Thrombin causes subsecond changes in protein phosphorylation of platelets

We have developed a general quenched-flow approach to study platelet function as early as 0.3 seconds after stimulation. Phosphorylation of 20- and 40-kd proteins has been analyzed during the first five seconds of platelet response to thrombin from 0.1 to 5.0 U/mL and compared with the progress of aggregation and serotonin secretion. The onset time for aggregation and phosphorylation of both proteins was less than one second, although with lowest (less than 0.5 U/mL) thrombin levels, a lag of up to 0.6 seconds occurred before 40K phosphorylation increased. The thrombin sensitivity of aggregation and 20K phosphorylation was approximately twice that of 40K phosphorylation, with Ka values of 0.51 and 0.53 v 1.10 U/mL, respectively. External calcium was necessary for maximal 20K phosphorylation, since EDTA inhibited this by 30%. The 40K phosphorylation was not affected by EDTA. Platelet activation by thrombin thus induced biochemical changes well before one second. The quenched-flow approach may help to reveal relationships between phospholipase activation, calcium fluxes, and protein phosphorylation during these early periods of platelet function.     

Enoxaparin and abciximab adjunctive pharmacotherapy during percutaneous coronary intervention

Randomized controlled trials of patients with non-ST segment elevation acute coronary syndromes have established the superiority of enoxaparin (versus unfractionated heparin) for reducing adverse ischemic outcomes. Furthermore, adjunctive abciximab therapy during percutaneous coronary intervention (PCI) is associated with improved clinical outcomes. Since algorithms for integrating these pharmacotherapies have not been determined, patients undergoing elective PCI were enrolled into 2 distinct and separate studies conducted by the National Investigators Collaborating on Enoxaparin (NICE) study groups (NICE 1 and NICE 4 studies). Patients in NICE 1 were administered enoxaparin 1.0 mg/kg intravenously (without abciximab) and those enrolled in NICE 4 were administered a reduced dose (0.75 mg/kg) of enoxaparin in combination with standard-dose abciximab intravenously during PCI. Bleeding events and ischemic outcomes assessed in-hospital and at 30-days post-PCI were infrequent with either pharmacologic regimen. In the dose regimens studied, enoxaparin with or without abciximab appears to provide safe and effective anticoagulation during PCI. The combination of reduced-dose enoxaparin and abciximab was associated with a low incidence of adverse outcomes (bleeding or ischemic events). Additional studies may be required to establish the relative safety and efficacy of this new adjunctive pharmacologic strategy when compared with the combination of low-dose, weight-adjusted unfractionated heparin and abciximab.     

Monoclonal antibodies recognizing epitopes on the extracellular face and intracellular N-terminus of the human erythrocyte anion transporter (band 3) and their application to the analysis of South East Asian ovalocytes

This report describes the production and characterization of 13 rodent monoclonal antibodies to the human erythrocyte anion transport protein AE1 (syn. band 3). Eleven antibodies (4 murine and 7 rat) recognize epitopes dependent on the integrity of the third extracellular loop of the protein. Two antibodies (1 murine and 1 rat) recognize epitopes on the N-terminal cytoplasmic domain. Quantitative binding studies using radioiodinated IgG and Fab fragments of antibodies to extracellular epitopes on AE1 ranged from 77,000 to 313,000 (IgG) and from 241,000 to 772,000 (Fab) molecules bound at saturation. The results indicate that the epitopes recognized by different antibodies vary in their accessibility and suggest that there is heterogeneity in the organization of individual AE1 molecules in the red blood cell membrane. Quantitative binding studies on South East Asian ovalocytes using several antibodies to AE1 and an anti-Wrb show a marked reduction in the number of antibody molecules bound at saturation. These results are consistent with the existence of highly cooperative interactions between transmembrane domains of AE1 in normal erythrocytes and the disruption of these interactions in the variant AE1 found in South East Asian ovalocytes.     

Prophylactic abciximab in elective coronary stenting: results of a randomized trial

BACKGROUND: The use of abciximab (c7E3 Fab; ReoPro , Eli Lilly & Company, Indianapolis, Indiana) during percutaneous coronary intervention (PCI) decreases the incidence of early (30-day) and late (6-month to 1 year) adverse cardiac ischemic events. In a high-risk population, abciximab also reduced the need for target lesion revascularization. PCI of lesions with complex morphology, particularly long lesions, is associated with more complicated outcomes. The use of multiple and/or long intracoronary stents to cover long coronary lesions may lower the incidence of acute or subacute occlusion, but is still limited by a high late restenosis rate. We characterized patients undergoing elective implantation of long or multiple overlapping coronary stents and determined the impact of abciximab administration on clinical and angiographic outcomes. METHODS AND RESULTS: In a prospective, single-center randomized trial, a total of 107 patients undergoing elective implantation of long or multiple overlapping coronary stents were randomly assigned to receive either standard-dose heparin (n = 53) or abciximab plus low-dose heparin (n = 54). The use of abciximab was not associated with an increased incidence of bleeding or vascular complications compared to standard heparin regimen (3.7% versus 3.8%, respectively; p = NS). A 68% reduction in composite in-hospital cardiac events (i.e., death, myocardial infarction, urgent revascularization) was observed in the abciximab group (3.7% versus 11.5%, p = 0.1). At 6-month follow-up, a 48% reduction of target lesion revascularization (11% versus 21%; p = 0.1) and a decrease in binary angiographic restenosis were observed for abciximab-treated patients (17% versus 34%; p < 0.05). CONCLUSION: The peri-procedural use of abciximab during implantation of long or multiple overlapping coronary stents is safe and effective, as it does not increase bleeding or vascular complications compared to standard heparin anticoagulation and reduces the incidence of in-hospital adverse cardiac events; moreover, abciximab improves 6-month clinical and angiographic outcomes in such a complex setting.     

