Citations

Experiments were designed to determine how ovariectomy modulates mitogenic factors in platelets and how these factors affect proliferation of coronary arterial smooth muscle. Platelet-derived growth factors (PDGFABand PDGFBB), transforming growth factors (TGF-β1and TGF-β2), and vascular endothelial growth factor (VEGF165) were quantified in platelet lysates and platelet-poor plasma from adult gonadally intact and ovariectomized female pigs by ELISA. Proliferation of cultured coronary arterial smooth muscle cells (SMCs) from both groups of pigs was determined in response to autologous or heterologous platelet lysates. Platelet concentrations of PDGFBB, but not PDGFAB, TGF-β1, and TGF-β2, increased with ovariectomy. VEGF165was not detected in platelets from either group. Proliferation of SMCs from ovariectomized females was significantly greater on exposure to autologous or heterologous platelet lysates than proliferation of SMCs from intact females. These results indicate that ovariectomy increases concentrations of PDGFBBin platelets. Higher levels of PDGFBBin platelets in synergy with other platelet-derived products could contribute to increased proliferative arterial response to injury after ovariectomy.

BACKGROUND The degree to which antithrombotic drugs suppress thrombin generation is unknown. Because hirudin, unlike antithrombin III, binds intravascular thrombin rapidly and selectively to yield a circulating inactive complex of 3- to 4-hour half-life, we used intravenous hirudin in humans to investigate the course of thrombin generation during and early after anticoagulation with this potent, direct antithrombin. METHODS AND RESULTS Intravascular thrombin was measured with an ELISA for the thrombin-hirudin complex formed during and for 18 hours after stopping a 6-hour infusion of hirudin at 0.1, 0.2, and 0.3 mg.kg-1.h-1 in three groups of six patients each. With free hirudin in 20- to 10,000-fold molar excess of thrombin and peak activated partial thromboplastin times of 2.3 to 3.0 times baseline, mean plasma thrombin-hirudin complex increased from 794 +/- 85 pg/mL (mean +/- SEM) 15 minutes after the start of the infusion to 1617 +/- 151 pg/mL at 6 hours of infusion to 2667 +/- 654 pg/mL at 24 hours. During the 24-hour observation period, plasma concentration of fragment 1.2 (the peptide released during conversion of prothrombin to thrombin) never fell below baseline but rather increased transiently during the hirudin infusion. Plasma concentrations of thrombin-antithrombin III complex (in ng/mL) decreased from 4.34 +/- 0.40 at baseline to 1.64 +/- 0.13 at 6 hours (P < .001) and gradually increased after stopping the infusion to 5.7 +/- 0.87 at 24 hours (nonsignificant compared with baseline). CONCLUSIONS Measurement of thrombin-hirudin complex may be used as a marker of thrombin generation in humans. Persistent accumulation of thrombin-hirudin complex and generation of fragment 1.2 during and after completion of potent anticoagulation with hirudin suggest thrombin generation is not blocked by high-affinity thrombin inhibition. The persistent formation of thrombin during declining plasma levels of hirudin may contribute to the pathogenesis of rethrombosis early after antithrombin therapy or during inadequate anticoagulation.

We studied the ability of a new instrument, the PlaCor PRT that measures shear-induced platelet aggregation in fingerstick, non-anticoagulated blood without added agonists, to detect platelet dysfunction ex vivo. Platelet reactivity time (PRT) and whole blood aggregation (WBA) were measured in 160 healthy volunteers, before and after aspirin and in 170 participants with established vascular disease or risk factors thereof treated with aspirin ± clopidogrel. Pretreatment PRT and WBA were significantly correlated (collagen r = −.63; arachidonate r = −.65; P < .0001). Following aspirin, the mean PRT increased from 82 to 142 seconds ( P < .0001), and in participants treated with clopidogrel–aspirin, the mean PRT (286 seconds, n = 65) was significantly longer than with aspirin alone (166 seconds, n = 105; P < .001). Only 13% of PRTs of participants treated with clopidogrel and aspirin were within the normal range. We conclude that the PlaCor PRT is a simple, rapid, point-of-care instrument that compares favorably with published descriptions of other platelet function instruments.

