient groups, such as those with prosthetic heart valves. When combined with aspirin, dipyridamole may be of value in the secondary prophylaxis of cerebrovascular disease, although further studies are clearly needed. In a significant proportion of cases, evidence-based medicine cannot support the current widespread continued prescription of dipyridamole in cardiological practice, but the jury is still out on cerebrovascular disease.

7E3 F(ab′)2 , a Monoclonal Antibody to the Platelet GPIIb/IIIa Receptor, Protects Against Microangiopathic Hemolytic Anemia and Microvascular Thrombotic Renal Failure in Baboons Treated With C4b Binding Protein and a Sublethal Infusion of Escherichia coli

We have used our previously described baboon model of infusion of both a sublethal dose of Escherichia coli and C4b binding protein to assess the impact of inhibiting platelet function with the F(ab′ )2 fragment of the monoclonal antibody 7E3, directed against the platelet glycoprotein (GP)IIb/IIIa receptor, on the characteristic microvascular changes. At a dose of 0.25 to 0.35 mg/kg bolus plus an infusion of 0.25 to 0.35 mg/kg over 6 hours, c7E3 F(ab′ )2 had only a minimal impact on fibrinogen consumption and delayed but did not prevent, the development of thrombocytopenia. Treatment with 7E3 F(ab′ )2 , however, produced significant protection from the development of microangiopathic hemolysis and renal insufficiency. Histologic examination supported these observations, with treated animals having fewer schistocytes on blood smear and less evidence of ischemic renal changes. Treated animals also had more rapid recovery of peripheral white blood counts, suggesting a possible protective effect of treatment on ischemic damage to the bone marrow. These data indicate that potent inhibition of platelet function via GPIIb/IIIa receptor blockade can decrease ischemic organ damage in this animal model that has features similar to those found in diffuse intravascular coagulation, hemolytic uremic syndrome, and thrombotic thrombocytopenic purpura.

Increased but highly dispersed levels of plasma glycocalicin in patients with disseminated intravascular coagulation

Thrombocytopenia is one of the most common laboratory manifestations of disseminated intravascular coagulation (DIC). To investigate whether thrombocytopenia in DIC is indeed due to platelet consumption, we measured the plasma levels of glycocalicin, a proteolytic fragment of the platelet membrane glycoprotein (GP) Ib alpha, a component of the GPIb/IX complex, in patients with solid tumors either with DIC(n=18) or without DIC (n=18). Patients with DIC had significantly elevated levels of glycocalicin(2.53 +/- 1.59 mg/1;n=18,p<0.05) compared to those without DIC (1.50 +/- 0.41 mg/1;n=18), indicating enhanced platelet consumption, or destruction, in patients with DIC. However, glycocalicin concentrations had a wide range (0.18-5.74 mg/1), and 3 DIC patients had levels lower than the normal lower limit. These findings suggest that, in patients with DIC, thrombocytopenia is not always due to increased platelet consumption, but it may be due to decreased production of platelets. Determination of plasma glycocalicin concentrations is an easy way to identify thrombocytopenia, due to bone marrow insufficiency in these patients.

Role of endothelial cells in the development of glomerular lesions of mesangiocapillary glomerulonephritis

The histological and ultrastructural changes of mesangiocapillary glomerulonephritis (MCGN) are not unique to this entity: splitting of basement membrane (BM) is seen in a number of conditions with an altered coagulation pattern. The distribution of endothelial cells in the glomerular capillaries in five cases of MCGN was studied by light and electron microscopy and immunocytochemistry; endothelial cells were stained with peroxidase or FITC-conjugated antibodies against Factor VIII-related antigen or CD34 antigen and observed with conventional light/immunofluorescence microscopy and confocal laser scanning microscopy for three-dimensional reconstruction. Electron microscopy was performed with colloidal gold labelling. Endothelial cells were shown to be present within the duplicated basement membranes of capillaries and continuity was demonstrated with endothelial cells lining the capillary lumina. These results suggest that endothelial cells as well as mesangial cells can participate in the formation of the characteristic double contour of capillary walls in MCGN, especially in the early stages. There are some similarities to the changes seen in larger arteries as a consequence of thrombotic disease.

