Alterations in coagulation after implantation of a pulsatile Novacor LVAD and the axial flow MicroMed DeBakey LVAD

BACKGROUND

The MicroMed DeBakey left ventricular assist device (LVAD) is a chamber and valveless axial flow blood pump. We investigated parameters of the coagulation system in patients after implantation of the axial flow LVAD and patients following implantation of a pulsatile Novacor LVAD.

METHODS

Six consecutive patients of both groups were investigated over a period of 6 weeks after implantation. beta-Thromboglobulin, platelet factor 4, factor XIIa, thrombin/antithrombin complexes, plasmin/alpha2-antiplasmin complexes, and D-Dimer levels were measured.

RESULTS

With the exception of the plasmin/alpha2-antiplasmin levels in the Novacor group, all parameters were elevated in both groups. The levels of beta-thromboglobulin, platelet factor 4, factor XIIa, and plasmin/alpha2-antiplasmin were significantly increased in the axial flow LVAD group.

CONCLUSIONS

The axial flow LVAD strongly influences the systems of contact activation and fibrinolysis. The elevation of platelet proteins appears to follow platelet damage. Although no thromboembolic events were observed in both groups, elevation of thrombin/antithrombin complexes provides convincing evidence of an increased activation of the coagulation system and the concomitant risk for the development of thromboembolism.

Spatiotemporal dynamics of fibrin formation and spreading of active thrombin entering non-recalcified plasma by diffusion

The spatiotemporal dynamics of clot growth was studied in non-stirred non-recalcified plasma where thrombin entered by diffusion. Under these conditions, the clot rapidly grew for 30-45 min and then stopped growing on reaching 0.4-0.5 mm in size. The dynamics of clot growth and its size almost did not depend on the thrombin concentration in the range from 50 to 400 nM. FITC-thrombin was shown to permeate the growing clot. The clot size in antithrombin-deficient plasma increases with decreasing antithrombin concentration, being 1.5 mm in the plasma depleted of antithrombin to 5% of its initial level. The data on the spatial distribution of amidolytic activity in the growth zone of the clot suggested that thrombin was not the sole source of this activity. Analysis showed that this additional activity arising during thrombin diffusion into plasma was largely accounted for by thrombin-alpha(2)-macroglobulin complex.

Hypercoagulable states

The hypercoagulable state has been defined as the potential to develop thrombosis in association with hereditary and noninherited genetic mutations and acquired disorders. It is a condition that places an individual at risk for, but does not in itself inevitably lead to, thrombosis. The focus of this article is understanding mechanisms in the hypercoagulable state that enhance and maintain the production of thrombin in circulating blood while preventing its progression to thrombosis. These mechanisms include reactions that produce thrombin from prothrombin, feedback loop mechanisms that affect the rate of thrombin production from prothrombin and the inactivation of thrombin in blood. The fibrinolytic system is involved in clot lysis but not in thrombin production and inactivation.

Evaluation of argatroban and DUP 714 as anticoagulants for blood gas, electrolyte and ionized calcium analyses

The objective of this study was to determine if the thrombin inhibitors Argatroban and DUP 714 could anticoagulate whole blood without influencing the analyses of blood gases, electrolytes, ionized calcium or CO-oximetry. The anticoagulant potency of DUP 714 (0.5-68 micromol/l) and Argatroban (1.5-390 micromol/l) was evaluated using the activated partial thromboplastin time (APTT), prothrombin time (PT) and whole blood clot time (WBCT). APTT and the PT were measured using a Behring Fibrintimer. APTT was found to be more sensitive to prolongation by both of the thrombin inhibitors than were the PT or WBCT assays. DUP 714 was found to a more potent anticoagulant than Argatroban. DUP 714 anticoagulated specimens (>2.2 micromol/l) did not clot for at least 2 days, whereas Argatroban preserved specimens (390 micromol/l) clotted within 5.5 h of collection. No statistically significant changes in the measurement of pH, PCO2, PO2, Na, K, ionized calcium, oxyhaemoglobin, deoxyhaemoglobin, methaemoglobin or carboxyhaemoglobin (measured using a Corning 288 Blood Gas/Electrolyte Analyzer and a Coming 270 CO-oximeter) were detected in DUP 714 (34 micromol/l) or Argatroban (390 micromol/l) anticoagulated whole blood specimens. In conclusion, DUP 714 and Argatroban are suitable anticoagulants for preserving blood prior to blood gas and electrolyte analyses.

