The TLR4-PAR1 Axis Regulates Bone Marrow Mesenchymal Stromal Cell Survival and Therapeutic Capacity in Experimental Bacterial Pneumonia

Bone marrow derived mesenchymal stromal cells have been shown to have significant therapeutic effects in experimental models of pneumonia and lung injury. The current study examined the roles of the toll like receptor 4 (TLR4) and protease activated receptor 1 (PAR1) pathways on mesenchymal stromal cell (MSC) survival and therapeutic activity in a murine model of pneumonia. MSCs from TLR4 -/- and R41Q-PAR1 mutated mice were isolated to test the effect of mutating these specific pathways on MSC survival when exposed to cytotoxic stimuli in vitro. An Escherichia coli pneumonia model was used to assess the effect of these specific pathways on MSC therapeutic activity in vivo. Our results showed that mutation of either the TLR4 or PAR1 pathways in MSCs impaired cell survival under conditions of inflammatory stress in vitro, and eliminated their therapeutic efficacy in vivo. Also, stimulation of the TLR4 pathway on MSCs led to secretion of low levels of prothrombin by MSCs, while disrupting the TLR4 pathway impaired canonical signaling through PAR1 in response to thrombin. Therefore, this study demonstrates that both TLR4 and PAR1 are required for MSC survival under inflammatory conditions in vitro and therapeutic capacity in vivo, and that the TLR4 pathway regulates signaling through PAR1 on MSCs. Stem Cells 2018;36:796-806.

The Frequency of Type I Heterozygous Protein S and Protein C Deficiency in 141 Unrelated Young Patients with Venous Thrombosis

The frequency of heterozygous protein C and protein S deficiency, detected by measuring total plasma antigen, in a group (n = 141) of young unrelated patients (<45 years old) with venous thrombotic disease was studied and compared to that of antithrombin III, fibrinogen, and plasminogen deficiencies. Among 91 patients not receiving oral anticoagulants, six had low protein S antigen levels and one had a low protein C antigen level. Among 50 patients receiving oral anticoagulant therapy, abnormally low ratios of protein S or C to other vitamin K-dependent factors were presented by one patient for protein S and five for protein C. Thus, heterozygous Type I protein S deficiency appeared in seven of 141 patients (5%) and heterozygous Type I protein C deficiency in six of 141 patients (4%). Eleven of thirteen deficient patients had recurrent venous thrombosis. In this group of 141 patients, 1% had an identifiable fibrinogen abnormality, 2% a plasminogen abnormality, and 3% an antithrombin III deficiency. Thus, among the known plasma protein deficiencies associated with venous thrombosis, protein S and protein C. deficiencies (9%) emerge as the leading identifiable associated abnormalities.

F-group bZIPs in barley-a role in Zn deficiency

Zinc (Zn) deficiency negatively impacts the development and health of plants and affects crop yield. When experiencing low Zn, plants undergo an adaptive response to maintain Zn homeostasis. We provide further evidence for the role of F-group transcription factors, AtbZIP19 and AtbZIP23, in responding to Zn deficiency in Arabidopsis and demonstrate the sensitivity and specificity of this response. Despite their economic importance, the role of F-group bZIPs in cereal crops is largely unknown. Here, we provide new insights by functionally characterizing these in barley (Hordeum vulgare), demonstrating an expanded number of F-group bZIPs (seven) compared to Arabidopsis. The F-group barley bZIPs, HvbZIP56 and HvbZIP62, partially rescue the Zn-dependent growth phenotype and ZIP-transporter gene regulation of an Arabidopsis bzip19-4 bzip23-2 mutant. This supports a conserved mechanism of action in adapting to Zn deficiency. HvbZIP56 localizes to the cytoplasm and nucleus when expressed in Arabidopsis and tobacco. Promoter analysis demonstrates that the barley ZIP transporters that are upregulated under Zn deficiency contain cis Zn-deficiency response elements (ZDREs). ZDREs are also found in particular barley bZIP promoters. This study represents a significant step forward in understanding the mechanisms controlling Zn responses in cereal crops, and will aid in developing strategies for crop improvement.

Improved hemostasis in hemophilia mice by means of an engineered factor Va mutant

BACKGROUND

Factor (F)VIIa-based bypassing not always provides sufficient hemostasis in hemophilia.

OBJECTIVES

To investigate the potential of engineered activated factor V (FVa) variants as bypassing agents in hemophilia A.

METHODS

Activity of FVa variants was studied in vitro using prothrombinase assays with purified components and in FV- and FVIII-deficient plasma using clotting and thrombin generation assays. In vivo bleed reduction after the tail clip was studied in hemophilia A mice.

RESULTS AND CONCLUSIONS

FVa mutations included a disulfide bond connecting the A2 and A3 domains and ones that rendered FVa resistant to inactivation by activated protein C (APC). '(super) FVa,' a combination of the A2-A3 disulfide (A2-SS-A3) to stabilize FVa and of APC-cleavage site mutations (Arg506/306/679Gln), had enhanced specific activity and complete APC resistance compared with wild-type FVa, FVL eiden (Arg506Gln), or FVaL eiden (A2-SS-A3). Furthermore, (super) FVa potently increased thrombin generation in vitro in FVIII-deficient plasma. In vivo, (super) FVa reduced bleeding in FVIII-deficient mice more effectively than wild-type FVa. Low-dose (super) FVa, but not wild-type FVa, decreased early blood loss during the first 10 min by more than two-fold compared with saline and provided bleed protection for the majority of mice, similar to treatments with FVIII. During the second 10 min after tail cut, (super) FVa at high dose, but not wild-type FVa, effectively reduced bleeding. These findings suggest that (super) FVa enhances not only clot formation but also clot stabilization. Thus, (super) FVa efficiently improved hemostasis in hemophilia in vitro and in vivo and may have potential therapeutic benefits as a novel bypassing agent in hemophilia.

Protein C supports platelet binding and activation under flow: role of glycoprotein Ib and apolipoprotein E receptor 2

BACKGROUND

Activated protein C (APC) regulates thrombin generation and inhibits apoptosis. Endothelial protein C receptor (EPCR)-bound protein C is activated by thrombomodulin-bound thrombin. APC inactivates coagulation factors (F)Va/VIIIa and generates cytoprotective signaling downstream of protease-activated receptor-1 (PAR-1). Binding of APC to EPCR both modifies and induces PAR-1 signaling, but it is unknown if protein C interacts with cells in an alternative manner.

AIM

To determine whether platelets possess receptors for protein C that can generate intracellular signals.

RESULTS

Immobilized protein C or APC supported platelet adhesion, lamellipodia formation and elevation of intracellular Ca(2+). Adhesion of platelets to protein C or APC was inhibited by soluble recombinant apolipoprotein E receptor 2' (ApoER2') and by receptor-associated protein (RAP), an inhibitor of the low-density lipoprotein receptor family. Under shear, surface-bound protein C supported platelet adhesion and aggregation in a glycoprotein (GP)Ibalpha-dependent manner, and adhesion of platelets to immobilized protein C was abrogated by the addition of soluble forms of ApoER2' or RAP. APC bound to purified recombinant ApoER2' or GPIbalpha.

CONCLUSIONS

Our data demonstrate that activation of platelets with rapid intracellular signaling caused by binding to immobilized protein C or APC occurs via mechanisms that require ApoER2 and GPIbalpha and that APC directly binds to purified ectodomains of the receptors ApoER2 and GPIbalpha. These findings imply that protein C and APC may directly promote cell signaling in other cells by binding to ApoER2 and/or GPIbalpha.

