Search

While conventional LDL-C, HDL-C, and triglyceride measurements reflect aggregate properties of plasma lipoprotein fractions, NMR-based measurements more accurately reflect lipoprotein particle concentrations according to class (LDL, HDL, and VLDL) and particle size (small, medium, and large). The concentrations of these lipoprotein sub-fractions may be related to risk of cardiovascular disease and related metabolic disorders. We performed a genome-wide association study of 17 lipoprotein measures determined by NMR together with LDL-C, HDL-C, triglycerides, ApoA1, and ApoB in 17,296 women from the Women's Genome Health Study (WGHS). Among 36 loci with genome-wide significance (P, Author Summary Genome-wide association studies (GWAS) of plasma lipoprotein fractions hold great promise for understanding lipid metabolism and its central role in cardiovascular disease and related disorders. Conventional assays for lipoprotein status determine total cholesterol content of low- or high-density lipoprotein particles (LDL-C or HDL-C, respectively) or total plasma triglyceride content (as an estimate of very-low density lipoprotein particle concentration [VLDL]). All three measures have been targets for recent GWAS. However, a more precise target for GWAS of lipoprotein metabolism would be the concentration of the individual lipoprotein particles according to class (LDL, HDL, VLDL) and size (small, medium, and large), all of which can be measured by NMR-based methods. In a population of 17,296 women of European ancestry from the Women's Genome Health Study, we have performed a GWAS for 22 lipoprotein measures derived from NMR-based and conventional assays. We find 43 genetic loci involved in lipoprotein metabolism, including 10 novel loci. The results offer a clearer picture of common genetic influences on lipoprotein metabolism than available previously, including genetic effects on the distribution of LDL, HDL, and VLDL particle size, as well as on IDL and VLDL particle concentration, neither of which can be assessed by conventional measures.

Background— Fibrinogen is a multifunctional circulating glycoprotein involved in wound healing, thrombosis, platelet aggregation, and inflammation, and elevated levels predict vascular disease. Despite evidence of crucial biological function and moderate heritability, comprehensive analysis of the influence of genetic variation on fibrinogen is not available. Methods and Results— To address this issue, we undertook a genome-wide association study evaluating the potential relationships between 337 343 single-nucleotide polymorphisms (SNPs) and plasma fibrinogen levels among 17 686 apparently healthy women participating in the Women’s Genome Health Study. As C-reactive protein is also an inflammatory marker known to predict cardiovascular diseases, we compared the determinants of fibrinogen levels with those of C-reactive protein. Four novel loci were identified, in addition to the fibrinogen gene cluster, which were associated with fibrinogen levels at genome-wide levels of significance (range of probability values from 8.82�10 −09 to 8.04�10 −39 ). Two of the loci are related to common chronic inflammatory diseases: the first, at locus 5q31.1 ( SLC22A5 , SLC22A4 , IRF1 ), lies immediately adjacent to a locus linked to Crohn disease ( P value for lead SNP, 1.24�10 −12 ) and the second, at locus 17q25.1 ( CD300LF , SLC9A3R1 , NAT9 ), has been associated with psoriasis ( P value for lead SNP, 7.72�10 −11 ). A third locus at 1q21.3 ( IL6R ) lies within the interleukin 6 receptor gene, a critical component of the inflammatory cascade ( P value for lead SNP, 1.80�10 −11 ). A novel locus at 2q34 ( CPSI ) participates in the urea cycle ( P =8.82�10 −09 ). The majority of implicated SNPs showed little evidence of dual association with C-reactive protein levels. Conclusions— A genome-wide survey of the human genome identifies novel loci related to common chronic inflammatory diseases as genetic determinants of fibrinogen levels, in addition to loci that relate to the inflammatory cascade, the urea cycle, and the fibrinogen gene cluster.

Background— Genome-wide genetic association analysis represents an opportunity for a comprehensive survey of the genes governing lipid metabolism, potentially revealing new insights or even therapeutic strategies for cardiovascular disease and related metabolic disorders. Methods and Results— We have performed large-scale, genome-wide genetic analysis among 6382 white women with replication in 2 cohorts of 970 additional white men and women for associations between common single-nucleotide polymorphisms and low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, apolipoprotein (Apo) A1, and ApoB. Genome-wide associations ( P −8 ) were found at the PCSK9 gene, the APOB gene, the LPL gene, the APOA1-APOA5 locus, the LIPC gene, the CETP gene, the LDLR gene, and the APOE locus. In addition, genome-wide associations with triglycerides at the GCKR gene confirm and extend emerging links between glucose and lipid metabolism. Still other genome-wide associations at the 1p13.3 locus are consistent with emerging biological properties for a region of the genome, possibly related to the SORT1 gene. Below genome-wide significance, our study provides confirmatory evidence for associations at 5 novel loci with low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, or triglycerides reported recently in separate genome-wide association studies. The total proportion of variance explained by common variation at the genome-wide candidate loci ranges from 4.3% for triglycerides to 12.6% for ApoB. Conclusion— Genome-wide associations at the GCKR gene and near the SORT1 gene, as well as confirmatory associations at 5 additional novel loci, suggest emerging biological pathways for lipid metabolism among white women.

Although elevated levels of C-reactive protein (CRP) independently predict increased risk of development of metabolic syndrome, diabetes, myocardial infarction, and stroke, comprehensive analysis of the influence of genetic variation on CRP is not available. To address this issue, we performed a genome-wide association study among 6345 apparently healthy women in which we evaluated 336,108 SNPs as potential determinants of plasma CRP concentration. Overall, seven loci that associate with plasma CRP at levels achieving genome-wide statistical significance were found (range of p values for lead SNPs within the seven loci: 1.9 x 10(-)(8) to 6.2 x 10(-)(28)). Two of these loci (GCKR and HNF1A) are suspected or known to be associated with maturity-onset diabetes of the young, one is a gene-desert region on 12q23.2, and the remaining four loci are in or near the leptin receptor protein gene, the apolipoprotein E gene, the interleukin-6 receptor protein gene, or the CRP gene itself. The protein products of six of these seven loci are directly involved in metabolic syndrome, insulin resistance, beta cell function, weight homeostasis, and/or premature atherothrombosis. Thus, common variation in several genes involved in metabolic and inflammatory regulation have significant effects on CRP levels, consistent with CRP's identification as a useful biomarker of risk for incident vascular disease and diabetes.

