FXII

Polyphosphate colocalizes with factor XII on platelet-bound fibrin and augments its plasminogen activator activity

Activated factor XII (FXIIa) has plasminogen activator capacity but its relative contribution to fibrinolysis is considered marginal compared with urokinase and tissue plasminogen activator. Polyphosphate (polyP) is released from activated platelets and mediates FXII activation. Here, we investigate the contribution of polyP to the plasminogen activator function of αFXIIa. We show that both polyP₇₀, of the chain length found in platelets (60-100 mer), and platelet-derived polyP significantly augment the plasminogen activation capacity of αFXIIa. PolyP₇₀ stimulated the autoactivation of FXII and subsequent plasminogen activation, indicating that once activated, αFXIIa remains bound to polyP₇₀ Indeed, complex formation between polyP₇₀ and αFXIIa provides protection against autodegradation. Plasminogen activation by βFXIIa was minimal and not enhanced by polyP₇₀, highlighting the importance of the anion binding site. PolyP₇₀ did not modulate plasmin activity but stimulated activation of Glu and Lys forms of plasminogen by αFXIIa. Accordingly, polyP₇₀ was found to bind to FXII, αFXIIa, and plasminogen, but not βFXIIa. Fibrin and polyP₇₀ acted synergistically to enhance αFXIIa-mediated plasminogen activation. The plasminogen activator activity of the αFXIIa-polyP₇₀ complex was modulated by C1 inhibitor and histidine-rich glycoprotein, but not plasminogen activator inhibitors 1 and 2. Platelet polyP and FXII were found to colocalize on the activated platelet membrane in a fibrin-dependent manner and decorated fibrin strands extending from platelet aggregates. We show that in the presence of platelet polyP and the downstream substrate fibrin, αFXIIa is a highly efficient and favorable plasminogen activator. Our data are the first to document a profibrinolytic function of platelet polyP.

Activated plasma coagulation β-Factor XII-induced vasoconstriction in rats

By inducing BK (bradykinin)-stimulated adrenomedullary catecholamine release, bolus injection of the β-fragment of activated plasma coagulation Factor XII (β-FXIIa) transiently elevates BP (blood pressure) and HR (heart rate) of anaesthetized, vagotomized, ganglion-blocked, captopril-treated bioassay rats. We hypothesized that intravenous infusion of β-FXIIa into intact untreated rats would elicit a qualitatively similar vasoconstrictor response. BN (Brown Norway) rats received for 60 min either: (i) saline (control; n=10); (ii) β-FXIIa (85 ng/min per kg of body weight; n=9); or (iii) β-FXIIa after 2ADX (bilateral adrenalectomy; n=9). LV (left ventricular) volume and aortic BP were recorded before (30 min baseline), during (60 min) and after (30 min recovery) the infusion. TPR (total peripheral resistance) was derived from MAP (mean arterial pressure), SV (stroke volume) and HR. Saline had no haemodynamic effects. β-FXIIa infusion increased its plasma concentration 3-fold in both groups. In adrenally intact rats, β-FXIIa infusion increased MAP by 6% (5±2 mmHg) and TPR by 45% (0.50±0.12 mmHg/ml per min), despite falls in SV (−38±8 μl) and HR [−18±5 b.p.m. (beats/min)] (all P<0.05). In 2ADX rats, β-FXIIa had no HR effect, but decreased SV (−89±9 μl) and MAP (−4±1 mmHg), and increased TPR by 66% (0.59±0.15 mmHg/ml per min) (all P<0.05). After infusion, adrenally intact rats exhibited persistent vasoconstriction (MAP, 10±1 mmHg; TPR, 0.55±0.07 mmHg/ml per min; both P<0.05), whereas in 2ADX rats, MAP remained 5±1 mmHg below baseline (P<0.05) and TPR returned to baseline. End-study arterial adrenaline (epinephrine) concentrations in the three groups were 1.9±0.6, 9.8±4.1 and 0.6±0.2 nmol/l respectively. Thus, in neurally intact lightly anaesthetized untreated rats, β-FXIIa infusion induces both adrenal catecholamine-mediated and adrenally independent increases in peripheral resistance.

Sum Frequency Generation Studies on Bioadhesion: Elucidating the Molecular Structure of Proteins at Interfaces

The study of bioadhesion is significant to applications in a variety of scientific fields. Techniques that are surface sensitive need to be utilized to examine these kinds of systems because bioadhesion occurs at the interface between two surfaces. Recently, Sum Frequency Generation (SFG) has been applied to investigate different bioadhesive processes because of its intrinsic surface specificity, excellent sensitivity and its ability to perform experiments in situ. SFG studies on the bioadhesion of fibrinogen, factor XII and mefp-3 on various surfaces will be discussed in this review.

Angiotensin converting enzyme-regulated, noncholinergic sympathoadrenal catecholamine release mediates the cardiovascular actions of human 'new pressor protein' related to coagulation beta-factor XIIa

BACKGROUND

Human 'new pressor protein' (NPP), related to coagulation beta-factor XIIa (beta-FXIIa), potently releases sympathoadrenal catecholamines in bioassay rats, with concurrent elevation of systolic and diastolic blood pressure (SBP/DBP) and heart rate (HR). Elevated plasma NPP/beta-FXIIa levels in hypertensive anephric pediatric patients on hemodialysis associated with fluid status and blood pressure changes were previously reported, suggesting that NPP/beta-FXIIa contributed to their hypertension.

OBJECTIVE

To investigate the mechanism of action of NPP/beta-FXIIa.

METHODS

Hemodynamic and sympathoadrenal responses to NPP (20 microL plasma equivalent/rat) or coagulation beta-FXIIa (300 ng/kg intravenously) were measured in rats treated with pentolinium (ganglion blockade [+GB]) and/or captopril (+CAP; angiotensin converting enzyme [ACE] inhibition).

RESULTS

In controls not receiving GB or CAP (-GB-CAP), NPP/beta-FXIIa raised plasma epinephrine (E) sixfold, SBP/DBP by 14/8 mmHg and HR by 15 beats/min. With blockade of the cholinergic pathway to the sympathoadrenal system (+GB), basal E, norepinephrine (NE), SBP, DBP and HR all dropped. However NPP/beta-FXIIa remained capable of raising E 20-fold, NE fourfold, SBP/DBP by 27/11 mmHg and HR by 20 beats/min, suggesting that it acted through a 'noncholinergic' mechanism. With +CAP alone, NPP/beta-FXIIa raised plasma E 18-fold, NE threefold, SBP/ DBP by 29/8 mmHg and HR by 73 beats/min, implicating an ACE-regulated 'peptidergic' mechanism. Combining +GB with +CAP potentiated NPP/beta-FXIIa actions further by raising E 50-fold, NE sevenfold, SBP/DBP by 55/20 mmHg and HR by 87 beats/min, strengthening the efficacy of this alternate pathway.

