Agkistrodon piscivorus piscivorus platelet aggregation inhibitor: a potent inhibitor of platelet activation

Applaggin (Agkistrodon piscivorus piscivorus platelet aggregation inhibitor) is a potent inhibitor of platelet activation. The protein is isolated from the venom of the North American water moccasin snake in three steps, including gel filtration, cation exchange, and reverse-phase HPLC procedures. The purified protein migrates as a 17,700-Da polypeptide by SDS/PAGE under nonreducing conditions and as a 9800-Da peptide in the presence of thiol. The behavior of applaggin on SDS/PAGE would indicate that the protein is a disulfide-linked dimer. Applaggin has been completely sequenced by Edman degradation and consists of 71 amino acids. The sequence is rich in cysteine and contains Arg-Gly-Asp at residues 50-52. Applaggin blocks platelet aggregation induced by ADP, collagen, thrombin, or arachidonic acid with IC50 values ranging from 12 to 128 nM (0.2-2.3 micrograms/ml) depending on the agonist and its concentration. This inhibition is found to correlate with inhibition of thromboxane A2 generation and of dense granule release of serotonin. Inhibition by applaggin of serotonin release induced by ADP, gamma-thrombin, and collagen was monitored in plasma under stirred conditions with [3H]serotonin-loaded platelets, and IC50 values for inhibition are found to range from less than 10 to 145 nM. At saturating concentrations, 125I-labeled applaggin (125I-applaggin) binds to 28,500 sites per unstimulated, washed platelet with a Kd of 1.22 x 10(-7) M. Binding of 125I-applaggin to platelets is inhibited by the synthetic undecapeptide Arg8-Gly-Asp-Val at 200 microM.

Thrombin-induced increase in surface expression of epitopes on platelet membrane glycoprotein IIb/IIIa complex and GMP-140 is a function of platelet age

Platelets are heterogeneous in the content of membrane glycoprotein (GP)IIb/IIIa complex. To determine whether this heterogeneity is related to changes associated with platelet aging in the circulation, newly released platelets, obtained during recovery from nonimmune-mediated acute experimental thrombocytopenia in baboons, were studied. Monoclonal antibody (MoAb) binding to epitopes expressed on GPIIb/IIIa complex (LJ-CP8), GMP-140 (S12), and GPIa/IIa (12F1) was measured on control platelets (comprising platelets with a normal age distribution; mean age 60 to 72 hours) and newly formed platelets (mean age 12 hours), both in the resting state and after thrombin stimulation. Whereas LJ-CP8 binding to resting control platelets increased by 34% upon stimulation by gamma-thrombin from 30,885 +/- 1,171 to 41,458 +/- 1,311 molecules/platelet at saturating concentrations of antibody, LJ-CP8 binding to resting young platelets did not increase significantly upon thrombin stimulation (31,878 +/- 3,330 and 33,791 +/- 3,486 molecules/platelet, respectively). Similarly, binding of antibody S12 in response to maximal thrombin stimulation was reduced by 42% from 10,246 +/- 834 molecules/platelet at saturating concentrations of S12 for control platelets to 5,971 +/- 665 molecules/platelet for young platelets (P = .001). S12 binding to unstimulated platelets was less than 10% of the binding observed after thrombin stimulation at all concentrations of S12 for both control and young platelets. However, maximal binding of antibody 12F1 to resting control platelets did not differ significantly from that observed with resting young platelets (2,926 +/- 167 and 2,857 +/- 208 molecules/platelet, respectively), and 12F1 binding was unchanged after thrombin stimulation for both control and young platelets. We conclude that the thrombin-induced increase in the expression of epitopes on platelet membrane GPIIb/IIIa complex and GMP-140 is a function of platelet age.

