Cardiolipin enhances protein C pathway anticoagulant activity

Study of the anti-angiogenic effects of cardiolipin by the aortic ring assay

Cardiolipin (CL), a phospholipid found in the inner mitochondrial membrane in all cell types, is critical for the function of the electron transport chain. The role of CL is not fully understood, but it is assumed that the molecule maintains membrane potential and architecture and compensates for alterations in homeostasis that could affect the energy metabolism. The objective of this project was to determine the effects of increasing CL concentrations on angiogenic sprouting by using the aortic ring assay model. For this, 5-day-old C57Bl/6 pups were euthanized by cervical dislocation prior to removal of the aortas. The vessels were cleaned, cut in 0.5 mm wide rings, and placed in a collagen growth matrix supplemented with CL. The results revealed a highly significant reduction of sprout growth (both length and quantity) at low, physiological concentrations. In conclusion, the results of this study demonstrate that CL significantly reduces microvessel formation and that it could potentially provide an interesting novel therapeutic target for angiogenesis.

Oxidized phospholipids as biomarkers of tissue and cell damage with a focus on cardiolipin

Oxidized phospholipid species are important, biologically relevant, lipid signaling molecules that usually exist in low abundance in biological tissues. Along with their inherent stability issues, these oxidized lipids present themselves as a challenge in their detection and identification. Often times, oxidized lipid species can co-chromatograph with non-oxidized species making the detection of the former extremely difficult, even with the use of mass spectrometry. In this study, a normal-phase and reverse-phase two dimensional high performance liquid chromatography (HPLC)-mass spectrometric system was applied to separate oxidized phospholipids from their non-oxidized counterparts, allowing unambiguous detection in a total lipid extract. We have utilized bovine heart cardiolipin as well as commercially available tetralinoleoyl cardiolipin oxidized with cytochrome c (cyt c) and hydrogen peroxide as well as with lipoxygenase to test the separation power of the system. Our findings indicate that oxidized species of not only cardiolipin, but other phospholipid species, can be effectively separated from their non-oxidized counterparts in this two dimensional system. We utilized three types of biological tissues and oxidative insults, namely rotenone treatment of lymphocytes to induce mitochondrial damage and cell death, pulmonary inhalation exposure to single walled carbon nanotubes, as well as total body irradiation, in order to identify cardiolipin oxidation products, critical to the cell damage/cell death pathways in these tissues following cellular stress/injury. Our results indicate that selective cardiolipin (CL) oxidation is a result of a non-random free radical process. In addition, we assessed the ability of the system to identify CL oxidation products in the brain, a tissue known for its extreme complexity and diversity of CL species. The ability of the two dimensional HPLC-mass spectrometric system to detect and characterize oxidized lipid products will allow new studies to be formulated to probe the answers to biologically important questions with regard to oxidative lipidomics and cellular insult. This article is part of a Special Issue entitled: Oxidized phospholipids - their properties and interactions with proteins.

Protein C anticoagulant and cytoprotective pathways

Plasma protein C is a serine protease zymogen that is transformed into the active, trypsin-like protease, activated protein C (APC), which can exert multiple activities. For its anticoagulant action, APC causes inactivation of the procoagulant cofactors, factors Va and VIIIa, by limited proteolysis, and APC's anticoagulant activity is promoted by protein S, various lipids, high-density lipoprotein, and factor V. Hereditary heterozygous deficiency of protein C or protein S is linked to moderately increased risk for venous thrombosis, while a severe or total deficiency of either protein is linked to neonatal purpura fulminans. In recent years, the beneficial direct effects of APC on cells which are mediated by several specific receptors have become the focus of much attention. APC-induced signaling can promote multiple cytoprotective actions which can minimize injuries in various preclinical animal injury models. Remarkably, pharmacologic therapy using APC demonstrates substantial neuroprotective effects in various murine injury models, including ischemic stroke. This review summarizes the molecules that are central to the protein C pathways, the relationship of pathway deficiencies to venous thrombosis risk, and mechanisms for the beneficial effects of APC.

Activated protein C plasma levels in the fasting and postprandial states among patients with previous unprovoked venous thromboembolism

INTRODUCTION

The protein C anticoagulant system is of major importance in the regulation of thrombotic risk, but it is not known whether low plasma levels of activated protein C (APC) in vivo reflect a compromised anticoagulant situation with increased thrombotic risk. Previous studies have reported low, normal or increased plasma APC levels in unselected patients with venous thromboembolism (VTE).