CONCLUSIONS

The cardiovascular effects of NPP/beta-FXIIa are considerably mediated by a noncholinergic (peptidergic) ACE-regulated mechanism for sympathoadrenal catecholamine release that is enhanced by +GB and/or +CAP. Under inflammatory procoagulant conditions, endogenously produced NPP/beta-FXIIa may interfere with the antihypertensive effects of ACE inhibition therapy.

Contact activation of blood-plasma coagulation

This opinion identifies inconsistencies in the generally-accepted surface biophysics involved in contact activation of blood-plasma coagulation, reviews recent experimental work aimed at resolving inconsistencies, and concludes that this standard paradigm requires substantial revision to accommodate new experimental observations. Foremost among these new findings is that surface-catalyzed conversion of the blood zymogen factor XII (FXII, Hageman factor) to the enzyme FXIIa (FXII [surface] --> FXIIa, a.k.a. autoactivation) is not specific for anionic surfaces, as proposed by the standard paradigm. Furthermore, it is found that surface activation is moderated by the protein composition of the fluid phase in which FXII autoactivation occurs by what appears to be a protein-adsorption-competition effect. Both of these findings argue against the standard view that contact activation of plasma coagulation is potentiated by the assembly of activation-complex proteins (FXII, FXI, prekallikrein, and high-molecular weight kininogen) directly onto activating surfaces (procoagulants) through specific protein/surface interactions. These new findings supplement the observation that adsorption behavior of FXII and FXIIa is not remarkably different from a wide variety of other blood proteins surveyed. Similarity in adsorption properties further undermines the idea that FXII and/or FXIIa are distinguished from other blood proteins by unusual adsorption properties resulting in chemically-specific interactions with activating anionic surfaces. IMPACT STATEMENT: This review shows that the consensus biochemical mechanism of contact activation of blood-plasma coagulation that has long served as a rationale for poor hemocompatibility is an inadequate basis for surface engineering of advanced cardiovascular biomaterials.

Aptamers influence the hemostatic system by activating the intrinsic coagulation pathway in an in vitro Chandler-Loop model

One class of oligonucleotides with a high potential for use in medical applications is short nucleic acids, widely known as aptamers. Although several aptamers are already being used clinically, there are very few studies dealing with the impact aptamers have on the hemostatic system. In this study, we have performed a comprehensive evaluation of the hemostatic system including coagulation, platelets, complement, and inflammatory activation by using different aptamer concentrations and fresh human whole blood in a well-established flow model. We found that single-stranded aptamers did not have a negative influence on platelets, complement, or inflammation but were able to activate factor XII, kallikrein, and prothrombin in a concentration-dependent manner. Consequently, the influence of aptamers on the coagulation system should be taken into consideration before the use of any aptamer-based drugs in patients.

Competitive-protein adsorption in contact activation of blood factor XII

Contact activation of blood factor XII (FXII, Hageman factor) is moderated by the protein composition of the fluid phase in which FXII is dissolved. Solution yield of FXIIa arising from FXII contact with hydrophilic activating particles (fully water-wettable glass) suspended in a protein cocktail is shown to be significantly greater than that obtained under corresponding activation conditions in buffer solutions containing only FXII. By contrast, solution yield of FXIIa arising from FXII contact with hydrophobic particles (silanized glass) suspended in protein cocktail is sharply lower than that obtained in buffer. This confirms that contact activation is not specific to anionic hydrophilic surfaces as proposed by the accepted biochemistry of surface activation. Rather, contact activation in the presence of proteins unrelated to the plasma coagulation cascade leads to an apparent specificity for hydrophilic surfaces that is actually due to a relative diminution of activation at hydrophobic surfaces and an enhancement at hydrophilic surfaces. Furthermore, the rate of FXIIa accumulation in whole-plasma and buffer solution is found to decrease with time in the continuous presence of activating surfaces, leading to a steady-state FXIIa yield dependent on the initial FXII solution concentration for both hydrophilic and hydrophobic procoagulant particles suspended in either plasma, protein cocktail, or buffer. These results strongly suggest that activation competes with an autoinhibition reaction in which FXIIa itself inhibits FXII-->FXIIa. Experimental results are modeled using a reaction scheme invoking FXII activation and autoinhibition linked to protein adsorption to procoagulant surfaces, where FXII activation is presumed to proceed by either autoactivation (FXII-->surface-->FXIIa) and autohydrolysis (FXII-->FXIIa-->2FXIIa) in buffer solution or autoactivation and reciprocal activation (kallikrein-mediated hydrolysis) in plasma. FXII adsorption competition with other proteins in the fluid phase is proposed to affect the balance of activation and autoinhibition, leading to the observed moderation of FXIIa yield.

Changes of plasma activated Factor XII type A (XIIaA) concentrations following percutaneous coronary intervention (PCI)

BACKGROUND

Recent research has demonstrated that in-vivo XIIa exists in a number of different types and that treatment with tenecteplase increases the plasma concentration of XIIaA. Only limited data exist on changes in activated Factor XII (XIIa) levels following mechanical revascularisation, such as percutaneous coronary intervention (PCI).

METHODS

Citrated blood samples were obtained from 31 PCI-treated patients admitted with ST-elevation myocardial infarction (STEMI) and 20 patients undergoing elective PCI. Samples were taken immediately before the invasive procedure, 30-90 min after PCI and (in patients undergoing primary PCI) 4-6 days following intervention. Additional samples were taken after angiography, just prior to the follow-on PCI procedure, in 16 of the patients undergoing elective PCI, to investigate possible effects of contrast fluid and heparin. XIIa measurements were performed using 2 ELISA assays designed to preferentially measure different types of XIIa; XIIaA and XIIaR.

RESULTS

In the group undergoing primary PCI, XIIaA showed a significant increase from 68 (48-93) pM in the pre-treatment sample to 100 (75-123) pM [median and 25- and 75% percentiles] in the 30-90-min post-treatment sample (p < 0.001), returning to pre-intervention levels by day 4-6. A similar increase in XIIaA was obtained in patients undergoing elective PCI. In contrast, no significant changes in XIIaR concentration were observed. Whilst XIIaA concentrations remained unchanged in 6 non-heparinised patients undergoing elective coronary angiography, XIIaA levels rose significantly from 56 (51-75) pM to 98 (71-125) pM [median and 25- and 75% percentiles], (p < 0.01) in 10 patients after the addition of heparin.

CONCLUSION

A significant short-lasting increase in specific types of XIIa (namely XIIaA) was observed following PCI. These increases are most likely induced by the concomitant treatment with heparin.

