Species specificity of anticoagulant activity of activated human protein C: involvement of factor V as well as protein S

Carbon Nanofiber-Ionic Liquid Nanocomposite Modified Aptasensors Developed for Electrochemical Investigation of Interaction of Aptamer/Aptamer-Antisense Pair with Activated Protein C

Selective and sensitive detection of human activated protein C (APC) was performed herein by using carbon nanofiber (CNF) and ionic liquid (IL) composite modified pencil graphite electrode (PGE) and electrochemical impedance spectroscopy (EIS) technique. A carbon nanomaterial-based electrochemical aptasensor was designed and implemented for the first time in this study for the solution-phase interaction of DNA-Apt with its cognate protein APC as well as APC inhibitor aptamer-antidote pair. The applicability of this assay developed for the determination of APC in fetal bovine serum (FBS) and its selectivity against different proteins (protein C, thrombin, bovine serum albumin) was also examined. CNF-IL modified aptasensor specific to APC provided the detection limit as 0.23 μg/mL (equal to 3.83 nM) in buffer medium and 0.11 μg/mL (equal to 1.83 nM) in FBS. The duration of the proposed assay from the point of electrode modification to the detection of APC was completed within only 55 min.

Comparison of the Therapeutic Effect of Allogeneic and Xenogeneic Small Extracellular Vesicles in Soft Tissue Repair

Purpose

Small extracellular vesicles (sEV) are a heterogeneous group of vesicles that consist of proteins, lipids and miRNA molecules derived from the cell of origin. Although xenogeneic sEV have been applied for soft tissue regeneration successfully, the regeneration effect of allogeneic and xenogeneic sEV has not been compared systematically.

Methods

Our previous study has shown that sEV derived from rat adipose tissue successfully induced neoadipose regeneration. In this study, sEV were isolated from rat adipose tissue (r-sEV-AT) and porcine adipose tissue (p-sEV-AT), the morphology, size distribution and marker proteins expression of r-sEV-AT and p-sEV-AT were characterized. Besides, the sEV/AT ratio was evaluated and compared between r-sEV-AT and p-sEV-AT. Rat adipose-derived stromal/stem cells (rASCs) and rat aorta endothelial cells (rECs) were adopted to test the cellular response to allogeneic and xenogeneic sEV-AT. The effects of allogeneic and xenogeneic sEV-AT on host cells migration and neoadipose formation were evaluated in a subcutaneous custom-designed model. A full-thickness skin wound healing model was used to further compare the ability of allogeneic and xenogeneic sEV-AT in inducing complex soft tissue regeneration.

Results

p-sEV-AT showed similar morphology and size distribution to r-sEV-AT. Marker proteins of sEV were detected in both r-sEV-AT and p-sEV-AT. The sEV/AT ratio of porcine was slightly higher than that of rat. The effects of r-sEV-AT and p-sEV-AT on the differentiation of rASCs and rECs showed no significant difference. When allogeneic and xenogeneic sEV-AT were subcutaneously implanted into the back of SD rats, the host cells chemotactic infiltration was observed in 1 week and neoadipose tissue formation was induced in 8 weeks; no significant difference was observed between allogeneic and xenogeneic sEV-AT. For complex soft tissue regeneration, both allogeneic and xenogeneic sEV-AT significantly promoted wound re-epithelialization, granulation tissue formation and hair follicle regeneration and then accelerated skin wound healing.

Conclusion

Our results demonstrated that sEV derived from the same tissues of different species might be loaded with similar therapeutic substance benefitting tissue repair and regeneration, and paved the way for future research aimed at xenogeneic sEV application.

Activated protein C induces endoplasmic reticulum stress and attenuates lipopolysaccharide-induced apoptosis mediated by glycogen synthase kinase-3β

This study investigated the relationship between antiapoptotic activities induced by activated protein C and endoplasmic reticulum stress. In this study, it was observed that activated protein C elicited a rise in glucose-regulated protein 78 and glycogen synthase kinase-3β and inhibited apoptosis in human umbilical vein endothelial cells induced by lipopolysaccharide. Calcium inhibition did not alter the antiapoptotic effect of activated protein C. The antiapoptotic efficiency of activated protein C was reduced in human umbilical vein endothelial cells following treatment with glycogen synthase kinase-3β-siRNA. In summary, activated protein C induced endoplasmic reticulum stress and attenuated lipopolysaccharide-induced human umbilical vein endothelial cell apoptosis mediated by glycogen synthase kinase-3β.