SummaryTo understand the role of the factor X (fX) activation peptide (AP), a deletion mutagenesis approach was employed. Two single-chain, variant enzymes were generated in which 41 residues were deleted from the AP: fXdes-137-183 and fXdes-137-183;N191A, which lacks a carbohydrate moiety at Asn191 due to an alanine substitution. Deletion of the fX AP did not impact fXa catalytic activity. Activation of the variant zymogens, however, was altered. Neither mutant enzyme was activated by the fX coagulant protein from Russell’s viper venom (RVV-X1). Activation by factor VIIa (fVIIa) and fVIIa in the presence of cofactor, lipidated tissue factor (TF), occurred at an accelerated rate for both variants as compared to wild-type fX (WTfX). Similar to fVII, the mutants auto-activated in a cofactor-independent manner, which was characterized by a lag period and accelerated dose-dependently by plasma fXa (kcat/Km, 0.046 ± 0.004 µM−1s−1). Both mutants were also found to be activated by fVIIa (0.31 ± 0.03 µM−1s−1), fIXa (0.30 ± 0.03 µM−1 s−1), and thrombin (0.00078 ± 0.00015 µM−1s−1). In all cases, the rate of activation was faster for fXdes-137-183;N191A as compared to fXdes-137-183. We propose that the fX AP and Asn191 carbohydrate serve primarily as negative autoregulation mechanisms to prevent spurious activation of fX and secondarily in cofactor dependence and activator specificity.The abbreviations used are: TF, human tissue factor; AP, activation peptide; HEPES, (N-[2-Hydroxyethyl]piperazine-N’-[2-ethanesulfonic acid]); PEG, polyethylene glycol 8000; BSA, bovine serum albumin; Tris, (Tris[hydroxymethyl] aminomethane); EDTA, (Ethylenedinitrilo)-tetraacetic acid; SDSPAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis; RVV-X, X activating protein from Russell’s viper venom; gla, γ-carboxylated glutamic acid; WTfX, wild type factor X; PC:PS, phosphatidylcholine:phosphatidylserine; fXa, fIXa, f Va, fVIIa, and fVIIIa, activated coagulation factor X, IX, V, VII, and VIII; ATIII, antithrombin; TFPI, tissue factor pathway inhibitor.

Based on homology, amino acids 326–336 (143–154 in chymotrypsin numbering) of factor X (fX) comprise a flexible surface loop, which is susceptible to self-proteolysis and influences substrate catalysis. To investigate the role of this autolysis loop in fX function, a recombinant variant with a new site for asparagine-linked glycosylation has been produced by changing glutamine 333 to asparagine. Q333N fX is activated normally by factor VIIa and tissue factor, factors IXa and VIIIa, and Russell's viper venom. Proteolysis of the loop is prevented by the mutation. Reactivity of the free enzyme toward substrates and inhibitors is attenuated 4–20-fold; relative to wild type fXa, Spectrozyme XaTMhydrolysis is 25%, inhibition by antithrombin III and the tissue factor pathway inhibitor is ∼20%, and prothrombin activation in the absence of the cofactor Va is only 5%. Surprisingly, activities of the variant and wild type enzymes are equivalent when part of the prothrombinase complex. N-Glycanase cleaves the new oligosaccharide from Q333N fXa leaving aspartic acid. Q333D fXa is ∼1.6-fold more reactive with Spectrozyme XaTM, antithrombin III and tissue factor pathway inhibitor, and prothrombin than its glycosylated counterpart, Q333N fXa, but still quite abnormal relative to wild type fXa. Like Q333N fXa, Q333D fXa is fully functional as part of the prothrombinase complex. We conclude that Gln-333 is geographically close to a site of proteolytic degradation but not to activator, cofactor, or membrane binding sites. Mutation of Gln-333 impairs catalytic function, but given normal prothrombin activation by the complexed enzyme, the importance of Gln-333 for catalysis is not manifest in the prothrombinase assembly, suggesting a conformational change in complexed fXa.

Herein we describe a recombinant factor X (fX) with a single substitution at position 347 (fXR347N). Activated fXR347N had a reduced affinity for factor Va (fVa), although the catalytic impact of fVa binding remained intact. The mutation was selective as demonstrated by normal activation and inhibition, except in the presence of subsaturating heparin where the rate of inhibition by antithrombin III (ATIII) was 15% of normal. The reactivity of fXaR347N toward prothrombin was equivalent to wild-type fXa (fXaWT) in the absence of fVa and phospholipid. Addition (without phospholipid) of fVa dramatically increased the catalytic efficiency of fXaWT toward prothrombin but had a negligible effect on fXaR347N. On addition of phosphatidylcholine:phosphatidylserine (PC:PS, 3:1) vesicles, fXaR347Ndisplayed an increased catalytic activity in response to fVa, but the apparent affinity for fVa on the phospholipid surface was 5-20-fold lower than that of fXaWT. On an activated platelet surface, however, fXaWT and fXaR347N activated prothrombin similarly. In a competitive binding assay that measures the displacement of radiolabeled fXa from fVa on a phospholipid surface, fXaR347N was approximately 10-fold less effective than fXaWT. Substitution of fXa at position 347 selectively attenuates the interaction between fXa and fVa without affecting its catalytic activity.

Blood coagulation factor X plays a pivotal role in the clotting cascade. When administered intravenously to mice, the majority of activated factor X (factor Xa) binds to α2-macroglobulin (α2M) and is rapidly cleared from the circulation into liver. We show here that the low-density lipoprotein receptor-related protein (LRP) is responsible for factor Xa catabolism in vivo. Mice overexpressing a 39-kD receptor-associated protein that binds to LRP and inhibits its ligand binding activity displayed dramatically prolonged plasma clearance of 125I-factor Xa. Preadministration of α2M-proteinase complexes (α2M*) also diminished the plasma clearance of125I-factor Xa in a dose-dependent fashion. The clearance of preformed complexes of 125I-factor Xa and α2M was similar to that of 125I-factor Xa alone and was also inhibited by mice overexpressing a 39-kD receptor-associated protein. These results thus suggest that, in vivo, factor Xa is metabolized via LRP after complex formation with α2M.

A molecular defect in factor X (fX) results from a point mutation that causes glycine substitution for γ-carboxylated glutamic acid at position 7. The variant (fXSt. Louis II) and wild type (fXWT) proteins were produced in a mammalian expression system and characterized. fXSt. Louis II has

In the European Union, biosimilar products have been approved since 2006 under an abbreviated pathway that leverages their similarity to an existing “reference” biological product. The products approved to date are based on recombinant versions of endogenous proteins with well-understood structures and pharmacology, but complicated safety and immunogenicity profiles. The period during the 2000s that included the first reviews, approvals, sale and use of biosimilars is referred to herein as “Biosimilars 1.0.” Over the next several years, a new and advanced tranche of biosimilars will be developed for complex reference products, including medicines used in the treatment of cancer and autoimmune diseases. A global market for biosimilars is developing and this may well foreshadow the beginning of the second era of product development. This Biosimilars 2.0 period will likely be characterized by the development of complex products, global harmonization of standards and the increasing demand for long-term monitoring of pharmaceuticals. The products developed in this period should exhibit high levels of fidelity to the reference products and should be rigorously evaluated in analytical, non-clinical and clinical comparisons. Additionally, Biosimilars 2.0 manufacturers should strive for transparency in their labels and take proactive strides to be accountable to providers and patients for the quality of their products. An important opportunity now exists for the healthcare community, industry and regulators to work in partnership, to outline the appropriate standards for these products and to facilitate increased access while meeting patients' needs.