Elevation of plasma antithrombin in the aging arteriosclerotic subject

Plasma samples from aging human subjects who had recovered from the trauma of a myocardial infarct and who were not on anticoagulant therapy were assayed for antithrombin activity. Antithrombin was assayed by methods which measure the ability of plasma to destroy an excess of thrombin, human or bovine in origin. Residual thrombin was quantitated either by clotting time or by hydrolysis of TAME ( p-toluene sulfonyl-l-arginine methyl ester-HCl). All methods showed unequivocally that plasma antithrombin increases up to 33% ( P < 0.002) in subjects who have fully recovered from a thrombotic episode.

Submitted on October 19, 1962

Use of thrombin inhibitors ex vivo allows critical care clinical chemistry and hematology testing on common specimens

OBJECTIVE

To evaluate the suitability of the thrombin inhibitors PPACK (D-phenylalanyl-L-prolyl-L-arginine chloromethylketone) or Argatroban for anticoagulation of blood prior to critical care testing of whole blood or plasma.

DESIGN AND METHODS

Initially we evaluated the effect of PPACK (0-200 microM) or Argatroban (0-590 microM) on serum glucose, urea, creatinine, calcium and electrolyte tests on two chemistry analyzers (Hitachi 717 and Ektachem 700XR). Subsequently plasma and serum from whole blood samples containing either heparin 15,000 IU/L or PPACK 75 microM or Argatroban 245 microM or no anticoagulant were tested and compared. We analysed and compared whole blood containing either PPACK 75 microM or Argatroban 245 microM or ethylenediaminetetraacetic acid (EDTA) using a Coulter STK-R hematology analyzer at intervals for 90 minutes.

RESULTS

The measurement of electrolytes, urea, creatinine, calcium or glucose was unaffected by either Argatroban or PPACK in either serum or anticoagulant-specific plasmas (p > 0.05). For specimens from individual donors, serum potassium was higher than plasma potassium, irrespective of anticoagulant used. Clinically equivalent complete blood counts were achieved for 60 minutes using EDTA-whole blood, or whole blood containing 245 microM Argatroban or 75 microM PPACK. However automated differential white cell counting was not reliable with either form of thrombin inhibitor-whole blood. Argatroban-anticoagulated blood demonstrated concentration and time dependent changes in platelet counts, whereas platelet counts were stable in blood containing 75 microM PPACK for up to 90 minutes.

CONCLUSION

Specimens of blood anticoagulated with either 75 microM PPACK or 245 microM Argatroban can be used for either critical care chemistry or hematology testing.

Anti-thrombogenic effects of 2-hydroxyethylmethacrylate-styrene block copolymer and argatroban in synthetic small-caliber vascular grafts in a rabbit inferior vena cava model

The high anti-thrombogenicity of 2-hydroxyethylmethacrylate (HEMA)-styrene block copolymer (HS) and argatroban-coated polyurethane tubes in a rabbit inferior vena cava model is reported. Polyurethane tubes (i.d. 3.0 mm, o.d. 4.0 mm, 12.5 cm) were implanted into the inferior vena cavas of 36 rabbits, weighing 2.5 to 3.5 kg, using the sleeve anastomotic technique. The animals were divided into four groups according to the type of prosthesis: uncoated tubes (Group 1, n = 9); HS-coated tubes (Group 2, n = 9); heparin-coated tubes (Group 3, n = 9); and HS/argatroban-coated tubes (Group 4, n = 9). Patency was evaluated at 1 week by ultrasonic flowmetry and microscopic examination of the grafts. Patency rates were 0 percent (0/9) in Group 1; 56 percent (5/9) in Group 2; 67 percent (6/9) in Group 3; and 100 percent (9/9) in Group 4 Groups 2 and 3 animals demonstrated statistically significantly superior patency compared to those of Group 1. Group 4 animals exhibited significantly superior anti-thrombogenicity compared to those of both Groups 1 and 2. Although Group 3 animals had an excellent patency rate, transmission and scanning electron microscopic views showed a thick protein layer and activated platelets adhering to the surface of Group 3 vessels. On the contrary, only a thin protein layer was noted in Group 4 animals. The HS-treated surface combined with the argatroban slow-release system exhibited excellent anti-thrombogenicity under venous-flow conditions.