Activated protein C

Protein C is a vitamin K-dependent plasma protein zymogen whose genetic mild or severe deficiencies are linked with risk for venous thrombosis or neonatal purpura fulminans, respectively. Studies over past decades showed that activated protein C (APC) inactivates factors (F) Va and VIIIa to down-regulate thrombin generation. More recent basic and preclinical research on APC has characterized the direct cytoprotective effects of APC that involve gene expression profile alterations, anti-inflammatory and anti-apoptotic activities and endothelial barrier stabilization. These actions generally require endothelial cell protein C receptor (EPCR) and protease activated receptor-1. Because of these direct cytoprotective actions, APC reduces mortality in murine endotoxemia and severe sepsis models and provides neuroprotective benefits in murine ischemic stroke models. Furthermore, APC reduces mortality in patients with severe sepsis (PROWESS clinical trial). Although much remains to be clarified about mechanisms for APC's direct effects on various cell types, it is clear that APC's molecular features that determine its antithrombotic action are partially distinct from those providing cytoprotective actions because we have engineered recombinant APC variants with selective reduction or retention of either anticoagulant or cytoprotective activities. Such APC variants can provide relatively enhanced levels of either cytoprotective or anticoagulant activities for various therapeutic applications. We speculate that APC variants with reduced anticoagulant action but normal cytoprotective actions hold the promise of reducing bleeding risk because of attenuated anticoagulant activity while reducing mortality based on direct cytoprotective effects on cells.

Disulfide bond-stabilized factor VIII has prolonged factor VIIIa activity and improved potency in whole blood clotting assays

BACKGROUND

Genetically engineered disulfide bonds in B-domain-deleted factor (F) VIII variants (C662-C1828 FVIII and C664-C1826 FVIII) improve FVIIIa stability by blocking A2 domain dissociation because the new disulfide covalently links the A2 and A3 domains in FVIIIa.

AIM

The aim of this study was to assess the hypothesis that these variants have physiologically relevant properties because of prolonged thrombin generation and improved clot formation in whole blood.

METHODS

Clot-formation properties in whole blood were measured in thromboelastogram assays. The thrombin generation capabilities of the wild-type (WT) FVIII and FVIII variants were determined, and half-lives of FVIIIa variants were determined in fresh whole blood serum.

RESULTS

Thromboelastogram assays were performed with fresh, severe hemophilia whole blood reconstituted with variant and WT FVIII. The two disulfide bond-stabilized FVIII variants and WT FVIII had comparable clotting times at all studied concentrations. However, when compared with WT FVIII at low concentrations, the two FVIII variants required only 10% as much FVIII to achieve comparable clot-formation rates, clot-formation times and clot firmness values. The differences between WT and FVIII variants were quite pronounced at low FVIII concentrations. Measurement of the endogenous thrombin potential in FVIII-deficient plasma supplemented with these FVIII variants confirmed that the disulfide bond-stabilized variants supported high levels of thrombin generation at lower concentrations than did WT FVIII. During the course of clot generation in whole blood, the disulfide bond-stabilized FVIIIa variants had approximately 5-fold increased half-lives relative to WT FVIIIa.

CONCLUSION

C662-C1828 FVIII and C664-C1826 FVIII have physiologically relevant superior clot-forming properties in a whole blood environment, most likely due to the increased half-life of these FVIIIa variants in whole blood.

Intrinsic stability and functional properties of disulfide bond-stabilized coagulation factor VIIIa variants

BACKGROUND

The utility of purified coagulation factor (F)VIII for treatment of hemophilia A is limited in part by its instability following activation by thrombin, which is caused by spontaneous dissociation of the A2 domain from the activated FVIII (FVIIIa) heterotrimer. To prevent this A2 domain dissociation in FVIIIa, we previously engineered a cysteine pair (C664-C1826) in recombinant FVIII that formed a disulfide bond cross-linking the A2 domain in the heavy chain to the A3 domain in the light chain. This engineered disulfide bond resulted in a more stable FVIIIa.

AIMS

Here, we characterize the functional parameters of C664-C1828 FVIII and of a new disulfide bond-stabilized FVIII (C662-C1828 FVIII).

METHODS

In order to assess whether these FVIII variants might be good candidates for a new therapeutic agent to treat hemophilia A, we investigated a variety of functional parameters that might affect the in vivo properties of the variants, including half-life of disulfide bond-stabilized FVIII and FVIIIa and the potency of these FVIIIa molecules in the FXase complex.

RESULTS

Both disulfide bond-stabilized variants had improved affinity for von Willebrand factor (VWF). In studies of FX activation by purified FIXa and FVIIIa, C662-C1828 FVIIIa had normal activity while C664-C1826 FVIIIa had reduced activity. Both C664-C1826 FVIIIa and C662-C1828 FVIIIa were inactivated by activated protein C (APC) but the rates of inactivation were different.

CONCLUSION

Overall, the specific location of the disulfide bridge between the A2 and A3 domains appears to affect functional properties of FVIIIa. In summary, introduction of engineered interdomain disulfides results in FVIIIa variants that resist spontaneous loss of activity while retaining susceptibility to APC proteolytic inactivation and maintaining VWF binding.

Limited generation of activated protein C during infusion of the protein C activator thrombin analog W215A/E217A in primates

Anticoagulation with activated protein C (APC) reduces the mortality of severe sepsis. We investigated whether the circulating protein C (PC) pool could be utilized for sustained anticoagulation by endogenous APC. To generate APC without procoagulant effects, we administered the anticoagulant thrombin mutant W215A;E217A (WE) to baboons. In preliminary studies, administration of high dose WE (110 microg kg(-1) i.v. bolus every 120 min; n = 2) depleted PC levels by 50% and elicited transient APC bursts and anticoagulation. The response to WE became smaller with each successive injection. Low dose WE infusion (5 microg kg(-1) loading + 5 microg kg(-1) h(-1) infusion; n = 5) decreased plasma PC activity by 15%, from 105% to 90%, to a new equilibrium within 60 min. APC levels increased from 7.5 ng mL(-1) to 86 ng mL(-1) by 40 min, then declined, but remained elevated at 34 ng mL(-1) at 240 min. A 22-fold higher dose WE (n = 5) decreased PC levels to 60% by 60 min without significant further depletion in 5 h. The APC level was 201 ng mL(-1) at 40 min and decreased to 20 ng mL(-1) within 120 min despite continued activator infusion. Co-infusion of WE and equimolar soluble thrombomodulin (n = 5) rapidly consumed about 80% of the PC pool with significant temporal increase in APC generation. In conclusion, low-grade PC activation by WE produced sustained, clinically relevant levels of circulating APC. Limited PC consumption in WE excess was consistent with the rapid depletion of cofactor activity before depletion of the PC zymogen. Reduced utilization of circulating PC might have similar mechanism in some patients.

Decreased plasma sensitivity to activated protein C by oral contraceptives is associated with decreases in plasma glucosylceramide

Oral contraceptive (OC) use increases venous thrombosis (VTE) risk and causes activated protein C (APC) resistance. Plasma glucosylceramide (GlcCer) deficiency is associated with VTE and GlcCer functions as an APC anticoagulant cofactor. Because estradiol decreases GlcCer in cultured cells, we hypothesized OC use would decrease plasma GlcCer and contribute to APC resistance. In a pilot study, seven female adults alternatively took second and third generation OCs and plasma samples were analyzed for GlcCer using high performance liquid chromatography and for APC sensitivity using modified prothrombin time assays. Second and third generation OC usage decreased the APC sensitivity ratio by 8.1% +/- 4.7% (P = 0.004) and 11.7% +/- 8.2% (P = 0.013) and plasma GlcCer levels by 10.1% +/- 6.8% (P = 0.008) and 11.0% +/- 5.1% (P = 0.002), respectively. The plasma GlcCer level correlated with the sensitivity of plasma to APC (P = 0.017, r = 0.51, n = 21 plasma samples). Thus, both second and third generation OC usage decreased plasma GlcCer which could cause a reduction in the plasma sensitivity to APC/protein S, thereby potentially increasing VTE risk.

