摘要:

In earlier studies from this laboratory evidence was obtained for a physiological function of tissue factor pathway inhibitor (TFPI) as a regulator of hemostasis capable of preventing thrombotic complications that might otherwise result from exposure of blood to trace amounts of tissue factor (TF). However, it was not possible to conclude that the protective effect of TFPI stemmed solely from inhibition of factor VIIa/TF catalytic activity, since TFPI neutralizes stoichiometric amounts of factor Xa in forming an inhibited factor Xa/TFPI/factor VIIa/TF complex. Therefore, we examined the effects of immunodepletion of TFPI on the extent of coagulation initiated in rabbits by exposure to factor Xa and phospholipid in the absence of TF. In one experimental approach, factor Xa was generated endogenously with the factor X-activating fraction of Russell's viper venom (0.33 /xg/kg) in rabbits receiving an infusion of phosphatidylcholine/phosphatidylserine (PCPS) vesicles, 1 nig/kg over 2 hours. In a second approach, rabbits were injected with a complex of factor Xa (0.75 jug/kg) and PCPS (12.5 yug/kg). In contrast with the observed sensitization of TFPI-depleted rabbits to TF-induced coagulation, TFPI-depleted rabbits were not sensitized to coagulation initiated by factor Xa and phospholipid in the absence of TF. These data support the conclusion that the physiological function of TFPI in regulating TF-dependent coagulation stems primarily from its ability to inhibit factor VIIa/TF catalytic activity.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Plasma levels of lipoprotein [a] (Lp[a]) are associated with increased risk of coronary artery disease and show an inverse correlation with apolipoprotein[a] (apo[a]) molecular weight. We determined Lp[a] levels and apo[a] phenotypes in 171 cases with preclinical extracranial carotid atherosclerosis as ascertained by B-mode ultrasound and in 274 control subjects free of carotid atherosclerosis. Lp[a] protein levels measured by enzyme-linked immunosorbent assay ranged from 4 to 361 /ig/mL in cases and from 2 to 392 jug/mL in controls, but median levels of Lp[a] were higher in cases than in controls (51 Aig/mL versus 33 /ig/mL,p<.003). In both groups, all 11 apo[a] polymorphs that are resolved by the procedure used were present, resulting in 43 and 39 different apo[a] phenotypes in cases and controls, respectively. An inverse relation between apo[a] polymorph size and Lp[a] level was observed in both cases (r=&#151; 0.49,p<.001) and controls (r=&#151;0.34, /><.001). Apo[a] phenotype distributions were similar in cases and controls. However, in 17 phenotypes with three or more subjects per group, the difference of mean Lp[a] concentrations between cases and controls was 32±36 /ig/mL (mean±SD). Thus, the higher Lp[a] levels in cases were not associated with a greater prevalence of small apo[a] polymorphs. Stepwise logistic regression analyses of known risk factors for coronary heart disease showed that plasma Lp[a] concentration was an independent predictor of case-control status, while Lp[a] phenotype was not, irrespective of the presence or absence of Lp[a] concentration in the model. These findings confirm the inverse correlation of apo[a] size with plasma Lp[a] levels but imply that sequences at the apo[a] gene locus other than those determining the number of apo[a] kringle type 2 units are involved in the increased expression of apo[a] in subjects with early atherosclerosis.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The levels of glycoprotein (GP) Ib and GPV and phospholipase C activity were measured in platelets from three Bernard-Soulier syndrome patients. The patients' platelets had 46%, 46%, and 24% of control levels of GPIbt* and 43%, trace, and 13% of control levels of GPV as determined by immunoblot analysis. Stimulation by thrombin, trypsin, the thromboxane analogue U46619, and the combination of U46619 and trypsin caused the formation of [32P] phosphatidic acid, an index of phospholipase C activity, in [32P]orthophosphate-prelabeled platelets. With all agonists, however, the formation of [32P] phosphatidic acid was markedly reduced in Bernard-Soulier syndrome platelets compared with control platelets. These data indicated a postreceptor defect in phospholipase C activation in Bernard-Soulier syndrome platelets and confirmed earlier observations of potential proteolytic and nonproteolytic mechanisms of platelet activation.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Aortic smooth muscle cells were cultivated as monolayers on plastic or within collagen lattices with lowand high-serum supplementation, and the expression of mRNAs specific for pro alpha 1 (I) and pro alpha 1 (HI) collagen were studied by slot blot hybridization. The steady-state levels of pro alpha 1 (I) and pro alpha 1 (HI) collagen mRNA of cells within collagen lattices were found to be higher than those grown on plastic, although the production of collagen was lower. The degradation of pro alpha 1 (I) and pro alpha 1 (HI) collagen mRNAs as revealed in the presence of actinomycin D was not affected by culturing the cells within a collagen lattice. In vitro translation assays of mRNAs of monolayerand lattice-cultured cells showed no differences in translatability. These data suggest the involvement of posttranslational control of collagen production in collagen lattice-cultured smooth muscle cells.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The effect of the sulfur-substituted fatty acid analogue 1,10 6i?