Evidence-based recommendations for the clinical use of recombinant human erythropoietin

In an era of increasing scrutiny regarding use of health care resources, it is critical that physicians have rational, evidence-based guidelines for treatment decisions. This review of more than 200 published papers constitutes a comprehensive approach to evaluating the current evidence regarding the clinical use of recombinant human erythropoietin therapy in renal failure patients. After this review, specific recommendations are provided regarding who should receive r-HuEPO; what the target hemoglobin should be; the best route of administration of r-HuEPO; how iron status should be evaluated and managed; and monitoring and follow-up of patients taking r-HuEPO. Throughout the article, areas for important future research are also identified.

Lipoproteins and the haemostatic system in atherothrombotic disorders

The early belief that the haemostatic system has no active role in the formation of the atheromatous plaque is no longer tenable. Rather, the association between hypercholesterolaemia and atherosclerosis appears to arise in part because of various effects of high concentrations of LDL and VLDL particles on the cellular and humoral components of the system, thereby promoting plaque growth and thrombosis. These may be summarized as follows: 1. High concentrations of native LDL have been reported to promote the adhesion of monocytes to the endothelial cell, suggesting that the latter undergoes a form of activation upon such exposure. Oxidized LDL is more potent in this respect, and persistent exposure of endothelium to such particles can eventually lead to cell injury. 2. Activated endothelial cells acquire characteristics on their luminal surface conducive to thrombin generation and fibrin production. Thrombin has several actions on the endothelial cell, monocyte, smooth muscle cell and platelet which in the presence of hypercholesterolaemia will promote the formation of atheroma. 3. Oxidatively modified LDL can activate circulating monocytes, when they also acquire procoagulant properties which favour thrombin production. 4. Platelets show an increased tendency to aggregate when exposed to hypercholesterolaemic plasma. This effect may arise in part because the platelet of the hypercholesterolaemic patient expresses an increased number of fibrinogen binding sites on its surface following activation by agonists such as ADP. These hyperaggregable platelets adhere to activated endothelial cells which express von Willebrand factor on their surface, and to subendothelial proteins exposed in the gaps that open between injured endothelial cells. Platelets exposed to raised LDL levels also show a reduced sensitivity to prostacyclin, an antiaggregatory agent. Oxidatively modified LDL has been reported to stimulate aggregation of platelets in the absence of other agonists such as ADP or thrombin (spontaneous aggregation). 5. Platelet aggregation and fibrin deposition at sites of endothelial injury will create microthrombi which become incorporated into the lesion by organization, thereby increasing the fibrous and cellular content of the atheromatous plaque. 6. Lipolysis of triglyceride-rich lipoproteins at the endothelial cell surface leads to transient activation of the coagulation mechanism with activation of factor VII. Activated factor VII is a potent procoagulant when it forms a complex with tissue factor in the atheromatous lesion. Persistent hypertriglyceridaemia is accompanied by raised concentrations of factor X, factor IX, factor VII and prothrombin. 7. Hypertriglyceridaemia is associated with an increased plasma concentration of PAI-1 and a reduction in plasma fibrinolytic activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of interleukin 6 on megakaryocytes and on canine platelet function

The multifunctional cytokine interleukin 6 (IL-6) is a potent promoter of megakaryocytic maturation in vitro. In vivo, IL-6 has similar effects on the maturation of megakaryocytes, as shown by enhancing size, ploidy and platelet production. IL-6 is capable of augmenting the platelet count in both normal animals and those with reduced megakaryocyte mass; ongoing clinical trials suggest a similar thrombocytopoietic effect in man. Moreover, IL-6 alters platelet function, rendering them more sensitive to activation by thrombin and platelet activating factor. Finally, IL-6 promotes increases in plasma fibrinogen and von Willebrand factor, and a decrease in free protein S concentration. These modifications of the platelet and coagulant phases of the clotting mechanism may result in an overall prohemostatic tendency, which may prove beneficial for the amelioration of bleeding propensity following chemotherapy. However, additional investigation will be required to determine if IL-6-mediated alterations of hemostasis may lead to pathologic thrombosis.