Thrombin inhibition in an ex vivo model of porcine heart xenograft hyperacute rejection

Prominent components of vascularized xenograft rejection such as platelet activation and microvascular thrombosis may be dependent upon thrombin generation in vivo. To study potential therapeutic benefits of a synthetic low-molecular-weight thrombin inhibitor, SDZ MTH 958, in hyperacute porcine heart rejection by human blood ex vivo, a working model of hyperacute rejection of porcine by fresh, heparinized (6 microM/ml) human blood with or without 1 microM SDZ MTH 958 was used. Thrombin-antithrombin complexes (TAT) and prothrombin fragment F1.2 levels as markers of thrombin activation were determined, and biopsies from rejected hearts were analyzed by immunohistopathology. Control porcine hearts (n=8) underwent a rapid and consistent decline in cardiac output, ceasing function by 60 min. Experimental cardiac output values of 14 ml/g (SEM 1.2) were significantly higher than seen in controls (5 ml/g SEM 0.6) after 5 min of cardiac work, and prolonged survival times up to 120 min were noted (P<0.05). Activity of SDZ MTH 958 was confirmed by functional assays throughout perfusion. Levels of TAT and F1.2 increased consistently in control samples when compared with plasma samples containing SDZ MTH 958. Immunohistopathological examination confirmed diminished fibrin deposition, reduced leukocyte adherence to endothelium, impaired diapedesis and less tissue necrosis in the hearts perfused with SDZ MTH 958. SDZ MTH 958, in this xenoperfusion model, prolonged survival, enhanced function of the explanted organ, and improved histological features at the time of rejection. Effective and specific antagonism of thrombin may be useful as an adjunct therapy to complement inhibition for xenograft rejection

Transient overexpression of human 15-lipoxygenase in aortic endothelial cells enhances tumor necrosis factor-induced vascular cell adhesion molecule-1 gene expression

15-lipoxygenase (15-LO) expression in artery wall cells has been demonstrated during the development of atherosclerosis in various animal models. We examined whether the expression of 15-LO in aortic endothelial cells affects the gene expression of the adhesion molecule, vascular cell adhesion molecule-1 (VCAM-1). Transient transfection of human 15-LO cDNA into bovine aortic endothelial cells led to the expression of 15-LO protein and enzymatic activity. We studied the induction of VCAM-1 mRNA in these cells. 15-LO expressing cells showed no detectable levels of VCAM-1 message. However, when TNF was added to these cells there was a synergistic increase in VCAM-1 expression relative to cells that were transfected with control plasmid pcDNA I. Our data suggest that 15-LO expression in aortic endothelium may amplify the expression of VCAM-1 induced by inflammatory stimulus during atherogenesis.

Ultrastructural localization of heparin to human mast cells of the MCTC and MCT types by labeling with antithrombin III-gold

BACKGROUND

Mast cells derived from human skin and lung have been reported to produce heparin and chondroitin sulfate E proteoglycans. However, no information about the proteoglycans distribution among the different human mast cell types (MCTC and MCT) is available. Conjugates of antithrombin III-gold were used to assess the presence of heparin in both human mast cell subsets.

EXPERIMENTAL DESIGN

Thin sections of human and rodent tissues and dispersed cell preparations were labeled with the conjugate in the presence of saline, heparin, and chondroitin sulfates A and E and particle densities were measured over granules, perigranular regions, and extracellular space. Control sections were preincubated with heparinase, chondroitinase ABC, or buffer.

RESULTS

Labeling with antithrombin III-gold particles was detected in essentially all granules of human mast cells in skin (predominantly MCTC type), lung alveolar wall, and bowel mucosa (predominantly MCT type), but was negligible over human eosinophils. Consistent with the known distribution of heparin in rodent mast cells, strong labeling was observed over rat peritoneal connective tissue type mast cells, but not over mucosal mast cells in bowel mucosa of Nippostrongylus brasiliensis-infected rats (which contain chondroitin sulfate di-B) nor over mouse PT-18 mast cells (which contain chondroitin sulfate E). Mast cell labeling was preferentially blocked by exogenous heparin, and virtually abolished by heparinase but not chondroitinase ABC preincubation.