Cholesterol enhances phospholipid-dependent activated protein C anticoagulant activity

The influence of cholesterol on activated protein C (APC) anticoagulant activity in plasma and on factor Va inactivation was investigated. Anticoagulant and procoagulant activities of phosphatidylcholine/phosphatidylserine (PC/PS) vesicles containing cholesterol were assessed in the presence and absence of APC using factor Xa-1-stage clotting and factor Va inactivation assays. Cholesterol at approximate physiological membrane levels (30%) in PC/PS (60%/10% w/w) vesicles prolonged the factor Xa-1-stage clotting time dose-dependently in the presence of APC but not in the absence of APC. APC-mediated cleavage of purified recombinant factor Va variants that were modified at specific APC cleavage sites (Q306/Q679-factor Va; Q506/Q679-factor Va) was studied to define the effects of cholesterol on APC cleavage at R506 and R306. When compared to control PC/PS vesicles, cholesterol in PC/PS vesicles enhanced factor Va inactivation and the rate of APC cleavage at both R506 and R306. Cholesterol also enhanced APC cleavage rates at R306 in the presence of the APC cofactor, protein S. In summary, APC anticoagulant activity in plasma and factor Va inactivation as a result of cleavages at R506 and R306 by APC is markedly enhanced by cholesterol in phospholipid vesicles. These results suggest that cholesterol in a membrane surface may selectively enhance APC activities.

Thrombophilic factors are not the leading cause of thrombosis in Behçet's disease

BACKGROUND

Venous and arterial thromboses occur in patients with Behçet's disease and are associated with significant morbidity and mortality. Studies on a possible association between the occurrence of thrombosis and thrombophilia in patients with this disease have been controversial.

OBJECTIVE

To determine the prevalence of the most common thrombophilias and dyslipidaemia in patients with Behçet's disease with and without thrombosis.

METHODS

Blood samples from 107 patients with Behçet's disease who had or did not have thrombosis were analysed for factor V Leiden, prothrombin G20210A polymorphism, methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism, factor VIII level, homocysteine and C reactive protein concentrations, dyslipidaemia, and plasma glucosylceramide.

RESULTS

There was no difference between patients with and without thrombosis in the prevalence of prothrombin G20210A polymorphism, factor V Leiden, homozygous MTHFR C677T, or plasma concentrations of homocysteine, C reactive protein, or glucosylceramide. In contrast, patients with thrombosis were found to have significantly higher mean levels of factor VIII, total cholesterol, triglycerides, VLDL cholesterol, and apolipoproteins B-100, C-II, and C-III than those without thrombosis. Multistepwise logistic regression analysis showed that triglyceride concentration was the best marker associated with thrombosis (p = 0.008), with an estimated odds ratio of 1.58 (95% confidence interval, 1.09 to 2.30) for a difference of 40 mg/dl.

CONCLUSIONS

Thrombophilia does not seem to play a major role in the tendency to thrombosis in Behçet's disease. However, dyslipidaemia, predominantly hypertriglyceridaemia, might be a risk factor.

Effect of hirudin vs heparin on haemostatic activity in patients with acute coronary syndromes; the GUSTO-IIb haemostasis substudy

AIMS

We compared the effects of hirudin and heparin on thrombin generation and activity among 350 patients with acute coronary syndromes enrolled in the GUSTO-IIb trial.

METHODS AND RESULTS

We obtained blood at baseline; at 4, 8, and 24h into infusion; at drug termination; and 6 and 24h after termination. We assayed for thrombin activity (fibrinopeptide A, activated protein C, thrombin-antithrombin complex), thrombin generation (prothrombin fragment 1.2), and platelet activation (platelet factor 4). Median baseline fibrinopeptide A and platelet factor 4 levels were elevated. Thrombin formation tended to increase with hirudin and decrease with heparin; by 8h into infusion, thrombin formation was significantly less for heparin (P<0.01). Most patients showed reduced thrombin activity and platelet activation during infusion of either agent. Hirudin-assigned patients had significantly lower fibrinopeptide A levels during infusion. Six h post-termination, both groups had increased thrombin activity. Thrombin formation was increased in heparin patients (P<0.0001), significantly more than with hirudin (P=0.005). Higher values of haemostasis markers tended to be associated with poorer 30-day outcomes.

CONCLUSION

Although hirudin did not prevent generation of new thrombin, it appeared to inhibit thrombin activity more than did heparin and produced slower increases in thrombin formation after discontinuation. The reelevation of thrombotic markers after stopping intravenous antithrombin therapy and the tendency toward increased thrombotic events with post-treatment increases in marker levels suggest an ongoing, clinically significant prothrombotic state. These results raise the possibility of improving on current antithrombotics by preventing thrombin generation and thrombin activity and by sustained suppression of the prothrombotic state.

Interaction of human plasma kallikrein and its light chain with C.hivin.1 inhibitor

The light chain of human plasma kallikrein contains the enzymatic active site. The inactivation of kallikrein and of its isolated light chain by C1 inhibitor was investigated to assess the functional contributions of the heavy-chain region of kallikrein and of high molecular weight kininogen to this reaction. The second-order rate constants for the inactivation of kallikrein or its light chain were respectively 2.7 X 10(6) and 4.0 X 10(6) M -1 min -1. High molecular weight kininogen did not influence the rate of kallikrein inactivation. The nature of the complexes formed between kallikrein or its light chain and C1 inhibitor was studied by using sodium dodecyl sulfate (SDS) gradient polyacrylamide slab gel electrophoresis. Kallikrein as well as its light chain combined with C1 inhibitor to form stable stoichiometric complexes that were not dissociated by SDS and that exhibited apparent molecular weights (Mr's) of 185 000 and 135 000, respectively, on nonreduced SDS gels. Reduction of the kallikrein-C1 inhibitor complex gave a band at Mr 135 000 that comigrated with the complex seen for the light chain-C1 inhibitor complex. During the inactivation of both kallikrein and its light chain, a Mr 94 000 fragment of C1 inhibitor was formed which was unable to inactivate or bind kallikrein or its light chain. Kallikrein inactivated by diisopropyl phosphofluoridate did not form SDS-stable complexes with C1 inhibitor. These results demonstrate that the functional binding site for C1 inhibitor is localized in the light chain of kallikrein.(ABSTRACT TRUNCATED AT 250 WORDS)

Causes of thrombophilia yet to be discovered: a personal view

Prediction of genetic risk factors for venous thrombosis might best be left for only wise soothsayers. Nonetheless, based on the principle that hypercoagulability, either systemic or vascular-bed-specific, predisposes to thrombosis, we venture some speculations. Hyperactivity of platelets could be caused by elevated numbers of surface glycoproteins or defective signal transduction pathways. The reported efficacy of aspirin for prevention of venous thrombosis is consistent with the prediction that certain platelet defects may increase the risk of venous thrombosis. Hyperlipidaemia is associated with hypercoagulability, and lipoproteins exhibit procoagulant (e.g. triglyceride-rich particles and oxidized low-density lipoprotein) or anticoagulant (e.g. high-density-lipoprotein's cofactor activity for activated protein C/protein S) activities. This leads to the prediction that defects in lipids and/or lipoproteins may increase the risk for venous thrombosis. Interestingly, statins were recently reported to prevent the occurrence of venous thrombosis in the HERS (Heart and Estrogen/Progestin Replacement) trial. We also predict that new defects in the protein C pathway (e.g. defective endothelial protein C receptor or novel cofactors for activated protein C/protein S) will be discovered. Risk factors affecting the majority of patients will likely involve new single nucleotide polymorphisms (SNPs) like the factor V nt G1691A or prothrombin nt G20210A SNPs. The Human Genome Project will soon accelerate discovery of new SNPs that are risk factors for venous thrombosis.