MATERIALS AND METHODS

We performed a population-based, case-control study in patients with a previous history of unprovoked VTE and subjected the participants to a standard fat tolerance test (1g fat/kg body weight) in order to promote physiological coagulation activation.

RESULTS

VTE patients had higher BMI (28.3 ± 4.4 kg/m(2) versus 26.3 ± 3.9 kg/m(2), p=0.045) and greater waist circumference (98.2 ± 12.5 cm versus 93.4 ± 13.4 cm, p=0.041) than age and sex matched controls. APC levels were equal in fasting plasma (3.00 ± 0.74 ng/ml and 2.99 ± 0.60 ng/ml, p=0.66) but higher in postprandial plasma (3.18 ± 0.57 ng/ml and 2.81 ± 0.38 ng/ml, p=0.008) collected from VTE patients and controls, respectively. Endogenous thrombin generation in plasma following a standardized meal, assessed by thrombin-antithrombin complex (TAT), increased similarly in both groups, whereas APC increased only among the VTE patients during the postprandial state. Plasma levels of APC increased linearly with TAT in the postprandial state (p for linear trend=0.012).

CONCLUSIONS

Our findings fail to support the hypothesis that low APC levels are linked to increased thrombotic risk in unprovoked VTE, and they suggest that plasma APC is a biomarker of thrombin generation.

An international multicentre-laboratory evaluation of a new assay to detect specifically lupus anticoagulants dependent on the presence of anti-beta2-glycoprotein autoantibodies

BACKGROUND

Antiphospholipid syndrome (APS) is diagnosed by the simultaneous presence of vascular thrombosis and/or pregnancy morbidity and detection of antiphospholipid antibodies in plasma.

OBJECTIVES

We have shown that prolongation of clotting time by anti-beta2-glycoprotein I (beta2GPI) antibodies correlates better with thrombosis than a positive classic lupus anticoagulant (LAC) assay in a single center study. To confirm or falsify this finding we have conducted a multicenter study.

METHODS AND RESULTS

In 325 LAC-positive samples, we found that the beta2GPI-dependent LAC correlated 2.0 times better with thrombosis than the classic LAC assay. Although significant, this was a minimal improvement compared with the 'classic' LAC. It was published that calcium influences the behavior of anti-beta2GPI antibodies in coagulation assays. To investigate whether calcium plays a role in the present study, we divided the patient population into two groups: (i) blood was collected in 0.109 m sodium citrate and (ii) blood was drawn in 0.129 m sodium citrate as anticoagulant. We found that a positive result with the beta2GPI-dependent LAC assay correlated better with thrombosis [odds ratio (OR): 3.3, 95% confidence interval (CI) 1.9-5.8] when 0.109 m sodium citrate was used compared with 0.129 m sodium citrate (OR: 0.4, 95% CI 0.1-1.1).

CONCLUSION

We were able to confirm in an international multicenter study that a positive result in a beta2GPI-dependent LAC assay correlates better with thrombosis than the classic LAC assay, but that the assay needs further study as it is sensitive to external factors such as the sodium citrate concentration used as anticoagulant in the test sample.

Protein S multimers and monomers each have direct anticoagulant activity

BACKGROUND AND OBJECTIVES

Plasma protein S (PS) is an essential anticoagulant that has activated protein C-independent, direct anticoagulant activity (PS-direct). It was reported that monomeric purified PS has poor PS-direct and that a subpopulation of multimeric purified PS has high PS-direct and high affinity for phospholipids. We independently examined the relative PS-direct and affinity for phospholipids of monomeric and multimeric PS and we obtained contrasting results.

METHODS AND RESULTS

Unpurified recombinant protein S (rPS) was monomeric and had PS-direct potency similar to that of both PS in plasma and multimeric affinity-purified PS, as measured in plasma assays for PS-direct and in thrombin-generation assays. Multimers of unpurified rPS were not induced by ethylenediaminetetraacetic acid (EDTA), pH 2.5, NaSCN, or barium adsorption/elution. Multimers were induced by chromatography in the presence of EDTA and thus may be concentration-dependent. In contrast to a different report, monomers, dimers, trimers, and higher-order PS forms were clearly separated in sedimentation velocity experiments and multimers were not dissociated by adding Ca(2+). Active plasma-derived and recombinant immunoaffinity-purified PS were fractionated into monomers and multimers. On a mass basis, monomers and multimers had similar specific PS-direct and ability to compete with prothrombinase components (factors Xa/Va) for limiting phospholipids. FXa ligand blotted to both monomers and multimers.