The binding of thrombin to fibrin is thought to be an important mechanism by which thrombi exhibit procoagulant activity; however, the extent to which other procoagulants are associated with thrombi has not been previously defined. This study was designed to determine whether clotting factors other than thrombin are bound to whole-blood clots and can thereby contribute to significant procoagulant activity. Clots formed in vitro from human blood exhibited minimal thrombin activity when incubated in plasma depleted of vitamin K-dependent factors by barium-citrate adsorption, as indicated by increases in the concentration of fibrinopeptide A (FPA), a marker of fibrin formation, to 72 nM after 30 min. Incubation of clots in barium-absorbed plasma repleted with 0.9 microM human prothrombin under the same conditions resulted in marked increases in the concentration of FPA (> 1,000 nM) and clotting by 30 min. The increases in FPA were attributable to activation of the added prothrombin by clot-associated Factor Xa, judging from concomitant increases in the concentration of prothrombin fragment 1.2. Similar results were obtained with thrombi induced in the axillary arteries of dogs by vascular injury and incubated with plasma in vitro. Activation of prothrombin was inhibited in a dose-dependent manner by tick anticoagulant peptide, a direct inhibitor of Factor Xa, at concentrations of 0.5-5.0 microM. Clot-associated Factor Xa activity was resistant to inhibition by anti-thrombin III, judging from the lack of inhibition of prothrombin activation during incubation of clots in plasma containing heparin pentasaccharide, an anti-thrombin III-mediated inhibitor of Factor Xa. Thus, the activity of Factor Xa appears to be an important determinant of the procoagulant activity of whole-blood clots and arterial thrombi, and is resistant to inhibition by anti-thrombin III-dependent inhibitors.

Genetic markers associated with cardiovascular disease, which may be predictive, have been identified by of genome-wide association studies, but their predictive ability has not been tested. The evaluation of a literature-based genetic risk score for cardiovascular disease is now possible using the online catalog maintained by the National Human Genome Research Institute of all genetic markers identified in genome-wide association studies. This prospective cohort study investigated the predictive ability of literature-based genetic risk scores for cardiovascular disease, and tested their relationship to incident cardiovascular events and their potential to improve prediction. The participants—a cohort of 19,313 initially healthy females enrolled in the Women's Genome Health Study—were followed for a median of 12.3 years. Genetic risk scores were constructed using the online National Human Genome Research Institute catalog of studies published between 2005 and 2009. The scores were based on the selection of single nucleotide polymorphisms (SNPs) that were known markers associated with either cardiovascular disease (myocardial infarction, stroke, coronary disease, or cardiovascular death), or an intermediate phenotype (total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, hypertension, and other phenotypes). A total of 101 SNPs were identified with a published risk allele and a P value of less than or equal to 10−7 for the association with cardiovascular disease or at least 1 intermediate phenotype; the addition of risk alleles created the genetic risk score. During the follow-up period, there were 777 incident cardiovascular events (199 myocardial infarctions, 203 strokes, 63 cardiovascular deaths, and 312 revascularizations). Adjustment for age showed that the 101 SNP genetic risk scores were associated with increased risk of cardiovascular disease: the age-adjusted hazard ratio for cardiovascular disease per allele for the101 SNP genetic risk scores was 1.02 per risk allele, with a 95% confidence interval of 1.00 to 1.03 per risk allele; P = 0.006). Over a 10-year study period, this represented an absolute cardiovascular disease risk of 3% in the lowest tertile of genetic risk (73–99 risk alleles) and 3.7% in the highest tertile (106–125 risk alleles). However, after adjusting for traditional risk factors, the ability of the risk score alone to discriminate between women at risk for cardiovascular events and those not at risk was minimal with a c index of 0.52 in the ATP III (Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults) risk score; the ATP III–adjusted hazard ratio per allele was 1.00, with a 95% CI of 0.99 to 1.01. In contrast, self-reported family history remained an independent risk factor in multivariate models for incident cardiovascular disease. These findings indicate that a genetic risk score comprised of 101 SNPs is not significantly associated with incident cardiovascular disease, after adjustment for traditional risk factors, and has no significant effect on discrimination or reclassification.

Background— Recent trial data have challenged the hypothesis that cholesteryl ester transfer protein (CETP) and high-density lipoprotein cholesterol (HDL-C) have causal roles in atherothrombosis. One method to evaluate this issue is to examine whether polymorphisms in the CETP gene that impact on HDL-C levels also impact on the future development of myocardial infarction. Methods and Results— In a prospective cohort of 18 245 initially healthy American women, we examined over 350 000 singe-nucleotide polymorphisms (SNPs) first to identify loci associated with HDL-C and then to evaluate whether significant SNPs within these loci also impact on rates of incident myocardial infarction during an average 10-year follow-up period. Nine loci on 9 chromosomes had 1 or more SNPs associated with HDL-C at genome-wide statistical significance ( P −8 ). However, only SNPs near or in the CETP gene at 16q13 were associated with both HDL-C and risk of incident myocardial infarction (198 events). For example, SNP rs708272 in the CETP gene was associated with a per-allele increase in HDL-C levels of 3.1 mg/dL and a concordant 24% lower risk of future myocardial infarction (age-adjusted hazard ratio, 0.76; 95% CI, 0.62 to 0.94), consistent with recent meta-analysis. Independent and again concordant effects on HDL-C and incident myocardial infarction were also observed at the CETP locus for rs4329913 and rs7202364. Adjustment for HDL-C attenuated but did not eliminate these effects. Conclusion— In this prospective cohort of initially healthy women, SNPs at the CETP locus impact on future risk of myocardial infarction, supporting a causal role for CETP in atherothrombosis, possibly through an HDL-C mediated pathway.

Background— Homocysteine is a sulfur amino acid whose plasma concentration has been associated with the risk of cardiovascular diseases, neural tube defects, and loss of cognitive function in epidemiological studies. Although genetic variants of MTHFR and CBS are known to influence homocysteine concentration, common genetic determinants of homocysteine remain largely unknown. Methods and Results— To address this issue comprehensively, we performed a genome-wide association analysis, testing 336 469 single-nucleotide polymorphisms in 13 974 healthy white women. Although we confirm association with MTHFR (1p36.22; rs1801133; P =8.1�10 −35 ) and CBS (21q22.3; rs6586282; P =3.2�10 −10 ), we found novel associations with CPS1 (2q34; rs7422339; P =1.9�10 −11 ), MUT (6p12.3; rs4267943; P =2.0�10 −9 ), NOX4 (11q14.3; rs11018628; P =9.6�10 −12 ), and DPEP1 (16q24.3; rs1126464; P =1.2�10 −12 ). The associations at MTHFR , DPEP1 , and CBS were replicated in an independent sample from the PROCARDIS study, whereas the association at CPS1 was only replicated among the women. Conclusions— These associations offer new insight into the biochemical pathways involved in homocysteine metabolism and provide opportunities to better delineate the role of homocysteine in health and disease.

This study was designed to define the procoagulant effects of different plasminogen activators in recalcified plasma. Accordingly, a two-stage assay procedure was developed in which citrated plasma was recalcified and incubated for 1–7 min with streptokinase (SK), urokinase (UK), or tissue-plasminogen activator (t-PA). An aliquot of this first-stage plasma was added to second-stage plasma; procoagulant activity was measured as the acceleration of the clotting time compared with that in control first-stage plasma to which plasminogen activators had not been added. With this procedure, second-stage clotting times were significantly accelerated after activation of plasminogen compared with those in control plasma and were shortest with 1000 i.u./ml SK. The presence of increased thrombin activity in the recalcified citrated plasma was verified by measurement of increased concentrations of fibrinopeptide A, which were inhibited by addition of I U/ml hirudin or or U/ml heparin to plasma during incubation with the plasminogen activators. Activation of factor X was induced in plasma incubated with SK. The rate of activation of factor X was increased when thrombin was elaborated. Induction of procoagulant activity was found to be dependent on depletion of α 2 -antiplasmin and on the presence of plasmin activity in plasma, and could be inhibited by aprotinin. Thus, procoagulant activity in response to pharmacologic activation of plasminogen is dependent on plasmin-mediated activation of factor X, and subsequent activation of prothrombin.

Human plasma contains an inhibitor of tissue factor-initiated coagulation known as the lipoprotein-associated coagulation inhibitor (LACI) or also known as the extrinsic pathway inhibitor (EPI). A competitive fluorescent immunoassay was developed to measure the plasma concentration of LACI in samples from normal individuals and patients with a variety of diseases. The LACI concentration in an adult control population varied from 60% to 160% of the mean with a mean value corresponding to 89 ng/mL or 2.25 nmol/L. Plasma LACI levels were not decreased in patients with severe chronic hepatic failure, warfarin therapy, primary pulmonary hypertension, thrombosis, or the lupus anticoagulant. Plasma LACI antigen was decreased in some, but not all patients with gram-negative bacteremia and evidence for disseminated intravascular coagulation. Plasma LACI levels were elevated in women undergoing the early stages of labor (29%), in patients receiving intravenous tissue-type plasminogen activator (45%), and in patients receiving intravenous heparin (375%). A radioligand blot of the pre- and post-heparin plasma samples shows the increase to be in a 40-Kd form of LACI. Very low levels of plasma LACI antigen were found in patients with homozygous abetalipoproteinemia and hypobetalipoproteinemia, diseases associated with low plasma levels of apolipoprotein B containing lipoproteins. Following the injection of heparin into one patient with homozygous abetalipoproteinemia, the plasma LACI antigen level increased to a level comparable with that in normal individuals after heparin treatment.

The lipoprotein-associated coagulation inhibitor (LACI) is present in vivo in at least three different pools: sequestered in platelets, associated with plasma lipoproteins, and released into plasma by intravenous heparin, possibly from vascular endothelium. In this study we have purified the heparin-relesable form of LACI from post-heparin plasma and show that it is structurally different from lipoprotein LACI. The purification scheme uses heparin-agarose chromatography, immunoaffinity chromatography, and size-exclusion chromatography and results in a 185,000-fold purification with a 33% yield. Heparin- releasable LACI (HRL), as analyzed by sodium dodecyl sulfate- polyacrylamide gel electrophoresis, under reducing conditions, appears as a major band at 40 Kd and a minor band at 36 Kd. Immunoblot analysis suggests that the 36-Kd band arises from carboxyl-terminus proteolysis that occurs during the purification. HRL has a specific activity similar to that of HepG2 or lipoprotein LACI. HRL and lipoprotein LACI combine with lipoproteins in vitro while purified HepG2 LACI does not. I125-labeled HRL, injected into a rabbit, is cleared more slowly than I125-labeled HepG2 LACI, which may be due to attachment to lipoproteins in vivo. Preliminary evidence suggests that HRL is associated with vascular endothelium, possibly by attachment to glycosaminoglycans.

About 30% of human plasma protein C is smaller than the predominant form as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It has been suggested that this species, referred to as beta protein C, is a degraded molecule. However, beta protein C is secreted in culture by the HepG2 cell line and is present in plasma collected directly into numerous proteinase inhibitors; the percentage of beta protein C does not change with time during culture or after blood collection. Neither thrombin, activated protein C, nor activated factor X converts the alpha form to beta in the presence or absence of calcium and phospholipids. The NH2-terminal sequences of the heavy chains of both forms are identical, and both release the same dodecapeptide and develop a functional active site when cleaved by thrombin. Both also react with antibodies to a synthetic COOH-terminal peptide. Timed digests with N-glycosidase are consistent with the interpretation that beta protein C has three N-linked oligosaccharide chains whereas alpha protein C has four. It is asparagine 329 that is not glycosylated in beta protein C since antibodies to a synthetic peptide based on the sequence around this amino acid react only with beta protein C. This site is unique in having cysteine instead of serine or threonine 2 residues distal. It is likely that the sulfhydryl group can substitute for the usual hydroxyl group as a hydrogen bond acceptor for the glycosylation reaction only until it forms a disulfide bond. The percentage of protein C that is glycosylated at this site may therefore depend at least in part on the rate of disulfide bond formation which may in turn be related to the rate of protein synthesis.

Standard therapy to prevent recurrent venous thromboembolism includes 3 to 12 months of treatment with full-dose warfarin with a target international normalized ratio (INR) between 2.0 and 3.0. However, for long-term management, no therapeutic agent has shown an acceptable benefit-to-risk ratio.Patients with idiopathic venous thromboembolism who had received full-dose anticoagulation therapy for a median of 6.5 months were randomly assigned to placebo or low-intensity warfarin (target INR, 1.5 to 2.0). Participants were followed for recurrent venous thromboembolism, major hemorrhage, and death.The trial was terminated early after 508 patients had undergone randomization and had been followed for up to 4.3 years (mean, 2.1). Of 253 patients assigned to placebo, 37 had recurrent venous thromboembolism (7.2 per 100 person-years), as compared with 14 of 255 patients assigned to low-intensity warfarin (2.6 per 100 person-years), a risk reduction of 64 percent (hazard ratio, 0.36 [95 percent confidence interval, 0.19 to 0.67]; P0.001). Risk reductions were similar for all subgroups, including those with and those without inherited thrombophilia. Major hemorrhage occurred in two patients assigned to placebo and five assigned to low-intensity warfarin (P=0.25). Eight patients in the placebo group and four in the group assigned to low-intensity warfarin died (P=0.26). Low-intensity warfarin was thus associated with a 48 percent reduction in the composite end point of recurrent venous thromboembolism, major hemorrhage, or death. According to per-protocol and as-treated analyses, the reduction in the risk of recurrent venous thromboembolism was between 76 and 81 percent.Long-term, low-intensity warfarin therapy is a highly effective method of preventing recurrent venous thromboembolism.

To understand the role of the factor X (fX) activation peptide (AP), a deletion mutagenesis approach was employed. Two single-chain, variant enzymes were generated in which 41 residues were deleted from the AP: fX (des-137-183) and fX(des-137-183;N191A), which lacks a carbohydrate moiety at Asn191 due to an alanine substitution. Deletion of the fX AP did not impact fXa catalytic activity. Activation of the variant zymogens, however, was altered. Neither mutant enzyme was activated by the fX coagulant protein from Russell's viper venom (RVV-X(1)). Activation by factor VIIa (fVIIa) and fVIIa in the presence of cofactor, lipidated tissue factor (TF), occurred at an accelerated rate for both variants as compared to wild-type fX (WTfX). Similar to fVII, the mutants auto-activated in a cofactor-independent manner, which was characterized by a lag period and accelerated dose-dependently by plasma fXa (kcat/Km, 0.046 +/- 0.004 micro M(-1) s(-1)). Both mutants were also found to be activated by fVIIa (0.31 +/- 0.03 micro M(-1) s(-1)), fIXa (0.30 +/- 0.03 micro M(-1) s(-1)), and thrombin (0.00078 +/- 0.00015 micro M(-1) s(-1)). In all cases, the rate of activation was faster for fX(des-137-183;N191A) as compared to fX(des-137-183). We propose that the fX AP and Asn191 carbohydrate serve primarily as negative autoregulation mechanisms to prevent spurious activation of fX and secondarily in cofactor dependence and activator specificity.

OBJECTIVES The study was done to determine whether the G20210A mutation in the prothrombin gene increases the risk of recurrent venous thromboembolism (VTE), both alone and in combination with factor V Leiden. BACKGROUND Several inherited defects of coagulation are associated with increased risk of first VTE, including a recently identified G20210A mutation in the prothrombin gene. However, whether the presence of this mutation confers an increased risk of recurrent venous thromboembolism is controversial. METHODS A total of 218 men with incident venous thromboembolism were genotyped for the prothrombin mutation and for factor V Leiden and were followed prospectively for recurrent VTE over a follow-up period of 7.3 years. RESULTS A total of 29 men (13.3%) suffered recurrent VTE. Five of the 14 carriers of the prothrombin mutation developed recurrent VTE (35.7%; incidence rate = 8.70 per 100 person-years), while 24 of 204 individuals who did not carry the prothrombin mutation developed recurrent VTE (11.8%; incidence rate = 1.76 per 100 person-years). Thus, presence of the G20210A mutation was associated with an approximate fivefold increased risk for recurrent VTE (crude relative risk [RR] 4.93; 95% confidence interval [CI] 1.9–12.9; p = 0.001; age-, smoking-, and body mass index-adjusted RR 5.28; 95% CI 2.0–14.0; p = 0.001). In these data, recurrence rates were similar among those with an isolated mutation in the prothrombin gene (18.2%) as compared to those with an isolated factor V Leiden mutation (19.2%). However, all three study participants who carried both mutations (100%) suffered a recurrent event during follow-up. CONCLUSIONS In a prospective evaluation of 218 men, the presence of prothrombin mutation was associated with a significantly increased risk of recurrent VTE, particularly among those who co-inherited factor V Leiden.

We reported previously that residue 347 in activated fX (fXa) contributes to binding of the cofactor, factor Va (fVa) (Rudolph, A. E., Porche-Sorbet, R. and Miletich, J. P. (2000) Biochemistry 39, 2861-2867). Four additional residues that participate in fVa binding have now been identified by mutagenesis. All five resulting fX species, fX(R306A), fX(E310N), fX(R347N), fX(K351A), and fX(K414A), are activated and inhibited normally. However, the rate of inhibition by antithrombin III in the presence of submaximal concentrations of heparin is reduced for all the enzymes. In the absence of fVa, all of the enzymes bind and activate prothrombin similarly except fXa(E310N), which has a reduced apparent affinity ( approximately 3-fold) for prothrombin compared with wild type fXa (fXa(WT)). In the absence of phospholipid, fVa enhances the catalytic activity of fXa(WT) significantly, but the response of the variant enzymes was greatly diminished. On addition of 100 nm PC:PS (3:1) vesicles, fVa enhanced fXa(WT), fXa(R306A), and fXa(E310N) similarly, whereas fXa(R347N), fXa(K351A), and fXa(K414A) demonstrated near-normal catalytic activity but reduced apparent affinity for fVa under these conditions. All enzymes function similarly to fXa(WT) on activated platelets, which provide saturating fVa on an ideal surface. Loss of binding affinity for fVa as a result of the substitutions in residues Arg-347, Lys-351, and Lys-414 was verified by a competition binding assay. Thus, Arg-347, Lys-351, and Lys-414 are likely part of a core fVa binding site, whereas Arg-306 and Glu-310 serve a less critical role.

Background —A single base pair mutation in the prothrombin gene has recently been identified that is associated with increased prothrombin levels. Whether this mutation increases the risks of arterial and venous thrombosis among healthy individuals is controversial. Methods and Results —In a prospective cohort of 14 916 men, we determined the prevalence of the G20210A prothrombin gene variant in 833 men who subsequently developed myocardial infarction, stroke, or venous thrombosis (cases) and in 1774 age- and smoking status–matched men who remained free of thrombosis during a 10-year follow-up (control subjects). Gene sequencing was used to confirm mutation status in a subgroup of participants. Overall, carrier rates for the G20210A mutation were similar among case and control subjects; the relative risk of developing any thrombotic event in association with the 20210A allele was 1.05 (95% CI, 0.7 to 1.6; P =0.8). We observed no evidence of association between mutation and myocardial infarction (RR=0.8, P =0.4) or stroke (RR=1.1, P =0.8). For venous thrombosis, a modest nonsignificant increase in risk was observed (RR=1.7, P =0.08) that was smaller in magnitude than that associated with factor V Leiden (RR=3.0, P Conclusions —In a large cohort of US men, the G20210A prothrombin gene variant was not associated with increased risk of myocardial infarction or stroke. For venous thrombosis, risk estimates associated with the G20210A mutation were smaller in magnitude than risk estimates associated with factor V Leiden.

A system is described for producing recombinant factor X with properties very similar to human plasma factor X. Optimization of the expression system for factor X resulted in the finding that human kidney cells (293 cells) are superior to the widely utilized baby hamster kidney cells (BHK cells) for the expression of functional factor X. It was also determined that production of factor X by 293 cells requires the substitution of the -2 residue (Thr-->Arg) which affords the removal of the factor X propeptide. Purification of recombinant and plasma factor X is accomplished using a calcium-dependent monoclonal antibody directed against the gla domain. The proteins are comparable by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The rate and extent of activation by the factor X coagulant protein from Russell's viper venom and by factors IXa and VIIIa are similar; activation of the recombinant protein by VIIa and tissue factor is mildly faster. The activated enzymes have the same activity toward a chromogenic substrate and the biologic substrate, prothrombin. Both enzymes have the same apparent affinity for the activated platelet surface as judged by their ability to activate prothrombin. Finally, inhibition by antithrombin, with or without heparin, and inhibition by the tissue factor pathway inhibitor are equivalent. Recombinant factor X produced by this method is therefore well suited for probing structure-function relationships by mutational analysis.

Previous reports suggest that younger carriers of the factor V Leiden mutation are at greater risk for venous thromboembolism than are older carriers. However, available data on thromboembolic risk are limited.To determine age-specific incidence rates of venous thromboembolism associated with the factor V Leiden mutation.Prospective cohort study.14,916 initially healthy men participating in the Physicians' Health Study who were followed from 1982 to August 1994 for the occurrence of deep venous thrombosis or pulmonary embolism.Polymerase chain reaction was used to determine factor V Leiden mutation status in 156 study participants who developed venous thromboembolism during follow-up and in 2406 study participants who remained free of vascular disease.Risks for venous thromboembolism in heterozygous carriers of factor V Leiden mutation increased with age at a rate significantly greater than that in noncarriers. Whereas incidence rates of venous thromboembolism were similar in men with and men without the factor V Leiden mutation who were younger than 50 years of age, incidence rate differences (per 1000 person-years of observation) between affected and unaffected men increased significantly from 1.23 (95% CI, -0.4 to 2.9) for those aged 50 to 59 years to 1.61 (CI, -0.5 to 3.7) for those aged 60 to 69 years of age to 5.97 (CI, 0.6 to 11.3) for those aged 70 years or older (P for trend = 0.008). For idiopathic venous thromboembolism, age-specific incidence rate differences between men with and without the factor V Leiden mutation increased significantly with age (P = 0.017). However, no significant relation was found for secondary events (P0.2).The findings support the hypothesis that the pathogenesis of venous thromboembolism involves acquired as well as genetic risk factors and indicate that determination of factor V Leiden mutation status should not be limited to young patients.