Plasma lipoproteins, hemostasis and thrombosis

Regulation of hemostasis and thrombosis involves numerous plasma factors that contribute to procoagulant and anticoagulant pathways. Lipid-containing surfaces provide sites where both procoagulant and anticoagulant enzymes, cofactors and substrates are assembled to express their activities. Plasma and lipoproteins can contribute to either procoagulant or anticoagulant reactions. Procoagulant lipids/lipoproteins include triglyceride-rich particles in plasma and oxidized low density lipoprotein (LDL) which can accelerate activation of prothrombin, factor X and factor VII. Potentially anticoagulant lipids and lipoproteins, each of which enhances inactivation of factor Va by activated protein C, include phosphatidylethanolamine, cardiolipin, the neutral glycosphingolipids glucosylceramide and Gb3 ceramide (CD77), and high density lipoprotein (HDL). Remarkably, treatment of hyperlipidemia with statins not only lowers lipids but also provides antithrombotic effects whose mechanisms remain to be clarified. We hypothesize that procoagulant and anticoagulant lipids and lipoproteins in plasma may contribute to a Yin-Yang balance that helps influence the up-regulation and down-regulation of thrombin generation.

Activated protein C and inflammation in human myocardium after heart surgery

To assess possible interactions between inflammation and activation of the anticoagulant protein C system during post-ischemic reperfusion protein C, APC, neutrophil L-selectin expression and myocardial myeloperoxidase activity (MPO) were measured in 19 patients undergoing cardiopulmonary bypass. After reperfusion for 10 min, APC to protein C ratio (APC/PC) increased from pre-reperfusion value 1.43 +/- 0.12 (mean +/- SEM) to 2.25 +/- 0.29, p = 0.015. Negative correlations were observed between APC/PC and MPO activity (Spearman r -0.64, p = 0.007) and APC/PC and neutrophil L-selectin expression (r = -0.7, p = 0.007, demonstrating that post-ishemic protein C activation was associated with decreased neutrophil tissue sequestration. Thus, physiological protein C activation may be involved in regulation of the inflammatory injury during reperfusion of human ischemic coronary circulation.

Anti-inflammatory, antithrombotic, and neuroprotective effects of activated protein C in a murine model of focal ischemic stroke

BACKGROUND

Activated protein C (APC) contributes to systemic anticoagulant and anti-inflammatory activities. APC may reduce organ damage by inhibiting thrombin generation and leukocyte activation. Neutrophils and cerebrovascular thrombosis contribute to ischemic neuronal injury, suggesting that APC may be a potential protective agent for stroke.

METHODS AND RESULTS

We examined the effects of APC in a murine model of focal ischemia. After middle cerebral artery occlusion/reperfusion, the average survival time in controls was 13.6 hours. Animals that received purified human plasma-derived APC 2 mg/kg IV either 15 minutes before or 10 minutes after stroke induction survived 24 hours and were killed for neuropathological analysis. APC 2 mg/kg given before or after onset of ischemia restored cerebral blood flow, reduced brain infarct volume (59% to 69%; P:<0.003) and brain edema (50% to 61%; P:<0.05), eliminated brain infiltration with neutrophils, and reduced the number of fibrin-positive cerebral vessels by 57% (P:<0.05) and 25% (nonsignificant), respectively. The neuroprotective effect of APC was dose-dependent and associated with significant inhibition of ICAM-1 expression on ischemic cerebral blood vessels (eg, 61% inhibition with 2 mg/kg APC). Intracerebral bleeding was not observed with APC.

CONCLUSIONS

APC exerts anti-inflammatory, antithrombotic, and neuroprotective effects in stroke. Central effects of APC are likely to be related to improved maintenance of the blood-brain barrier to neutrophils and to reduced microvascular obstructions and fibrin deposition.

Plasma glucosylceramide deficiency as potential risk factor for venous thrombosis and modulator of anticoagulant protein C pathway

To assess the relationship between venous thrombosis and plasma glucosylceramide (GlcCer) or phosphatidylethanolamine (PE), plasma levels of GlcCer and PE were determined for 70 venous thrombosis patients referred for evaluation and 70 healthy blood donors. The mean GlcCer level, but not the PE level, was lower in patients versus controls (4.9 vs 6.5 microg/mL [P =.0007] and 66 vs 71 microg/mL [P =.48], respectively). As a measure of relative risk, the odds ratio for deep vein thrombosis in subjects with GlcCer levels below the 10th percentile of controls was 5.7 (95% CI, 2.3-14). To assess the influence of glycolipids on anticoagulant response to activated protein C (APC):protein S in modified prothrombin time assays, the effects of depleting endogenous plasma GlcCer by glucocerebrosidase treatment or of adding exogenous purified GlcCer or other neutral glycolipids to plasma were tested. Glucocerebrosidase treatment reduced plasma sensitivity to APC:protein S in parallel with GlcCer reduction. Exogenously added GlcCer and the homologous Glc-containing globotriaosylceramide (Gb3Cer), but not galactosylceramide, dose-dependently prolonged clotting times of normal plasma in the presence, but not absence, of APC:protein S, which suggests that GlcCer or Gb3Cer can enhance protein C pathway anticoagulant activity. In studies using purified proteins, inactivation of factor Va by APC:protein S was enhanced by GlcCer alone and by GlcCer in multicomponent vesicles containing phosphatidylserine and phosphatidylcholine. These results suggest that the neutral glycolipids GlcCer and Gb3Cer may directly contribute to the anticoagulant activity of the protein C pathway and that deficiency of plasma GlcCer may be a risk factor for venous thrombosis. (Blood. 2001;97:1907-1914)

Potent anti-Trypanosoma cruzi activities of oxidosqualene cyclase inhibitors

Trypanosoma cruzi is the protozoan agent that causes Chagas' disease, a major health problem in Latin America. Better drugs are needed to treat infected individuals. The sterol biosynthesis pathway is a potentially excellent target for drug therapy against T. cruzi. In this study, we investigated the antitrypanosomal activities of a series of compounds designed to inhibit a key enzyme in sterol biosynthesis, oxidosqualene cyclase. This enzyme converts 2,3-oxidosqualene to the tetracyclic product, lanosterol. The lead compound, N-(4E,8E)-5,9, 13-trimethyl-4,8, 12-tetradecatrien-1-ylpyridinium, is an electron-poor aromatic mimic of a monocyclized transition state or high-energy intermediate formed from oxidosqualene. This compound and 27 related compounds were tested against mammalian-stage T. cruzi, and 12 inhibited growth by 50% at concentrations below 25 nM. The lead compound was shown to cause an accumulation of oxidosqualene and decreased production of lanosterol and ergosterol, consistent with specific inhibition of the oxidosqualene cyclase. The data demonstrate potent anti-T. cruzi activity associated with inhibition of oxidosqualene cyclase.

Preliminary noninvasive back-pressure recordings of bladder pressure

Obstructive voiding is best evaluated with urodynamics, including bladder pressure and urine flow rates. Until recently, the recording of bladder pressure required the use of a urethral catheter. In preliminary observations, a noninvasive back-pressure method using an external condom catheter has been introduced to determine bladder pressure. This device uses a side tube for pressure recording and an outlet tube that is clamped for short periods of time. We have investigated design criteria for back-pressure recording techniques. In the laboratory setting using a plastic model, we determined that a low compliance condom is needed. In addition, a back flow of fluid during the clamping procedure helps to obtain quick back pressures and facilitates evaluation of pressure when low flow rates are present. These modified condom devices were evaluated in four male subjects. Back pressures were not statistically different than bladder pressures recorded with a urethral catheter. The use of back pressures in the evaluation for obstructive uropathy can be enhanced by using a pressure and flow nomogram.