CONCLUSIONS

Plasma PS-direct is similar to that of affinity-purified PS and unpurified rPS. Under our conditions, monomeric and multimeric PS have similar PS-direct and ability to compete for phospholipids. Discordant earlier findings are likely due to loss of PS-direct during conventional purification procedures.

Synthesis and biological evaluation of gemcitabine-lipid conjugate (NEO6002)

A novel gemcitabine-lipid conjugate 5 was synthesized and tested for its in vivo efficacy and toxicity. Compound 5 was tested in BxPC-3 human pancreatic tumor model in SCID mice and exhibited promising activity and lower toxicity when compared with Gemzar.

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.

An efficient and novel method for the synthesis of cardiolipin and its analogs

A novel synthetic method has been developed for cardiolipin and its analog via a chlorophosphoramidite coupling reaction followed by oxidation. The reagent, N,N-diisopropylmethylphosphoramidic chloride, couples effectively with 1,2-O-dimyristoyl-sn-glycerol in the presence of an amidite activator to form a phosphoamidite intermediate, which then reacts with 2-O-benzylglycerol in the presence of a basic catalyst followed by in situ oxidation to give the corresponding protected cardiolipin. Deprotection of the protecting groups provides tetramyristoyl cardiolipin in good overall yield of 60%. The synthetic method is applicable to large-scale synthesis of cardiolipin and various analogs with or without unsaturation for liposomal drug delivery.

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.

Importance of protein S and phospholipid for activated protein C-mediated cleavages in factor Va

The procoagulant function of activated factor V (FVa) is inhibited by activated protein C (APC) through proteolytic cleavages at Arg306, Arg506, and Arg679. The effect of APC is potentiated by negatively charged phospholipid membranes and the APC cofactor protein S. Protein S has been reported to selectively stimulate cleavage at Arg306, an effect hypothesized to be related to reorientation of the active site of APC closer to the phospholipid membrane. To investigate the importance of protein S and phospholipid in the APC-mediated cleavages of individual sites, recombinant FV variants FV(R306Q/R679Q) and FV(R506Q/R679Q) (can be cleaved only at Arg506 and Arg306, respectively) were created. The cleavage rate was determined for each cleavage site in the presence of varied protein S concentrations and phospholipid compositions. In contrast to results on record, we found that protein S stimulated both APC cleavages in a phospholipid composition-dependent manner. Thus, on vesicles containing both phosphatidylserine and phosphatidylethanolamine, protein S increased the rate of Arg306 cleavage 27-fold and that of Arg506 cleavage 5-fold. Half-maximal stimulation was obtained at approximately 30 nm protein S for both cleavages. In conclusion, we demonstrate that APC-mediated cleavages at both Arg306 and Arg506 in FVa are stimulated by protein S in a phospholipid composition-dependent manner. These results provide new insights into the mechanism of APC cofactor activity of protein S and the importance of phospholipid composition.

Glucosylceramide, a neutral glycosphingolipid anticoagulant cofactor, enhances the interaction of human- and bovine-activated protein C with negatively charged phospholipid vesicles

The effect of glucosylceramide (GlcCer) on activated protein C (APC)-phospholipid interactions was examined using fluorescence resonance energy transfer. Human APC, labeled with either fluorescein (Fl-APC) or dansyl (DEGR-APC) donor, bound to phosphatidylcholine/phosphatidylserine (PC/PS, 9:1 w/w) vesicles containing octadecylrhodamine (OR) acceptor with a K(d) (app) = 16 micro g/ml, whereas Fl-APC (or DEGR-APC) bound to PC/PS/GlcCer(OR) (8:1:1) vesicles with a K(d) (app) = 3 micro g/ml. This 5-fold increase in apparent affinity was not species-specific since bovine DEGR-APC also showed a similar GlcCer-dependent enhancement of binding of APC to PC/PS vesicles. From the efficiency of fluorescence resonance energy transfer, distances of closest approach of approximately 63 and approximately 64 A were estimated between the dansyl on DEGR-APC and rhodamine in PC/PS/GlcCer(OR) and PC/PS(OR), respectively, assuming kappa(2) = 2/3. DEGR-APC bound to short chain C8-GlcCer with an apparent K(d) of 460 nm. The presence of C8-GlcCer selectively enhanced the binding of C16,6-NBD-phosphatidylserine but not C16,6-7-nitrobenz-2-oxa-1,3-diazole (NBD)-phosphatidylcholine to coumarin-labeled APC. These data suggest that APC binds to GlcCer, that PC/PS/GlcCer vesicles like PC/PS vesicles bind to the N-terminal gamma-carboxyglutamic acid domain of APC, and that one mechanism by which GlcCer enhances the activity of APC is by increasing its affinity for membrane surfaces containing negatively charged phospholipids.