CONCLUSIONS

The data with rodent mast cells indicate that antithrombin III-gold labels cells that contain heparin, but not those that contain only over-sulfated chondroitin sulfates. Specificity of the procedure for detecting heparin is further demonstrated by inhibition of labeling after preincubation with heparinase and by competition with exogenous heparin. On this basis, we conclude that heparin is present in essentially all mast cells in normal skin, lung alveolar wall, and bowel mucosa. The presence of heparin in all human mast cells is different than for rodent mast cells, and probably accounts for the inability to clearly distinguish different human mast cell types from one another with histochemical stains based on proteoglycan content.

Adsorption of nafamostat mesilate by hemodialysis membranes

The adsorption of the anticoagulant nafamostat mesilate (FUT-175) by five different hemodialysis membranes was studied in vivo and in vitro. In vivo, FUT-175 was adsorbed strongly by a polyacrylonitrile (AN69) membrane and slightly by another polyacrylonitrile (J-PAN) membrane but not by Cuprophan (CU), hemophan (HE), or polymethylmethacrylate (PMMA) membranes during hemodialysis performed in 4 patients in whom FUT-175 was used as an anticoagulant. Only during hemodialysis using the AN69 membrane did FUT-175 not induce a significant prolongation of celite-activated coagulation time. In vitro studies showed that FUT-175 was adsorbed by the AN69, J-PAN, and PMMA membranes but not by the CU and HE membranes. Methylene blue, a dye that possesses a cationic portion in its chemical structure, stained AN69, J-PAN, and PMMA membranes. Since FUT-175 also possesses a cationic portion, we conclude that FUT-175 is adsorbed by negatively charged membranes via an ionic bond and is unsuited for use as an anticoagulant in hemodialysis using an AN69 membrane because of that membrane's marked capacity to adsorb FUT-175.

An evaluation of prothrombin assay method using MD805 by means of warfarin-treated plasma

The prothrombin assay method using the synthetic thrombin-inhibitor MD805 was standardized by fixing the concentrations of MD805 and S-2238 through their extinction coefficients (epsilon 333 for MD805 and epsilon 316 for S-2238). The prothrombin assay was directly proportional to the concentration of plasma up to 200% of the normal level and was not significantly influenced by the variety of three kinds of commercially available tissue thromboplastin preparations. Using plasma from Warfarin-treated patients and healthy volunteers, the correlation was studied between the prothrombin assay and the conventional coagulation tests such as Prothrombin time (INR), Thrombotest and Hepaplastintest (Normotest), and the correlation coefficients of -0.85, 0.81 and 0.94 were obtained respectively. FUT-175 and MD805 in the test plasma hardly affected the prothrombin assay in the concentration ranges which affected remarkably the conventional coagulation tests. These results indicated that the prothrombin assay was useful for monitoring the hyper- or hypoprothrombin state even on anticoagulant therapy. Eighteen healthy volunteers at 18 to 20 years old showed the mean and standard deviation of 0.96 +/- 0.097.

Crystallographic analysis at 3.0-A resolution of the binding to human thrombin of four active site-directed inhibitors

The mode of binding of four active-site directed inhibitors to human thrombin has been determined by x-ray crystallographic analysis. The inhibitors studied are benzamidine, PPACK, NAPAP, and MD-805, of which the last three are compounds evolved specifically to inhibit thrombin. Crystal structures were determined in the presence of both the inhibitor and the undecapeptide [des-amino Asp55]hirudin(55-65) which binds distant from the active site. Despite having significantly different chemical structures, NAPAP and MD-805 bind to thrombin in a very similar "inhibitor binding mode" which is not that expected by direct analogy with the binding of substrate. Both inhibitors bind to thrombin in a similar way as to trypsin, but thrombin has an extra loop, the "Tyr-Pro-Pro-Trp loop," not present in trypsin, which gives further binding interactions and is seen to move somewhat to accommodate binding of the different inhibitors. The fact that NAPAP and MD-805 require different stereochemistry for potent inhibition is demonstrated, and its structural basis clarified. The wealth of data on analogs and variants of these lead compounds is shown to be compatible with this inhibitor binding mode.