Flow cytometric analysis of megakaryocytes from patients with abnormal platelet counts

Megakaryocytes (MKs) from 40 patients with quantitative platelet disorders and 19 normal volunteers were analyzed by flow cytometry for size, fine cell internal structure and granularity, membrane expression of the glycoprotein (GP) IIb/IIIa complex, and for ploidy distribution. Analysis was performed on unfractionated minimally manipulated marrows obtained from routine bone marrow aspirates. MKs were labeled with a fluorescent lineage-specific monoclonal antibody to the GPIIb/IIIa complex followed by DNA staining with propidium iodide. Eight hundred to 3,000 MKs were analyzed in each sample. The modal ploidy distribution in normals was 16N, comprising about half of the megakaryocytic population, with 22.6% of the cells less than or equal to 8N and 22.0% greater than or equal to 32N. Twelve thrombocytopenic patients with decreased marrow MKs on biopsy (mean platelet count [MPC] 44,600/microliters) showed an increase in low ploidy cells with 53.2% less than or equal to 8N (P less than .01); cell size was reduced in three patients when compared to normal cells of identical ploidy (P less than .05). Eight thrombocytopenic patients with enhanced platelet destruction (with normal or increased MKs on biopsy and shortened platelet survival; MPC 41,400/microliters) showed an increased proportion of high ploidy cells greater than or equal to 32N to 39.2% (P less than .01). Increased cell size and granularity were found in four of these patients (P less than .05). Six patients with thrombocytopenia secondary to multiple mechanisms affecting both platelet production and destruction (MPC 66,700/microliters) showed no shift in ploidy. Four patients with primary thrombocytosis (two with thrombocythemia and two with polycythemia vera; MPC 822,500/microliters) showed a marked shift toward high ploidy cells with 42.3% greater than or equal to 32N and 7.6% greater than or equal to 64N cells (P less than .01). The shift was accompanied by a marked increase in cell size and granularity in the patients with thrombocythemia. Ten patients with thrombocytosis secondary to chronic blood loss, malignant or inflammatory disorders (MPC 714,000/microliters), showed variable distributions with four patients exhibiting a shift in ploidy to the right similar to that found in the patients with increased platelet destruction. Based upon the present data, flow cytometric ploidy distribution may be diagnostically useful in thrombocytopenic patients by discriminating between disorders of platelet production and destruction. (ABSTRACT TRUNCATED AT 400 WORDS)

Demonstration of single chain urokinase-type plasminogen activator on human platelet membrane

Fibrinolytic activity was found to be associated with sonicated platelet membranes after separation from cytosol by differential centrifugation. This fibrinolytic activity was attributed to the presence of a plasminogen activator, which was immunochemically identified as urinary-type plasminogen activator (uPA) by antibody neutralization assay, immunoblotting, and immunofluorescence. The molecular weight (mol wt) of this uPA was 54,000 and was present as the single chain form, although a small amount was detected in a higher mol wt complex indicative of a uPA-inhibitor complex. Treatment of membrane preparations with Triton X-100, 3 mol/L KCl, and 0.1 mol/L glycine, (pH 2.3), but not 10 mmol/L ethylenediamine tetraacetic acid (EDTA), removed the uPA from the membrane. This suggests that uPA is a peripheral membrane protein and that metal ions do not mediate protein-membrane association. Immunofluorescent staining revealed the presence of uPA on the outer surface of the platelet in preparations of intact unstimulated platelets. Thus, uPA is associated with the outer leaflet of the platelet membrane and may be involved with the acceleration of thrombus degradation observed with platelet-rich thrombi.

Menstrual cyclic thrombocytopenia

We studied three patients with cyclic thrombocytopenia which occurred in phase with the menstrual cycle. The platelet count in each patient reached a nadir of 5-20 x 10(9)/l at the onset of menses. Thrombocytopenia was associated with bruising, epistaxis and menorrhagia and was followed 5-14 d later by normal or elevated platelet counts (up to 900 x 10(9)/l). Repeat bone marrow examinations performed at the time of reduced platelet counts showed megakaryocytic hyperplasia. 111In-platelet-disappearance from the circulation was measured in one patient; T50, time to half activity, was shortened to 0.7 d during the period of thrombocytopenia and was prolonged to 3.2 d when the platelet count increased (normal platelet T50 is about 4.8 d). In two of three patients platelet-associated anti-glycoprotein Ib autoantibodies were present and remained elevated despite normalization of the platelet count. In both of two patients the decrease in platelet count at the onset of menses was associated with an increase in the expression of monocyte Fc gamma receptors. Based on the reported capacity of oestrogenic hormones to modulate macrophage Fc gamma receptor expression, we propose that hormonal changes during the menstrual cycle may alter the Fc gamma receptor-mediated clearance of antibody-coated platelets by macrophages, modulate platelet survival, and cause cyclic thrombocytopenia.

