Purification and characterization of Protein C activator from Agkistrodon acutus Venom.

Protein C (PC) plays an important role in the balance of coagulation and anticoagulation. Thus, the detection of PC activity is diagnostically significant for patients with cardiovascular diseases. Presently, the key methods to detect PC activity are the chromogenic assay and activated partial thromboplastin time (APTT) test. PROTAC used in the chromogenic assay is isolated from Agkistrodon contortrix venom as protein C activator (PCA). However, the use of the chromogenic assay is limited because of the high price of PROTAC. In this study, PCA was successfully purified from Agkistrodon acutus venom (AAV) by ion-exchange and gel chromatography. PCA from AAV has a relative molecular mass of 24 kD, calculated from the measurement of 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The components of PCA were identified by MALDI-TOF/TOF-MS and mascot searches revealed that the coverage rate between PCA and zinc metalloproteinase AaPA from AAV was 21%. The chromogenic assay and APTT test were used to measure the enzymatic activity of PCA, and the results showed that PCA from AAV could specifically activate PC. In summary, the chromogenic assay described herein is highly sensitive and easy to perform.

[ACTIVATION OF PROTEIN C IN THE IN VITRO THROMBOLYSIS].

Physiological conditions of formation and subsequent lysis of thrombus were reconstituted in vitro in our research. Thrombus formation was initiated either by addition of exogenous thrombin or by contact of blood with anionic surface, which stimulates spontaneous coagulation of blood. Tissue plasminogen activator and/or protein C were previously added in the blood sample. The time of the beginning and total degradation of formed thrombi as well as the level of PC in lysates was controlled then. Only an addition of protein C alone or in combination with tissue plasminogen activator led to the most effective lysis of thrombi: their residual weight was 18% and 5% comparing to control. Addition of exogenous tissue plasminogen activator alone or in combination with protein C caused a 83% and 74% decrease of PC level in lysates of spontaneously formed thrombi, and 72% and 56% decrease for thrombi formed by thrombin, respectively. Without an addition of tissue plasminogen activator protein C level in lysates of thrombi formed by thrombin was 54% down on spontaneously formed thrombi. Thus, changes of PC concentration in isolated volume of clot seem to be controlled by thrombin at the stage of thrombus formation and by fibrinolytic system at the stage of fibrinolysis. Concentration of PC in lysates from clots formed by exogenous thrombin was decreasing over the next 10 hours of thrombolysis, which can also be the evidence of the interaction between the fibrinolytic and PC activation systems. A hypothesis is. formulated about an existence of endothelium-independent mechanism of PC activation in blood plasma with blood cells participation, which effectiveness increases in the process of thrombolysis.

Thrombin mutant W215A/E217A treatment improves neurological outcome and attenuates central nervous system damage in experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) is a neuroinflammatory disease characterized by demyelination and axonal damage of the central nervous system. The pathogenesis of MS has also been linked to vascular inflammation and local activation of the coagulation system, resulting in perivascular fibrin deposition. Treatment of experimental autoimmune encephalomyelitis (EAE), a model of human MS, with antithrombotic and antiinflammatory activated protein C (APC) reduces disease severity. Since recombinant APC (Drotecogin alfa), originally approved for the treatment of severe sepsis, is not available for human MS studies, we tested the hypothesis that pharmacologic activation of endogenous protein C could likewise improve the outcome of EAE. Mice were immunized with murine myelin oligodendrocyte glycoprotein (MOG) peptides and at the onset of EAE symptoms, were treated every other day with either WE thrombin (25 µg/kg; i.v.), a selective recombinant protein C activator thrombin analog, or saline control. Mice were monitored for changes in disease score until euthanized for ex vivo analysis of inflammation. Administration of WE thrombin significantly ameliorated clinical severity of EAE, reduced inflammatory cell infiltration and demyelination, suppressed the activation of macrophages comprising the CD11b + population and reduced accumulation of fibrin (ogen) in the spinal cord. These data suggest that symptomatic MS may respond to a treatment strategy that involves temporal pharmacological enhancement of endogenous APC generation.

Effects of activated protein C on the size of modeled ischemic focus and morphometric parameters of neurons and neuroglia in its perifocal zone.

