Relationship between markers of activated coagulation, their correlation with inflammation, and association with coronary heart disease (NPHSII).

OBJECTIVE: To determine whether activation of coagulation increases in parallel with inflammation and whether coagulation activation markers (CAMs) are independently associated with coronary heart disease (CHD), in the prospective study, NPHSII. METHODS: Surveillance of 2997 men between 50 and 63 years yielded 314 first CHD events during 36507 person-years of observation. The plasma levels of activated factor XII (FXIIa), the peptides released upon activation of factor X (FXpep) and factor IX (FIXpep), activated factor VII (FVIIa), prothrombin fragment 1 + 2 (F1 + 2) and fibrinopeptide A (FpA) served as indices of activity along the coagulation pathway. C reactive protein (CRP) provided a marker of inflammatory activity. RESULTS: While borderline or significant correlations were identified for each CAM with inflammation, as determined by CRP levels, these did not reach as high a numerical value as was shown for fibrinogen with CRP. FVIIa and FIXpep possessed independent associations with CHD: a one SD increase in adjusted FIXpep and FVIIa level was associated with a relative hazard of 1.20 (95% CI 1.00-1.43) and 0.70 (CI 0.58-0.86), respectively, using a group including all CHD events, compared with 'no-event'. CONCLUSIONS: Inflammation has significant but minimal impact upon CAMs of the extrinsic coagulation pathway. Reduced FVIIa and increased FIXpep levels were found to be significant, independent, predictors of CHD.

Epidemiological and genetic associations of activated factor XII concentration with factor VII activity, fibrinopeptide A concentration, and risk of coronary heart disease in men.

BACKGROUND: The relations of plasma activated factor XII (FXIIa) concentration and a common polymorphism (C46T) of the factor XII gene with hemostatic status and risk of coronary heart disease (CHD) were examined by prospective surveillance. METHODS AND RESULTS: Genotyping for the C46T variant was performed in 2624 men 50 to 61 years of age who were free of CHD at baseline. The genotype distribution was as follows: CC, 56.7%; CT; 36.9%; and TT, 6.6%. Plasma FXIIa was measured by ELISA on 1745 samples collected 1 year after baseline; median levels were (ng/mL) CC, 2.0; CT, 1.4; and TT, 0.8 (P:<0.0001). Respective values for plasma fibrinopeptide A (FPA, nmol/L) were 1.52, 1.35, and 1.15 (P:<0.0001); for factor VII coagulant activity (FVIIc, % standard), 114.5, 116.2, and 109.3 (P:=0.02). Group differences in FVIIc were unchanged by adjustment for body mass index and serum triglycerides. Whereas CHD incidence did not differ significantly by genotype, rates (per 1000 person-years) by thirds of FXIIa distribution were for <1.5 ng/mL, 7. 2; for 1.5 to 2.0 ng/mL, 7.2; and for >2.0 ng/mL, 13.6. Respective hazard ratios with the low third as reference group were 1.01 and 1. 96 (P:=0.007), which were essentially unchanged after allowance for genotype, blood lipids, blood pressure, body mass index, FVIIc, and FPA. CONCLUSIONS: The C46T polymorphism is a determinant of FXIIa, FPA, and possibly FVIIc, suggesting that FXII influences the activity state of the coagulation pathway and FPA cleavage from fibrinogen in vivo. Plasma FXIIa is increased in middle-aged men at high risk of CHD.

A monoclonal antibody raised against human beta-factor XIIa which also recognizes alpha-factor XIIa but not factor XII or complexes of factor XIIa with C1 esterase inhibitor.