Background The 4G allele of the 4G/5G polymorphism in the promoter of the plasminogen activator inhibitor (PAI-1) gene is associated with increased PAI-1 activity. In a small group of young Swedish men, this allele has been reported to predict risk of myocardial infarction. Whether this polymorphism increases risk of arterial and venous thrombosis among middle-aged men is unknown. Methods and Results Among 14 916 men 40 to 84 years old participating in the Physicians' Health Study who provided baseline blood samples for DNA analysis, 374 suffered first myocardial infarction and 121 had venous thromboembolism during 8.6 years of follow-up. Distributions of the 4G/5G polymorphism in the PAI-1 gene promoter were assessed in these men as well as in a sample of study participants matched on age and smoking who did not develop vascular occlusion during the prospective follow-up period. The distributions of the 4G/4G, 4G/5G, and 5G/5G genotypes among men who developed myocardial infarction (0.27, 0.51, 0.22; P =.7) or venous thromboembolism (0.30, 0.49, 0.21; P =.5) were virtually identical to those of men who remained free of vascular disease (0.27, 0.50, 0.23). Thus, the relative risk of future thrombosis among those with the 4G/4G genotype compared with those without the 4G/4G genotype was 1.02 (95% CI, 0.8 to 1.3). There was no effect modification by age, smoking status, family history of premature thrombosis, history of hypertension, hypercholesterolemia, or aspirin use. Conclusions These data indicate that the 4G/5G polymorphism in the promoter of the PAI-1 gene is not a major pathogenetic risk factor for arterial or venous thrombosis among middle-aged men.

A specific point mutation in the gene coding for coagulation factor V is associated with resistance to degradation by activated protein C, a recently described abnormality of coagulation that may be associated with an increased risk of venous thrombosis. Whether this mutation also predisposes patients to arterial thrombosis is unknown, as is the value of screening for the mutation in order to define the risk of venous thrombosis among unselected healthy people.Among 14,916 apparently healthy men in the Physicians' Health Study who provided base-line blood samples, 374 had myocardial infarctions, 209 had strokes, and 121 had deep venous thrombosis, pulmonary embolism, or both, during a mean follow-up of 8.6 years. We determined whether a mutation at nucleotide position 1691 of the factor V gene was present or absent in these 704 men and in an equal number of matched participants who remained free of vascular disease.The prevalence of heterozygosity for the mutation among men who had myocardial infarctions (6.1 percent, P = 0.9) or strokes (4.3 percent, P = 0.4) was similar to that among men who remained free of vascular disease (6.0 percent). However, the prevalence of the mutation was significantly higher among men who had venous thrombosis, pulmonary embolism, or both (11.6 percent, P = 0.02). In adjusted analyses, the relative risk of venous thrombosis among men with the mutation was 2.7 (95 percent confidence interval, 1.3 to 5.6; P = 0.008). This increased risk was seen with primary venous thrombosis (relative risk, 3.5; 95 percent confidence interval, 1.5 to 8.4; P = 0.004) but not with secondary venous thrombosis (relative risk, 1.7; 95 percent confidence interval, 0.6 to 5.3; P = 0.3), and it was most apparent among older men. Specifically, the prevalence of the mutation among men over the age of 60 in whom primary venous thrombosis developed was 25.8 percent (relative risk, 7.0; 95 percent confidence interval, 2.6 to 19.1; P0.001).In a large cohort of apparently healthy men, the presence of a specific point mutation in the factor V gene was associated with an increased risk of venous thrombosis, particularly primary venous thrombosis. The presence of the mutation was not associated with an increased risk of myocardial infarction or stroke. This mutation appears to be the most common inherited factor thus far recognized that predisposes patients to venous thrombosis.

BACKGROUND Platelet activation occurs in vivo during pharmacologic thrombolysis and may contribute to recurrent thrombosis. Plasmin does not directly activate platelets except at high concentrations; thus, the mechanisms for platelet activation during thrombolysis remain undefined. Increases in thrombin activity also occur in patients treated with fibrinolytic agents and may contribute to activation of platelets. We have shown that one mechanism for increased thrombin activity is activation of the coagulation system by plasmin. METHODS AND RESULTS In the present study we sought to determine whether activation of platelets in response to pharmacologic activation of plasminogen in plasma is due primarily to plasmin or mediated by increased thrombin activity. Platelet-rich citrated plasma (PRP) was recalcified and incubated with 1,000 IU/ml of streptokinase or 1.0 caseinolytic units/ml of plasmin. Concentrations of fibrinopeptide A, a marker of thrombin activity, increased markedly over 10 minutes in plasma incubated with streptokinase or plasmin, but not in PRP incubated without plasminogen activator. Platelet activation characterized by the secretion of 14C-serotonin occurred within 2-4 minutes after thrombin activity increased. In stirred recalcified PRP, platelet aggregation was accelerated from 3.6 +/- 0.5 to 2.5 +/- 0.3 minutes (p less than 0.01) when incubated with 1,000 IU/ml of streptokinase. Leupeptin and aprotinin, inhibitors of plasmin activity, markedly attenuated platelet activation in response to pharmacologic activation of plasminogen. However, inhibition of thrombin with heparin, hirudin, or D-Phe-D-Pro-L-Arg-chloromethylketone was more effective in inhibiting the acceleration of platelet activation induced by plasminogen activation, despite the elaboration of plasmin activity. CONCLUSIONS Activation of platelets during coronary thrombolysis may be due in part to increased procoagulant activity induced by plasminogen activation as well as other factors that promote platelet activation in vivo.