(carboxymethylthio)decane, also known as 3-thiadicarboxylic acid, on puromycin aminonucleoside-induced nephrotic hyperlipidemia was studied in rats. Treatment with 3-thiadicarboxylic acid (250 mg/kg) for 5 days reduced plasma levels of triglycerides from 5.8 to 2.7 mmol/L and cholesterol from 11.0 to 7.7 mmol/L. This was accounted for by decreases in very-low-density lipoprotein triglycerides, very-low-density lipoprotein cholesterol, and low-density lipoprotein cholesterol, without any major changes in the composition of plasma lipoproteins. The activities of two enzymes involved in fatty acid synthesis (ATP:citrate lyase and fatty acid synthetase) were inhibited by 3-thiadicarboxylic acid treatment, whereas acetyl-coenzyme A carboxylase activity was unchanged. In contrast, treatment with the sulfur-substituted fatty acid analogue induced the peroxisomal /3-oxidation of fatty acids ninefold and the mitochondrial β-oxidation by 54% to 73%, depending on the substrate used. This was accompanied by a 26% reduction in hepatic triglyceride secretion rate. The hepatic phosphatidate phosphohydrolase activity was unchanged. 3-Thiadicarboxylic acid treatment suppressed the activity of the rate-limiting enzyme in cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, by 58%, whereas hepatic LDL receptor expression was unaltered. The activities of lipoprotein lipase and hepatic lipase were unchanged by treatment. These results demonstrated that treatment with 3-thiadicarboxylic acid ameliorates hyperlipidemia in experimental nephrosis primarily by decreasing the overproduction of very-low-density lipoprotein present. The data also indicate that hepatic very-lowdensity lipoprotein synthesis and secretion is strongly influenced by the availability of the fatty acid substrate under the same hyperlipidemic conditions.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Elevated levels of endogenous tissue-type plasminogen activator (t-PA) appear to be a marker for preclinical atherosclerosis. At present, however, data describing potential relations between plasma t-PA level and established lipid risk factors for coronary atherosclerosis are sparse. To explore these potential relations, we measured plasma levels of t-PA antigen (t-PA:ag) in 633 apparently healthy men in the Physicians' Health Study as well as total cholesterol, high-density lipoprotein (HDL) cholesterol, HDL2cholesterol, HDL, cholesterol, and apolipoproteins A-I, A-II, and B-100. Overall, plasma t-PA:ag levels were inversely correlated with HDL cholesterol (r=−.1616,p<.0005), HDL2cholesterol (r=−.1632,p<.0005), and HDL] cholesterol (r=−.O927, P=.O19). In stratified analyses, the inverse association between t-PA:ag and HDL cholesterol was present among frequent (P trend=.002) and infrequent (P trend=.004) consumers of alcohol as well as among the subgroups of frequent exercisers (P trend <.001), men in the lower half of body mass index (P trend=.001), and nonsmokers (P trend<.001). In contrast, there was no association between t-PA:ag and total cholesterol (r=.O219, P=.58), whereas relations of t-PA:ag with apolipoproteins A-I, A-II, and B-100 were minimal and of borderline significance. These data indicate that plasma levels of endogenous t-PA:ag are inversely related to HDL cholesterol as well as HDL2and HDL, cholesterol. Further research will be required to determine whether these modest but highly significant associations are due to a direct effect of lipids on fibrinolytic function or to independent associations of both t-PA:ag and lipids with atherosclerosis or are mediated by a third unmeasured variable.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Leech antiplatelet protein (LAPP) is a specific inhibitor of collagen-induced human platelet aggregation and adhesion to collagen under static conditions. Recombinant LAPP (rLAPP) and L-366,763 (acetylated- Cys-Asn-Pro-Arg-Gly-Asp-Cys-NH2), a peptidyl fibrinogen receptor antagonist, were evaluated in an anesthetized baboon thrombosis model using a collagen-coated graft segment of an arteriovenous shunt to elicit thrombus formation. Animals were randomized to receive systemic intravenous administration of rLAPP (100 fig &#149; kg"1&#149; min"1; n=5), L-366,763 (8.5 /tg &#149; kg"1&#149; min"1; n=3), or saline (n=3). Despite complete and selective inhibition of type I collagen-induced ex vivo aggregation of platelets, rLAPP had no significant effect on the rate or the extent of '"In-labeled platelet deposition onto the collagen graft and no effect on template bleeding time. In contrast, L-366,763 completely prevented platelet deposition, maintained blood flow, and significantly prolonged bleeding time at the dosage that inhibited ex vivo aggregation in response to all agonists studied. In this study, the absence of an antithrombotic benefit of rLAPP contrasted sharply with the efficacy of the fibrinogen receptor antagonist. These results demonstrate that specific inhibition of collagen-mediated platelet aggregation alone is not sufficient to prevent platelet-dependent thrombosis in this baboon model.