Interactions between fibrin and the plasminogen activators produced by cultured endothelial cells

Serum-free conditioned medium (CM) from cultured bovine aortic endothelial cells (BAEs) was fractionated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and analyzed for plasminogen activator (PA) activity by fibrin autography. Distinct size forms of PA with molecular weights (mol wt) of 100,000, 74,000, and 52,000 were readily identified by this approach. When fibrinogen and thrombin were added to CM containing these forms, approximately 55% of the total activity was found to associate with the resultant fibrin clot. The other 45% remained free in the supernatant. This relationship did not change at higher fibrin concentrations. Subsequent analysis revealed that only the larger PA forms (mol wt 74,000-100,000) were recovered in the clot. The 52,000 form did not bind to the polymerizing fibrin under these conditions. The fibrin-binding forms also bound to immobilized concanavalin-A and could be separated from those forms that did not interact with fibrin by concanavalin-A affinity chromatography. The PA activity of the separated forms was then compared by assessing their ability to cleave 125I-plasminogen. Although cleavage by the 52,000 mol wt form was apparent, little if any cleavage was initiated by the mixture containing the 74,000-100,000 forms. The addition of fibrin to this sample resulted in the generation of a potent PA activity. These results indicate that cultured BAEs produce multiple forms of PA that differ both in size and in behavior toward fibrin and concanavalin-A. These forms include molecules that functionally and immunochemically resemble human urokinase, and others that resemble human tissue-type PA.     

Molecular characterization of a high A2 beta thalassemia by direct sequencing of single strand enriched amplified genomic DNA

Two families, one of Anglo-Saxon-Dutch descent, and the other, West Indian black, have an atypical beta thalassemia characterized by an unusually high level of Hb A2 in the heterozygous state. Restriction endonuclease mapping showed a deletion of about 1.35 kilobase (kb) in the 5' region of the beta globin gene. Direct sequencing of a specific region of genomic DNA amplified by a new modification of the polymerase chain reaction defined the deletion to be 1,393 base pairs (bp) and to be the same in both families. The deletion extends from 485 bp 5' to the mRNA CAP site to the middle of the second intervening sequence. This deletion, together with three others previously described that remove the 5' end of the beta gene but leave the delta gene intact, are all associated with unusually high levels of Hb A2 in the heterozygous state.     

Impact of coronary culprit lesion calcium in patients undergoing paclitaxel-eluting stent implantation (a TAXUS-IV sub study)

Randomized clinical trials have shown that paclitaxel-eluting stents significantly reduce restenosis after percutaneous coronary intervention. The impact of lesion calcification on the efficacy of paclitaxel-eluting stents is unknown. In the TAXUS-IV trial, 1,314 patients who underwent percutaneous coronary intervention were randomly assigned to a bare-metal or paclitaxel-eluting stent. By core laboratory analysis, 247 lesions (19%) were moderately or severely calcified. At the 9-month angiographic follow-up examination, the paclitaxel-eluting stent had significantly reduced the amount of late loss compared with the control stent (0.26 +/- 0.56 vs 0.51 +/- 0.48 mm, p = 0.015) within the analysis segment in the calcific lesions. The analysis segment restenosis rate was similar in patients with calcified and noncalcified lesions after paclitaxel-eluting stent implantation (7.5% vs 8.0%, respectively; p = 1.0). The rate of ischemia-driven target lesion revascularization (TLR) at 1 year was reduced by 56% in patients with calcified lesions (11.9% vs 5.1%, p = 0.09) and by 75% in noncalcified lesions (15.7% vs 4.3%, p <0.0001). By interaction testing, the efficacy of the paclitaxel-eluting stent in reducing TLR at 1 year was similar in the calcified and noncalcified lesions (p = 0.30). Moreover, by multivariate analysis, implantation of the paclitaxel-eluting stent was a powerful independent predictor of freedom from TLR, with similar hazard ratios for efficacy in calcified and noncalcified lesions (0.30 and 0.26, respectively). In conclusion, implantation of paclitaxel-eluting stents in patients with de novo coronary lesions significantly reduced restenosis in patients with and without calcified lesions.