To the Editor: Several large-scale studies indicate that factor V Leiden (FVL) is not associated with an increased risk of acute myocardial infarction (MI) in middle-aged or elderly populations.[1-7][1]However, Rosendaal et al[8][2] have hypothesized that FVL might increase the risk of myocardial

Type 2 diabetes is a leading cause of morbidity and mortality. While genetic variants have been found to influence the risk of type 2 diabetes mellitus, relatively few studies have focused on genes associated with glycated hemoglobin, an index of the mean blood glucose concentration of the preceding 8–12 weeks. Epidemiologic studies and randomized clinical trials have documented the relationship between glycated hemoglobin levels and the development of long-term complications in diabetes; moreover, higher glycated hemoglobin levels in the subdiabetic range have been shown to predict type 2 diabetes risk and cardiovascular disease. To examine the common genetic determinants of glycated hemoglobin levels, we performed a genome-wide association study that evaluated 337,343 SNPs in 14,618 apparently healthy Caucasian women. The results show that glycated hemoglobin levels are associated with genetic variation at the GCK (rs730497; P = 2.8×10−12), SLC30A8 (rs13266634; P = 9.8×10−8), G6PC2 (rs1402837; P = 6.8×10−10), and HK1 (rs7072268; P = 6.4×10−9) loci. While associations at the GCK, SLC30A8, and G6PC2 loci are confirmatory, the findings at HK1 are novel. We were able to replicate this novel association in an independent validation sample of 455 additional non-diabetic men and women. HK1 encodes the enzyme hexokinase, the first step in glycolysis and a likely candidate for the control of glucose metabolism. This observed genetic association between glycated hemoglobin levels and HK1 polymorphisms paves the way for further studies of the role of HK1 in hemoglobin glycation, glucose metabolism, and diabetes., Author Summary Type 2 diabetes is a leading cause of morbidity and mortality in both the developed and developing world. Because the main metabolic characteristic of diabetes is increased blood glucose concentration, we sought to uncover the genetic determinants of glycated hemoglobin, an index of the mean blood glucose concentration of the preceding 8–12 weeks. Taking advantage of new technologies allowing us to interrogate genetic variation on a whole-genome basis, we found that variations in the GCK, SLC30A8, G6PC2, and HK1 genes are important determinants of glycated hemoglobin concentrations. While associations with the GCK, SLC30A8, and G6PC2 genes have previously been identified in genetic studies of diabetes and blood glucose concentration, the findings at HK1 are novel. HK1 encodes the enzyme hexokinase, responsible for the first step in glucose utilization and a likely candidate for the control of glucose metabolism. This observed genetic association between glycated hemoglobin levels and HK1 genetic variants paves the way for further studies of the role of HK1 in glucose metabolism and diabetes.

Lipoprotein-associated coagulation inhibitor (LACI) appears to inhibit tissue factor (TF)-induced blood coagulation by forming a quaternary inhibitory complex containing factor Xa, LACI, factor VIIa, and TF. A genetically engineered hybrid protein consisting of the light chain of factor Xa and the first Kunitz-type inhibitor domain of LACI is shown to directly inhibit the activity of the factor VIIa-TF catalytic complex. Unlike inhibition of factor VIIa-TF activity by native LACI, inhibition by the hybrid protein is not dependent on factor Xa. In an assay of TF-induced coagulation, 50% TF inhibition occurs with hybrid protein at 35 nanograms per milliliter, whereas LACI at 2.5 micrograms per milliliter is required for an equivalent effect. gamma-Carboxylation of glutamic acid residues in the factor Xa light chain portion of the hybrid protein is required for inhibitory activity, indicating that the first Kunitz-type domain of LACI alone is not sufficient for inhibition of factor VIIa-TF.

No assays presently available test all aspects of protein C function. Overall, the potential for misdiagnosis is high

Recurrent pregnancy loss may result from hypercoagulability.To determine whether women with factor V Leiden mutation, a common inherited defect of coagulation, are at increased risk for recurrent pregnancy loss.Case-control study.University hospital.113 consecutive women referred for evaluation of recurrent spontaneous abortion (case-patients) and 437 postmenopausal women with at least one successful pregnancy and no history of pregnancy loss (controls). An additional survey of 387 postmenopausal women with at least one pregnancy loss was also conducted.Prevalence of factor V Leiden mutation determined by a second-generation screening test for resistance to activated protein C with genetic confirmation of all borderline and low-value results.Prevalence of the factor V Leiden mutation was greater among case-patients (8.0%) than among controls (3.7%) (odds ratio, 2.3 [95% CI, 1.0 to 5.2]; P = 0.050). In the subgroup of case-patients with three or more pregnancy losses and no successful pregnancies, prevalence of the mutation was 9.0% (odds ratio, 2.6 [CI, 1.0 to 6.7]; P = 0.048). Among the additional women surveyed, the prevalence of the mutation in those with three or more pregnancy losses (7.5%) was almost identical to that in case-patients. Thus, in all evaluated women with several pregnancy losses, the prevalence of factor V Leiden was increased 2.2-fold (P = 0.026).These data are compatible with the hypothesis that factor V Leiden mutation may play a role in some cases of unexplained recurrent pregnancy loss.

Objective. —To estimate ethnic-specific prevalence rates of factor V Leiden, an inherited defect of hemostasis associated with risk of venous thrombosis. Design. —Survey of 4047 American men and women participating in the Physicians' Health Study (PHS) or in the Women's Health Study (WHS). All study participants were free of myocardial infarction, stroke, or venous thrombosis. Main Outcome Measure. —Prevalence ofG1691ALeiden mutation in the gene coding for coagulation factor V was determined in the PHS group using polymerase chain reaction techniques and, in the WHS group, a second-generation activated protein C (APC)—resistance screening test with genetic confirmation of all borderline and low-value results. Results. —In 2468 Caucasian Americans, carrier frequency of factor V Leiden was 5.27% (95% confidence interval [CI], 4.42%-6.22%). Carrier frequency was 2.21% in 407 Hispanic Americans, 1.23% in 650 African Americans, 0.45% in 442 Asian Americans, and 1.25% in 80 Native Americans. Thus, prevalence of factor V Leiden was less among minority subjects (P=.001). Carrier frequencies were similar in Caucasian men and women (5.53% vs 4.85% respectively,P=.5). Conclusion. —These data indicate that prevalence of factor V Leiden is greater among Caucasians than minority Americans. These data have implications for clinicians considering whether to screen for factor V Leiden in high-risk groups such as those with prior venous thromboses or coexistent defects of anticoagulation and women at risk for postpartum thrombosis or seeking oral contraceptives.

Thrombin activity reflected by increased plasma concentrations in vivo of fibrinopeptide A (FPA) increases when streptokinase (SK) is administered to patients with acute myocardial infarction. Although procoagulant effects have been found in vitro, the use of anticoagulated plasma limits the extent to which the phenomena observed can be viewed to implicate procoagulant effects in vivo. Accordingly, we characterized the procoagulant effects of SK and tissue plasminogen activator (t-PA) in nonanticoagulated whole blood. Blood was collected from normal volunteers by venipuncture (No. 19 gauge steel needle) directly into polypropylene tubes containing either t-PA, SK, SK and heparin, t-PA and heparin, or saline. The concentration of FPA after 10 min of incubation with saline was 150 +/- 46 nM (n = 14)(SE). In contrast, in blood incubated with SK FPA was consistently and markedly increased after 10 min: 2318 +/- 416 nM (100 IU/ml SK) and 10,889 +/- 1156 nM (1000 IU/ml SK) (p less than 0.001 compared with control). Less marked elevations of FPA occurred after 10 min in blood incubated with t-PA (3171 +/- 604 nM with 2500 ng/ml t-PA, p less than 0.01 compared with 1000 IU/ml SK). Increases in FPA were less than 100 nM in blood incubated with activators and heparin. The extent to which plasminogen was activated, as measured by the release of the B beta 1-42 fibrinopeptide, was related to the magnitude of elevation of FPA. Procoagulant activity induced by extensive plasminogen activation may contribute to undesirable effects in vivo, such as a propensity to recurrent thrombosis or delayed fibrinolysis.