Inhibition of platelet-dependent thrombus formation by human activated protein C in a primate model

The in vivo antithrombotic properties of human plasma activated protein C (APC), a natural anticoagulant enzyme, were investigated in a baboon model of thrombus formation on prosthetic vascular grafts. Infusion of 0.25 to 1.1 mg/kg/h purified, human, APC inhibited blood clotting, as measured by the activated partial thromboplastin time (APTT), and reduced vascular graft platelet deposition by 40% to 70%, as determined by the real-time scintillation camera imaging of 111In-labeled platelet deposition. APC infusion also preserved graft patency. Hemostatic plug formation remained normal, as measured by the template bleeding times. These results suggest that APC administration may produce immediate antithrombotic effects under arterial flow conditions.

Incidence of cholesteatoma with cleft palate

The overall incidence of cholesteatoma in Iowa has been estimated to be 6.01/100,000 population, or less than 0.01%. However, in patients with cleft palate seen at the University of Iowa Cleft Palate Clinic between 1947 and 1968 and followed for at least 10 years, the risk of developing cholesteatoma was 9.2%. In order to determine whether this high risk of cholesteatoma is still valid, a comparable retrospective study was undertaken of 153 patients with cleft palate who were born between 1969 and 1977, were enrolled in the University of Iowa Cleft Palate Clinic within 1 year of birth, and were followed by the interdisciplinary team for a minimum of 10 consecutive years. Cholesteatoma occurred in four patients (2.6%), a substantial decrease in the risk of developing cholesteatoma in a well-defined and longitudinally followed population.

Preformed confluent endothelial cell monolayers prevent early platelet deposition on vascular prostheses in baboons

We assessed the capacity of preformed confluent endothelial cell (EC) monolayers on small-caliber prosthetic grafts to prevent early platelet deposition in a baboon model. Cultured human umbilical vein ECs were attached to expanded polytetrafluoroethylene (Gore-Tex, 4 mm inner diameter, 3 cm length) precoated with type I collagen and perfused in vitro for 2 hours at 15 ml/min with serum-containing culture medium to achieve cell spreading into confluent monolayers. Cell numbers were quantified by deoxyribonucleic acid assay or isotopic counting of indium 111-labeled ECs. Saturation density for cell attachment was 3.55 +/- 0.29 x 10(5) cells per square centimeter of graft. After 1 hour of in vitro perfusion at 100 ml/min, 92.8% +/- 1.8% of cells remained attached and the flow surface was morphologically confluent. When grafts were inserted as extension segments into arteriovenous silicone rubber (Silastic) shunts in baboons, thereby exposing the endothelialized grafts to native flowing blood (100 ml/min) for 1 hour, the EC monolayers remained confluent with 81.05% +/- 5.88% of the cells attached. Indium 111-labeled platelet deposition onto grafts was quantified by dynamic scintillation camera imaging. Platelet deposition on 10 endothelialized grafts was markedly reduced (0.16 +/- 0.04 x 10(9) platelets per graft) compared with 10 untreated control grafts (1.84 +/- 0.59 x 10(9) platelets, p less than 0.02), eight grafts with early attached unspread ECs (2.38 +/- 0.66 x 10(9) platelets, p less than 0.005), and 11 grafts treated with collagen alone (5.93 +/- 0.72 x 10(9) platelets, p less than 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Flow cytometric analysis of normal human megakaryocytes

Megakaryocytes from normal routine human bone marrow aspirates were analyzed by flow cytometry for size, fine cell structure and granularity, membrane expression of glycoprotein (GP) IIb/IIIa and ploidy. Marrow cells were initially enriched for megakaryocytes by a Percoll density gradient and megakaryocytes were labeled with a fluoresceinated monoclonal antibody directed to the GPIIb/IIIa complex. The cells were fixed with paraformaldehyde and stained with propidium iodide (PI) for DNA quantitation. Using two-color flow cytometry, megakaryocytes were identified by their high membrane immunofluorescence and their ploidy was determined according to the relative fluorescence intensity of the PI. Forward light scatter (FSC), correlating with cell size, 90 degrees side light scatter (SSC), reflecting primarily cell internal fine structure and granularity, and total cell membrane fluorescence were examined. To evaluate independently the relationship between size and cell membrane fluorescence obtained by flow cytometry, megakaryocytes were sorted directly on slides and analyzed by a laser-based anchored cell analyzer (ACAS). There was a strong correlation among size, SSC, and the level of membrane fluorescence. The mean diameter of megakaryocytes was 28.1 +/- 12.3 micron. The modal ploidy distribution was 16N with approximately one-fifth of the cells less than or equal to 4N. The mean FSC and SSC levels increased with increasing ploidy. However, the marked overlap observed between the ranges of these parameters in adjacent ploidy classes suggested that size and SSC increase continuously rather than by discrete steps as is characteristic for ploidy. The total surface membrane fluorescence was correlated with cell size (r = 0.98) as measured by FSC or directly by the ACAS (r = 0.85), and with cell ploidy (r = 0.99) indicating an augmentation in total membrane GPIIb/IIIa expression with an increase in cell size and ploidy. However, estimated GPIIb/IIIa fluorescence density was inversely correlated with FSC suggesting that the GPIIb/IIIa surface epitope density is decreased with increasing cell maturity. We conclude that flow cytometry is a useful technique for the rapid analysis of human megakaryocytes obtained by marrow aspiration, and should be applicable to studies of pathologic states.

Interruption of acute platelet-dependent thrombosis by the synthetic antithrombin D-phenylalanyl-L-prolyl-L-arginyl chloromethyl ketone

Since the antithrombin action of heparin fails to interrupt arterial thrombosis, a mediating role for thrombin (EC 3.4.21.5) in the formation of high-shear platelet-dependent thrombus has been unproven. To determine whether thrombin is important in acute arterial thrombus formation and to assess the therapeutic potential of inhibiting its action, the effects of the synthetic covalent antithrombin D-phenylalanyl-L-prolyl-L-arginyl chloromethyl ketone (FPRCH2Cl) on arterial-flow vascular graft thrombosis and occlusion have been studied in a nonhuman primate model. Continuous intravenous infusion of FPRCH2Cl (100 nmol/kg per min) into vascular graft-bearing baboons (Papio anubis) abolished (i) vascular graft 111In-platelet deposition, (ii) vascular graft occlusion, (iii) thrombus-associated in vivo release of platelet-specific proteins and fibrinopeptides, (iv) platelet hemostatic plug formation, (v) thrombin-induced platelet aggregation ex vivo, and (vi) thrombin-induced blood clotting. The effects of FPRCH2Cl largely disappeared within 15 min after the infusion had been discontinued. FPRCH2Cl produced no detectable cardiovascular or other acute side effects. In contrast, sustained comparably anticoagulating levels of heparin had no effect upon 111In-platelet graft deposition, graft occlusion, platelet function as measured by the bleeding time, platelet aggregation ex vivo, or release of platelet-specific proteins in vivo. We conclude that thrombin is the principal mediator of platelet-dependent hemostatic plug formation and of the formation of platelet-dependent high-flow acute graft thrombosis and occlusion. Moreover, FPRCH2Cl or other synthetic antithrombins may provide effective antithrombotic therapy for both arterial and venous thrombosis by simultaneously inhibiting platelet activation and fibrin formation.

Durability of confluent endothelial cell monolayers on small-caliber vascular prostheses in vitro

Since implantation of small-caliber vascular grafts with preformed confluent endothelial cell monolayers (ECMs) may prevent acute platelet deposition and thrombus formation, we have evaluated the conditions necessary to produce durable ECMs. Cultured human umbilical-vein ECs in buffer were attached to vascular grafts--either expanded polytetrafluoroethylene (ePTFE) or knitted Dacron, both with inside diameters of 4 mm--precoated with collaten type I and perfused in vitro with serum-containing culture medium to achieve cell spreading into confluent monolayers. The number of cells attached was quantified by DNA measurements and indium-111 labeling. Morphology was evaluated by scanning electron microscopy. The maximum number of cells that attached acutely was 3.6 X 10(5) cells/cm2 graft, and the minimum number needed for confluence was 1.4 X 10(5) cells/cm2 graft. Confluence was morphologically complete after 2 hours of in vitro perfusion at 15 ml/min. When ECMs were exposed to varying flow rates, cell retention after 1 hour was 96.1% +/- 5.6% at 50 ml/min, 94.6% +/- 6.1% at 100 ml/min, 77.6% +/- 10.8% at 200 ml/min (p less than 0.001), and 40.1% +/- 10.4% at 400 ml/min (p less than 0.0001). Confluence was maintained for all grafts exposed to flows of 100 ml/min or less. Fewer cells were retained when acutely attached, unspread cells (71.5% +/- 11.5%) were compared with established ECMs (89.9% +/- 6.7%) at a flow rate of 100 ml/min (p less than 0.0001). ECMs on knitted Dacron were more durable than on ePTFE (82.7% +/- 5.3% versus 75.5% +/- 4.8% remained attached at 200 ml/min, P less than 0.05). 111Indium-labeled and unlabeled cells were equivalent with respect to saturation level attachment, spreading time to confluence, and durability under flow at 100 ml/min. We conclude that confluent and durable endothelial cell monolayers can be established on small-caliber vascular grafts within 2 hours.

Local intra-arterial fibrinolytic therapy in acute carotid territory stroke. A pilot study

The possibility that intra-arterial local infusion of fibrinolytic agents may achieve recanalization of previously occluded carotid territory arteries in acute stroke was tested in a prospective angiography-based open pilot study at two centers. Fifteen of 20 patients with acute symptoms (mean treatment-onset interval 7.6 hours) demonstrated complete recanalization; 10 of the 15 patients exhibited clinical improvement of varying degree by the time of hospital discharge. Four of the 20 patients suffered hemorrhagic transformation of the infarcted territory without clinical deterioration or demise. Because of the study format and the limited number of patients, dose responses for recanalization and risk relations were not established. We conclude that local intra-arterial fibrinolytic therapy may lead to cerebral arterial recanalization in acute carotid territory thrombotic stroke. The particular implications and limitations of this approach are discussed.

Migraine equivalent as a cause of episodic vertigo

There are many transient neurologic disturbances associated with various types of migraine. Visual symptoms, such as scintillating scotomata are most common, but somatosensory, motor, cranial nerve, and brain stem symptoms also occur. Among the brain stem symptoms, vestibular manifestations are quite common and include nonspecific dizziness, disequilibrium, vertigo, and motion intolerance. Auditory symptoms are less common. These transient neurologic symptoms can precede the headache as an aura, can occur during the headache, or, uncommonly, can immediately follow the headache. It is also well documented that the neurologic symptoms can occur in the period between headaches, a situation termed "migraine equivalent." Migraine equivalents usually occur in patients who have experienced typical migraine headaches earlier in life or who have migraine headaches at times other than when they experience equivalent symptoms. Rarely, typical migraine equivalent symptoms precede the development of the headaches by months or years, or occur in individuals who never develop headaches. Five patients with migraine equivalent symptoms that include vertigo are presented. The vertigo was the dominant symptom in some cases and was accompanied by nausea and vomiting. Differentiation from peripheral labyrinthine disorders is difficult, but a personal or family history of migraine, the temporal association of the neuro-otologic symptoms with other migraine equivalent symptoms, a characteristic pattern of occurrence of the symptoms, and a positive response to antimigrainous therapy are features that strengthen the diagnosis of a migraine equivalent phenomenon.

Effects of monoclonal antibodies against the platelet glycoprotein IIb/IIIa complex on thrombosis and hemostasis in the baboon

To assess the hemostatic consequences and antithrombotic effectiveness of blocking the platelet glycoprotein (GP) IIb/IIIa receptor for fibrinogen and other adhesive glycoproteins in vivo, well characterized murine monoclonal antibodies against the platelet GP IIb/IIIa complex, AP-2 and LJ-CP8, were infused intravenously into baboons. Four animals each received doses of 0.2, 0.4, and 1.0 mg/kg of purified AP-2 IgG, and three animals were given 1.0 mg/kg of the F(ab)2 fragment of AP-2. Five additional animals were given 10 mg/kg LJ-CP8 IgG. At the highest dose, radiolabeled AP-2 IgG bound to an average of 33,000 sites on the circulating platelets. Serial measurements included platelet count, bleeding time, platelet aggregation (induced by ADP, collagen, and gamma-thrombin), and 111In-platelet deposition onto Dacron vascular grafts. Bleeding times were markedly prolonged after injection of 1.0 mg/kg AP-2 IgG (19.2 +/- 3.4 min), 1.0 mg/kg AP-2 F(ab)2 (16.5 +/- 1.8 min), and 10 mg/kg LJ-CP8 (greater than 30 min) vs. control studies (4.6 +/- 0.2 min), and remained prolonged for 48 h. With each antibody platelet aggregation was initially reduced or absent, with partial recovery over 48 h in a manner that was inversely related to dose. AP-2, both whole IgG and F(ab)2 fragment, but not LJ-CP8, caused a dose-dependent reduction (20-46%) in the circulating platelet count over 24 h. Neither AP-2 nor LJ-CP8 caused a reduction in intraplatelet platelet factor 4, beta-thromboglobulin, or [14C]serotonin. Graft-associated platelet thrombus formation was reduced by 73% (1.0 mg/kg AP-2 IgG and 10 mg/kg LJ-CP8) and 53% (1.0 mg/kg AP-2 F(ab)2) relative to control values. In contrast, neither heparin (100 U/kg) nor aspirin (32.5 mg/kg twice a day) showed antithrombotic efficacy in this model. Thus, antibodies that functionally alter the platelet GP IIb/IIIa complex may produce immediate, potent, and transient, antihemostatic, and antithrombotic effects.

Selective decrease in platelet dense granule adenine nucleotides during recovery from acute experimental thrombocytopenia and ensuing thrombocytosis in baboons

Serial measurements of platelet volume, platelet content of adenine nucleotides, beta-thromboglobulin (beta-TG), platelet factor 4 (PF4) and ex vivo platelet aggregation were made in baboons under basal, steady-state conditions of normal platelet production, and during recovery from acute thrombocytopenia induced by the exposure of flowing blood to spherical glass microbeads. The mean basal platelet count of 509 +/- 107 X 10(9)/l (+/- 1 SD; n = 4) fell acutely to 36.8 +/- 12.6 X 10(9)/l after the insertion of glass bead columns and blood filters, placed distally, for 60 min into surgically implanted arteriovenous-shunts in heparinized baboons. After the irreversible removal of up to 90% of the baseline circulating platelet population, recovery from thrombocytopenia was characterized by a constant rate of increase in circulating platelet counts (115 +/- 11 X 10(9)/l/d) and a rebound thrombocytosis to 1.5 times the basal platelet count after 7 d. Steadystate thrombocytopoiesis was achieved by 3-4 weeks after the onset of thrombocytopenia. Platelet dense granule ADP and ATP decreased significantly from 3.89 +/- 0.20 and 2.33 +/- 0.25 mumol/10(11) platelets respectively at baseline to 2.17 +/- 0.37 and 1.68 +/- 0.37 mumol/10(11) platelets respectively after 7 d (P less than 0.001 in both cases) and normalization was achieved only after 4 weeks. By contrast, the mean platelet volume and platelet content of beta-TG and PF4 did not change significantly throughout the course of study (P greater than 0.1 in both cases). Platelet function, assessed by platelet aggregation ex vivo, demonstrated that platelet function was not impaired despite the significant decrease in dense granule ADP. We conclude that a selective, temporal reduction in platelet dense granule adenine nucleotides reflects changes in the thrombocytopoietic control mechanism secondary to induction of acute thrombocytopenia.

Purification of human megakaryocytes by fluorescence-activated cell sorting

For direct studies of growth control, a method was developed to purify viable human megakaryocytes to homogeneity from routine normal bone marrow aspirates. An initial separation of marrow over a 1.050 g/mL Percoll density cut was used to enrich megakaryocytes. After washing, the cells were specifically labeled with a fluoresceinated monoclonal antibody or F(ab')2 fragment to the platelet glycoprotein (GP) IIb/IIIa complex. Megakaryocytes were selectively sorted by using Becton Dickinson FACStar flow cytometer on the basis of a fluorescence intensity greater than 50-fold that of control cells. To increase resolution and purity the sorting rate was adjusted to one cell in 13 formed drops, and negative events that coincided with positive ones were aborted. Two thirds of the isolated cells were large, morphologically recognizable megakaryocytes with a forward light scatter fourfold that of the main cell population. Microscopic examination showed these cells to be greater than or equal to 98% megakaryocytes with a diameter of 20 to 46 microns and a ploidy range of 2N to 64N with a mode of 16N. The small highly fluorescent cells were 10 to 21 microns in diameter, and their ploidy range from 2N to 32N with main ploidy classes of 2N and 4N. The majority of these small cells also positively reacted with monoclonal antibody to platelet GPIb. The isolated cells were cultured in either Iscove's or leucine, lysine-deficient RPMI 1640 medium with 10% human plasma. The cells were maintained in culture more than three days and were capable of synthesis of both DNA and protein as assessed by radiolabeled thymidine and amino acid incorporation. Moreover, the isolated megakaryocytes were capable of responding to recombinant granulocyte-macrophage colony-stimulating factor. The data show that human megakaryocytes can be purified from routine marrow aspirates on the basis of a lineage marker and that they are capable of growth in vitro.

Effective antiplatelet drug concentrations in experimental arterial thromboembolism

Although drugs that modify platelet function have been widely studied as antithrombotic agents in experimental and clinical studies, there is limited information regarding the relationship between in vivo drug blood concentrations and antithrombotic efficacy. This study compared the pharmacokinetics of three antiplatelet agents with their antithrombotic effects in an experimental model of arterial thromboembolism in baboons. Thrombus formation was measured as steady-state platelet utilization induced by thrombogenic arteriovenous cannulae. The drugs studied were aspirin, dipyridamole and sulfinpyrazone. Aspirin was administered in daily doses of 20 mg/kg, dipyridamole in daily doses of 2.5 and 10 mg/kg, and sulfinpyrazone in daily doses of 20 and 100 mg/kg; each drug was given in two equal doses per day. Multiple blood samples were collected for drug analysis after steady-state had been reached. The average concentrations of dipyridamole at steady-state were 26 +/- 15 and 79 +/- 69 ng/ml after 2.5 and 10 mg/kg/day. These concentrations were associated with 28 and 87% inhibition of cannula platelet consumption, respectively. The average steady-state concentrations of acetylsalicylic and salicylic acids were 0.67 +/- 0.80 and 3.76 +/- 2.60 micrograms/ml, respectively, after 20 mg/kg/day. Aspirin had no effect on platelet consumption. Average concentrations of sulfinpyrazone were 1.05 +/- 0.45 and 12.25 +/- 5.73 micrograms/ml after 20 and 100 mg/kg/day, with significant concentrations of the sulfide metabolite. These concentrations were associated with 23 and 85% inhibition of platelet consumption, respectively. No significant pharmacokinetic interactions were observed after concurrent administration of aspirin and dipyridamole or sulfinpyrazone. As the experimental model used involves thrombus formation on an artificial surface, it is likely that these results are most relevant to patients with arterial prosthetic devices.

Baboon models of acute arterial thrombosis

In conclusion, we believe that the baboon offers many advantages as an experimental animal to study vascular disease, thrombus formation and dissolution, the effects of mediating variables, and the relative efficacy of therapeutic interventions. Each specific application for testing therapeutic agents may require testing in different model systems. For example, the AV vascular graft model is efficient, cost effective and well adapted to study interventions for acute arterial thrombosis. As the antithrombotic products of genetic engineering and molecular biology emerge, it will be increasingly important to have relevant, reproducible, and quantitative approaches to evaluate their effects in vivo.

Benign paroxysmal vertigo of childhood

Benign paroxysmal vertigo of childhood is a vestibular disorder characterized by multiple sudden brief episodes of true vertigo with nystagmus usually beginning after the age of 4. The diagnosis is based on the characteristic history, because the otologic and neurologic examinations, electronystagmogram, audiogram, and electroencephalogram are usually normal. The etiology of the disorder remains unknown, although a vascular disturbance of the posterior circulation with ischemia of the labyrinth or vestibular nuclei is most commonly postulated. A review of the literature and five new cases are used to acquaint otolaryngologists with this entity, review the characteristic clinical history, discuss differential diagnosis, and emphasize the usual clinical course.