Anticoagulant dysfunction of human Arg352Trp-activated protein C caused by defective factor Va inactivation

The dysfunctional mutant R352W-protein C was found in two patients with venous thrombosis. The mutant R352A-protein C was constructed to define the contribution of charge/size of the residue at 352 on protein C (chymotrypsin numbering 187). Compared with wild type-protein C, R352W-protein C showed no difference in activation by thrombin-thrombomodulin or alpha-thrombin. However, R352W-activated protein C (APC) anticoagulant activity (aPTT assay) was reduced to approximately 65%. Although the catalytic efficiency of R352W-APC towards the oligopeptide substrate S-2366 was unperturbed, factor Va and R506Q-factor Va were not efficiently inactivated by R352W-APC compared with wild type-APC. R352A-APC showed reduced anticoagulant activity and reduced efficiency in factor Va inactivation and in factor VIIIa-inactivation in the presence of protein S. These observations suggest that the dysfunction of R352W-APC in factor Va inactivation may be one of the mechanisms leading to venous thrombosis in affected patients and that R352 plays an important role in the physiological functioning of APC.

Chemical synthesis and spontaneous folding of a multidomain protein: anticoagulant microprotein S

Because of recent high-yield native ligation techniques, chemical synthesis of larger multidomain bioactive proteins is rapidly coming within reach. Here we describe the total chemical synthesis of a designed "microprotein S," comprising the gamma-carboxyglutamic acid-rich module, the thrombin-sensitive module, and the first epidermal growth factor-like module of human plasma protein S (residues 1-116). Synthetic microprotein S expressed anticoagulant cofactor activity for activated protein C in the down-regulation of blood coagulation, and the anticoagulant activity of microprotein S was not neutralized by C4b-binding protein, a natural inhibitor of native protein S in plasma. The correct folding of this complex multidomain protein was enhanced compared with individual modules because the gamma-carboxyglutamic acid-rich module and the thrombin-sensitive module markedly facilitated correct folding of the first epidermal growth factor-like module compared with folding of the first epidermal growth factor-like module alone. These results demonstrate that total chemical synthesis of proteins offers an effective way to generate multidomain biologically active proteins.

Three-dimensional model of coagulation factor Va bound to activated protein C

A complete molecular model of blood coagulation factor Va (FVa) bound to anticoagulant activated protein C (APC) and to a phospholipid membrane was constructed. The three homologous A domains and the two homologous C domains of FVA were modeled based on the X-ray crystallographic structures of ceruloplasmin and C2 domain of factor V, respectively. The final arrangement of the five domains in the complete FVa model bound to a membrane incorporated extensive published experimental data. FVa binds the phospholipid membrane through its C2 domain while the A-domain trimer is located from 40 through 100 A above the membrane plane. From our model we infer a probable role for metal ions at the interface between FVa light and heavy chains, provide an explanation for the slower APC cleavage at Arg306 relative to Arg506, and predict specific interactions between positively and negatively charged exosites in APC and FVa, respectively.

Conformational changes in activated protein C caused by binding of the first epidermal growth factor-like module of protein S

The first epidermal growth factor-like module of human plasma protein S (EGF1, residues 76-116) was chemically synthesized and tested for its ability to inhibit the anticoagulant cofactor activity of protein S for the anticoagulant protease, activated protein C (APC). EGF1 completely inhibited the stimulation of APC activity by protein S in plasma coagulation assays, with 50% inhibition at approx. 1 microM+ EGF1, suggesting direct binding of EGF1 to APC. To investigate a direct interaction between EGF1 and APC, fluorescence resonance energy transfer (FRET) experiments were employed. APC labelled in the active site with fluorescein as the donor, and phospholipid vesicles containing octadecylrhodamine as the acceptor, showed that EGF1 association with APC caused an increase in energy transfer consistent with a relocation of the active site of APC from 94 A (9.4 nm) to 85 A above the phospholipid surface (assuming kappa(2)=2/3). An identical increase in energy transfer between the APC active site-bound fluorescein and phospholipid-bound rhodamine was obtained upon association of protein S or protein S-C4b-binding protein complex with APC. The latter suggests the presence of a ternary complex of protein S-C4b-binding protein with APC on the phospholipid surface. To confirm a direct interaction of EGF1 with APC, rhodamine was covalently attached to the alpha-N-terminus of EGF1, and binding of the labelled EGF1 to APC was directly demonstrated using FRET. The data suggested a separation between the active site of APC and the N-terminus of EGF1 of 76 A (kappa(2)=2/3), placing the APC-bound protein S-EGF1 close to, but above, the phospholipid surface and near the two EGF domains of APC. Thus we provide direct evidence for binding of protein S-EGF1 to APC and show that it induces a conformational change in APC.

The autolysis loop of activated protein C interacts with factor Va and differentiates between the Arg506 and Arg306 cleavage sites

The anticoagulant human plasma serine protease, activated protein C (APC), inactivates blood coagulation factors Va (FVa) and VIIIa. The so-called autolysis loop of APC (residues 301-316, equivalent to chymotrypsin [CHT] residues 142-153) has been hypothesized to bind FVa. In this study, site-directed mutagenesis was used to probe the role of the charged residues in this loop in interactions between APC and FVa. Residues Arg306 (147 CHT), Glu307, Lys308, Glu309, Lys311, Arg312, and Arg314 were each individually, or in selected combinations, mutated to Ala. The purified recombinant protein C mutants were characterized using activated partial thromboplastin time (APTT) clotting assays and FVa inactivation assays. Mutants 306A, 308A, 311A, 312A, and 314A had mildly reduced anticoagulant activity. Based on FVa inactivation assays and APTT assays using purified Gln506-FVa and plasma containing Gln506-FV, it appeared that these mutants were primarily impaired for cleavage of FVa at Arg506. Studies of the quadruple APC mutant (306A, 311A, 312A, and 314A) suggested that the autolysis loop provides for up to 15-fold discrimination of the Arg506 cleavage site relative to the Arg306 cleavage site. This study shows that the loop on APC of residues 306 to 314 defines an FVa binding site and accounts for much of the difference in cleavage rates at the 2 major cleavage sites in FVa. (Blood. 2000;96:585-593)

Prognostic value of protein C concentrations in neutropenic patients at high risk of severe septic complications

OBJECTIVE

To assess the prognostic value of protein C, endogenous activated protein C, and D-dimer concentrations in patients at high risk of developing severe septic complications secondary to cytostatic chemotherapy.

DESIGN

Prospective, comparative, single-center study.

SETTING

Specialized ward for treating patients with acute leukemia and associated intensive care unit at a university hospital.

SUBJECTS

Twenty-six consecutive patients who developed either severe sepsis (n = 13) or septic shock (n = 13) during chemotherapy-induced neutropenia (leukocytes <1,000/microL).

INTERVENTION

None, other than standard care.

MEASUREMENTS AND MAIN RESULTS

Baseline blood samples were obtained from 97 adult patients treated with intensive cytostatic chemotherapy. Serial blood sampling was performed in 62 of 97 patients who developed fever (>38.3 degrees C). Thirteen patients progressed to severe sepsis and 13 patients to septic shock. Protein C, endogenous activated protein C, and D-dimer were measured in these 26 patients. At fever onset, protein C concentrations decreased from normal baseline concentrations and were significantly lower in the group of patients who progressed to septic shock compared with those who developed severe sepsis (medians for protein C activity: 23.1% vs. 69.5%; p = .0003). The median elapsed time between detection of fever and the diagnosis of severe sepsis or septic shock was 16 hrs and 12 hrs, respectively. All septic shock patients died, whereas patients who progressed only to severe sepsis survived.

CONCLUSIONS

Septic shock in neutropenic patients is associated with increased protein C consumption. The data demonstrate that the coagulation cascade is activated and produces a hypercoagulable state before the onset of clinical symptoms of severe sepsis and septic shock. Low protein C concentrations at the onset of fever and before the onset of clinical symptoms of severe sepsis or septic shock may have prognostic value in predicting an unfavorable outcome. Protein C measurements may help identify patients at risk in an early phase of neutropenic sepsis. It is also attractive to speculate that because low protein C concentrations were seen in these patients, protein C replacement may be beneficial in sepsis.