[Synthetic anticoagulant]

Anticoagulant as well as anti-platelet drugs are important medicines for the prophylaxis in various kinds of thrombotic diseases. However, the conventional anticoagulant drugs, heparin and coumarin congeners, have some disadvantages and limitations in clinical usage. Recently newly anticoagulants, both synthetic and recombinant, have been developing. They include synthetic thrombin inhibitor, recombinant hirudin, protein C and thrombomodulin. Here we reviewed synthetic thrombin inhibitor, Argipidine (MD805) in clinical trial and investigated its effect on thrombin catalyzed protein C activation on endothelial cells. Argipidine inhibited the protein C activating activity of thrombin on endothelium in a dose response manner. Next we examined the effect of Argipidine on thrombin-induced endothelin release from cultured endothelial cells. The augmentation of endothelin release from endothelial cells by thrombin was also inhibited by Argipidin. The effect was considered one of the advantage of this drug in the treatment of thrombosis. Recombinant thrombomodulin had potent antithrombotic effect on thrombin-induced acute thromboembolism in mice, suggesting that this may be expectant anticoagulant for DIC or thromboses in human.

Non-enzymatic glycation reduces heparin cofactor II anti-thrombin activity

The effects of non-enzymatic glycation on heparin cofactor II activity, at glucose concentrations which might be expected in physiological or diabetic conditions have been evaluated in this study. Radiolabelled glucose incorporation was associated with a loss of heparin cofactor anti-thrombin activity. The heparin cofactor heparin and dermatan sulfate-dependent inhibition of thrombin was significantly reduced, showing a remarkable decrease of the maximum second order rate constant. This study shows that heparin cofactor can be glycated at glucose concentrations found in the blood, and that this phenomenon produces a loss of heparin cofactor-antithrombin activity. These data suggest, furthermore, a possible link between heparin cofactor glycation and the pathogenesis of thrombosis in diabetes mellitus.

Low molecular weight heparin restores antithrombin III activity from hyperglycemia induced alterations

Alteration of antithrombin III (ATIII) activity, glycemia level dependent, exists in diabetes mellitus. In this study the ability of a low molecular weight heparin (LMWH) (Fluxum, Alfa-Wassermann S.p.A., Bologna, Italy), as well as unfractioned héparin, to preserve ATIII activity from glucose-induced alterations, both in vitro and in vivo, is reported. The subcutaneous and intravenous LMWH and heparin administration increases basal depressed ATIII activity in diabetic patients. Heparin shows an equivalent effect on both anti-IIa and anti-Xa activity of ATIII, while LMWH is more effective in preserving the anti-Xa activity. Similarity, heparin preserves ATIII activity from hyperglycemia-induced alterations, during hyperglycemic clamp, and LMWH infusion is able to preserve a significant amount of anti-Xa activity from glucose-induced alterations. Since diabetic patients show a high incidence of thrombotic accidents, LMWH appears to be a promising innovation for the prevention of diabetic thrombophylia.

Quantitation of 13-hydroxyoctadecadienoic acid (13-HODE) by radioimmunoassay

Antibodies against 13-hydroxyoctadecadienoic acid (13-HODE) were produced in rabbits by immunizing the animal with 13-HODE-thyroglobulin conjugate. The antibodies appeared to be rather specific for 13-HODE since other hydroxy fatty acids showed minimal crossreaction. The radioimmunoassay was capable of detecting 50 pg per assay tube and was applied to the study of the biosynthesis of 13-HODE in platelets and leukocytes. In contrast to reported findings from endothelial cells, A-23187, thrombin and collagen stimulated synthesis and release of 13-HODE from platelets. However, insignificant synthesis of 13-HODE was found in leukocytes following A-23187 stimulation. Exogenous addition of linoleic acid stimulated the synthesis of 13-HODE from both platelets and leukocytes. The majority of 13-HODE synthesized was found in the medium. These studies suggest that both types of blood cells possess active (omega-6) lipoxygenase. Platelets may use endogenously released linoleic acid to synthesize 13-HODE, whereas leukocytes may utilize linoleic acid released from other cell types for 13-HODE synthesis.