Anti-platelet therapy in graft thrombosis: results of a prospective, randomized, double-blind study

Hemodialysis (HD) vascular access thrombosis remains a major cause of morbidity, accounting for 17.4% of all HD patient hospital admissions in 1986. We initiated this prospective, randomized, double-blind, placebo-controlled, parallel group study to examine if dipyridamole and/or aspirin decreased the rate of thrombosis of expanded polytetrafluoroethylene (ePTFE) grafts in HD patients. Two patient groups were studied: Type I--with a new ePTFE graft; and Type II--with thrombectomy and/or revision of a previously placed ePTFE graft. One hundred and seven patients were followed for 18 months or until the first thrombotic episode. Actuarial analysis of Type I patients showed cumulative thrombosis rates (mean +/- SEM) of 21 +/- 9% on dipyridamole alone, compared with 25 +/- 11% on dipyridamole and aspirin combination, 42 +/- 13% on placebo, and 80 +/- 12% on aspirin alone. The relative risk of thrombosis with dipyridamole was 0.35 (P = 0.02) and that for aspirin was 1.99 (P = 0.18). In Type II patients, the rate of thrombosis was high in all study drug and placebo groups (overall 78% thrombosis) and actuarial analysis was not carried out because of the small number of patients enrolled. We conclude that dipyridamole is beneficial in patients with new ePTFE grafts and that aspirin does not improve the risk of thrombosis in ePTFE grafts. Neither dipyridamole nor aspirin has any beneficial effect in patients with prior thrombosis of ePTFE grafts.

Relative importance of immune and non-immune causes of platelet refractoriness

In this prospective study, 26 consecutive patients being treated for haematological malignancies receiving standard (i.e. non-leucocyte-depleted) blood components were observed for the development of refractoriness to platelet transfusions. One hundred and sixteen of the 266 (44%) platelet transfusions failed to produce a satisfactory response. In 102/116 (88%), the poor response was in the presence of non-immune factors known to be associated with platelet refractoriness. Non-immune factors were present alone in 78/116 (67%), and in combination with immune factors in a further 24/116 (21%). Immune factors (HLA and platelet-specific antibodies) were present during 29/116 (25%) of unsuccessful platelet transfusions. Statistical analysis confirmed that platelet refractoriness was significantly associated with the presence of non-immune factors. The non-immune factors associated with refractoriness were often multiple, most frequently a combination of fever, infection and antibiotic therapy. This study provides evidence that immune mechanisms were not the predominant cause of platelet refractoriness in the patient population studied. It also suggests that measures for the prevention of HLA alloimmunisation, such as leucocyte depletion, may have a limited impact in reducing the incidence of refractoriness to platelet transfusions.

Clinical importance of thrombocytopenia occurring in the hospital phase after administration of thrombolytic therapy for acute myocardial infarction. The Thrombolysis and Angioplasty in Myocardial Infarction Study Group

OBJECTIVES

The purpose of this study was to examine the incidence and clinical implications of thrombocytopenia that occurs in hospital after administration of thrombolytic therapy for acute myocardial infarction.

BACKGROUND

The use of thrombolytic therapy in patients with acute myocardial infarction has improved mortaltiy rates, but hemorrhage remains a major complication. Because thrombocytopenia may be associated with hemorrhage after thrombolytic therapy, we examined the incidence and clinical implications of thrombocytopenia after administration of thrombolytic therapy for acute myocardial infarction.

METHODS

The patient population comprised 1,001 patients enrolled in Phases 2, 3 and 5 of the Thrombolysis and Angioplasty in Myocardial Infarction (TAMI) trial and the urokinase trial. Patients received recombinant tissue-type plasminogen activator, urokinase or combination therapy in various dosing schemes. All patients received heparin, aspirin and a calcium-channel blocking agent. Thrombocytopenia occurring anytime after thrombolytic therapy was defined as a nadir platelet count either < 100,000/microliters or < 1/2 baseline. Blood loss was quantified by a bleeding index. Multiple logistic regression was used to evaluate the independent contribution of thrombocytopenia in a model predicting in-hospital mortality.

RESULTS

Thrombocytopenia occurred in 16.4% of patients, with no difference among the thrombolytic regimens. Patients with thrombocytopenia had a lower median acute ejection fraction and a higher likelihood of three-vessel coronary artery disease than patients without thrombocytopenia. Patients with thrombocytopenia had more hemorrhage, a higher in-hospital mortality rate and a more complicated hospital course than patients without thrombocytopenia, even after consideration of other important variables, including age, acute ejection fraction, number of diseased vessels, bypass surgery and use of intraaortic balloon counterpulsation.

CONCLUSIONS

Thrombocytopenia after thrombolytic therapy is a common event and is associated with excess hemorrhage and mortality. Platelet counts should be monitored daily after administration of thrombolytic therapy because the appearance of thrombocytopenia identifies a subset of patients at increased risk for hemorrhage and death.