Inactivation of active thrombin-activable fibrinolysis inhibitor takes place by a process that involves conformational instability rather than proteolytic cleavage

Thrombin-activable fibrinolysis inhibitor (TAFI) is present in the circulation as an inactive zymogen. Thrombin converts TAFI to a carboxypeptidase B-like enzyme (TAFIa) by cleaving at Arg(92) in a process accelerated by the cofactor, thrombomodulin. TAFIa attenuates fibrinolysis. TAFIa can be inactivated by both proteolysis by thrombin and spontaneous temperature-dependent loss of activity. The identity of the thrombin cleavage site responsible for loss of TAFIa activity was suggested to be Arg(330), but site-directed mutagenesis of this residue did not prevent inactivation of TAFIa by thrombin. In this study we followed TAFI activation and TAFIa inactivation by thrombin/thrombomodulin in time and characterized the cleavage pattern of TAFI using matrix-assisted laser desorption ionization mass spectrometry. Mass matching of the fragments revealed that TAFIa was cleaved at Arg(302). Studies of a mutant R302Q-TAFI confirmed identification of this thrombin cleavage site and, furthermore, suggested that inactivation of TAFIa is based on its conformational instability rather than proteolytic cleavage at Arg(302).

Cardiolipin enhances protein C pathway anticoagulant activity

The anticoagulant activity of activated protein C (APC) was studied using factor Xa-1-stage assays of both the procoagulant and anticoagulant activities of phospholipid vesicles containing phosphatidylserine or cardiolipin as active phospholipids. In the absence of APC, phosphatidylserine vesicles showed higher procoagulant activity than cardiolipin vesicles whereas cardiolipin vesicles supported APC-dependent anticoagulant activity better than phosphatidylserine vesicles. Enhancement of APC anticoagulant activity in plasma by cardiolipin was markedly stimulated by the APC cofactor protein S. In purified reaction mixtures, cardiolipin in phospholipid vesicles dose-dependently enhanced APC anticoagulant activity. This effect of cardiolipin was partially dependent on protein S, and immunoblotting studies showed that cardiolipin enhanced the APC-mediated cleavage of the factor Va heavy chain at Arg506 and Arg306. In solid-phase binding assays, increasing amounts of cardiolipin in multicomponent phospholipid vesicles increased the affinity for protein S and to a lesser extent APC. These data are consistent with the hypothesis that cardiolipin stimulates the anticoagulant protein C pathway by increasing the affinity of phospholipid surfaces for protein S:APC and by enhancing inactivation of factor Va by APC due to cleavages at Arg506 and Arg306 in factor Va. Based on this, it is further hypothesized that anti-cardiolipin or anti-oxidized cardiolipin antibodies may be thrombogenic because they inhibit phospholipid-dependent expression of the anticoagulant protein C pathway.

Cardiolipin is a normal component of human plasma lipoproteins

Anticardiolipin (anti-CL) antibodies, diagnostic for antiphospholipid antibody syndrome, are associated with increased risks of venous and arterial thrombosis. Because CL selectively enhances activated protein C/protein S-dependent anticoagulant activities in purified systems and because CL is not known to be a normal plasma component, we searched for CL in plasma. Plasma lipid extracts [chloroform/methanol (2:1, vol/vol)] were subjected to analyses by using TLC, analytical HPLC, and MS. A plasma lipid component was purified that was indistinguishable from reference CL (M:1448). When CL in 40 fasting plasma lipid extracts (20 males, 20 females) was quantitated by using HPLC, CL (mean +/- SD) was 14.9 +/- 3.7 microgram/ml (range 9.1 to 24.2) and CL was not correlated with phosphatidylserine (3.8 +/- 1.7 microgram/ml), phosphatidylethanolamine (64 +/- 20 microgram/ml), or choline-containing phospholipid (1,580 +/- 280 microgram/ml). Based on studies of fasting blood donors, CL (>/=94%) was recovered in very low density, low density, and high density lipoproteins (11 +/- 5.3%, 67 +/- 11.0%, and 17 +/- 10%, respectively), showing that the majority of plasma CL (67%) is in low density lipoprotein. Analysis of relative phospholipid contents of lipoproteins indicated that high density lipoprotein is selectively enriched in CL and phosphatidylethanolamine. These results shows that CL is a normal plasma component and suggest that the epitopes of antiphospholipid antibodies could include CL or oxidized CL in lipoproteins or in complexes with plasma proteins (e. g., beta(2)-glycoprotein I, prothrombin, protein C, or protein S) or with platelet or endothelial surface proteins.

Structural basis for hemophilia A caused by mutations in the C domains of blood coagulation factor VIII

Three dimensional homology models for the C1 and C2 domains of factor VIII (FVIII) were generated. Each C domain formed a beta-sandwich, and C1 was covalently connected to C2 in a head-to-head orientation. Of the >250 missense mutations that cause FVIII deficiency and hemophilia A, 34 are in the C domains. We used the FVIII C1-C2 model to infer the structural basis for the pathologic effects of these mutations. The mutated residues were divided into four categories: 15 conserved buried residues that affect normal packing of the hydrophobic side chains, 2 non-conserved buried residues that affect structure, 11 conserved exposed residues and 6 non-conserved exposed residues. The effects of all 34 missense mutations can be rationalized by predictable disruptions of FVIII structure while at most four mutations (S2069F, T2154I, R2209Q/G/L and E2181D) may affect residues directly involved in intermolecular interactions of FVIII/VIIIa with other coagulation factors or vWF.

C-terminal residues 621-635 of protein S are essential for binding to factor Va

Protein S is anticoagulant in the absence of activated protein C because of direct interactions with coagulation Factors Xa and Va. Synthetic peptides corresponding to amino acid sequences of protein S were tested for their ability to inhibit prothrombinase activity. The peptide containing the C-terminal sequence of protein S, residues 621-635 (PSP14), reversibly inhibited prothrombinase activity in the presence but not in the absence of Factor Va (K(i) approximately 2 microM). PSP14 inhibition of prothrombinase was independent of phospholipids but could be competitively overcome by increasing Factor Xa concentrations, suggesting that the C-terminal region of protein S may compete for a Factor Xa binding site on Factor Va. Studies using peptides with amino acid substitutions suggested that lysines 630, 631, and 633 were critical residues. PSP14 inhibited Factor Va activity in Factor Xa-one-stage clotting assays. PSP14 inhibited protein S binding to immobilized Factor Va. When preincubated with protein S, antibodies raised against PSP14 inhibited binding of protein S to Factor Va and blocked inhibition of prothrombinase activity by protein S. These results show that the C-terminal region of protein S containing residues 621-635 is essential for binding of protein S to Factor Va and that this interaction contributes to anticoagulant action.

Modified alpha wrap techniques for dynamic urethral graciloplasty in an animal model

Urethral sphincter reconstruction with a stimulated skeletal muscle flap has been used for treatment of severe intrinsic sphincter deficiency. Urethral strictures and failures were reported in some of the initial experiences. The etiology of these problems is not known, but elevated resting urethral pressures and excessive urethral displacement with stimulation are possible causes. We modified two operative techniques in forming dynamic urinary graciloplasty (DUG) in an attempt to minimize resting urethral pressure without stimulation and urethral mobility during stimulation. Two types of DUG were used. In the first group, a small flap (partial muscle wrap) from the gracilis muscle with an attachment site on the muscle was constructed in four dogs. In the second group, three dogs with a modified alpha wrap and proximal attachments were used. All of the gracilis muscle wraps were stimulated using an implanted programmable pulse stimulator with electrodes attached over the motor nerve. Following a 2-week, postrecovery period, urethral pressure measurements were obtained with and without stimulation. Five weeks were used for stimulation to condition the muscle. This was followed by 4 weeks of continuous stimulation. Thus, devices were implanted for 11 weeks. Before conditioning of the muscles was initiated, the partial muscle wrap pressure at rest was 42 +/- 27 cm H2O, which was higher than the incomplete alpha wrap resting pressure of 20 +/- 4 cm H2O. Stimulated partial flap pressure was 161 +/- 50 cm H2O, and stimulated modified alpha wrap pressures was 71 +/- 27 cm H2O. After conditioning with the modified alpha wrap, the resting and stimulated pressures were unchanged from before conditioning. Technical problems precluded collection of data during the conditioning period in dogs with partial flaps. During stimulation, the partial muscle wrap demonstrated marked deviation, whereas the modified alpha wrap had minimal urethral movement. Postmortem evaluation indicated no urethral stricture or fistula formation with either of the two types of wraps. The modified alpha wrap had several positive features. Advantages over the partial wrap were minimal resting pressures, reduced urethral mobility, and adequate sustained pressures during stimulation. Therefore, in contrast to the partial gracilis muscle wrap, aspects of the incomplete alpha wrap should be considered further for DUG.