AbstractAlthough current antiplatelet therapies provide potent antithrombotic effects, their efficacy is limited by a heightened risk of bleeding and failure to affect vascular remodeling after injury. New lines of research suggest that thrombosis and hemorrhage may be uncoupled at the interface of pathways controlling thrombosis and inflammation. Here, as one remarkable example, studies using a novel and highly selective pharmacologic inhibitor of the spleen tyrosine kinase Syk [PRT060318; 2-((1R,2S)-2-aminocyclohexylamino)-4-(m-tolylamino)pyrimidine-5-carboxamide] coupled with genetic experiments, demonstrate that Syk inhibition ameliorates both the acute and chronic responses to vascular injury without affecting hemostasis. Specifically, lack of Syk (murine radiation chimeras) attenuated shear-induced thrombus formation ex vivo, and PRT060318 strongly inhibited arterial thrombosis in vivo in multiple animal species while having minimal impact on bleeding. Furthermore, leukocyte-platelet–dependent responses to vascular injury, including inflammatory cell recruitment and neointima formation, were markedly inhibited by PRT060318. Thus, Syk controls acute and long-term responses to arterial vascular injury. The therapeutic potential of Syk may be exemplary of a new class of antiatherothrombotic agents that target the interface between thrombosis and inflammation.

Abstract —Arterial thrombophilia independent of vascular pathology has not been previously defined either experimentally or epidemiologically. To address the existence of an individual propensity to arterial thrombosis, we exploited a previously developed procedure entailing traumatic (crush) injury of paired porcine carotid arteries for generating platelet-rich thrombi. Porcine carotid arteries were injured bilaterally by serial hemostat crushes. Thrombus generation was monitored by local accumulation of autologous 111 In-labeled platelets and Doppler blood flow. Within this cohort of animals of similar age and size, the lowest to the highest responders in thrombus mass spanned a 7-fold range, showing no correlation with shear, platelet or leukocyte count, or plasma concentrations of fibrinogen or von Willebrand factor. However, there was strong intra-individual correlation ( r 2 =0.80; P <0.001) of thrombus deposition between carotid artery pairs. The wide variation in thrombotic response to a standardized stimulus, not accounted for by shear stress or typical hematological variables, appears to be an intrinsic propensity of the individual. The experimental system for thrombus generation is sufficiently quantitative for assessment of variables determining this propensity.

Abstract Immunohistochemical analysis of surgically obtained porcine tissue samples reveals ubiquitous staining for prothrombin in organs rich in smooth muscle content and universal staining of smooth muscle in tissue vasculature. The native character of tissue prothrombin is verified first by chromogenic substrate hydrolysis and hirudin inhibition after incubation of tissue extracts with taipan snake venom and phospholipid. Western analysis of tissue extracts confirms the native zymogen molecular weight. In addition, prothrombin purified in good yield from porcine uterus is activated by Echis carinatus venom which, like taipan venom, is 4-carboxyglutamic acid-sensitive. After correction for blood (gross heme) and interstitial fluid (albumin), excess functional prothrombin is observed in extracts of tissues having abundant smooth muscle. In contrast with factor X, the yield of prothrombin purified from porcine uterus greatly exceeds that attributable to contamination by whole blood. Northern blot analysis from selected bovine tissues extracted for polyadenylated messenger RNA is equivocal for prothrombin mRNA with the exception of liver, which is positive. It is concluded that functionally intact prothrombin is widely distributed among tissues owing to smooth muscle content, although the mechanism of emplacement and physiologic significance of prothrombin in these tissues remains unclear.