The effects of activated protein C (APC) on the quantitative parameters of neurons and neuroglia in the perifocal zone of infarction induced in the left hemispheric cortex were studied in two groups of rats. Group 1 animals served as control (control infarction). Group 2 rats were injected with APC (50 µg/kg) in the right lateral cerebral ventricle 3 h after infarction was induced, and after 72 h the infarction size was evaluated and the neurons and neuroglia in the perifocal zone were counted. APC reduced the infarction size 2.5 times in comparison with the control and reduced by 16% the neuronal death in the perifocal zone layer V, causing no appreciable changes in layer III, and did not change the size of neuronal bodies but increased (by 11%) the size of neuronal nuclei in layer III. The protein maintained the sharply increased count of gliocytes in the perifocal zone of infarction and promoted their growth. Hence, APC protected the neurons from death in the ischemic focus by increasing the gliocyte count and stimulating the compensatory reparative processes.

Vascular immunotargeting to endothelial determinant ICAM-1 enables optimal partnering of recombinant scFv-thrombomodulin fusion with endogenous cofactor.

The use of targeted therapeutics to replenish pathologically deficient proteins on the luminal endothelial membrane has the potential to revolutionize emergency and cardiovascular medicine. Untargeted recombinant proteins, like activated protein C (APC) and thrombomodulin (TM), have demonstrated beneficial effects in acute vascular disorders, but have failed to have a major impact on clinical care. We recently reported that TM fused with an scFv antibody fragment to platelet endothelial cell adhesion molecule-1 (PECAM-1) exerts therapeutic effects superior to untargeted TM. PECAM-1 is localized to cell-cell junctions, however, whereas the endothelial protein C receptor (EPCR), the key co-factor of TM/APC, is exposed in the apical membrane. Here we tested whether anchoring TM to the intercellular adhesion molecule (ICAM-1) favors scFv/TM collaboration with EPCR. Indeed: i) endothelial targeting scFv/TM to ICAM-1 provides ~15-fold greater activation of protein C than its PECAM-targeted counterpart; ii) blocking EPCR reduces protein C activation by scFv/TM anchored to endothelial ICAM-1, but not PECAM-1; and iii) anti-ICAM scFv/TM fusion provides more profound anti-inflammatory effects than anti-PECAM scFv/TM in a mouse model of acute lung injury. These findings, obtained using new translational constructs, emphasize the importance of targeting protein therapeutics to the proper surface determinant, in order to optimize their microenvironment and beneficial effects.

Activated protein C cofactor function of protein S: a novel role for a γ-carboxyglutamic acid residue.

Protein S has an important anticoagulant function by acting as a cofactor for activated protein C (APC). We recently reported that the EGF1 domain residue Asp95 is critical for APC cofactor function. In the present study, we examined whether additional interaction sites within the Gla domain of protein S might contribute to its APC cofactor function. We examined 4 residues, composing the previously reported "Face1" (N33S/P35T/E36A/Y39V) variant, as single point substitutions. Of these protein S variants, protein S E36A was found to be almost completely inactive using calibrated automated thrombography. In factor Va inactivation assays, protein S E36A had 89% reduced cofactor activity compared with wild-type protein S and was almost completely inactive in factor VIIIa inactivation; phospholipid binding was, however, normal. Glu36 lies outside the ω-loop that mediates Ca(2+)-dependent phospholipid binding. Using mass spectrometry, it was nevertheless confirmed that Glu36 is γ-carboxylated. Our finding that Gla36 is important for APC cofactor function, but not for phospholipid binding, defines a novel function (other than Ca(2+) coordination/phospholipid binding) for a Gla residue in vitamin K-dependent proteins. It also suggests that residues within the Gla and EGF1 domains of protein S act cooperatively for its APC cofactor function.

Relative antithrombotic and antihemostatic effects of protein C activator versus low-molecular-weight heparin in primates.

The anticoagulant and anti-inflammatory enzyme, activated protein C (APC), naturally controls thrombosis without affecting hemostasis. We therefore evaluated whether the integrity of primary hemostasis was preserved during limited pharmacological antithrombotic protein C activator (PCA) treatment in baboons. The double-mutant thrombin (Trp215Ala/Glu217Ala) with less than 1% procoagulant activity was used as a relatively selective PCA and compared with systemic anticoagulation by APC and low-molecular-weight heparin (LMWH) at doses that inhibited fibrin deposition on thrombogenic segments of arteriovenous shunts. As expected, both systemic anticoagulants, APC (0.028 or 0.222 mg/kg for 70 minutes) and LMWH (0.325 to 2.6 mg/kg for 70 minutes), were antithrombotic and prolonged the template bleeding time. In contrast, PCA at doses (0.0021 to 0.0083 mg/kg for 70 minutes) that had antithrombotic effects comparable with LMWH did not demonstrably impair primary hemostasis. PCA bound to platelets and leukocytes, and accumulated in thrombi. APC infusion at higher circulating APC levels was less antithrombotic than PCA infusion at lower circulating APC levels. The observed dissociation of antithrombotic and antihemostatic effects during PCA infusion thus appeared to emulate the physiological regulation of intravascular blood coagulation (thrombosis) by the endogenous protein C system. Our data suggest that limited pharmacological protein C activation might exhibit considerable thrombosis specificity.