Anticoagulant responses to thrombin are enhanced during regression of atherosclerosis in monkeys

BACKGROUND

Diet-induced atherosclerosis in monkeys produces abnormal anticoagulant responses to thrombin, including decreased generation of activated protein C (APC). We tested the hypothesis that anticoagulant responses to thrombin increase toward normal during regression of atherosclerosis.

METHODS AND RESULTS

Six cynomolgus monkeys were fed a high-fat atherogenic diet for 44 months and then a low-fat regression diet for 8 months. Serum total cholesterol decreased from 417+/-44 to 68+/-6 mg/dL (mean+/-SEM) and LDL cholesterol decreased from 375+/-44 to 27+/-5 mg/dL after the regression diet. In response to infusion of thrombin, the activated partial thromboplastin time (APTT) increased by 11+/-3 seconds before the regression diet and by 41+/-22 seconds after the regression diet (P=0.01). The peak level of circulating plasma APC was 52+/-9 ng/mL before the regression diet and 88+/-17 ng/mL after the regression diet (P=0.01). The APC sensitivity of plasma factor V was identical before and after the regression diet. Three additional atherosclerotic monkeys that remained on the high-fat diet for 8 months demonstrated no change in APTT or activation of protein C in response to thrombin.

CONCLUSIONS

Short-term dietary regression of atherosclerosis produces enhanced anticoagulant responses to thrombin in vivo.

Activated protein C: potential therapy for severe sepsis, thrombosis, and stroke

Activated protein C (APC) reduced all-cause 28-day mortality by 19% in patients with severe sepsis (sepsis associated with acute organ dysfunction) in the Protein C Evaluation in Severe Sepsis (PROWESS) trial, leading to recent approval of recombinant APC for treatment of this condition in adults. This review summarizes current knowledge derived from studies of a variety of animal models in which infused human APC demonstrated beneficial activities. Based on in vivo and also in vitro data, APC manifests antithrombotic, profibrinolytic, anti-inflammatory, and antiapoptotic activities. APC is a normal circulating component of plasma, derived from the protein C zymogen, and is thus a natural endogenous protective homeostatic factor. Because of its multiple activities, APC has a potential role in the treatment of complex and challenging medical disorders, including thrombosis and stroke.

Neutral glycosphingolipid-dependent inactivation of coagulation factor Va by activated protein C and protein S

To test whether neutral glycosphingolipids can serve as anticoagulant cofactors, the effects of incorporation of neutral glycosphingolipids into phospholipid vesicles on anticoagulant and procoagulant reactions were studied. Glucosylceramide (GlcCer), lactosylceramide (LacCer), and globotriaosylceramide (Gb(3)Cer) in vesicles containing phosphatidylserine (PS) and phosphatidylcholine (PC) dose dependently enhanced factor Va inactivation by the anticoagulant factors, activated protein C (APC) and protein S. Addition of GlcCer to PC/PS vesicles enhanced protein S-dependent APC cleavage in factor Va at Arg-506 by 13-fold, whereas PC/PS vesicles alone minimally affected protein S enhancement of this reaction. Incorporation into PC/PS vesicles of GlcCer, LacCer, or Gb(3)Cer, but not galactosylceramide or globotetraosylceramide, dose dependently prolonged factor Xa-1-stage clotting times of normal plasma in the presence of added APC without affecting baseline clotting times in the absence of APC, showing that certain neutral glycosphingolipids enhance anticoagulant but not procoagulant reactions in plasma. Thus, certain neutral glycosphingolipids (e.g. GlcCer, LacCer, and Gb(3)Cer) can enhance anticoagulant activity of APC/protein S by mechanisms that are distinctly different from those of phospholipids alone. We speculate that under some circumstances certain neutral glycosphingolipids either in lipoprotein particles or in cell membranes may help form antithrombotic microdomains that might enhance down-regulation of thrombin by APC in vivo.

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)