Factor XI dependent and independent activation of thrombin activatable fibrinolysis inhibitor (TAFI) in plasma associated with clot formation

Thrombin Activatable Fibrinolysis Inhibitor (TAFI) also known as plasma procarboxypeptidase B is activated by relatively high concentrations of thrombin in a reaction stimulated by thrombomodulin. In plasma an intact factor XI-dependent feed back loop via the intrinsic pathway is necessary to generate sufficient thrombin for TAFI activation. This thrombin generation takes place after clot formation with consequent down-regulation of fibrinolysis. We developed a specific and sensitive assay for activated TAFI (TAFIa) and studied its factor XI-dependent generation during clot formation. In the absence of thrombomodulin, addition of 20 nM thrombin to normal plasma generated 5-10% of the amount of TAFIa generated by 20 nM thrombin in the presence of 8 nM thrombomodulin. Minimal activation of TAFI was detected in factor II deficient plasma when clotting was initiated by 20 nM thrombin. Addition of 320-640 nM of thrombin to factor II deficient plasma resulted in the same amount of TAFIa as in normal plasma, suggesting that approximately 50% of factor II has to be converted to thrombin for extensive activation of TAFI. A Mab that neutralizes activated factor XII had no effect on TAFI activation indicating that an intact contact system is not necessary for the activation of TAFI. The dependency of TAFI activation of factor XI was tested using a Mab that neutralizes activated factor XI. When plasmas from 13 healthy individuals were tested, this Mab reduced TAFI activation by 65% (range 35-89%). Our results indicate that activation of TAFI in serum after clot formation can be quantitated and that it takes place in both factor XI-dependent and factor XI-independent mechanisms.

Tissue plasminogen activator (tPA) deficiency exacerbates cerebrovascular fibrin deposition and brain injury in a murine stroke model: studies in tPA-deficient mice and wild-type mice on a matched genetic background

Although the serine protease, tissue plasminogen activator (tPA), is approved by the US Food and Drug Administration for therapy to combat focal cerebral infarction, the basic concept of thrombolytic tPA therapy for stroke was challenged by recent studies that used genetically manipulated tPA-deficient (tPA-/-) mice, which suggested that tPA mediates ischemic neuronal damage. However, those studies were potentially flawed because the genotypes of tPA-/- and wild-type control mice were not entirely clear, and ischemic neuronal injury was evaluated in isolation of tPA effects on brain thrombosis. Using mice with appropriate genetic backgrounds and a middle cerebral artery occlusion stroke model with nonsiliconized thread, which does lead to microvascular thrombus formation, in the present study we determined the risk for cerebrovascular thrombosis and neuronal injury in tPA-/- and genetically matched tPA+/+ mice subjected to transient focal ischemia. Cerebrovascular fibrin deposition and the infarction volume were increased by 8.2- and 6. 7-fold in tPA-/- versus tPA+/+ mice, respectively, and these variables were correlated with reduced cerebral blood flow up to 58% (P<0.05) and impaired motor neurological score by 70% (P<0.05). Our findings indicate that tPA deficiency exacerbates ischemia-induced cerebrovascular thrombosis and that endogenous tPA protects the brain from an ischemic insult, presumably through its thrombolytic action. In addition, our study emphasizes the importance of appropriate genetic controls in murine stroke research.

Dermatan sulfate and LMW heparin enhance the anticoagulant action of activated protein C

Unfractionated heparin potentiates the anticoagulant action of activated protein C (APC) through several mechanisms, including the recently described enhancement of proteolytic inactivation of factor V. Possible anticoagulant synergism between APC and physiologic glycosaminoglycans, pharmacologic low molecular weight heparins (LMWHs), and other heparin derivatives was studied. Dermatan sulfate showed potent APC-enhancing effect. Commercial LMWHs showed differing abilities to promote APC activity, and the molecular weight of LMWHs correlated with enhancement of APC activity. Degree of sulfation of the glycosaminoglycans influenced APC enhancement. However, because dextran sulfates did not potentiate APC action, the presence of sulfate groups per se on a polysaccharide is not sufficient for APC enhancement. As previously for unfractionated heparin, APC anticoagulant activity was enhanced by glycosaminoglycans when factor V but not factor Va was the substrate. Thus, dermatan sulfate and LMWHs exhibit APC enhancing activity in vitro that could be of physiologic and pharmacologic significance.

Cardiopulmonary bypass and activation of antithrombotic plasma protein C

OBJECTIVE

We hypothesized that antithrombotic plasma-activated protein C plays a defensive antithrombotic role during coronary ischemia and postischemic reperfusion.

METHODS AND RESULTS

We evaluated protein C activation during cardiopulmonary bypass and coronary reperfusion in 20 patients undergoing coronary bypass surgery. During cardiopulmonary bypass and during the 10 minutes after aortic unclamping, the plasma levels of protein C (mean +/- standard error of the mean) decreased from 123% +/- 7% to 74% +/- 5% of normal mean. In contrast, the levels of activated protein C in plasma increased from 122% +/- 8% to 159% +/- 21%, and the activated protein C/protein C ratio increased from 1.04 +/- 0.08 to 2.29 +/- 0. 31 (P =.006, 2-tailed Wilcoxon signed rank test). Patients were stratified on the basis of the increase in activated protein C in the coronary sinus plasma at 10 minutes after reperfusion by means of the arbitrary value of 1.5 for the activated protein C/protein C ratio. Within 24 hours, the patients with low increases in activated protein C (ratio < 1.5, n = 8) had a significantly (P <.05) lower cardiac output and mean pulmonary artery pressure, as well as a higher systemic vascular resistance, than patients (n = 11) with high increases in activated protein C (ratio > 1.5). The rapid increase in activated protein C during the first 10 minutes after aortic unclamping indicated protein C activation in the reperfused vascular beds.

CONCLUSIONS

The antithrombotic protein C pathway was significantly activated during cardiopulmonary bypass mainly during the minutes after aortic unclamping in the ischemic vascular beds. Suboptimal protein C activation during ischemia may impair the postischemic recovery of human heart and circulation.

Protein synthesis by native chemical ligation: expanded scope by using straightforward methodology

The total chemical synthesis of proteins has great potential for increasing our understanding of the molecular basis of protein function. The introduction of native chemical ligation techniques to join unprotected peptides next to a cysteine residue has greatly facilitated the synthesis of proteins of moderate size. Here, we describe a straightforward methodology that has enabled us to rapidly analyze the compatibility of the native chemical ligation strategy for X-Cys ligation sites, where X is any of the 20 naturally occurring amino acids. The simplified methodology avoids the necessity of specific amino acid thioester linkers or alkylation of C-terminal thioacid peptides. Experiments using matrix-assisted laser-desorption ionization MS analysis of combinatorial ligations of LYRAX-C-terminal thioester peptides to the peptide CRANK show that all 20 amino acids are suitable for ligation, with Val, Ile, and Pro representing less favorable choices because of slow ligation rates. To illustrate the method's utility, two 124-aa proteins were manually synthesized by using a three-step, four-piece ligation to yield a fully active human secretory phospholipase A(2) and a catalytically inactive analog. The combination of flexibility in design with general access because of simplified methodology broadens the applicability and versatility of chemical protein synthesis.