The refined 1.9 A crystal structure of human alpha-thrombin: interaction with D-Phe-Pro-Arg chloromethylketone and significance of the Tyr-Pro-Pro-Trp insertion segment

A stoichiometric complex formed between human alpha-thrombin and D-Phe-Pro-Arg chloromethylketone was crystallized in an orthorhombic crystal form. Orientation and position of a starting model derived from homologous modelling were determined by Patterson search methods. The thrombin model was completed in a cyclic modelling-crystallographic refinement procedure to a final R-value of 0.171 for X-ray data to 1.92 A. The structure is in full agreement with published cDNA sequence data. The A-chain, ordered only in its central part, is positioned along the molecular surface opposite to the active site. The B-chain exhibits the characteristic polypeptide fold of trypsin-like proteinases. Several extended insertions form, however, large protuberances; most important for interaction with macromolecular substrates is the characteristic thrombin loop around Tyr60A-Pro60B-Pro60C-Trp60D (chymotrypsinogen numbering) and the enlarged loop around the unique Trp148. The former considerably restricts the active site cleft and seems likely to be responsible for poor binding of most natural proteinase inhibitors to thrombin. The exceptional specificity of D-Phe-Pro-Arg chloromethylketone can be explained by a hydrophobic cage formed by Ile174, Trp215, Leu99, His57, Tyr60A and Trp60D. The narrow active site cleft, with a more polar base and hydrophobic rims, extends towards the arginine-rich surface of loop Lys70-Glu80 that probably represents part of the anionic binding region for hirudin and fibrinogen.

C-terminal peptide alcohol, acid and amide analogs of desulfato hirudin54-65 as antithrombin agents

Analogs of the antithrombin peptide hirudin54-65 with C-terminal modifications have been synthesized in order to examine the requirements for alpha-thrombin inhibition. The C-terminal residue, Gln65, could be replaced with L-amino acids or amino alcohols with neutral or charged hydrophilic side chains without greatly affecting the peptide's antithrombin potency as determined by inhibition of thrombin-induced clot formation in human plasma in vitro. Derivatives with D- or L-amino carboxamides at position 65 had significantly reduced potency, but still retained activity. Deletion of residue 65 with conversion of residue 64 to the amide or alcohol derivative resulted in a three-fold loss of potency. In addition to these results the solid-phase synthesis of peptide alcohols via direct displacement of p-nitrobenzhydrylideneisonitroso resin attached peptides with the desired C-terminal amino alcohol is reported.

Design, synthesis and antithrombin activity for conformationally restricted analogs of peptide anticoagulants based on the C-terminal region of the leech peptide, hirudin

Synthetic peptides cyclized via disulfide linkages have been synthesized as conformationally restricted analogs of a novel class of antithrombotic peptides that inhibit fibrinogen cleavage by binding to a non-enzymatic site on thrombin. Several conformational models for these inhibitors have been considered and cyclic analogs were synthesized to test their validity. Compounds designed on an alpha-helical model yielded several cyclic analogs that retained antithrombin activity. [D-Cys58, Cys61]-hirudin54-65, 5, and [D-Cys60, Cys63]-hirudin54-65, 6, had IC50 values of 26 and 30 microM, respectively, in an in vitro clot assay compared with a value of 3.7 microM for the linear hirudin54-65.

Assignment of the 1H-n.m.r. spectra of heparin and heparan sulphate

Resonances from the main repeating unit of heparan, ----4)-beta-D-GlcA-(1----4)-alpha-D-GlcNAc-(1----, have been assigned by using a sample of the capsular polysaccharide of E. coli K5. Comparison of the spectra of heparan sulphate samples before and after O- and/or N-desulphation, with re-N-acetylation or re-N-sulphation, allowed assignment of some of the H-1 doublets in terms of sequence effects. Chemical shifts for H-1 of unsulphated uronic acid residues are influenced by 6-sulphation of the nearest neighbour GlcN on the reducing side; those of GlcN residues vary according to whether they have IdoA or GlcA as the nearest neighbour on the reducing side. The H-1 doublets due to residues in the binding sequence for antithrombin have been assigned by comparison of the spectra of heparins having high and low affinities for immobilised antithrombin.