A monoclonal antibody (mAb 2/215) against human beta-factor XIIa (beta-FXIIa), was shown by equilibrium binding studies to have a high affinity for alpha-factor XIIa (alpha-FXIIa) (Kd 1.8 nM) and beta-FXIIa (Kd 0.65 nM) but no detectable reaction with FXII zymogen or alpha-FXIIa:C1 esterase inhibitor (C1-INH) complex. Surface plasmon resonance studies showed that the mAb 2/215 bound to immobilized alpha-FXIIa with high affinity (KD 3.93 +/- 1.46 x 10(-11) M). Western blots employing mAb 2/215 indicated that human plasma contained small amounts of alpha-FXIIa but no beta-FXIIa. mAb 2/215 did not inhibit the amidolytic activity of beta-FXIIa and protected beta-FXIIa from inhibition by C1-INH. The recovery by ELISA,employing mAb 2/215 as the capture antibody, of alpha-FXIIa added to plasma was 11.3%, 42% after inhibition of alpha-FXIIa with 3:4dichloroisocoumarin, and 82% when 0.5% Triton-X100 was added to the assay. Gel filtration showed that the majority of plasma alpha-FXIIa existed as a complex (Mr approximately 170,000). This distinctive mAb increases the capacity to study the contact system in health and disease.

Very low activated factor VII and reduced factor VII antigen in familial abetalipoproteinaemia.

Abetalipoproteinaemia is a rare disorder of apolipoprotein B metabolism associated with extremely low plasma concentrations of triglyceride. To discover whether the general positive association between factor VII and triglyceride levels extends to this condition, 5 patients were compared with 18 controls. All patients had a triglyceride below 100 micromol/l. Plasma unesterified fatty acid concentration was normal. Although factor IX activity was only slightly reduced (mean 88% standard) and factor IX antigen was normal, mean activated factor VII in patients was strikingly reduced to 34% of that in controls, a level similar to that found in haemophilia B. The patients' mean factor VII activity and factor VII antigen were also significantly reduced to 54% and 63% of those in controls, respectively. Mean factor XI activity and tissue factor pathway inhibitor activity were reduced in patients to 70% and 75% of control values respectively, while factor XII, factor XI antigen, factor X, prothrombin and protein C were normal.

Risk of coronary heart disease and activation of factor XII in middle-aged men.

Increased activity is known to be present in the extrinsic, intrinsic, and final common pathways of the hemostatic system in men at high risk of coronary heart disease (CHD), but the status of the contact system of coagulation in this condition is uncertain. Plasma levels of activated factor XII (XIIa), the initial product of contact activation, have therefore been measured by ELISA in 2464 men aged 51 to 62 years, clinically free of CHD, who were taking part in a prospective cardiovascular survey based in general medical practices. Statistically significant, independent, and positive associations of XIIa were found with serum cholesterol and triglyceride concentrations, blood pressure, body mass index, factor VII activity, plasma fibrinogen concentration, and tobacco smoking, all associated with CHD. Plasma XIIa also increased with recent alcohol intake. Men in the highest quintile of risk according to their conventional risk factors had a mean XIIa of 2.07 ng/mL (95% confidence interval 1.99-2.16), 31% higher than that of men in the lowest quintile (1.58; 95% confidence interval 1.51-1.65). Thus, the contact system of coagulation appears to be activated when CHD risk is increased. Furthermore, the independent associations of XIIa with the major conventional CHD risk factors and its broad range of values in the general population (0.1 to 12.5 ng/mL), combined with a relatively low day-to-day variability in individuals (the within-person component of its total variation being 14.7%), suggest its potential usefulness as a marker of atherosclerotic vascular damage.

Elucidation of the core residues of an epitope using membrane-based combinatorial peptide libraries.

Combinatorial peptide libraries have proved to be a valuable tool for the study of the interaction of a functional protein with its ligand. Here, the epitope for a monoclonal antibody 201/9, raised against beta-factor XIIa, has been identified with a two-step approach using peptide libraries attached to a polymer (polyvinylidene difluoride) membrane. First, the octapeptide libraries with two amino acids defined at position 2 and 4, represented by the formula X-O2-X-O4-X-X-X-X, were synthesized on a sheet of polymer membrane in which X represents a mixture of all the natural -amino acids except cysteine, while O2 and O4 each represent a single amino acid. The libraries were probed with the antibody 201/9, and the bound antibody was detected with a sensitive chemiluminescent method. In the first cycle, the peptide mixtures X-Phe-X-Gln-X-X-X-X showed the strongest signal development. In the second cycle Phe and Gln were incorporated into new libraries consisting of sequences O1-Phe-X-Gln-X-X-X-X, X-Phe-O3-Gln-X-X-X-X, X-Phe-X-Gln-O5-X-X-X, X-Phe-X-Gln-X-O6-X-X, X-Phe-X-Gln-X-X-O7-X, and X-Phe-X-Gln-X-X-X-O8. After probing these new peptides, the residues representing the core sequence of the epitope for monoclonal antibody 201/9 were elucidated. The sequence Ser-Phe-Leu-Gln-Glu-Asn, identified as the immunodominant epitope, correlates well with the sequence Ser-Phe-Leu-Gln-Glu-Ala previously identified (Gao, B., and Esnouf, M. P. (1996) J. Immunol. 157, 183-188) in a scan of overlapping peptides based on the sequence of human beta-factor XIIa.