Thrombosis and atherosclerosis: regulatory role of interactions among blood components and endothelium

Complex interactions among constituents of blood and components of the vessel wall are involved in the pathogenesis of atherosclerosis and its subsequent thrombotic complications. Alterations in the endothelium are central both to the slowly progressive process of atherogenesis and to the acute events leading to thrombotic occlusion. Recent data, obtained by systematic evaluation of chronologic events that occur in diet-induced atherosclerosis, have extended our understanding of interactive processes among endothelium, monocytes, platelets, vascular smooth muscle cells, and humoral hemostatic elements in atherogenesis.

Role of platelets and thrombosis in mechanisms of acute occlusion and restenosis after angioplasty

The vascular disruption produced by angioplasty initiates platelet deposition through the processes of platelet adhesion and recruitment of circulating platelets to form an enlarging mural platelet thrombus. Thrombin produced by simultaneous activation of the coagulation cascade by subendothelial connective tissue structures enhances platelet deposition and stabilizes the forming thrombus with enmeshing fibrin. Platelet recruitment involves the expression of the glycoprotein IIb/IIIa receptor for fibrinogen and other cytoadhesive proteins including fibronectin, thrombospondin and von Willebrand factor. Platelet deposition and thrombus formation caused by angioplasty appear to be important in the development of 2 complications: acute thrombotic occlusion and restenosis. Experimental mechanical vascular injury produces a predictable, although rather variable, amount of vascular narrowing due to transient smooth muscle cell proliferative intimal lesion formation. This intimal thickening by proliferating smooth muscle cells is in part mediated by platelet mitogens, particularly platelet-derived growth factor, which are released into the damaged vessel from platelets at the time of angioplasty. Platelet-derived growth factor may also be released from other associated vascular and blood cells in response to mechanical injury, e.g., endothelium, monocyte/macrophage and smooth muscle cells themselves. The actual mitogens, and their cells of origin, that mediate restenosis after therapeutic angioplasty remain to be established. Various oral antiplatelet agents have been shown to reduce arterial thrombotic occlusion in a number of controlled clinical trials, e.g., aspirin in transient ischemic attacks and unstable angina, aspirin and dipyridamole in saphenous vein coronary artery bypass and progression of peripheral vascular disease and dipyridamole in artificial heart valves. Acute arterial thrombosis may require more potent, immediate and transient intervention, e.g., monoclonal antibody to platelet receptor expression.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro endothelialization of small-caliber vascular grafts

To establish the conditions for achieving immediate and complete endothelial cell coverage of the luminal surfaces of small-caliber (internal diameter:4 mm) vascular grafts in vitro, the attachment and spread of endothelial cells cultured from human umbilical veins to expanded polytetrafluoroethylene (PTFE) and knitted Dacron grafts was studied. Cell number was quantified by fluorescent measurements of deoxyribonucleic acid. The completeness of cell coverage and cell junction formation were assessed by means of both scanning and transmission electron microscopy. Cell attachment was compared after expanded PTFE or knitted Dacron grafts were precoated with gelatin, laminin, fibronectin, fibrin, or collagen, singly or in combination. Saturation cell attachment of 3.5 +/- 0.7 X 10(5) cm-2 was completed within 15 minutes when (1) type I collagen was used to form the substrate matrix, (2) human umbilical vein endothelial cells were suspended in phosphate-buffered saline solution supplemented with calcium and magnesium, and (3) the suspended cell number was greater than or equal to 5 X 10(5). In contrast, attachment to untreated or laminin-treated surfaces was 1.3 +/- 0.33 X 10(5) cells cm-2 and attachment to fibrin- or fibronectin-treated surfaces was 2.8 +/- 0.47 and 2.4 +/- 1.1 cells X 10(5) cm-2, respectively. However, to produce a confluent flow surface, the attached cells required several hours in culture medium to spread completely. Maintenance of confluent cell coverage on the graft surface for 3 days in vitro was achieved by means of continuous perfusion with oxygenated tissue culture medium RPMI-1640-HEPES supplemented with 20% fetal bovine serum. We conclude that optimum immediate confluent endothelial coverage of small-caliber vascular grafts requires a high concentration of cells, attachment to collagen-precoated grafts, and several hours of incubation in complete culture medium.