Extensive venous and arterial thrombosis associated with an inhibitor to activated protein C

Activated protein C resistance (APCR) in the absence of alterations in the factor V gene has been observed during pregnancy, in patients on oral contraceptives, in the presence of antiphospholipid antibodies, and in patients with ischemic stroke. We report a 49-year-old woman with recurrent major venous and arterial thromboses who displayed pronounced APCR, yet no changes in the activated protein C (APC) cleavage sites of factor V. The APCR values determined by four different assays were similar to those obtained in plasma from a homozygote for factor V Q506. Addition of IgG isolated from the patient's serum to normal plasma lowered the APCR ratio from 2.4 to 1.6. Incubation of patient's IgG with normal APC resulted in a profound change in the mobility of APC in crossed immunoelectrophoresis. APC was also shown to bind to patient's IgG immobilized on a protein A agarose column. Factor Va inactivation by APC was inhibited by patient's IgG, but not by control IgG in the presence or absence of either phospholipids or protein S. These results provide evidence for the existence of an acquired antibody against APC in the patient's plasma, which gave rise to the APCR phenotype and was probably responsible for the major thrombotic events. We suggest that acquired APCR due to anti-APC antibodies be considered a potential cause for severe venous and arterial thromboses.

Impaired anticoagulant response to infusion of thrombin in atherosclerotic monkeys associated with acquired defects in the protein C system

To examine the effects of atherosclerosis on the protein C anticoagulant pathway in vivo, we measured anticoagulant responses to intravenous administration of human alpha-thrombin or activated protein C (APC) in cynomolgus monkeys. Two groups of monkeys were fed either a control diet (n=18) or an atherogenic diet (n=12) that produces both hypercholesterolemia and moderate hyperhomocyst(e)inemia. A third group (n=8) was fed an atherogenic diet for 15 months, and then fed the atherogenic diet supplemented with B vitamins for 6 months to correct the hyperhomocyst(e)inemia. The plasma homocyst(e)ine level was higher in monkeys fed the atherogenic diet (9.6+/-1.0 micromol/L) than in monkeys fed the control diet (3.7+/-0.2 micromol/L) or the atherogenic diet with B vitamins (3.6+/-0.2 micromol/L) (P<0.001). Infusion of thrombin produced a much greater prolongation of the activated partial thromboplastin time in monkeys fed the control diet (52+/-10 seconds) than in monkeys fed the atherogenic diet either with (24+/-4 seconds) or without (27+/-5 seconds) supplemental B vitamins (P<0.02). Thrombin-dependent generation of circulating APC was higher in control (294+/-17 U/mL) than in atherosclerotic (240+/-14 U/mL) monkeys (P<0.05), although levels of fibrinogen, plasminogen, D-dimer, and thrombin-antithrombin complexes were similar in each group. Injection of human APC produced a similar prolongation of the activated partial thromboplastin time in control (31+/-3 seconds) and atherosclerotic (29+/-2 seconds) monkeys. These findings provide evidence for impaired anticoagulation, due partly to decreased formation of APC, in atherosclerosis. The blunted anticoagulant response to thrombin in hypercholesterolemic monkeys was not corrected by supplementation with B vitamins.

Two multiplex PCR-based DNA assays for the thrombosis risk factors prothrombin G20210A and coagulation factor V G1691A polymorphisms

Two coagulation factor polymorphisms, G1691A in the factor V gene and G20210A in the prothrombin gene, are currently the most common known genetic risk factors for venous thrombosis in caucasian populations. Experimental conditions that permit simultaneous determination of these two polymorphisms using PCR-based DNA assays with the restriction enzyme, Hind III, were developed. Moreover, novel PCR-based DNA assays were established using primers that introduce specific cleavage sequences which then permit the simultaneous determination of these polymorphisms using Sac I restriction digestion analysis. Multiplex PCR-based DNA assays were used to analyze a family with a history of venous thrombosis in which these polymorphisms were both present and the results confirm the interesting variability of these genetic risk factors among family members who are symptomatic.

Brain-specific protein C activation during carotid artery occlusion in humans

BACKGROUND AND PURPOSE

Activation of plasma protein C (PC) zymogen by thrombin-thrombomodulin at the endothelial surface is an important endogenous antithrombotic mechanism. It is unknown whether activated protein C (APC) is generated in vivo in the cerebrovasculature, because there is only limited thrombomodulin expression in human brain vascular endothelium. Therefore, we tested the hypothesis that carotid occlusion produces brain-specific PC activation.

METHODS

Blood samples were simultaneously collected from the ipsilateral internal jugular vein and radial artery before and during carotid cross-clamping and on "de-occlusion" in 8 awake patients undergoing routine carotid endarterectomy. Plasma PC zymogen and circulating APC levels were measured using enzyme immunocapture assay and expressed as percent of pooled plasma controls.

RESULTS

Internal jugular vein APC levels increased 28% exclusively during carotid occlusion and then decreased 32% with de-occlusion (F=8.1, P<0.005). PC zymogen increased only 5.9% with occlusion (F=6.3, P<0.02), consistent with hemoconcentration. There were no changes in radial artery PC or APC levels.

CONCLUSIONS

These findings demonstrate brain-specific protein C activation in humans during carotid occlusion and suggest a protective role for endogenous APC generation during cerebrovascular occlusion.

High-density lipoprotein enhancement of anticoagulant activities of plasma protein S and activated protein C

Low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol levels are associated, respectively, with either increased risk or apparent protective effects for atherothrombosis. The ability of purified LDL and HDL to downregulate thrombin formation, a contributor to atherothrombotic processes, was assessed. Purified HDL, but not LDL, significantly enhanced inactivation of coagulation factor Va by activated protein C (APC) and protein S, and HDL stimulated protein S-dependent proteolytic inactivation of Va by APC, apparently due to cleavage at Arg306 in Va. In normal plasma, added HDL enhanced APC/protein S anticoagulant activity in modified prothrombin-time clotting assays. When the anticoagulant potency of HDL was compared with phospholipid (PL) vesicles of well-defined composition using this assay, HDL appeared qualitatively different from PL vesicles because HDL showed only good anticoagulant activity, whereas PL vesicles were rather procoagulant. When 20 normal plasmas were tested using this clotting assay, apoA-I levels correlated with anticoagulant response to APC/protein S (r = 0.47, P = 0.035), but not with activated partial thromboplastin time-based APC resistance ratios. Because HDL enhances the anticoagulant protein C pathway in vitro, we speculate that HDL may help downregulate thrombin generation in vivo and that this anticoagulant action is one of HDL's beneficial activities.

Homology models of the C domains of blood coagulation factors V and VIII: a proposed membrane binding mode for FV and FVIII C2 domains

We present homology models of the C domains of coagulation factors V (FV) and VIII (FVIII). Using a threading approach, we identified the binding domain of galactose oxidase as an appropriate template for each C domain. The C1 and C2 domains of FV associate to form an elongated cylinder of 80A long and 30A diameter. The folding unit is a beta-sandwich with a long axis of 40A and a diameter of 30A. The current model allows us to propose a membrane binding mode for the C2 domains of FV and FVIII with three major characteristics: 1) solvent-exposed hydrophobic side chains from three loops at one end of the beta-sandwich are buried in the hydrophobic layer of the outer phospholipid leaflet; 2) a crown of positively charged residues is located in the polar zone of the phospholipid head groups; and 3) the long axis of the beta-sandwich of the C2 domain is perpendicular to the plane of the membrane. This proposal satisfies experimentally observed characteristics of membrane binding for the C2 domain and the light chain of FVa.