The respective and combined anticoagulant effects of recombinant human activated protein C, melagatran and heparins using CAT.

INTRODUCTION: Combinations of anticoagulants might be beneficial in some patients with sepsis, but most anticoagulants require specific clotting assays for monitoring. Thrombin generation assay, however, is a global function test of hemostasis. MATERIALS AND METHODS: We performed an in vitro investigation of the respective effects of recombinant human activated protein C (rhAPC) alone and in combination with either melagatran (a new direct thrombin inhibitor), unfractionated heparin (UH) or low molecular weight heparin (LMWH) in varying concentrations on the thrombin generation (TG) using the calibrated automated thrombography. RESULTS: RhAPC, UH, LMWH and melagatran dose-dependently prolonged the lag time and the time to peak, and significantly suppressed the endogenous thrombin potential (ETP). Combined application of rhAPC with either melagatran, UH or LMWH induced an additive prolongation of the lag time; this effect was more pronounced in a combination of rhAPC with UH or LMWH. CONCLUSION: In our in vitro study adding either melagatran, UH or LMWH augmented the capacity of rhAPC to suppress thrombin generation in human plasma. These findings suggest that patients with severe sepsis might benefit from a treatment with combinations of anticoagulant agents.

[Study on the mechanism of thrombosis by lupus anticoagulant inhibited protein C pathway].

OBJECTIVE: To study the mechanism of thrombosis in systemic lupus erythematosus (SLE) patients with protein C (PC) pathway inhibition by lupus anticoagulant(LA). METHODS: Phosphoethylamine(PE) dependent activated protein C (APC) inhibiting assay (modifed DRVVT) was used to observe the inhibition of APC activity after incubation of IgG from both normal and SLE patients with PE. RESULTS: The activity of anticoagulation of APC was augmented by PE. Proportionally to its concentration, LA could inhibit the PE dependent anticoagulation of APC. The inhibition of LA-IgG on APC in the LA positive SLE patients with thrombosis was stronger than that in LA negative non-thrombosis patients; but IgG has no effect on the APC activity in normal person. CONCLUSION: LA inhibiting the PC pathway by interfering with PE may be the important reason of thrombosis in SLE patients.

Expression and activity of thrombomodulin in human gingival epithelium: in vivo and in vitro studies.

Epidermal keratinocytes thrombomodulin (TM) has been shown to regulate thrombin at sites of cutaneous injury in addition to a role for epidermal differentiation. TM, a major anticoagulant proteoglycan of the endothelial cell membrane, is a thrombin receptor that acts as a co-factor for protein C activation. Thrombin has pro-inflammatory effects for periodontitis. However, little is known about TM in gingival tissue with periodontitis. We used immunohistochemistry to examine expression of TM in gingival epithelium from patients with periodontitis. In vitro, we observed TM expression at varying Ca2+ concentrations by confocal laser scanning microscopy, examined the expression of TM mRNA and tested TM co-factor activity. Furthermore, we measured TM concentration in gingival crevicular fluid (GCF) from 11 severe adult cases of periodontitis using enzyme-linked immunosorbent assay. Immunoreactive TM was present in gingival epithelium and junctional epithelium, and was reduced in inflamed gingival epithelium compared to healthy gingival epithelium. Ultrastructurally, TM, including microvilli, was observed on the cell membrane. TM localization in cells cultured in 0.09 mM Ca2+ differed from that in cells exposed to 1.2 mM Ca2+. Northern analysis demonstrated TM mRNA in gingival keratinocytes more than in human umbilical vein endothelial cells (HUVEC). Gingival keratinocytes also facilitated protein C activation by thrombin, although less strongly than HUVEC. TM in GCF at sites with bleeding on probing in patients was significantly elevated (p < 0.001, Student's t-test). TM in gingival epithelium may regulate thrombin activity at sites of coagulation and inflammation with periodontal disease, although inflammation may impair this regulation of thrombin.