Species-specific anticoagulant and mitogenic activities of murine protein S

BACKGROUND

The protein C pathway down-regulates thrombin generation and promotes cytoprotection during inflammation and stress. In preclinical studies using models of murine injury (e.g., sepsis and ischemic stroke), murine protein S may be required because of restrictive species specificity.

DESIGN AND METHODS

We prepared and characterized recombinant murine protein S using novel coagulation assays, immunoassays, and cell proliferation assays.

RESULTS

Purified murine protein S had good anticoagulant co-factor activity for murine activated protein C, but not for human activated protein C, in mouse or rat plasma. In human plasma, murine protein S was a poor co-factor for murine activated protein C and had no anticoagulant effect with human activated protein C, suggesting protein S species specificity for factor V in addition to activated protein C. We estimated that mouse plasma contains 22+/-1 microg/mL protein S and developed assays to measure activated protein C co-factor activity of the protein S in murine plasma. Activated protein C-independent anticoagulant activity of murine protein S was demonstrable and quantifiable in mouse plasma, and this activity was enhanced by exogenous murine protein S. Murine protein S promoted the proliferation of mouse and human smooth muscle cells. The potency of murine protein S was higher for mouse cells than for human cells and similarly, human protein S was more potent for human cells than for mouse cells.

CONCLUSIONS

The spectrum of bioactivities of recombinant murine protein S with mouse plasma and smooth muscle cells is similar to that of human protein S. However, in vitro and in vivo studies of the protein C pathway in murine disease models are more appropriately performed using murine protein S. This study extends previous observations regarding the remarkable species specificity of protein S to the mouse.

Human activated protein C variants in a rat model of arterial thrombosis

BACKGROUND

Activated protein C (APC) inhibits coagulation by degrading activated factor V (FVa) and factor VIII (FVIIIa), protein S (PS) functioning as a cofactor to APC.

METHODS

By mutagenesis of the vitamin K-dependent Gla domain of APC, we have recently created an APC variant having enhanced anticoagulant activity due to increased affinity for negatively charged phospholipid membranes. In the present study, the potential antithrombotic effects of this APC variant, and of a variant APC that is additionally mutated in the serine protease domain, have been evaluated in a blind randomized study in a rat model of arterial thrombosis. In this model, we have previously found the combination of bovine APC and PS to be highly antithrombotic. Four treatment groups each containing 10 rats were, in a blind random fashion, given intravenous bolus injections of wild-type or mutant variants of APC (0.8 mg/kg) together with human PS (0.6 mg/kg) or human PS (0.6 mg/kg) alone. A control group with 20 animals where given vehicle only.

RESULTS

A trend to increased patency rates was noted in a group receiving one of the APC variants, but it did not reach statistical significance.

CONCLUSION

In conclusion, administration of human APC variants having enhanced anticoagulant efficacy together with human PS in a rat model of arterial thrombosis did not give an efficient antithrombotic effect. The lack of effect may be due to species-specific differences between the human protein C system and the rat hemostatic system.

Development of a calibrated automated thrombography based thrombin generation test in mouse plasma

BACKGROUND

Mouse models have become increasingly important in thrombosis research. However, only a limited number of assays are available for assessment of the coagulation system in mouse plasma.

OBJECTIVES

To quantify tissue factor-initiated thrombin generation in murine platelet-rich and platelet-free plasma and to develop a test for measurement of resistance to activated protein C (APC) in mouse plasma.

METHODS

Thrombin generation was monitored with calibrated automated thrombography (CAT) using a low-affinity fluorogenic substrate for thrombin.

RESULTS

To overcome the higher activity of coagulation inhibitors in mouse plasma as compared with human plasma, the reaction temperature was lowered to 33 degrees C and the assay was carried out at a 2-fold higher final plasma dilution (1:3) than commonly used for CAT in human plasma. This increased the endogenous thrombin potential (ETP) 4- to 5-fold and enabled reliable measurement of thrombin generation in both platelet-free and platelet-rich mouse plasma. For the APC resistance measurement, the reaction conditions were further optimized with respect to tissue factor, phospholipid, APC and CaCl(2) concentrations. The test was validated using plasma of mice with different genetic background with respect to the factor V Leiden mutation (FV Leiden). Mice homozygous for FV Leiden had higher APC sensitivity ratios (mean 5.46; 95% CI 4.88-6.03) than heterozygous FV Leiden mice (mean 4.21; 95% CI 3.53-4.89) and than wild-type mice (mean 2.71; 95%CI 2.15-3.27).

CONCLUSIONS

We have established reaction conditions for measurement of thrombin generation and APC resistance in mouse plasma. This assay enables evaluation of the coagulation system and the function of the protein C system in mouse models.

Activated protein C improves intestinal microcirculation in experimental endotoxaemia in the rat

Introduction

Successful treatment of severe sepsis and septic shock remains a major challenge in critical care medicine. The recently introduced recombinant human activated protein C (APC) remarkably improved the outcome of septic patients. The influence of APC on intestinal circulation is still poorly understood. Therefore, the present study aimed to investigate the effects of APC on intestinal microcirculation during experimental endotoxaemia in rats by using intravital microscopy.

Methods

A total of 44 male Lewis rats were randomly assigned to receive intravenous injections of 15 mg/kg lipopolysaccharide alone (LPS) (n = 11) or LPS followed by subsequent injection of 2 mg/kg recombinant human APC (LPS + APC) (n = 11), whereas control animals received either APC (n = 11) or saline (n = 11). Animals underwent observations of functional capillary density and leucocyte adherence on venular endothelium in the microcirculation of the intestinal wall by means of intravital fluorescence microscopy. Indicators of macrocirculation as well as plasma levels of tumour necrosis factor-α, interleukin (IL)-1β, IL-6, and IL-10 were measured.

Results

Although APC administration of both LPS-treated and control rats did not change macrocirculation or release of inflammatory cytokines, it increased mucosal and muscular functional capillary density (p < 0.001 and p < 0.05, respectively) and reduced the number of firmly adhering leucocytes in intestinal submucosal V1 and V3 venules (p < 0.01) in LPS + APC-treated compared with LPS-treated animals, which did not receive APC. No remarkable differences that could be attributed to APC treatment were observed between the two control groups.

Conclusion

APC administration during experimental endotoxaemia improved intestinal microcirculation by protecting functional capillary density as a measure of microvascular perfusion and exerted anti-inflammatory effects by reducing leucocyte adherence to the endothelium in submucosal venules. Therefore, beneficial effects of APC in septic patients might be due, in part, to improved intestinal microcirculation.

Therapeutic levels of human protein C in rats after retroviral vector-mediated hepatic gene therapy

Protein C deficiency results in a thrombotic disorder that might be treated by expressing a normal human protein C (hPC) gene in patients. An amphotropic retroviral vector with a liver-specific promoter and the hPC cDNA was delivered to rat hepatocytes in vivo during liver regeneration. Expression of hPC varied from 55 to 203 ng/ml (1.3-5.0% of normal) for 2 wk after transduction. Expression increased to an average of 900 ng/ml (22% of normal) in some rats and was maintained at stable levels for 1 yr. All of these rats developed anti-hPC antibodies and exhibited a prolonged hPC half-life in vivo. The hPC was functional as determined by a chromogenic substrate assay after immunoprecipitation. We conclude that most rats achieved hPC levels that would prevent purpura fulminans, and that hepatic gene therapy might become a viable treatment for patients with severe homozygous hPC deficiency. Anti-hPC antibodies increased the hPC half-life and plasma levels in some rats, but did not interfere with its functional activity. Thus, the development of antibodies against a plasma protein does not necessarily abrogate its biological effect in gene therapy experiments.