Specific types of activated Factor XII increase following thrombolytic therapy with tenecteplase

BACKGROUND

Activated Factor XII (XIIa) is believed to participate in a number of pathophysiological processes including inflammation, thrombosis and fibrinolysis. Increasing XIIa levels following thrombolytic therapy have previously been reported. In contrast to other thrombolytics, tenecteplase (TNK-tpa) does not show paradoxical thrombin activation, indicating a lower procoagulant effect of this fibrin-selective thrombolytic agent. Recent research has demonstrated that in-vivo XIIa exists in a number of different types, and the aim of this study was to investigate plasma variations of different types of XIIa following thrombolytic treatment with TNK-tpa.

METHODS

Citrated blood samples were obtained from 34 patients admitted with acute ST-elevation myocardial infarction (STEMI) treated with TNK-tpa. Samples were taken immediately prior to treatment, 30-90 min after and 4 days post-treatment. XIIa measurements were performed using 2 ELISA assays designed to preferentially measure different types of XIIa; XIIaA and XIIaR. Both assays utilised a monoclonal antibody 2/215, which is highly specific for XIIa, as the solid phase capture antibody. The assay for XIIaA used a conjugate based on a polyclonal antibody against the entire XIIa molecule, whilst the assay for XIIaR incorporated a reagent to release otherwise unavailable XIIa and used a conjugate based on a monoclonal antibody against beta-XIIa.

RESULTS

Changes in plasma XIIaA concentration as a result of therapy were more evident than changes in XIIaR concentration. XIIaA showed a significant increase from 67.1 (49.0-84.4) pM to 97.8 (75.5-133.1) pM [median and 25 and 75% percentiles] in the 30-90 min sample (P < 0.001), returning to pre-intervention levels 61.5 (47.5-81.0) pM by day 4. In contrast, no significant change in XIIaR concentration was observed following thrombolytic therapy with TNK-tpa.

CONCLUSION

In patients admitted with STEMI, thrombolytic therapy with TNK-tpa resulted in a significant short-lasting increase in specific types of XIIa (namely XIIaA), whereas other types of XIIa (XIIaR) were largely unaffected by this intervention.

Ordered adsorption of coagulation factor XII on negatively charged polymer surfaces probed by sum frequency generation vibrational spectroscopy

Electrostatic interactions between negatively charged polymer surfaces and factor XII (FXII), a blood coagulation factor, were investigated by sum frequency generation (SFG) vibrational spectroscopy, supplemented by several analytical techniques including attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance (QCM), zeta-potential measurement, and chromogenic assay. A series of sulfonated polystyrenes (sPS) with different sulfonation levels were synthesized as model surfaces with different surface charge densities. SFG spectra collected from FXII adsorbed onto PS and sPS surfaces with different surface charge densities showed remarkable differences in spectral features and especially in spectral intensity. Chromogenic assay experiments showed that highly charged sPS surfaces induced FXII autoactivation. ATR-FTIR and QCM results indicated that adsorption amounts on the PS and sPS surfaces were similar even though the surface charge densities were different. No significant conformational change was observed from FXII adsorbed onto surfaces studied. Using theoretical calculations, the possible contribution from the third-order nonlinear optical effect induced by the surface electric field was evaluated, and it was found to be unable to yield the SFG signal enhancement observed. Therefore it was concluded that the adsorbed FXII orientation and ordering were the main reasons for the remarkable SFG amide I signal increase on sPS surfaces. These investigations indicate that negatively charged surfaces facilitate or induce FXII autoactivation on the molecular level by imposing specific orientation and ordering on the adsorbed protein molecules.

Immunodepletion of albumin for two-dimensional gel detection of new mouse acute-phase protein and other plasma proteins

Immunodepletion of albumin to improve the 2-D gel resolution of human plasma proteins has recently been described. With the importance of mouse models in many studies in which serum or plasma is often analyzed, we have adopted this approach to immunoprecipitate mouse albumin and evaluated its effectiveness for 2-D separation of mouse plasma proteins. Purified polyclonal antibodies against mouse albumin were effective depleting intact albumin as well as its numerous fragments from mouse plasma samples. Removal of albumin resulted in better resolution of mouse plasma proteins. Three proteins, alpha2-macroglobulin, coagulation factor XII, and hemopexin, that were previously either undetectable or poorly resolved, were identified from albumin-depleted 2-D gels by peptide mass fingerprinting. Albumin depletion also led to partial loss of several other proteins such as clusterin and gelsolin. This loss can be attributed to the interaction with albumin itself because the specificity of the antibody was demonstrated by Western blot. When applying this method to the 2-D separation of plasma from inflamed mouse induced by cutaneous burn injury with superimposed Pseudomonas aeruginosa infection, the upregulation of inter alpha-trypsin inhibitor heavy chain 4 (ITIH4) and hemopexin was unambiguously detected along with other mouse acute-phase proteins (APP), including haptoglobin and serum amyloid A. Based on the significant increase of ITIH4, we propose that this protein is a new member of mouse APP that are upregulated during the inflammatory response.

Plasma levels of factor XII, prekallikrein and high molecular weight kininogen in normal blood donors and patients having suffered venous thrombosis

INTRODUCTION

The contact system proteins factor XII (FXII), prekallikrein (PK) and high molecular weight kininogen (HK) have roles in coagulation, fibrinolysis, thrombin-induced platelet activation, cell adhesion and angeogenisis. It has been suggested that inherited or acquired deficiencies of these proteins may be risk factors for thrombosis. Studies on the levels of FXII in plasma from normal and thrombotic patient populations have been reported, to our knowledge however, no systematic study on plasma levels of PK and HK in large populations of normal blood donors and patients having had venous thrombotic events has been performed.

MATERIALS AND METHODS

Chromogenic substrate assays were used to measure plasma levels of FXII, PK and HK in 300 normal blood donors (ND) and 300 patients attending our anticoagulant clinic who had a history of venous thrombosis (deep vein thrombosis or pulmonary embolism [VT]). All subjects were Caucasian, antiphospholipid antibody negative and had normal liver function.

RESULTS

Mean values +/- SD were: FXII: ND 99.4 +/- 26.7%: VT 91.0 +/- 27.2%: PKK: ND 99.7 +/- 19.8%: VT 99.1 +/- 21.2%: HK: ND 101.0 +/- 20.5%: VT 110.7 +/- 32.3%. Statistical analysis of the data revealed significantly lower (p< or =0.001) mean values for FXII and significantly higher (p< or =0.001) mean values for HK in the VT group. Calculated lower limits of normal for each parameter were: FXII: 49.1%, PKK: 66.8%, HK: 63.4%. The prevalence of values below the lower limit of normal were FXII-ND 2.3%: FXII-VT 8.0%, PKK-ND 3.0%: PKK-VT 4.7%, HK-ND 2.3%: HK-VT 5.0%. No homozygous deficiency patients were found for any parameter. One VT patient had combined FXII and HK deficiency and one ND and two VT patients had combined PK and HK deficiency.

CONCLUSIONS

FXII levels were lower and HK levels and the prevalence of FXII, PK and HK deficiency higher in a population of patients with a history of VT than in a population of healthy blood donors.

Hemocompatibility of PMEA Coated Oxygenators Used for Extracorporeal Circulation Procedures

An inflammatory response to cardiopulmonary bypass (CPB) caused by bioincompatibility of extracorporeal circuits is one of the major clinical issues in cardiac surgery. Recently a new coating material, poly-2-methoxyethylacrylate (PMEA), was developed to improve the biocompatibility of blood contacting surfaces. In a simulated cardiopulmonary bypass model, using fresh human whole blood, 15 membrane oxygenators (Capiox SX18, Terumo Corp., Tokyo, Japan) were compared. Five of them had the PMEA coating, five had a heparin-coated surface, and five had no surface treatment. Blood samples were taken at several time-points during a 90 minute circulation period. Changes in coagulation, complement, and blood cell alteration factors were measured by ELISA methods, plasma bradykinin levels were measured by radioimmunoassay, and expression of genes encoding cytokines TNF-alpha, interleukin-1beta, interleukin-6, and interleukin-8 was determined by semiquantitative real time RT-PCR. Platelet adhesion was significantly reduced in both the PMEA and the heparin coated circuits. Release of platelet activation marker beta-thromboglobulin was significantly higher in the uncoated control group (p < 0.01). After 5 minutes of blood circulation bradykinin levels significantly increased in all three groups (p < 0.01); however, the group with the PMEA coated oxygenators showed the lowest values. Expression of genes encoding proinflammatory cytokines in monocytes was increased in all groups, with the lowest being in the PMEA coated group. PMEA coated CPB surfaces in an in vitro experimental model showed an improved thrombogenicity, reduced bradykinin release, less platelet activation and less proinflammatory cytokines gene expression in comparison with a noncoated group. The authors assume that PMEA coating may ameliorate some of intra- and postperfusion syndromes, particularly hypotension, unspecific inflammation, hyperfibrinolysis, and blood loss.

Are cardiovascular and sympathoadrenal effects of human "new pressor protein" preparations attributable to human coagulation beta-FXIIa?

"New pressor protein" (NPP) derived from normal human plasma is an extra renal enzyme that shares strong sequence homology with human coagulation beta-FXIIa. Under our bioassay conditions, human NPP (10-20 microl plasma equivalent/ approximately 300 g rat iv) can raise the systolic blood pressure (SBP) by 40-50 mmHg, the diastolic blood pressure (DBP) by 15-20 mmHg, and the heart rate (HR) by 70-90 beats/min. Plasma epinephrine (of adrenal medullary origin) and norepinephrine rise by about 50- and 10-fold, respectively. Because beta-FXIIa is not normally associated with pressor properties, we endeavored to substantiate that the hypertensive effects of impure NPP preparations used in our experiments are attributable to their content of beta-FXIIa. We carried out comparisons with highly purified (>90%) commercial human beta-FXIIa and found that by gel filtration (Sephadex G-100 and G-75), NPP bioactivity appeared in the approximately 30-kDa elution zone, consistent with the molecular mass of beta-FXIIa. Retention time using fast-protein liquid chromatography anion exchange chromatography was identical. Molecular mass and comigration were confirmed by SDS-PAGE gel electrophoresis, and the recovered approximately 30-kDa protein bands yielded beta-FXIIa fragments identified by mass spectrometry. Matched doses of the NPP preparations produced dose-response curves very similar to those elicited by beta-FXIIa with respect to increments of SBP, DBP, and HR, whereas plasma catecholamine increments were generally comparable. We propose that beta-FXIIa is substantially, if not exclusively, responsible for the observed effects of our NPP preparations and that this points to a novel axis connecting the FXII coagulation cascade and the sympathoadrenal gland to other cardiovascular regulatory mechanisms.

Angiotensin-converting enzyme insertion/deletion genotype is associated with the activities of plasma coagulation factor VII and X independent of triglyceride metabolism

BACKGROUND

The D allele of angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism and coagulation activity play important roles in cardiovascular events, however, the precise association between these two risk factors remains unclear.

METHODS

We identified the ACE I/D genotype and measured the plasma coagulation factor VII and X (FVII and FX) activities and serum lipids in 172 patients (110 men and 62 women, mean age 56.7+/-13.3 years) undergoing coronary angiography.

RESULTS

The frequency of the D allele was significantly higher in those with a history of myocardial infarction (MI) than in those with normal coronary arteries, but there was no significant association between FVII and FX activities and the stage of coronary disease. Plasma coagulation factor VII and FX activities were significantly lower in the DD genotype (n=42) than in the II genotype (n=67, P<0.001 and P<0.001, respectively) or the ID genotype (n=63, P<0.01 and P<0.05, respectively). The association of the ACE D allele with lower activities of FVII and FX was also seen in patients with coronary artery disease (CAD). There was a significant association between serum triglyceride levels with FVII and FX, but not with the ACE I/D genotype.

CONCLUSION

We concluded that the ACE I/D polymorphism may contribute more to the onset of MI than the activities of FVII and FX and that the ACE D allele might be associated with lower plasma activities of FVII and FX. The potential link between ACE I/D polymorphism and the plasma activities of FVII and FX is probably independent of triglyceride metabolism.

Protein adsorption to oligo(ethylene glycol) self-assembled monolayers: experiments with fibrinogen, heparinized plasma, and serum

Low protein adsorption is believed advantageous for blood-contacting materials and ethylene glycols (EG)-based polymeric compounds are often attached to surfaces for this purpose. In the present study, the adsorption of fibrinogen, serum, and plasma were studied by ellipsometry on a series of well-defined oligo(EG) terminated alkane-thiols self-assembled on gold. The layers were prepared with compounds of the general structure HS-(CH2)15-CONH-EGn, where n = 2, 4, and 6. Methoxy-terminated tri(EG) undecanethiol and hydroxyl-terminated hexadecanethiol self-assembled monolayers (SAMs) were used as references. The results clearly demonstrate that the adsorption depends on the experimental conditions with small amounts of fibrinogen adsorbing from a single protein solution, but larger amounts of proteins from serum and plasma. The adsorption of fibrinogen and blood plasma decreased with an increasing number of EG repeats and was temperature-dependent. Significantly less serum adsorbed to methoxy tri(EG) than to hexa(EG) and more proteins remained on the latter surface after incubation in a sodium dodecyl sulfate (SDS) solution, indicating a looser protein binding to the methoxy-terminated surface. All surfaces adsorbed complement factor 3 (C3) from serum and plasma, although no surface-mediated complement activation was observed. The present study points to the importance of a careful choice of the protein model system before general statements regarding the protein repellant properties of potential surfaces can be made.

Human serum-induced expression of E-selectin on porcine aortic endothelial cells in vitro is totally complement mediated

BACKGROUND

Whereas complement is a key mediator of hyperacute xenograft rejection, its role in acute vascular rejection (AVR) is a matter of controversy. AVR is associated with de novo synthesis of endothelial cell-derived inflammatory mediators, including the leukocyte-recruiting adhesion molecule E-selectin. Here we investigate the role and mechanism of complement in human serum-induced porcine endothelial cell activation.

METHODS

An in vitro xenotransplantation method was designed using porcine aortic endothelial cells stimulated with human serum in microculture wells. E-selectin expression was measured by cell-enzyme immunoassay. Complement inhibitors acting at different levels in the cascade were investigated for their effect on E-selectin expression.

RESULTS

E-selectin was strongly induced by normal human serum but not by heat-inactivated serum. Compstatin, a synthetic C3 inhibitor, markedly reduced human serum-induced E-selectin expression. Purified C1-inhibitor suppressed E-selectin induction completely, indicating activation through the classical or lectin pathway. Furthermore, a monoclonal antibody (mAb) that inhibits cleavage of C5 or another mAb that blocks the function of C7, completely inhibited the expression of serum-induced E-selectin, consistent with the terminal C5b-9 complement complex being the mediator of the endothelial cell activation. Inhibition of the alternative pathway using a novel antifactor D mAb did not reduce E-selectin expression.

CONCLUSION

Human serum-induced expression of porcine E-selectin is totally complement dependent, induced by a C1-inhibitor regulated pathway and mediated through the terminal complement complex. The data may have implications for therapeutic strategies, particularly of C1-inhibitor and anti-C5 mAb, to protect against endothelial cell activation and subsequent AVR of porcine xenografts.

In vitro investigation of the blood response to medical grade PVC and the effect of heparin on the blood response

This paper reports the results of an investigation into the blood response of polymers in vitro, using non-anticoagulated and heparinised blood and plasma. The materials studied were regenerated cellulose, (Cuprophan), an acrylonitrile-allyl sulphonate copolymer (AN69S), and medical grade polyvinyl chloride plasticised with di-2-ethyl-hexyl-phthalate (PVC/DEHP). Blood-material or plasma-material contact was achieved using a parallel plate flow cell, and C3a generation and FXII-like activity measured. The results of the study with non-anticoagulated human blood show that PVC/DEHP is a high complement activator. C3a concentration in the blood was higher after contact with PVC/DEHP than after contact with regenerated cellulose. The introduction of heparin in the blood induced complex alterations in the blood response. C3a generation could be elevated, decreased, or remain the same, depending on the material. The FXII-like activity on the surface of the PVC/DEHP after contact with plasma was also higher than the other two polymers. The introduction of heparin could increase or decrease FXII-like activity, depending on material. The patterns of response obtained with non-anticoagulated blood in vitro for AN69S and Cuprophan bore a strong resemblance with patterns of response obtained in the clinic, whereas those obtained with heparinised blood in vitro did not.

FXII levels, FXIIa-like activities and kallikrein activities in normal subjects and patients undergoing cardiac surgery

A new chromogenic peptide substrate assay kit was used to measure factor XII (FXII) levels in plasma samples from 115 male patients with heart disease awaiting cardiac surgery, 40 age-matched normal healthy male blood donors and 20 patients before, during and after cardiopulmonary bypass surgery (CPB). Kallikrein-like and FXIIa-like activities were also determined in the CPB patient group. FXII levels were significantly lower (p = 0.0049) in the heart disease patients awaiting surgery when compared with values for the healthy donors and 13 patients (11.3%) had FXII levels below 50% compared with 1 normal donor (2.5%). During CPB significant decreases in FXII levels and significant increases in FXIIa-like and kallikrein-like activities were found indicating activation of the FXII-plasma kallikrein pathway during CPB.

Increased coagulation and bradykinin-release in shed pleural blood during cardiac surgery

Retransfusion of shed pleural blood is generally believed to contribute to a decrease of intraoperative blood requirements, however, hemodynamic or hemostatic side effects are nevertheless still controversial. Some 13 patients (age: 58 +/- 11) undergoing CPB surgery including the use of the internal mammaria artery (IMA) were investigated. For IMA preparation, pleura of the left hemithorax was opened, allowing blood to accumulate within the pleural cavity. Some 472 +/- 258 ml blood volumes were retransfused after 79 +/- 11 min clamp time. After 50 +/- 15 s, mean arterial blood pressure (AP) dropped from 68 +/- 15 to 36 +/- 8 mm Hg, and the calculated systemic vascular resistance (SVR) decreased from 1124 +/- 263 to 596 +/- 153 dyn s(-1) cm5 (p < 0.01). Bradykinin levels in the retransfused shed blood showed significantly higher values (205 +/- 88 fmol/ml) compared to the systemic blood (24 +/- 19 fmol/ml). Thrombin-antithrombin-III complexes were strongly elevated in the shed pleural blood, and after retransfusion the systemic blood values increased significantly. After retransfusion of shed pleural blood during CPB an acute drop in AP and SVR occurred, probably caused by high bradykinin concentrations. We therefore recommend that the accumulation of shed blood is avoided by continuous retransfusion as is now the standard procedure in our University hospital.

Coating-techniques to improve the hemocompatibility of artificial devices used for extracorporeal circulation

OBJECTIVE

Extracorporeal circulation procedures have been shown to induce complement and leukocyte activation, release of endotoxin and inflammatory mediators, including cytokines, nitric oxide, oxygen free radicals, and platelet activating factors. The contact between the blood and the various artificial surfaces of the extracorporeal system results in an unspecific post-perfusion syndrome. For diminishing these negative side effects several coating-techniques have been developed to create devices with improved hemocompatibility.

METHODS

This review deals with the current knowledge of heparin-coated and otherwise surface-modified perfusion systems. The pathway how heparin-coated surfaces work is discussed and techniques for surface-coatings, both clinically introduced as well as newly developed are presented.

RESULTS

Numerous clinical studies compared heparin-coated versus non-coated circuits. Heparin-bonded devices showed lessened humoral and cellular activation, in particular a reduced complement activation with a reduced inflammatory post-perfusion syndrome. Also platelet protection and more favorable post-operative lung function are of particular note. Recent clinical trials demonstrated shortened hospital stays, less drainage bleeding, and reduced cerebral complications using heparin-coated oxygenation systems. The diminished expression of the leukocyte adhesion molecules CD 11b/c in CBAS devices points to a decreased activation of neutrophils. In addition, one research group found a reduced production of oxygen radicals. Heparin-bonding minimizes oxygenator failure by a significant reduced pressure gradient across the oxygenator, probably caused by decreased fibrin and platelet deposition at the hollow fiber surfaces. A meta analysis examined the impact of heparin-bonded systems on clinical outcomes and resulting costs. Using heparin-bonded circuits led to total cost savings from US $1000 to 3000. Several authors demonstrated reduced blood loss and better clinical outcome by reduction of systemic heparinization and the employment of heparin-coated devices.