The megakaryocyte platelet system and vascular disease

Platelets form a heterogeneous population of cells produced from the uniquely large polyploid cell found in the bone marrow, the megakaryocyte. The platelet megakaryocyte axis forms a dynamic equilibrium varying in normal biology and in disease. Prolonged platelet destruction leads to the production of large platelets from large, high ploidy megakaryocytes. In vivo and ex vivo studies show that such platelets have more haemostatic potential than smaller less dense platelets. The evidence suggesting that prothrombotic changes in the megakaryocyte platelet axis precede coronary artery thrombosis and the importance of platelet reactivity in atherosclerosis will be reviewed.

Cilostazol, a novel cyclic AMP phosphodiesterase inhibitor, prevents reocclusion after coronary arterial thrombolysis with recombinant tissue-type plasminogen activator

Inhibitors of cyclic nucleotide phosphodiesterase hydrolysis of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate are known to inhibit platelet aggregation, which plays an important role in acute reocclusion after thrombolysis in acute myocardial infarction. In the present study of a canine preparation of coronary artery thrombosis superimposed on high-grade stenosis, we tested whether the antithrombotic agent cilostazol, an inhibitor of cAMP phosphodiesterase, could prevent acute reocclusion or sustain coronary blood flow after thrombolysis when used with recombinant tissue-type plasminogen activator (rt-PA) and heparin. Intravenous infusion of rt-PA (0.5 mg/kg body wt for 30 minutes) and heparin (a 150 IU/kg body wt i.v. bolus and then 25 IU/kg body wt per hour i.v.) was combined with cilostazol (0.6 or 1.8 mg/kg body wt for 60 minutes). Without cilostazol, reperfusion was observed in seven of eight dogs, but reocclusion occurred in six of these seven dogs after 9 +/- 2 minutes. After administration of 1.8 mg/kg body wt cilostazol (group B-2; a 120-minute observation after the start of rt-PA infusion), reperfusion occurred in all seven dogs (p < 0.05 versus control group), and brief cyclic reocclusion was observed in only one dog 63 minutes after reperfusion. At the same dose of cilostazol (group B-2L; a 240-minute observation after the start of rt-PA infusion), reperfusion occurred in all five dogs (p < 0.05 versus control group), and coronary blood flow was well maintained except for one short reocclusion in one dog. Cilostazol inhibited cyclic flow reduction in a dose-dependent fashion.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical aspects of autologous fibrin glue derived from ammonium sulfate precipitation

The autologous fibrin glue (AFG) was produced from 30 human donors using the ammonium sulfate precipitation method, and a study of its biochemical composition was performed. The fibrinogen concentration ranged 13 to 57 mg/mL, the yield averaged 54.6%, and there was a direct relationship between the level of fibrinogen in plasma and AFG which had been made from the same donor's plasma. Our results suggest that the quality of this category of AFG depends partially on the fibrinogen level of donor's plasma. Quality control of the AFG is discussed. Additionally, the effectiveness of three fibrinolysis inhibitors were compared to find an optimum one which inhibits autofibrinolysis of this glue. Tranexamic acid and epsilon aminocaproic acid (EACA) were acceptable alternatives to aprotinin.

Submandibular hemangioma as the initial manifestation of Kasabach-Merritt syndrome

Kasabach-Merritt syndrome (thrombocytopenia, consumption coagulopathy and occasional hemolysis) is an infrequent but often fatal complication of rapidly growing hemangiomas in infants. We describe a 1-month-old infant with a huge hemangioma involving the left submandibular region associated with a severe consumptive coagulopathy, who was successfully treated with transfusion of blood products, prednisone and radiation therapy. It is stressed that pediatric otorhinolaryngologists should always be aware of the lethal status of this condition in infants.

The regulation of megakaryocyte polyploidization and its implications for coronary artery occlusion

Polyploidization is a distinctive feature of megakaryocyte differentiation. The physiological meaning and the regulation of this process are obscure. Megakaryocyte ploidy varies in normal biology and in disease. Here we review the evidence suggesting that ploidy changes may have a role in the determination of platelet reactivity and in the aetiology of coronary artery occlusion. We also present a hypothesis that may serve as a framework to explore the regulation of megakaryocyte polyploidization at the molecular level and also may provide a rational basis to explain the occurrence of ploidy changes in ischaemic heart disease.