Addition of exogenous plasminogen activator inhibitor-1 (PAI-1) to fibrin clots inhibits fibrinolysis in vivo. However, it is unknown whether the localized concentrations of active PAI-1 necessary to produce this antifibrinolytic effect can be recruited to acute arterial thrombi by endogenous mechanisms. We measured PAI-1 activity and antigen in porcine coronary artery thrombi that formed in response to acute vascular injury. Mean PAI-1 activity in thrombi (n=5) was 36±5.1 μg/mL, which is >2000 times its concentration in normal porcine plasma. The presence of markedly elevated concentrations of active PAI-1 in thrombi was confirmed by an immunoactivity assay and by demonstrating formation of sodium dodecyl sulfate–stable complexes after addition of 125 I-urokinase to thrombus extracts. Comparative analysis of PAI-1 antigen by Western blotting and urokinase inhibition assay suggested that approximately one third of thrombus-associated PAI-1 was active. Histological examination of coronary thrombi revealed that they consisted predominantly of dense aggregates of platelets with interspersed islands of fibrin, which closely resemble the histological appearance of thrombi in patients with myocardial infarction and unstable angina pectoris. Washed porcine platelets prepared from peripheral blood contained sufficient PAI-1 antigen and activity to account for the concentrations observed in coronary artery thrombi. However, the specific activity of human platelet PAI-1 was lower than that of porcine platelet PAI-1 (2% versus 50% active, respectively), and human platelets inhibited in vitro fibrinolysis to a lesser extent than did porcine platelets. These results indicate that active PAI-1 accumulates in porcine coronary artery thrombi in concentrations markedly higher than those present in plasma and that PAI-1 may be an important determinant of the known resistance of platelet-rich thrombi to lysis by tissue-type plasminogen activator. These studies also underscore the importance of considering possible species differences in protein function when comparing animal models of thrombosis to acute coronary thrombosis in humans.

Abstract Mutations in one of the two genes encoding type I procollagen (COL1A1 and COL1A2) are frequently the cause of osteogenesis imperfecta (OI), a disorder characterized by brittle bones. Here we tested whether patients with low bone density also have mutations in these genes. The 26 patients studied had no apparent metabolic bone disease, but most had a positive family history of osteopenia or osteoporosis. Although a diagnosis of OI was considered by the clinician in some cases, the clinical criteria for OI were not satisfied. Our strategy for mutation analysis consisted of PCR amplification of cDNA made to fibroblast mRNA using primers specific for the coding regions of COL1A1 and COL1A2. The PCR products were then sequenced directly with primers located within each PCR product. We found that 3 of 26 patients had mutations that altered the encoded amino acid. One mutation, at position α2(I)-661 has been reported (Spotila et al. 1991 Proc Natl Acad Sci USA PNAS 88: 5423). The other 2 patients, who were not related to each other, had a mutation that altered the proline codon at α1(I)-27 to alanine. This mutation was not found in 81 normal individuals or in 37 additional osteopenic individuals. However, its effect on the biologic function of type I collagen, as well as its role in osteopenia, is uncertain. In addition to the two mutations, we found a polymorphism in codon α2(I)-459. Although this polymorphism involved an amino acid substitution, it was present with equal frequency in the patient and the normal population. By analyzing this and previously reported neutral sequence variants in the COL1A2 gene, we determined that all patients expressed both alleles of the COL1A2 gene. The 12 patients who were heterozygous for a COL1A1 neutral sequence variant also expressed both alleles. Here we present all PCR primer and sequencing primer information. The results suggest that surveying a larger group of similarly selected individuals may reveal additional mutations in the COL1A1 or COL1A2 genes.

Objective— To test the hypothesis that statins will acutely inhibit platelet thrombus formation, intravenous lovastatin was assessed in our well-characterized porcine carotid injury model. Methods and Results— The first carotid artery was crush-injured and harvested after 30 minutes. Pigs then received intravenous lovastatin (100 μg/kg bolus+100 μg/kg/h infusion, n=6) or saline (n=11) before injury of the second carotid artery. Thrombus size was quantified by scintillation detection of autologous 111 In-platelets. Sequential carotid injury produced a thrombus more than 50% greater in volume in the second (3149±2053×10 6 /cm 2 ) relative to the first injured artery (2081±1552×10 6 /cm 2 ; P =0.04) in control pigs. This augmentation was inhibited by intravenous lovastatin which acutely reduced platelet deposition (944±246×10 6 /cm 2 ) relative to saline control ( P =0.02). Flow chamber closure times increased on average by 2.45-fold in response to whole blood lovastatin incubation. Lovastatin ( P <0.05) and simvastatin ( P <0.05) reduced platelet dense granule secretion in vitro. Conclusions— Sequential arterial injury augments the thrombotic response suggesting that the propensity for arterial thrombosis is at least partially acquired. This thrombotic augmentation can be acutely attenuated by intravenous lovastatin which may result from a pleiotropic impact on platelet function. These results appear to be a class effect of 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors.