The activation of the contact system of human plasma by polysaccharide sulfates

The Haemocompatibility of Biomaterials In Vitro: Investigations on the Mechanism of the Whole-blood Clot Formation Test

Twenty years ago Imai & Nose introduced a whole-blood clotting test for the estimation of haemocompatibility of biomaterials in vitro In our paper a modification of this assay is described and the mechanism of clot formation further elucidated. It was found that neither the inhibition of platelet function nor the removal of platelets from blood significantly changed the clot formation rate on glass and polyvinyl chloride in comparison to the rate tor whole blood. Scanning electron microscopy demonstrated that platelets were not involved in clot formation near the blood/biomaterial interface. Thus, it was concluded that the system of contact activation of the coagulation cascade dominates during clot formation under static conditions. The latter conclusion was supported by the fact that preadsorption of human serum albumin or human fibrinogen onto the glass plates used, decreased the clot formation rate in the same manner.

Genetic determinants of activity and antigen levels of contact system factors

Essentials Genetic variation may provide valuable insight into the role of the contact system in thrombosis. Explored associations of genetic variants with activity, antigen, and disease in RATIO study. Two novel loci were identified: KLKB1 rs4253243 for prekallikrein; KNG1 rs5029980 for HMWK levels. Contact system variants and haplotypes were not associated with myocardial infarction or stroke. SUMMARY: Background The complex, interdependent contact activation system has been implicated in thrombotic disease, although few genetic determinants of levels of proteins from this system are known. Objectives Our primary aim was to study the influence of common F11, F12, KLKB1, and KNG1 variants on factor (F) XI activity and FXI, FXII, prekallikrein (PK) and high-molecular-weight kininogen (HMWK) antigen levels, as well as the risk of myocardial infarction and ischemic stroke. Patients/methods We analyzed samples from all 630 healthy participants, 182 ischemic stroke patients and 216 myocardial infarction patients in the RATIO case-control study of women aged < 50 years. Forty-three tagging single nucleotide variants (SNVs) were genotyped to represent common genetic variation in the contact system genes. Antigen and activity levels were measured with sandwich-ELISA-based and one-stage clotting assays. We performed single variant, age-adjusted, linear regression analyses per trait and disease phenotype, assuming additive inheritance and determined conditionally independent associations. Haplotypes based on the lead SNV and all conditionally independent SNVs were tested for association with traits and disease. Results We identified two novel associations of KLKB1 SNV rs4253243 with PK antigen (βconditional = -12.38; 95% CI, -20.07 to -4.69) and KNG1 SNV rs5029980 with HMWK antigen (βconditional = 5.86; 95% CI, 2.40-9.32) and replicated previously reported associations in a single study. Further analyses probed whether the observed associations were indicative of linkage, pleiotropic effects or mediation. No individual SNVs or haplotypes were associated with the disease outcomes. Conclusion This study adds to current knowledge of how genetic variation influences contact system protein levels and clarifies interdependencies.

The initiation and effects of plasma contact activation: an overview

The plasma contact system sits atop the intrinsic coagulation cascade and plasma kallikrein-kinin pathway, and in vivo its activation contributes, respectively, to coagulation and inflammation mainly via two downstream pathways. This system has been widely investigated, its activation mechanisms by negatively charged surfaces and the interactions within its components, factor XII, prekallikrein and high molecular weight kininogen are well understood at the biochemical level. However, as most of the activators that have been discovered by in vitro experiments are exogenous, the physiological activators and roles of the contact system have remained unclear and controversial. In the last two decades, several physiological activators have been identified, and a better understanding of its roles and its connection with other signaling pathways has been obtained from in vivo studies. In this article, we present an overview of the contact pathway with a focus on the activation mechanisms, natural stimuli, possible physiological roles, potential risks of its excessive activation, remaining questions and future prospects.

Characterization of currently marketed heparin products: adverse event relevant bioassays

The polyanion oversulfated chondroitin sulfate (OSCS) was identified as a contaminant in heparin products and was associated with severe hypotensive responses and other symptoms in patients receiving the drug. The OSCS associated adverse reactions were attributed to activation of the contact system via the plasma mediator, activated factor XII (FXIIa), which triggers kallikrein (KK) activity. Unlike heparin alone, OSCS, is able to activate FXII in plasma and stably bind to FXIIa enhancing plasma KK activity and the induction of vasoactive mediators such as bradykinin (BK), C3a and C5a. Similarly OSCS can interfere with heparin neutralization by the polycationic drug protamine. Here, we assess heparin (heparin sodium, dalteparin, tinzaparin or enoxaparin)-protamine complex formation and plasma based bioassays of KK, BK and C5a in a 96-well plate format. We establish the normal range of variation in the optimized bioassays across multiple lots from 9 manufacturers. In addition, because other oversulfated (OS) glycosaminoglycans (GAGs) besides OSCS could also serve as possible economically motivated adulterants (EMAs) to heparin, we characterize OS-dermatan sulfate (OSDS), OS-heparan sulfate (OSHS) and their native forms in the same assays. For the protamine test, OS-GAGs could be distinguished from heparin. For the KK assay, OSCS and OSDS were most potent followed by OSHS, and all had similar efficacies. Finally, OSDS had a greater efficacy in the C5a and BK assays followed by OSCS then OSHS. These data established the normal range of response of heparin products in these assays and the alteration in the responses in the presence of possible EMAs.

Bradykinin forming capacity of oversulfated chondroitin sulfate contaminated heparin in vitro

Oversulfated chondroitin sulfate (OSCS) contaminated heparin has been associated with severe anaphylactoid reaction (AR), mainly in dialysed patients. Although attributed to bradykinin (BK) released during contact system activation by OSCS, no definitive evidence exists until now for a BK release during incubation of contaminated heparin with human plasma. In this study, we investigated the kinin forming capacity of OSCS and OSCS contaminated heparin when incubated in vitro with a pool of human plasma. At 100 microg/mL, OSCS liberates BK in a profile similar but not identical to dextran sulfate, a well known activator of the plasma contact system. The results have highlighted that the quantity of BK accumulated during contact system activation depends not only on the concentration of OSCS but also on the plasma dilution and the presence of an angiotensin converting enzyme inhibitor. We demonstrate a highly significant correlation between the concentration of OSCS present in the contaminated heparin and BK released concentration. In conclusion, for the first time, we show that OSCS contaminated heparin incubated with human plasma has the capacity to liberate BK at a concentration that could explain the role of this inflammatory peptide in the pathophysiology of AR associated with OSCS contaminated heparin.

DISCLAIMER

The findings and conclusions in this article have not been formally disseminated by the Food and Drug Administration and should not be construed to represent any Agency determination or policy.

Variability of biological effects of silicas: Different degrees of activation of the fifth component of complement by amorphous silicas

A biogenic and a pyrogenic amorphous silica were incubated in normal human plasma and compared on a per unit surface basis for their ability to split C5 molecules and yield small C5a peptides. Since C5a peptides induce selective chemotactic attraction of polymorphonuclear leukocytes (PMN), measurement of PMN-induced chemotaxis was used as an index of C5 activation. Though to a lesser extent than the crystalline forms, amorphous silicas can promote the cleavage of C5 protein and generation of C5a-like fragment. The biogenic silica, which differs from the pyrogenic variety in particle shape, level of contaminants, and degree of surface hydrophilicity, besides specific surface, induced a greater response. Both silicas activated C5 through a process which seems to involve multiple events similar to those induced by crystalline silica. C5 molecules are adsorbed and hydroxyl radicals are generated through Haber Weiss cycles catalyzed by the redox-active iron present at the particle surface either as trace impurities or chelated from plasma by silanol groups. In turn, these radicals convert native C5 to an oxidized C5-like form C5(H2O2). Finally, C5(H2O2) is cleaved by protease enzymatic action of plasma kallikrein activated by the same silica dusts, yielding a product, C5a(H2O2), having the same functional characteristic as C5a.

Safety of Cartrophen Vet in the dog: review of adverse reaction reports in the UK

Suspected adverse reactions (SARs) reported for Cartrophen Vet (100 mg sodium pentosan polysulphate/ml) to the Veterinary Medicines Directorate in the UK for the period January 1991 to October 1999 were reviewed. Of the 161 reports, 28 were probably product related, 54 were possibly product related, 71 were unlikely to be related and eight were unclassified. An estimated real incidence of adverse reactions probably and possibly associated with Cartrophen Vet of 0.074 per cent on an individual dose basis was calculated (assuming only 10 per cent were documented due to underreporting). Sixty-two SARs (38.5 per cent) documented emesis, 22 (35.5 per cent) of which were product related (onset five to 15 minutes after administration). Sixty-eight SARs (42.2 per cent) documented general changes to demeanour, 10 (14.7 per cent) were product related (lethargy and/or mild depression and/or mild inappetence lasting up to two days after administration). Six SARs were considered likely to be associated with concurrently administered carprofen. Cartrophen Vet had a low incidence of side effects that were mild and transitory.

Inhibition of contact activation by a kininogen peptide (HKH20) derived from domain 5

Contact activation can be initiated by interaction of Factor XII, prekallikrein (PK) and high molecular weight kininogen (HK) with inorganic negatively charged biologic macromolecules, or upon cell surfaces, or interaction with membrane protein derivatives such as aggregated beta amyloid. The latter two examples are zinc-dependent. The interaction with cells is dependent on peptides derived from HK domains 3 and 5 termed LDC27 and HKH20, respectively. We have tested the ability of each of these peptides to inhibit HK-dependent contact activation. HKH20 inhibited activation of prekallikrein when a mixture containing HK, prekallikrein and Factor XII was incubated with dextran sulfate, gC1qR, amyloid beta or endothelial cells. Comparable quantities of LDC27 had no effect. The binding of biotinylated HK or biotinylated Factor XII was inhibited in a dose response fashion by increasing concentrations of HKH20 while LDC27, again had no effect. The N-terminal region of HKH20 (amino acids 475-485) is of particular importance for binding and histidine 485 prominently enhances the reaction as assessed employing overlapping and deleted peptides. Since there is a role for HK heavy chain in binding to endothelial cells and LDC27 can be employed as an affinity ligand to isolate the binding proteins, we increased the LDC27 concentration from 10-fold to 250-fold to determine whether it is functional. Inhibition of endothelial cell-dependent prekallikrein activation required 100-fold greater concentration of LDC27 when compared to HKH20 to achieve significant inhibition. We conclude that the interactions of the light chain of HK via HKH20 is of particular importance for activation of the bradykinin forming cascade in zinc-dependent or independent reactions and is true for all "surface" initiators tested thus far.

Cleavage of the fifth component of human complement and release of a split product with C5a-like activity by crystalline silica through free radical generation and kallikrein activation

The effects of the same form of crystalline silica variously modified were compared to investigate the mechanisms by which silica activates C5 molecules. After incubation in human plasma, silica generated C5a-type fragments that stimulated polymorphonuclear leukocyte chemotaxis. This activity was totally abolished when plasma, adsorbed with antiserum against C5a or thermally inactivated, was used. Pretreatment of plasma with deferoxamine, 1,3 dimethyl-2-thiourea, or aprotinin markedly inhibited or totally abolished C5 activation. Finally, a significant increase in kallikrein activity was detected after incubation of silica particles in plasma. The results seem to indicate that the activation of C5 by crystalline silica occurs through a complex mechanism: the redox-active iron possibly present at the silica surface catalyzes, via Haber-Weiss cycles, the production of hydroxyl radicals, which in turn convert native C5 to an oxidized C5-like form. This product is then cleaved by kallikrein, activated by the same silica particles, yielding oxidized C5a with the same functional properties as C5a. The different types of the same form of silica exhibited different reactivity. Two separate properties of the dusts seem to contribute to C5 activation: the potential to release hydroxyl radicals and the extent of C5 adsorption at the surface. The degree of surface hydrophobicity/hydrophilicity appeared sufficient to explain the different responses.

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.

Surface modification of chitosan membranes by complexation-interpenetration of anionic polysaccharides for improved blood compatibility in hemodialysis

Chitosan membrane surface was modified by complexation and interpenetration of anionic polysaccharides--heparin and dextran sulfate--for improved blood compatibility in hemodialysis. Electron spectroscopy for chemical analysis results showed a characteristic sulfur (S) and sodium (Na) peaks after modification with dextran sulfate. The sulfur/carbon (S/C) atomic composition ratio increased from 0.03 to 0.08 when the bulk dextran sulfate concentration used for modification was increased from 2.5 to 10 mg ml-1. The permeability of urea and creatinine did not change significantly upon modification with heparin or dextran sulfate. Surface modification, however, did decrease the permeability coefficients of glucose, vitamin B-2, and vitamin B-12. Unlike Cuprophan, chitosan and surface-modified chitosan membranes did not significantly activate the complement system as measured by the serum iC3b concentration. Compared to forty and sixty fully-activated platelets present on control surfaces, surface modification with heparin and dextran sulfate significantly reduced the number of adherent platelets per 25,000 microns 2 area and the extent of platelet activation. Surface modification with anionic polysaccharides, however, did significantly shorten the plasma recalcification time leading to fibrin clot formation. The results of this study show that chitosan membrane surface can be modified by complexation-interpenetration of anionic modifying agents. The modified membranes do resist complement activation and platelet adhesion and activation.

Activation of the coagulation pathway during ongoing allergic cutaneous reactions in humans

The levels of histamine, fibrinopeptide A (FPA), and IgG were determined in chamber fluids overlying sites of antigen versus buffer incubation for up to 7 hours in seven atopic and four antigen-nonreactive subjects. Significant increases in histamine were observed at antigen versus buffer sites in the atopic subjects throughout the 7-hour period. FPA and IgG levels were higher in antigen than in buffer sites from 0 to 5 hours in the atopic subjects. Furthermore, FPA levels correlated with the magnitude of induration at 6 hours after antigen injection in atopic subjects. There were no differences in the levels of histamine, FPA, or IgG at antigen versus buffer sites in the skin test-negative subjects. We suggest that the combination of vascular leakage of proteins, induced by vasoactive mediator release, and activation of these proteins during ongoing cutaneous reactions is responsible for fibrin formation that contributes to the pathophysiology of late-phase allergic responses in the skin.

FXII

The plasma protein FXII (Hageman factor) has been shown to be linked with the plasma defence systems of coagulation, fibrinolysis, kallikrein-kinin and complement. It can be activated by surface contact activation and in solution. Surface contact activation is a complex phenomenon involving negatively charged surfaces, FXII, high molecular weight kininogen and plasma kallikrein. Fluid-phase activation can be effected by a variety of serine proteases. In both types of activation the FXII zymogen is converted to active enzymes. FXII levels in plasma are low or undetectable in both inherited deficiencies and in a variety of clinical conditions. FXII levels can also be elevated in some clinical conditions. Although discovered as a clotting protein FXII appears to play an important role in the kallikrein-kinin and fibrinolytic systems and also has effects on cells. Recent studies suggest that therapeutic blockade of activation of FXII can be of benefit in certain clinical conditions.