Multiple interactive residues of recognition: elucidation of discontinuous epitopes with linear peptides.

The discontinuous epitopes of beta-factor XIIa for three mAbs were mapped by a linear peptide-based immunoblotting technique, referred to as multiple interactive residues of recognition. The Abs were incubated with a set of overlapping synthetic peptides, deduced from the cDNA sequences of beta-factor XIIa, on a polymer membrane, and the signal was amplified by an ECL assay. Several discrete sequences of the protein were recognized by each Ab. The recognized peptides were further characterized using alanine substitution analogues and peptides of different lengths. The discontinuous epitopes found for each Ab were formed by several peptides and were composed of 20 to 31 residues. The sequence FLQEA was recognized by all three Abs and was the immunodominant peptide. Abs 201/9 and 2/15 bound to very similar discontinuous sequences, but with subtle differences. The sequences 76RLHEAFSP83, 88HDLALLRLQE97, 178GFLEG182, 146FLQEA150, and 237IRE239 formed the epitope for mAb 201/9, whereas 76RLHEAFSP83, 90LALLRLQE97, 146FLQEA150, and 235AWIREHT241 formed the epitope for Ab 2/15. The third Ab 202/7 recognized the sequences 79EAFSP83, 93LRLQE97, 133WGHQF137, and 146FLQEA150. We suggest that these sequences represent the sites to which the Abs bind. This procedure provides a sensitive and convenient tool to elucidate discontinuous epitopes for the binding of Abs, receptor ligand-binding sites, or enzyme inhibitor binding sites.

Activation of factor VII during alimentary lipemia occurs in healthy adults and patients with congenital factor XII or factor XI deficiency, but not in patients with factor IX deficiency.

Factor VII activity (FVIIc), a risk marker for coronary heart disease, is increased during postprandial lipemia. Factor VII activation accompanies lipolysis of triglyceride-rich lipoproteins, but the nature of this association and whether it is causal remain uncertain. To explore this issue, four patients with homozygous factor XII deficiency, four with complete factor XI deficiency, six with factor IX deficiency, and their respective age- and sex-matched controls were given two isocaloric dietary regimens, one providing on average 136 g fat and the other 19 g fat. Blood was taken before breakfast, immediately before lunch at 195 minutes, and at completion of the study at 390 minutes. All samples for each subject and matched control were assayed as one batch for FVIIc, activated factor VII, and factor VII antigen (FVIIag). Activation of factor VII was observed with the high-fat regimen but not with the low-fat regimen in all controls, factor XII-deficient patients, and factor XI-deficient patients. No factor VII activation was observed during either regimen in factor IX-deficient patients, but a normal postprandial responsiveness of factor VII to dietary fat was restored in one patient who replicated the study after factor IX therapy. Plasma FVIIag was not altered postprandially in either regimen in any group of patients or controls. Factor IX apparently plays an obligatory role in the postprandial activation of factor VII, although the mechanism remains to be determined.

An enzyme-linked immunosorbent assay (ELISA) for the measurement of activated factor XII (Hageman factor) in human plasma.

A direct enzyme-linked immunosorbent assay (ELISA) employing 2/215 mouse monoclonal hybridoma antibody is described. The assay is capable of detecting activated factor XII in human plasma and can be used to assess early detection of the intrinsic blood coagulation pathway. No cross reactivity with human factor XII zymogen has been found. The assay was used to assess activation of factor XII in patients with renal failure, pregnancy and diabetes compared to a control group.

Factor VII-deficient substrate plasmas depleted of protein C raise the sensitivity of the factor VII bio-assay to activated factor VII: an international study.