Factor V enhances the cofactor function of protein S in the APC-mediated inactivation of factor VIII: influence of the factor VR506Q mutation.

Factor V and protein S are cofactors of activated protein C (APC) which accelerate APC-mediated factor VIII inactivation. The effects of factor V and protein S were quantitated in a reaction system in which plasma factor VIII was inactivated by APC and the loss of factor VIII activity was monitored in a factor X-activating system in which a chromogenic substrate was used to probe factor Xa formation. Factor V increased the rate of APC-mediated factor VIII inactivation in a dose-dependent manner in representative plasma samples with protein S or factor V deficiency, abnormal factor V (heterozygous or homozygous for factor VR506Q), or a combination of heterozygous protein S deficiency and heterozygous factor VR506Q. This effect was much less pronounced in the plasma samples with a decreased protein S level, but the impaired response in these plasmas was corrected by addition of protein S, indicating that both factor V and protein S are required for optimal inactivation of factor VIII by APC. The effects of factor V and protein S were also studied in a reaction system with purified proteins. APC-catalysed factor VIII inactivation was enhanced 3.7-fold in the presence of 1.1 nM factor V and 1.5-fold in the presence of 2.4 nM protein S. When both 1.1 nM factor V and 2.4 nM protein were present the rate enhancement was 11-fold. Factor V is a more potent cofactor than protein S, as can be concluded from the fact that 0.04 nM factor V gave the same stimulation as 2.4 nM protein S. Protein S lost its cofactor function after complexation with C4b binding protein, which indicates that it is free protein S that acts as a cofactor. To investigate the effect of the R506Q mutation in factor V on APC-mediated factor VIII inactivation, factor V was purified from the plasma of patients homozygous for factor VR506Q. In the absence of protein S, factor VR506Q did not enhance factor VIII inactivation by APC, but in the presence of 2.4 nM protein S a slight enhancement was observed. The APC cofactor activity of factor V was lost when factor V was activated with thrombin or with the factor V activator from Russell's viper venom. These data indicate that optimal inactivation of factor VIII by APC requires the presence of an intact factor V molecule and free protein S.

A modification of the APC resistance test and its application to the study of patients on coumarin therapy.

APC resistance appears to be caused, predominantly, by a mutation in coagulation factor V (nucleotide 1691: G to A). This phenomenon is usually studied by performing APTTs in the absence and presence of added APC. We studied a modification of the assay involving dilution of the test plasma in factor V deficient plasma, to render the assay more factor V specific. This modification was applied to 76 patients with venous thrombosis on coumarin treatment and to 45 controls. Two out of 45 controls (4.4%) showed abnormal results with the modified test. They also showed loss of factor V exon 10 Mnl I restriction site, associated to APC resistance. All remaining controls, with normal functional results by the modified assay, showed normal restriction profile. We detected 9 affected patients (11.8%), one of them homozygous or double heterozygous. In conclusion, the modified assay is very sensitive for factor V dependent APC resistance, and can successfully be applied to patients on coumarin therapy.

Activation of recombinant human protein C.

We have produced recombinant human Protein C (rHPC) in the milk of transgenic swine. After purification, we have analyzed the interaction of teh zymogen with Protac, thrombin/thrombomodulin and thrombin alone. The amidolytic and anticoagulant activities of rAPC after Protac activation were approximately 80% those of its human plasma counterpart. Upon the excision of the activation peptide by thrombin/thrombomodulin complex, both the natural and recombinant activation products had similar enzymatic and biological activities. This observation can be attributed to the difference in the mechanism of action between the two activators and structural differences between HPC and rHPC.

Clinical significance of activated protein C resistance as a potential marker for hypercoagulable state.

The activated protein C (APC)-resistance test is a simple and reliable method for detecting reduced sensitivity to the anticoagulant action of this protein. We investigated the sensitivity to APC in 180 Japanese controls and in 96 Japanese patients with venous and arterial thrombosis (28 with deep vein thrombosis; 13 with pulmonary thromboembolism; 41 with cerebral infarction; and 14 with coronary artery disease). All of the patient groups showed significantly reduced sensitivity to APC, reflected by the lower normalized APC-sensitivity ratio (n-APC-SR), as compared with healthy control. The APC-sensitivity ratio was negatively correlated with plasma activated factor VII levels. These results suggest that the low n-APC-SR is related to venous or arterial thrombotic disease. The APC resistance may serve as a potential marker for assessing the hypercoagulable state.