CONCLUSION

Above and beyond the long-term applications, routine heart operations have also markedly begun to utilize heparin-coated devices. This trend will assuredly continue in the coming years and is an important step toward higher hemocompatibility of blood-contacting surfaces in the ECC device. Heparin-coatings are merely the beginning of improved hemocompatibility for all materials that come into contact with human blood or tissues. Intelligent materials with almost completely physiological surfaces will be at the surgeon's disposal within the next few years.

Evaluation of markers of deep vein thrombosis in patients undergoing surgery for maxillofacial malignancies

During and following significant surgical intervention, deep venous thrombosis prophylaxis by application of anticoagulants is routinely used. However, patients with malignant disorders are subject to an especially high risk of deep venous thrombosis progressing in severe cases to subsequent pulmonary embolism. The present study focuses on appraising modern markers of deep vein thrombosis in 34 patients undergoing major maxillofacial surgery, with some malignant disorders. No significant differences between the two patient groups were noted using the markers of the kallikrein-kinin-system. From the first postoperative day plasma levels of the coagulation indicator thrombin-antithrombin-III complexes were significantly higher in the group of tumour patients. Markers of fibrinolysis indicated corresponding results: on the first postoperative day tissue-plasminogen activator values rose to 18.9 +/- 3.2 micrograms/l in the group of malignant patients, but only to 7.4 +/- 1.1 micrograms/l (P < 0.05) in the control group. Also postoperative D-dimer concentrations in the malignancy group were significantly above those of the control group. In the present study it could be demonstrated that patients with malignant neoplasia undergoing major maxillofacial surgery are exposed postoperatively to a particularly high risk of developing thromboembolic complications. All in all, the status of anti-thrombotic therapy requires reappraisal with respect to the current treatment approach adopted in tumour patients.

Fibrinolytic properties of activated FXII

Activated factor XII (FXIIa), the initiator of the contact activation system, has been shown to activate plasminogen in a purified system. However, the quantitative role of FXIIa as a plasminogen activator in contact activation-dependent fibrinolysis in plasma is still unclear. In this study, the plasminogen activator (PA) activity of FXIIa was examined both in a purified system and in a dextran sulfate euglobulin fraction of plasma by measuring fibrinolysis in a fibrin microtiter plate assay. FXIIa was found to have low PA activity in a purified system. Dextran sulfate potentiated the PA activity of FXIIa about sixfold, but had no effect on the PA activity of smaller fragments of FXIIa, missing the binding domain for negatively charged surfaces. The addition of small amounts of factor XII (FXII) to FXII-deficient plasma induced a large increase in contact activation-dependent PA activity, as measured in a dextran sulfate euglobulin fraction, which may be ascribed to FXII-dependent activation of plasminogen activators like prekallikrein. When more FXII was added, PA activity continued to increase but to a lesser extent. In normal plasma, the addition of FXII also resulted in an increase of contact activation-dependent PA activity. These findings suggested a significant contribution of FXIIa as a direct plasminogen activator. Indeed, at least 20% of contact activation-dependent PA activity could be extracted from a dextran sulfate euglobulin fraction prepared from normal plasma by immunodepletion of FXIIa and therefore be ascribed to direct PA activity of FXIIa. PA activity of endogenous FXIIa immunoadsorped from plasma could only be detected in the presence of dextran sulfate. From these results it is concluded that FXIIa can contribute significantly to fibrinolysis as a plasminogen activator in the presence of a potentiating surface.

A chromogenic substrate assay kit for factor XII: evaluation and use for the measurement of factor XII levels in cardiopulmonary bypass patients

Factor XII levels were determined in plasma samples from 75 patients before undergoing aortocoronary bypass grafting and from 40 healthy age-matched donors by using a microtitre plate adaptation of a new chromogenic peptide substrate assay kit for factor XII. The chromogenic peptide substrate assay values for factor XII correlated well with those obtained in clotting (r=0.90; y= 15.811+0.8236x) and immunochemical (r=0.88; y=17.90+0.817x) assays in the normal donor samples. Factor XII levels in the patients were significantly lower than those in the normal donors (83.3+/-23.2% versus 103.4+/-23.1: p=0.004), and nine patients (12%) had factor XII values below 50% compared with only one of the normal donors (2.5%). Factor XII levels and kallikrein-like activities (a measure of contact system activation) were followed before, during, and one day after cardiopulmonary bypass in 20 patients. Factor XII levels were significantly reduced, and kallikrein-like activities significantly elevated after 5 and 30 minutes cardiopulmonary bypass. One day after cardiopulmonary bypass both factor XII levels and kallikrein-like activities were significantly lower than preoperation values.

Haemocompatibility of paediatric membrane oxygenators with heparin-coated surfaces

Extracorporeal circulation (ECC) in paediatric patients with heparin-coated oxygenation systems is rarely investigated. The objective of this study was to evaluate, preclinically, the haemocompatibility of paediatric membrane oxygenators with heparin-coated surfaces. We compared 16 paediatric membrane oxygenators (Minimax, Medtronic) in an in vitro heart-lung machine model with fresh human blood. Eight of these oxygenation systems had a covalent heparin coating (Carmeda bioactive surface). After 90 min simulated ECC, the heparin-coated systems showed significantly higher platelet count, lower platelet-factor 4 release, reduced contact activation (factor XIIa and kallikrein), and lower neutrophil elastase levels (p < 0.05), compared to the noncoated oxygenator group. More biocompatible materials for paediatric operations may ameliorate the various postperfusion syndromes arising from ECC procedures, particularly unspecific inflammation, hyperfibrinolysis and blood loss.

Contact activation of plasmatic coagulation on polymeric membranes measured by the activity of kallikrein in heparinized plasma

Kallikrein is involved in the generation of bradykinin during extracorporal circulation, that is believed to play an important role in cases of anaphylactic shock during hemodialysis. Therefore, a method for the assessment of kallikrein generation was developed, based on the chromogenic substrate S-2302. Comparison of kallikrein-like activity on glass using citrate or heparinized plasma demonstrated enhanced activity in the presence of heparin. The applicability of the assay, and the time course of kallikrein generation was demonstrated with glass and cuprophan. Membranes based on pure polyacrylonitrile, or its copolymers differing in their content of acrylic acid, 2-hydroxyethyl acrylate, and allylsulphonate were investigated with respect to kallikrein-like activity, and physicochemical surface properties. It was found that high content in 2-hydroxyethyl acrylate, and acrylic acid caused a substantial activation of the contact system while low content in allylsulphonate (less than 2 mol%) did not result in enhanced kallikrein-like activity. The activating materials were characterized to be highly wettable, and had the most negative zeta potentials.

Activation of FXII during haemodialysis

This study was designed to provide information on the kinetics of FXIIa activity and C3d release during haemodialysis. Dialysis was performed twice in 9 stable patient for 240 min with the same conditions except for a change in dialysate sodium profile (using a linear sodium programme starting at 138 and ending at 148 mmol/l or vice versa). Using paired statistics there was a significant (p < 0.02) increase in both C3d release and the FXIIa activity. The sodium profiles did not alter the outcome. The increase in FXIIa activity, which is maximal at the end of dialysis, is continuous, unlike the C3d release, which is maximal within 15 min of dialysis and then levels off. Both interactions are induced by the blood membrane contact. These results indicate that the FXIIa activation is not strictly coupled to the activation of the complement system.

A novel 5'-upstream mutation in the factor XII gene is associated with a TaqI restriction site in an Alu repeat in factor XII-deficient patients

The factor XII gene from factor XII-deficient patients was screened for mutations at the genomic level. In patients negative for cross-reacting material, a T to C transition 224 bp upstream of exon 3 was identified (exon 3-224 (T --> C)) that creates an additional TaqI restriction site in intron B. This mutation is located within a putative hormone responsive element and within a B box promoter of an Alu repeat of the Sb0 family. The TaqI site is associated with a G to C transversion upstream of the transcription initiation site (exon 1-8 (G --> C)). We discuss the possible roles of these elements in factor XII gene regulation.

The influence of biomaterials on inflammatory responses to cardiopulmonary bypass

The nature of cardiopulmonary bypass and the complexity of the inflammatory response make the detection and interpretation of a biomaterial influence difficult. However, if mediation of the inflammatory response is considered to be an appropriate clinical goal, alteration to the biomaterial influence merits further investigation.

Influence of heparin, heparin plus aprotinin and hirudin on contact activation in a cardiopulmonary bypass model

In the present study we used an in vitro cardiopulmonary bypass model to compare activation of the FXII-plasma kallikrein systems, coagulation pathway and blood cell changes, with heparin (3 U/ml), heparin plus aprotinin (3 U/ml and 250 KIU/ml) and recombinant hirudin (6 micrograms/ml). After 90 min circulation the results showed that with heparin plus aprotinin and with hirudin the activation of these cascade reactions was markedly lower. In particular kallikrein-like activities and PMN-Elastase-alpha 1-PI levels were significantly lower in the latter two groups. The least activation was detected with hirudin. Our results confirm that the contact systems of blood are activated during CPB with heparin as anticoagulant, that aprotinin reduces this activation, and that recombinant hirudin may be preferred to heparin as an anticoagulant in cardiac surgery.

Determination of contact phase activation by the measurement of the activity of supernatant and membrane surface-adsorbed factor XII (FXII): its relevance as a useful parameter for the in vitro assessment of haemodialysis membranes

We investigated hemodialysis membrane biocompatibility with respect to contact phase activation by determination of FXII-like activity (FXIIA) on the membrane surface and in the supernatant phase, during plasma contact with various hemodialysis membranes using an in vitro incubation test cell. The results were compared to the influence of these membranes on the activation of purified FXII. A time course for the generation of activated FXII using purified FXII solution at physiologic concentrations on two similar negatively charged polymers was performed. The membranes assessed were regenerated cellulose (Cuprophan; Akzo Faser AG, Germany), modified cellulosic (Hemophan; Akzo Faser AG), acrylonitrile-sodium methallyl copolymer-based membrane AN69S (Hospal, France), and SPAN, a new polyacrylonitrile-based copolymer (akzo Nobel AG). The plasma FXIIA at the membranes surface was significantly different between the membranes, while the supernatant phase FXIIA exhibited no significant differences. In contrast, activation of purified FXII in a plasma-free system with respect to supernatant activity indicated significant differences between the materials. A similar finding for the membrane-bound factor XIIA was also observed when purified factor XII was used. The membrane-bound FXIIA values observed in the plasma system containing heparin were significantly greater than in citrated plasma. This demonstrated the strong influence of heparin and the interaction of other plasma components to the membrane surface on the activation of contact phase of coagulation.

C3 is activated in hereditary angioedema, and C1/C1-inhibitor complexes rise during physical stress in untreated patients

Seven patients with hereditary angioedema (HAE) were studied to understand further how physical exercise may induce attacks. The most pronounced differences between patients and controls, however, were independent of the controlled bicycle run (mean values in patients/ controls); C4(g/L): 0.12/0.28 (P = 0.0122); C4bc (AU/ml): 137.0/18.0 (P = 0.0002); C4d (mg/mL): 5.03/2.35 (P = 0.0004); C3bc (AU/ml): 8.4/6.3 (P = 0.0049); C3a (AU/ml): 11.1/5.6 (P = 0.0102). The ratio C4bc to C4 was 1141 versus 64. Consequently, a substantial part of the low amount of C4 left in HAE patients consists of activation products, and the authors show for the first time that a mild but significant activation of C3 occurs in HAE. The two HAE patients treated with danazol had values of C1-INH function and antigen, C4, and C2 in-between those of normal and untreated patients, and lower levels of split products from C4 and high molecular weight kininogen than untreated patients. As a result of the exercise, fibrinolysis increased significantly in both patients and controls, while C1/C1-INH complexes rose significantly only in the five HAE patients without treatment when compared to the seven controls (P = 0.0089). This study thus suggests that complement activation is enhanced in untreated HAE patients following physical stress.

In vitro contact phase activation with haemodialysis membranes: role of pharmaceutical agents

Contact phase activation was investigated in vitro using flat sheet type of haemodialysis membranes, Cuprophan (Akzo, Faser, Germany) and AN69S (Hospal, France), and a negatively charged polyamide Ultipor NR 14225 membrane as a control. The investigation focussed on the determination of factor XII-like activity (FXIIA) as an indicator of contact phase activation in the supernatant phase and at the membrane surface after plasma-membrane contact using an incubation test cell. The findings were compared with the observations from a plasma-free system utilizing purified unactivated factor XII. The plasma FXIIA bound to the membrane surface was significantly different between the membranes, while the supernatant phase FXIIA exhibited no significant differences. In contrast, the plasma-free system exhibited significant differences in the supernatant FXIIA and membrane-bound FXIIA for all the materials used and the magnitude of the activity was significantly greater for negatively charged materials. This finding demonstrated the strong influence of the interaction of other plasma constituents on the membrane surface and as such the binding and subsequent activation of factor XII may be altered possibly due to competitive binding and steric hindrance. On the addition of anticoagulants such as heparin, low-molecular-weight heparin, citrate and hirudin, no significant differences were observed in plasma supernatant phase FXIIA. However, each anticoagulant appears to have a distinct influence on the magnitude of plasma membrane-bound FXIIA. On the addition of aprotinin (a kallikrein inhibitor), no significant differences were observed in the plasma supernatant FXIIA. In contrast, aprotinin appears to significantly reduce membrane-bound FXIIA on Cuprophan and polyamide NR, but significantly increase the magnitude of the membrane-bound FXIIA on AN69S.

Lower cardiac troponin T levels in patients undergoing cardiopulmonary bypass and receiving high-dose aprotinin therapy indicate reduction of perioperative myocardial damage

Nowadays in many European heart centers the activation of the fibrinolytic system, always occurring during cardiopulmonary bypass, is routinely reduced by high-dose application of the proteinase inhibitor aprotinin (total of > 4 million KIU). In this study parameters of myocardial ischemic injury were investigated with the aim of identifying further benefits of aprotinin, particularly the protection of the myocardium during the ischemic period of aortic crossclamping. Forty patients with coronary artery disease who underwent aorta-coronary bypass grafting were randomly and in a double-blind fashion divided into two groups, one that received high-dose aprotinin therapy and one that received only saline solution. Markers such as troponin T, with high specificity for detection of myocardial ischemia and infarction, and markers with more general specificity such as creatine kinase, its isoenzyme, and lactate dehydrogenase showed significantly increased values after ischemia in both groups. In patients who received high-dose aprotinin therapy 3 days after cardiopulmonary bypass all parameters measured showed significantly lower levels compared with those in the control group. Therefore we can presume that the application of high-dose aprotinin provides myocardial protection from perioperative ischemic injury.

Hageman factor and its binding sites are present in senile plaques of Alzheimer's disease

Hageman factor (HF) or factor XII participates in several defense systems of the body. These include coagulation, fibrinolysis and complement activation. We investigated the expression of HF and its mRNA in control and Alzheimer's disease (AD) brain, using immunohistochemistry and polymerase-chain reaction (PCR) techniques. HF mRNA was detected in control and AD brain extracts, indicating that HF can be produced by endogenous brain cells. HF-like immunoreactivity was present in residual serum of capillaries in both control and AD brain, consistent with its known presence in the circulation. In addition, AD senile plaques were stained. The staining was dramatically enhanced when AD sections were incubated with solutions containing HF, indicating that plaques contain not only HF but also binding sites for HF. The enhanced staining was eliminated by pretreatment of solutions with the HF-binding agent kaolin. It was also eliminated by pretreatment of sections with protamine, an agent which strongly binds to negative surfaces. These data suggest that negatively charged surfaces in plaques might bind HF in vivo. Since HF can be activated by contact with negative surfaces, locally released HF could be playing a role in initiating a variety of inflammatory responses in AD brain.

Effect of time, temperature and additives on a functional assay of C1 inhibitor

There are different recommendations for the handling of blood samples for analyses of the kallikrein-kinin or complement system, respectively. C1 inhibitor (C1-INH) takes a crucial part in both systems. In order to establish recommendations for blood specimen collection and transport for making the diagnosis of hereditary angioedema (HAE), the effect of time, temperature and different additives on C1-INH function and antigen was determined. We used blood samples from normals and patients suffering from HAE type I. Plasma containing EDTA, heparin, sodium citrate or polybrene-EDTA, and serum were assayed after incubations at 4 degrees C or 37 degrees C for 6 or 24 h. In addition, pooled serum was incubated for up to 5 days at room temperature. A modest decrease in C1-INH function was observed as an effect of storage-time in samples from normals (p = 0.039) and a substantial decrease was seen for the HAE patients (p = 0.0002). No significant effect of temperature (4 degrees C or 37 degrees C) was found. Clotting did not reduce C1-INH activity. Plasma containing heparin or polybrene interfered with the functional assay, yielding falsely high and low values, respectively. C1-INH functional assay performed within 24 h in serum, EDTA-treated or citrated plasma discriminated well between HAE patients and normals. This was also the case for serum kept at room temperature for up to 5 days, although a modest fall in C1-INH function was seen in the incubation period. For practical purposes we recommend serum as the sample of choice, preferably received within 48 h.

Effect of surface-immobilized heparin on the activation of adsorbed factor XII

Two different heparin surfaces, structurally closely related and of similar negative charge characteristics, were compared with regard to adsorption and activation of coagulation Factor XII (FXII). One surface was prepared by immobilization of unfractioned heparin, which yielded a surface containing both heparin molecules with high and with low affinity for antithrombin (unfractioned [UF] heparin surface). The other surface consisted of a fraction of heparin molecules with low affinity for antithrombin (LA heparin surface) and essentially devoid of antithrombin-binding as well as anticoagulant activity. Both surfaces adsorbed FXII from plasma to a similar extent, and essentially the same quantities of bound factor could be recovered from the surfaces. The two heparin surfaces, however, differed markedly with regard to activation of the adsorbed FXII. On the LA heparin surface, a major portion of the surface-bound FXII was recovered in its enzymatically active form (FXIIa), but only trace amounts of the FXII taken up by the UF heparin surface had undergone activation. When FXII-deficient plasma was used instead of normal plasma, no surface-associated enzyme activity could be recovered on either surface. The presence of free standard heparin or low molecular weight heparin in the plasma exposed to the LA heparin surface did not prevent conversion of FXII to FXIIa.

Chromogenic peptide substrate assays and their clinical applications

Chromogenic peptide substrates were first introduced into research laboratories in the early 1970s and were quickly utilised to develop assays for the determination of enzymes, proenzymes and inhibitors of the coagulation system. These assays were gradually introduced into coagulation and clinical chemistry laboratories as laboratory tools in the diagnosis and treatment of coagulation disorders. From the knowledge of the structures of the natural substrates attacked by enzymes other than those of the coagulation system or by synthesis and random screening, substrates for enzymes of the fibrinolytic, plasma and glandular kallikrein and complement systems were produced. These allowed various research groups to develop assays for components of these systems and subsequently led to the use of these assays in studies on various clinical conditions. Substrates for activated protein C ensured that assays for this enzyme and its inhibitors could be developed and introduced into the haematological routine. With the introduction of substrates for limulus lysate not only were assays for endotoxins in clinical samples produced but the control of all disposable products and injectables for endotoxin contamination can now be effected. Initially high costs and time-consuming manual assays were a hinderence to the general acceptance of the use of chromogenic peptide substrate assays and they were only used routinely in a few specialised laboratories. With the introduction of automated and microtitre plate methods however, these assays are are now available in most hospital laboratories. Since the first chromogenic peptide substrate was described thousands of articles have been published on the use of chromogenic substrate assays to measure proenzymes, enzyme activators, enzyme cofactors and inhibitors in blood and other body fluids in normal subjects and clinical material. We have endeavoured to cover as many of these as possible in this review.