Plasma from healthy individuals, pregnant women and patients on warfarin were distributed to 3 laboratories supporting major cardiovascular surveys (Northwick Park, Muenster and Houston) for assay of factor VII coagulant activity (VIIc) with their own bio-assays. The mean VIIc in 147 samples agreed to within 1% of standard in Northwick Park and Houston, but was 14% of standard lower in Muenster owing to its more potent standard. In samples with an increased VIIc the Northwick Park assay gave a higher result than the other assays owing to its increased responsiveness to activated factor VII (VIIa). Thus when VIIa concentrations were determined directly with a clotting assay which utilises a soluble recombinant tissue factor, the increase in VIIc with increase in VIIa was considerably greater with the Northwick Park assay than the Muenster assay. This feature of the Northwick Park assay was traced to the virtual absence of protein C in its substrate plasma. Factor Va appears rate-limiting for the coagulant expression of VIIa in test plasma. If the thrombotic response to release of tissue factor is determined by the circulating concentration of VIIa, then the Northwick Park factor VII bio-assay may be preferable to other bio-assays currently employed to estimate risk of acute coronary events.

Mechanisms of thrombin generation during surgery and cardiopulmonary bypass.

Although in vitro studies have been invaluable in revealing the complex biochemistry of the blood coagulation system, the mechanisms involved during the in vivo response to hypercoagulable stimuli are still unclear. We have used plasma-based enzyme-linked immunosorbent assays (ELISAs) to study the mechanisms by which the coagulation system is activated in vivo during human cardiopulmonary bypass (CPB) surgery (n = 8). A novel immunoassay for factor XIIa was used to detect activation of the contact system, factor IX activation peptide (FIXAP) was used as a marker for activation of factor IX, and prothrombin fragment F1 + 2 (F1 + 2) was used as a marker for thrombin generation. The ELISA for FIXAP is described for the first time herein. F1 + 2 levels increased early in response to surgical intervention: from a baseline of 38.7 +/- 9.7 ng/mL (mean +/-SE), levels increased rapidly during surgery and bypass to a maximum of 448.5 +/- 92.0 ng/mL. A modest yet significant increase in factor XIIa levels from 3.47 +/- 0.54 ng/mL to 4.33 +/- 0.85 ng/mL was evident during surgery before bypass, but no further significant increase was detected on establishing extracorporeal circulation. FIXAP levels demonstrated a small and late increase during surgery from 4.98 +/- 0.55 ng/mL to a maximum of 10.20 +/- 1.23 ng/mL, the increase beginning at the time of near maximal F1 + 2 levels. There was no association between activation of the contact system (factor XIIa levels) and the generation of thrombin (F1 + 2 levels). However, a strong association (r = .705) was apparent between the generation of thrombin (F1 + 2 levels) and activation of factor IX (FIXAP levels), despite the delay between the activation of prothrombin and factor IX. The data do not support the established view that contact activation resulting from exposure of blood to foreign surfaces is the major procoagulant stimulus in CPB. Instead, the results suggest that the main trigger to coagulation during CPB surgery was provided via the tissue factor-factor VIIa mechanism in response to the cutting of blood vessels, which directly activated factor X and then prothrombin. The late activation of factor IX, which presumably also contributed to maximal prothrombin activation, could have arisen due to direct tissue factor-factor VIIa action, or by secondary feedback action of thrombin on the intrinsic system.

The autoactivation of factor XII in the presence of long-chain saturated fatty acids--a comparison with the potency of sulphatides and dextran sulphate.

The incubation of purified human factor XII (Hageman factor [HF]) in the presence of long-chain saturated fatty acids (FA) like stearate (C-18) or behenate (C-22) resulted in a time-dependent increase of amidolytic activity. The HF autoactivation progress curves were sigmoidal. The first order rate for the initial period was constant; this was followed by a period of decreasing rate and a plateau of zero rate. These progress curves were similar to those obtained on the incubation of HF in the presence of sulphatide vesicles or dextran sulphate. The initial rate of autoactivation of HF was dependent on the FA concentration of contact surface and increased with increasing concentration of HF. At constant concentration of contact surface and varying concentration of HF, autoactivation rates in the presence of behenate, sulphatide vesicles or dextran sulphate followed Michaelis-Menten kinetics. The Km values for all three contact surfaces were above the physiological plasma concentration of HF whereas the catalytic efficiency in the presence of behenate (0.034 microM-1s-1) was about 2/3 of that in the presence of sulphatide vesicles (0.053 microM-1s-1) and considerably higher than that in the presence of dextran sulphate (0.004 microM-1s-1). Long-chain saturated FA bound to human serum albumin at the high- or low-affinity sites are ineffective, whereas the crystalline non-bound stearate or behenate provided a potent contact surface.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative study of reaction kinetics in membrane and agarose bead affinity systems.

Compared to conventional agarose bead affinity supports, a microporous nylon membrane exhibits greatly improved reaction kinetics as quantified in the reaction between gamma-globulin and immobilised protein A. The improvement is only observed when the solution of gamma-globulin is forced through the membrane pores. In the absence of flow in the pores, it is possible to relate approximately the rate of uptake onto either type of affinity support to independently determined diffusion coefficients. In the presence of flow, the reaction rate is similar for membranes having 0.45 and 3.0 microns diameter pores, and considerably smaller than predicted by the Smoluchowski formula.

The increased rate of activation of factor XII in late pregnancy can contribute to the increased reactivity of factor VII.

The amidolytic activity of enzymes derived from factor XII (XIIa) was 3-fold higher in plasmas collected during pregnancy than from control subjects. Factor VII coagulant activity (VIIc) and XIIa increased in both kinds of plasmas on incubation on ice for 24 h (cold activation). These increases could be attributed to the decreased potency of C1 inhibitor (C1INH). However, variations in the concentration of C1INH and of factor XII could not explain the differences in VIIc and in XIIa between late pregnancy and control plasmas following cold activation under the same conditions. It is concluded that in vitro the increased amount of contact surface in the late pregnancy plasma promotes a higher rate of generation of XIIa and consequently a higher rate of activation of factor VII. The increased amount of contact surface could also be responsible for the increased concentration of XIIa in non-treated plasma from late pregnancy and could contribute in vivo to the higher reactivity of factor VII in this condition.

The prothrombin activation peptide regulates synthesis of the vitamin K-dependent proteins in the rabbit.

The turnover of 125I-bovine prothrombin fragment 1 was studied in the rabbit. The t1/2 of the peptide in the intravascular compartment was 11.5 hours and this compartment accounted for between 7.9 and 14.4% of the injected radioactivity. The rest of the radioactivity was distributed between two compartments in the extravascular space. The injection of the peptide (10 mg/rabbit) was associated with a transient increase in the plasma concentration of prothrombin and of factor X, with maximum concentration of prothrombin between 40 and 66 hours from the injection and between 26 and 40 hours for factor X. It is concluded that the injection of fragment 1 in the rabbit induced a transient increase in the synthesis of the vitamin K-dependent proteins that is compensated for by an increased absolute catabolic rate. It is suggested that the prothrombin activation peptide serves as regulatory message which induces the subsequent restoration of the appropriate concentration of the vitamin K-dependent proteins.

A novel method for the purification of HIV-1 p24 protein from hybrid Ty virus-like particles (Ty-VLPs).

The self-assembly properties of a protein encoded by the yeast retrotransposon Ty can be exploited to produce large amounts of recombinant, particulate fusion proteins as hybrid Ty virus-like particles (Ty-VLPs). This system has now been adapted to allow the release of the additional protein by incorporation of a protease cleavage site between the yeast carrier protein and the protein of interest. The purification of the additional protein is facilitated by exploiting the ease with which Ty-VLPs can be purified from other yeast cell components due to their particulate nature. We have used this modified system to produce hybrid particles containing the HIV-1 p24 protein downstream of the recognition sequence for the blood coagulation factor Xa. The p24 was released from the particles by proteolytic cleavage and rapidly separated from the residual particulate material using centrifugation and standard chromatography techniques. This procedure has been used to purify milligram quantities of HIV-1 p24 protein that reacts with anti-p24 sera and elicits the production of p24-specific antibodies in experimental animals.

HIV-1 TAT "activates" presynthesized RNA in the nucleus.