Lipoprotein-Associated Coagulation Inhibitor (LACI) is a factor Xa dependent inhibitor of the factor VII(a)/Tissue Factor catalytic complex. Deduced from partial cDNA sequence, LACI's amino acid sequence has recently been reported. Northern blot analysis showed LACI cDNA hybridizes to RNAs of 1.4 and 4.0 kb in size. To complete the characterization of the LACI message(s), overlapping LACI cDNAs were isolated from a human endothelial cell library. Sequence analysis revealed the clones' inserts span 4023 bases of sequence, consisting of 381 bases of 5' untranslated sequence, an open reading frame of 912 bases, 2682 bases of 3' untranslated sequence and 48 bases of poly(A) sequence. In addition, a short 1.4 kb insert which encodes for LACI was found to contain 49 bases of 3' untranslated sequence and a 3' poly(A) tail. The 1.4 kb of sequence is contained in the 4.0 kb sequence, except for 14 bases of 5' sequence, suggesting that the LACI messages arise by the use of alternative termination and polyadenylation signals during processing. Northern blot analysis of RNA isolated from cells treated with actinomycin D showed both RNA species appear to be relatively stable. Using a bovine papilloma virus vector, LACI cDNA was transfected into mouse C127 fibroblasts. The recombinant LACI is recognized by polyclonal anti-LACI IgG, binds to factor Xa and inhibits VII(a)/Tissue Factor activity in a similar fashion as LACI purified from HepG2 cell conditioned media.

Several murine monoclonal anti-human Factor VII antibodies were produced using hybridoma technology. Two noncompetitive monoclonal antibodies were used to examine by Western blotting the Factor VII cross-reactive material (CRM) in normal human plasma and three commercially available congenitally Factor VII-deficient plasmas, and to construct a facile "sandwich" immunoassay for plasma Factor VII. A second, previously undescribed, form of Factor VII CRM was detected in human plasma, which on Western blotting stained with an apparent intensity 5-8% that of Factor VII. This glycoprotein, tentatively called VII*, has a molecular weight 4,500 D less than Factor VII, lacks detectable Factor VII functional activity, does not bind to barium citrate, and is not recognized by a monoclonal antibody that recognizes Factor VII but not alpha-chymotrypsin-treated Factor VII. VII* was not proteolytically produced from Factor VII during in vitro coagulation or after infusion of human Factor VII into rabbits. As determined by Western blotting, the human hepatoma cell line, HepG2, cultured in the presence of vitamin K, secreted relatively greater levels of VII* in proportion to VII (75%) than that found in human plasma. Warfarin treatment of HepG2 cells decreased the quantity of VII secreted by 77%, whereas it only inhibited the secretion of VII* by 14%. Immunologic studies of the plasmas from a patient on chronic warfarin therapy and an individual given a short course of high dose warfarin therapy corroborated the in vitro synthetic studies obtained with HepG2 cells. The data are consistent with the production of VII* by posttranslational, proteolytic, modification of VII, that, at least in the HepG2 cells studied, occurs intracellularly. However, other mechanisms for the production of VII*, in particular, alternative RNA splicing of the transcript from a single gene, cannot be excluded.

Factor V (Va) is essential for binding of factor Xa to the surface of platelets. After thrombin treatment, normal platelets release at least five times more factor Va activity than is required for maximal factor Xa binding. The concentration of factor V activity obtained after thrombin stimulation of 10(7) normal platelets is sufficient to allow half-maximal factor Xa binding to 10(8) platelets (10% normal, 90% factor-V deficient). Therefore, factor Va activity is not limiting in platelet-surface factor Xa binding and prothrombin activation in normal platelets; some other components limit the number of binding sites. We report studies of a patient (M.S.) with a moderate to severe bleeding abnormality whose platelets are deficient in the platelet-surface component required for the factor Va-factor Xa binding. The patient's platelet factor Va activity released after thrombin treatment is normal, but factor Xa binding is 20%-25% of control values at saturation. Abnormal prothrombin consumption in a patient with normal plasma coagulation factors and platelet function suggests a disorder in platelet-surface thrombin formation.

Four cDNAs extending into the 5'-noncoding region of the human von Willebrand factor cDNA have been characterized. Thirty-four residues of amino-terminal protein sequence for von Willebrand antigen II matched that predicted from the cDNA sequence, confirming that the propeptide of von Willebrand factor is von Willebrand antigen II. Among the known cDNA sequences there are four confirmed single nucleotide differences, of which two may be in linkage disequilibrium, and two would alter the protein sequence. Based on comparisons among the four repeated D domains, an evolutional model has been proposed to account for the distribution of these sequence elements in prepro-von Willebrand factor.

Stimulation with thrombin or the calcium ionophore, A23187 caused human platelets to release a coagulation inhibitor similar to the Lipoprotein Associated Coagulation Inhibitor (LACI). This was documented functionally, with clotting assays measuring tissue factor inhibition and factor Xa inhibition, as well as immunologically, in a competitive immunoassay. The total amount of LACI released by 3 x 10(8) platelets after two hours stimulation was 7% to 8% of the amount found in 1 mL of serum. Half of the LACI was released by five minutes. The LACI was present in the platelet supernatant and was not associated with the platelet membrane or shed vesicles. The tissue factor and factor Xa inhibitory activities that were released were neutralized by preincubating the platelet supernatants with specific rabbit polyclonal anti-LACI IgG. On Western blot, platelet LACI appeared to run as a doublet with a molecular weight (mol wt) 45,000 to 47,000. Blood samples obtained from the site of a wound (template bleeding time) demonstrated a progressive increase in LACI concentration. A cDNA probe, derived from endothelial cell LACI cDNA, hybridized selectively to 4.0 and 1.4 kb transcripts in a preparation of platelet mRNA.

Human platelets have binding sites for plasma coagulation Factor X(a) that are available only after the platelet release reaction. Platelets from 15 normal donors bound 216+/-52 (SD) molecules of Factor X(a) per platelet. The association of Factor X(a) with its platelet surface receptor results in a 300,000-fold increase in the catalytic activity of Factor X(a) in forming thrombin from prothrombin. The turnover number for platelet-bound Factor X(a) was 1,850+/-460 mol thrombin/ml per min per mol Factor X(a) in experiments with platelets from 15 normal donors. Platelets from five patients with varying degrees of Factor V deficiency were investigated to determine whether or not coagulation Factor V participates in either aspect of the Factor X(a)-platelet interaction. The binding of Factor X(a) to platelets and the accompanying increase in rate of thrombin formation were either reduced in parallel or absent in each case with values ranging from 0 to 45% of control values. The apparent affinity of Factor X(a) from Factor V-deficient patients was normal when platelet binding was detected. The supernate from thrombin-treated control platelets, which contains Factor V activity, corrected the Factor X(a) binding deficiency of the platelets from three patients tested. Immunoreactive Factor V determined with an homologous antibody corresponded to the functional Factor V activity of platelets from one patient with Factor V deficiency, suggesting that the patient's platelets have a decreased amount of normal Factor V. The ability of platelets from the patients to bind Factor X(a) and increase the rate of thrombin formation correlated with the severity of each patient's bleeding disorder better than the plasma level of Factor V. The results indicate that Factor V is required for the Factor X(a)-platelet interaction and that thrombin formation at the platelet surface is important in normal hemostasis.