The Structure and Function of Murine Factor V and Its Inactivation by Protein C

Factor V (FV) is a central regulator of hemostasis, serving both as a critical cofactor for the prothrombinase activity of factor Xa and the target for proteolytic inactivation by the anticoagulant, activated protein C (APC). To examine the evolutionary conservation of FV procoagulant activity and functional inactivation by APC, we cloned and sequenced the coding region of murine FV cDNA and generated recombinant wild-type and mutant murine FV proteins. The murine FV cDNA encodes a 2,183-amino acid protein. Sequence comparison shows that the A1-A3 and C1-C2 domains of FV are highly conserved, demonstrating greater than 84% sequence identity between murine and human, and 60% overall amino acid identity among human, bovine, and murine FV sequences. In contrast, only 35% identity among all three species is observed for the poorly conserved B domain. The arginines at all thrombin cleavage sites and the R305 and R504 APC cleavage sites (corresponding to amino acid residues R306 and R506 in human FV) are invariant in all three species. Point mutants were generated to substitute glutamine at R305, R504, or both (R305/R504). Wild-type and all three mutant FV recombinant proteins show equivalent FV procoagulant activity. Single mutations at R305 or R504 result in partial resistance of FV to APC inactivation, whereas recombinant murine FV carrying both mutations (R305Q/R504Q) is nearly completely APC resistant. Thus, the structure and function of FV and its interaction with APC are highly conserved across mammalian species.

The Structure and Function of Murine Factor V and Its Inactivation by Protein C

Factor V (FV) is a central regulator of hemostasis, serving both as a critical cofactor for the prothrombinase activity of factor Xa and the target for proteolytic inactivation by the anticoagulant, activated protein C (APC). To examine the evolutionary conservation of FV procoagulant activity and functional inactivation by APC, we cloned and sequenced the coding region of murine FV cDNA and generated recombinant wild-type and mutant murine FV proteins. The murine FV cDNA encodes a 2,183-amino acid protein. Sequence comparison shows that the A1-A3 and C1-C2 domains of FV are highly conserved, demonstrating greater than 84% sequence identity between murine and human, and 60% overall amino acid identity among human, bovine, and murine FV sequences. In contrast, only 35% identity among all three species is observed for the poorly conserved B domain. The arginines at all thrombin cleavage sites and the R305 and R504 APC cleavage sites (corresponding to amino acid residues R306 and R506 in human FV) are invariant in all three species. Point mutants were generated to substitute glutamine at R305, R504, or both (R305/R504). Wild-type and all three mutant FV recombinant proteins show equivalent FV procoagulant activity. Single mutations at R305 or R504 result in partial resistance of FV to APC inactivation, whereas recombinant murine FV carrying both mutations (R305Q/R504Q) is nearly completely APC resistant. Thus, the structure and function of FV and its interaction with APC are highly conserved across mammalian species.

Species specificity of the anticoagulant activity of human urinary soluble thrombomodulin

The anticoagulant activities of human urinary soluble thrombomodulin (UTM) in blood taken from various species using several anticoagulant assay systems were compared; it was examined which coagulant assay system is appropriate for evaluation of the antithrombotic effects of UTM and how the species specificity of UTM is involved in the mechanisms of action of UTM. When anticoagulant activities were compared using activated partial thromboplastin time (APTT), thromboelastography (TEG), and thrombin generation test (TGT), the effect of UTM was found to be the strongest in humans among various species tested. Among the anticoagulant assays tested, TGT reflecting protein C (PC) activation by UTM, appeared to be more sensitive than APTT and TEG in detection of thrombomodulin activity. In the study of the mechanisms of action of UTM, UTM exhibited nearly the same antithrombin activity against human and rat thrombin; the rate of activation of human PC by thrombin/UTM complex was much higher than that of rat PC. Therefore, the species specificity of the anticoagulant activity of UTM may be attributable to thrombin/UTM-PC interaction, but not to UTM-thrombin interaction. From these results, we concluded that TGT reflecting PC activation by UTM will be a more useful assay than APTT and TEG for estimating the antithrombotic effects of UTM in humans. Furthermore, our findings suggest that UTM will exhibit more potent antithrombotic effects in humans than those in rats by strongly enhancing thrombin-catalyzed PC activation.