Replication of the human immunodeficiency virus (HIV-1) depends upon the viral TAT protein. TAT stimulates gene expression via a target response sequence (TAR) located within the HIV-1 LTR. As TAR is located in the transcribed region it could act as a signal in either the DNA, the RNA, or both. To test whether TAT acts on transcription and/or posttranscriptionally, we produced TAT in yeast and monitored its activity after microinjection into the nucleus or cytoplasm of Xenopus oocytes. The TAT protein stimulated TAR-dependent expression, but this activation was not inhibited by transcriptional inhibitors. Furthermore, TAR-containing RNA, produced in vitro, was "activated" by TAT after coinjection into oocytes. This activation only occurred, however, when the RNA was injected into the nucleus and not into the cytoplasm. Our data indicate, therefore, that in the Xenopus system TAT acts on presynthesized RNA and that the nucleus is involved in this action.

The activation of the contact phase of coagulation by physiologic surfaces in plasma: the effect of large negatively charged liposomal vesicles.

The endogenous, negatively charged surface that induces activation of the contact coagulation factors was investigated in plasmas taken from women in late pregnancy and control subjects of child-bearing age. The plasmas from the two groups of subjects were incubated at 4 degrees C for 24 hours either in plastic or in glass tubes and the factor VII coagulant activity (VIIc) was assayed in the treated plasmas. The activation of factor VII under these conditions involves the generation of enzymes derived from factor XII (XIIa). The contact surface is rate-limiting for the activation of factor VII in the plasmas in both groups of subjects and can be supplemented by large multilamellar liposomal vesicles carrying the appropriate density of negative charge. The size of these vesicles is within the range of sizes of the large lipoprotein particles (chylomicrons, very low and intermediate-density lipoproteins). The relationship between the density of negative charge on the liposomal vesicles and VIIc was similar in the late pregnancy and the control plasmas incubated in plastic tubes. At a saturating density of negative charge the observed relative VIIc was similar in both sets of plasmas. The incubation of late pregnancy or control plasma in plastic tubes in the presence of sodium stearate caused VIIc to increase with increasing concentration of the added fatty acid. These results suggest that large lipoprotein particles carrying the appropriate free fatty acid at a sufficient density of negative charge could provide the contact surface that induces the generation of factor XIIa and the subsequent activation of factor VII. Moreover, plasmas from women in late pregnancy have a higher concentration of potential surface and a higher density of negative charge than the plasmas from nonpregnant women.

The role of beta-hydroxyaspartate and adjacent carboxylate residues in the first EGF domain of human factor IX.

beta-Hydroxyaspartic acid is a post-translationally modified amino acid found in a number of plasma proteins in a domain homologous to epidermal growth factor. Its presence can be correlated with a high affinity Ca2+ binding site, with a dissociation constant of 10-100 microM. We describe a system for the expression of human coagulation factor IX in dog kidney cells in tissue culture, in which the post-translational modifications and the biochemical activity are indistinguishable from factor IX synthesized in vivo. This system has been used to express eight different point mutations of human factor IX in the first epidermal growth factor domain in order to study the role of beta-hydroxyaspartate at residue 64, and the adjacent carboxylate residues at positions 47, 49 and 78. We conclude that this domain is essential for factor IX function and suggest that Ca2+ binds to carboxylate ions in this domain and stabilizes a conformation necessary for the interaction of factor IXa with factor X, factor VIII and phospholipid in the next step of the clotting cascade.

Vitamin K-dependent blood coagulation proteins form hetero-dimers.

The later stages of the blood coagulation cascade are characterized by the presence of vitamin K-dependent proteins and their involvement in membrane-bound, multi-protein converting complexes with an essential requirement for calcium ions. Specific interactions between zymogens and activating enzymes have not yet been identified. Here we describe a crystallographic study of prothrombin fragment 1 (residues 1-156 of prothrombin) which indicates that vitamin K-dependent coagulation proteins have specific association sites that allow them to form hetero-dimers. The calcium-induced formation of a hetero-dimer between fragment 1 and factor X is demonstrated by cross-linking. Such hetero-dimers of vitamin K-dependent proteins could be significant in the coagulation system.