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Prothrombinase complex assembly, in real time, on platelets adherent to immobilized von Willebrand Factor (vWf) was examined by total internal reflection fluorescence spectroscopy (TIRFS). Electron microscopy showed that the platelets adhered to vWf in a largely unactivated state and could be activated by thrombin. Antibody binding to glycoprotein (GP) Ib and functional GPIIb-IIIa receptor molecules on adherent platelet membranes monitored by TIRFS also indicated that platelets adhered in a largely unactivated state. Maximal expression of the receptor form of GPIIb-IIIa detected by antibody binding was seen only after thrombin stimulation of the adherent platelets. Antibody binding to GPIb was detected on adherent platelets. A reduction in antibody binding was observed after thrombin stimulation of the platelets, indicating a change in GPIb as a consequence of thrombin stimulation of the platelets. The binding of the protein components of the prothrombinase complex to adherent and thrombin-stimulated adherent platelets was then studied individually. Factor Va bound to adherent and thrombin-stimulated adherent platelets with an estimatedKaof 58 nmoI/L. Minimal factor Xa binding was observed on adherent platelets before thrombin stimulation. Factor Xa binding was, however, readily observed on thrombin-stimulated adherent platelets. This factor Xa binding was not saturable, and noKdvalue could be estimated. Direct measurement of prothrombinase complex assembly was demonstrated by using an energy transfer phenomenon between fluorescein-labeled factor Va and rhodamine-labeled factor Xa. Prothrombinase complex assembly was observed on both adherent and thrombin-stimulated adherent platelets. The estimatedKAfor the factor Va/factor Xa interaction was 4 nmol/L. TIRFS demonstrated that adherent platelets have the ability to support prothrombinase complex assembly, as shown by a direct energy transfer reaction between fluorescently labeled factors Va and Xa.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The possibility that platelets release microvesicles on adherence to either von Willebrand factor (vWf) or collagen was examined by flow cytometry analysis of the supernatant above layers of adherent platelets. No microvesicle release was detected as a result of adherence to vWf or to collagen, a known platelet agonist. Approximately 8% of the total platelet mass was released as microvesicles after thrombin stimulation of the vWfor collagen-adherent platelets. A larger portion of the vWf-adherent platelet membranes (approximately 21%) was released as microvesicles subsequent to platelet stimulation with the nonphysiological agonist calcium ionophore A23187. Calpeptin, a calpain inhibitor, had no effect on microvesicle release, suggesting that calpain proteolysis of platelet cytoskeletal proteins was not responsible for microvesicle shedding under the conditions studied. Examination of the vWf-adherent platelets by scanning electron microscopy showed that virtually no microvesicles bound to exposed vWf multimers. No microvesicle binding to the adherent platelets was observed, indicating that the majority of the microvesicles were shed from the platelet and vWf surface on platelet activation. The ability of the microvesicle population to support procoagulant activity was measured with a prothrombinase activity assay and was compared with the activity supported by the adherent platelet membranes. More than 85% of the total prothrombinase activity remained associated with the adherent platelet membranes, both for unstimulated platelets and platelets stimulated with physiological agonists. Furthermore, the residual activity found in the buffer fraction containing detached platelets and any released microvesicles could be attributed to the detached platelets. No activity could be attributed to the microvesicles, as thrombin stimulation of either vWfor collagen-adherent platelets did not promote increased procoagulant activity relative to the unstimulated adherent platelets, even though microvesicle release was detected as a result of agonist addition. Neither full platelet activation nor microvesicle shedding played an essential role in generating procoagulant activity in the adherent platelet system.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Recently, the presence of small, dense low-density lipoprotein (LDL) has been recognized as a risk factor for coronary heart disease. There has been little work on correlates of LDL size in population-based studies and none in Mexican Americans. We examined the relationship of LDL size and pattern to anthropometric and metabolic variables in 466 Mexican Americans and non-Hispanic whites in the San Antonio Heart Study. LDL size in Angstrom units was significantly lower in Mexican Americans (255.8+0.6) than in non-Hispanic whites (257.9±0.7)p»=0.041) after adjustment for gender and age. The percentage of subjects with pattern B tended to be higher in Mexican Americans than in non-Hispanic whites (40.0% versus 34.4%, respectively), although this difference did not reach statistical significance. In univariate analysis, LDL size was significantly associated with glucose (r=&#151;.20), insulin (r=&#151;.19), male gender (r=&#151;.2O), total cholesterol (r= &#151;.22), high-density lipoprotein cholesterol (HDL-C) (r=.53), and triglyceride concentrations (r=&#151;.63). In multivariate analyses, higher triglyceride, insulin, and glucose concentrations, lower HDL-C, and male gender were independent correlates of smaller, denser LDL. Correlates of LDL size were similar in Mexican Americans and non-Hispanic whites. Our results confirm previous reports that triglyceride and HDL-C concentrations are the most important variables associated with LDL size. The additional findings of independent effects of male gender, glucose, and insulin concentrations suggest that sex hormones and the insulin resistance syndrome may also play an important role. Mexican Americans did have significantly smaller LDL, but this appears to be associated with higher triglyceride, glucose, and insulin concentrations in this population.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID