Fetal hydrocephalus and neonatal stroke as the first presentation of protein C deficiency.

Severe protein C-deficiency is a rare heritable thrombophilia of the newborn. Infants with biallelic PROC mutations present purpura fulminans and intracranial thromboembolism, while the prenatal onset of mutated heterozygotes remains unclear. We herewith present the first case of fetal ventriculomegaly and neonatal stroke associated with heterozygous PROC mutation. The infant was born to a healthy mother at 38 gestational weeks. The fetal growth had been normal, but the routine ultrasound screening had indicated mild hydrocephalus at 28 weeks of gestation. He developed convulsions two days after birth. Computed tomography of the brain revealed multiple hemorrhagic infarctions and ventriculomegaly. Dissociated levels of the plasma activity between protein C (21%) and protein S (42%) reached to determine the heterozygote of PROC c.574_576delAAG, a common thrombophilic predisposition in Asian ancestries. PC-mutant heterozygotes may have a limited high risk of cerebral thromboembolism during the perinatal course.

Protein C Thr315Ala variant results in gain of function but manifests as type II deficiency in diagnostic assays.

Protein C (PC) is a vitamin K-dependent plasma glycoprotein, which upon activation by thrombin in complex with thrombomodulin (TM), regulates the coagulation cascade through a feedback loop inhibition mechanism. PC deficiency is associated with an increased risk of venous thromboembolism (VTE). A recent cohort study aimed at establishing a normal PC range identified a healthy PC-deficient subject whose PC antigen level of 65% and activity levels of 50% (chromogenic assay) and 36% (clotting assay) were markedly low. The proband has a negative family history of VTE. Genetic analysis revealed the proband has a heterozygous missense mutation in which Thr-315 of the PC heavy chain has been substituted with Ala. We expressed this mutant in HEK-293 cells and purified it to homogeneity. A similar decrease in both anticoagulant and anti-inflammatory activities of the activated protein C mutant was observed in plasma- and cell-based assays. Interestingly, we discovered if functional assays were coupled to PC activation by the thrombin-TM complex, the variant exhibits improved activities in all assays. Sequence analysis revealed Thr-315 is a consensus N-linked glycosylation site for Asn-313 and that its elimination significantly (∼four- to fivefold) improves the maximum velocity of PC activation by the thrombin-TM complex, explaining the basis for the proband's negative VTE pedigree.

Antithrombotic activity of protein S infused without activated protein C in a baboon thrombosis model.

Protein S (ProS) is an essential plasma protein that enhances the anticoagulant activity of activated protein C (APC). In vitro , purified native human Zn2+-containing ProS also exerts direct anticoagulant activity by inhibiting prothrombinase and extrinsic FXase activities independently of APC. We investigated antithrombotic effects of ProS infused without APC in a baboon shunt model of thrombogenesis that employs a device consisting of arterial and venous shear flow segments. In in vitro experiments, the Zn2+-containing human ProS used for the studies displayed >10-fold higher prothrombinase inhibitory activity and anticoagulant activity in tissue factor-stimulated plasma, and four-fold higher inhibition of the intrinsic pathway than the Zn2+-deficient ProS used. In the thrombosis model, ProS (33 µg/minute for 1 hour) or saline was infused locally; platelet and fibrin deposition in the shunt were measured over 2 hours. During experiments performed at 50 ml/minute blood flow, Zn2+-containing ProS inhibited platelet deposition 73-96% in arterial-type flow segments and 90-99% in venous-type flow segments; Zn2+-deficient ProS inhibited platelet deposition 52% in arterial-type flow segments and 65-73% in venous-type flow segments. At 100 ml/min blood flow rate, Zn2+-containing ProS inhibited platelet deposition by 39% and 73% in the respective segments; Zn2+-deficient ProS inhibited platelet deposition by 5% and 0% in the respective segments. Zn2+-containing ProS suppressed fibrin deposition by 67-90%. Systemic APC-independent ProS activity was significantly increased and thrombin-antithrombin complex levels were significantly decreased after infusion of ProS. Thus, infused human Zn2+-containing ProS is antithrombotic in primates, and may have therapeutic potential even in protein C-deficient human patients.

Characteristics of fibrin formation and clot stability in individuals with congenital type IIb protein C deficiency.

Many studies have shown that unregulated or excessive thrombin formation is potentially a cause of thrombosis; however, studies examining processes that contribute to fibrin stabilization in individuals predisposed to thrombosis are limited. In this study, we investigate a family with familial thrombosis via type IIb protein C (PC) deficiency. Using contact pathway inhibited whole blood, thrombin generation, fibrin clot formation and factor (f)XIII activation were monitored over time in control (n=5) and PC deficient (n=4, 34 - 69% PC by activity) subjects. The dynamics of thrombin generation varied significantly with the time required to reach the maximal rate of thrombin-antithrombin formation being much shorter in PC deficiency (5.8 ± 0.4 minutes) than in controls (9.7 ± 0.4 minutes; p < 0.001). PC deficient clots were significantly heavier than control clots (p < 0.001) and this difference could not be contributed exclusively to differences in fibrinogen levels between groups. FXIII was consumed faster in PC deficient subjects (23.7 ± 2.0 nM/minute) than in controls (5.1 ± 1.5 nM/minute; p < 0.0001) suggesting increased fXIII activation and incorporation of fXIIIa substrates into the clot. In plasma, the clot lysis time was increased in PC deficiency by both TAFIa dependent and independent mechanisms. Since PC deficient clots are both denser and show a greater degree of resistance to fibrinolysis, these clots would likely resist fibrinolysis and potentiate fibrin deposition observed in thrombosis.

Evaluation of Pro-C global for identification of defects in protein C/S anticoagulant pathway.

BACKGROUND: Detection of protein C and S deficiency forms a major investigation in the laboratory evaluation of thrombophilia screening. It has key role in the diagnosis of protein C and S deficiency. The objective of this study is to determine the utility of ProC Global as a screening test for identifying the defects of protein C and S anticoagulant pathways. METHODS: Two Hundred patients with venous thromboembolism were studied at the Department of Haematology, Armed Forces Institute of Pathology, Rawalpindi, from October 2004 to March 2006. ProC Global test (Dade Behring Diagnostics) was performed and was followed up by protein C and S assays. ProC Global is an activated partial thromboplastin time based assay in which Protac (snake venom from Aghistroden contortrix) is used for activation of the endogenous protein C of the plasma sample. The protein C activation time in the presence of the activator was set in relation to a parallel determination of PCAT/O with addition of a buffer instead of activator reagent. The ratio PCAT: PCAT/O was transformed in normalized ratio by relating them to a calibrator. Control plasma for normal range and ProC control plasma for pathological range (Dade Behring Diagnostics) were assayed in each run for quality control. RESULTS: A total of 200 patients, 132 (66%) males and 68 (34%) females with age ranging from 1 to 68 years were studied. ProC Global was positive in 29/200 (14.5%) patients. ProC Global was found to be 86% sensitive, 94% specific and its overall efficiency turned out to be 94%. CONCLUSION: Pro-C Global can be used effectively as a screening test to detect abnormalities in protein C and S anticoagulant pathways.

The protein C omega-loop substitution Asn2Ile is associated with reduced protein C anticoagulant activity.

We report a kindred with heritable protein C (PC) deficiency in which two siblings with severe thrombosis showed a composite type I and IIb PC deficiency phenotype, identified using commercial PC assays (proband: PC antigen 42 u/dl, amidolytic activity 40 u/dl, anticoagulant activity 9 u/dl). The independent PROC nucleotide variations c.669C>A (predictive of Ser181Arg) and c.131C>T (predictive of Asn2Ile) segregated with the type I and type IIb PC deficiency phenotypes respectively, but co-segregated in the siblings with severe thrombosis. Soluble thrombomodulin (sTM)-mediated inhibition of plasma thrombin generation from an individual with PC-Asn2Ile was lower (endogenous thrombin potential (ETP) 56 +/- 1% that of ETP determined without sTM) than control plasma (ETP 15 +/- 2%) indicating reduced PC anticoagulant activity. Recombinant APC-Asn2Ile exhibited normal amidolytic activity but impaired anticoagulant activity. Protein S (PS)-dependent anticoagulant activity of recombinant APC-Asn2Ile and binding of recombinant APC-Asn2Ile to endothelial protein C receptor (EPCR) were reduced compared to recombinant wild-type APC. Asn2 lies within the omega-loop of the PC/APC Gla domain and this region is critical for calcium-induced folding and subsequent interactions with anionic phospholipids, EPCR and PS. The disruption of these interactions in this naturally-occurring PC variant highlights their collective importance in mediating APC anticoagulant activity in vivo.

A model for the formation, growth, and lysis of clots in quiescent plasma. A comparison between the effects of antithrombin III deficiency and protein C deficiency.

A mathematical model comprised of 23 reaction-diffusion equations is used to simulate the biochemical changes and transport of various reactants involved in coagulation and fibrinolysis in quiescent plasma. The growth and lysis of a thrombus, as portrayed by the model equations, is governed by boundary conditions that include the surface concentration of TF-VIIa, the generation of XIa by contact activation (in vitro), and the secretion of tPA due to endothelial activation. We apply the model to two clinically relevant hypercoagulable states, caused by deficiency of either antithrombin III or protein C. These predictions are compared with published experimental data which validate the utility of the developed model under the special case of static conditions. The incorporation of varying hemodynamic conditions in to the current fluid static model remains to be performed.

The cytoprotective protein C pathway.

Protein C is best known for its mild deficiency associated with venous thrombosis risk and severe deficiency associated with neonatal purpura fulminans. Activated protein C (APC) anticoagulant activity involves proteolytic inactivation of factors Va and VIIIa, and APC resistance is often caused by factor V Leiden. Less known is the clinical success of APC in reducing mortality in severe sepsis patients (PROWESS trial) that gave impetus to new directions for basic and preclinical research on APC. This review summarizes insights gleaned from recent in vitro and in vivo studies of the direct cytoprotective effects of APC that include beneficial alterations in gene expression profiles, anti-inflammatory actions, antiapoptotic activities, and stabilization of endothelial barriers. APC's cytoprotection requires its receptor, endothelial cell protein C receptor, and protease-activated receptor-1. Because of its pleiotropic activities, APC has potential roles in the treatment of complex disorders, including sepsis, thrombosis, and ischemic stroke. Although much about molecular mechanisms for APC's effects on cells remains unclear, it is clear that APC's structural features mediating anticoagulant actions and related bleeding risks are distinct from those mediating cytoprotective actions, suggesting the possibility of developing APC variants with an improved profile for the ratio of cytoprotective to anticoagulant actions.

Focal arterial inflammation is augmented in mice with a deficiency of the protein C gene.

Increased risk of thrombosis, with propitious conditions for fibrin deposition, along with upregulation of inflammation, are important factors that enhance plaque formation in atherosclerosis. Evidence supporting the role of anticoagulant protein C (PC) as an inflammatory agent has emerged, supplementing its well-known function as an anticoagulant. Thus, we sought to examine whether a PC deficiency would lead to an enhanced response to an acute arterial hyperplasic challenge. The presentation of early arterial inflammation was studied using a copper/silicone arterial cuff model of accelerated focal neointimal remodeling in mice with a heterozygous total deficiency of PC (PC+/-). Increased inflammation, cell proliferation, cell migration, fibrin elevation, and tissue necrosis were observed in the treated arteries of PC+/- mice, as compared to arteries of equally challenged age- and gender-matched WT mice. These results indicate that PC+/- mice subjected to this challenge displayed enhanced focal arterial inflammation and thrombosis, leading to larger neointimas and subsequent localized occlusion, as compared to their WT counterparts.

Protein C Sapporo (protein C Glu 25 --> Lys): a heterozygous missense mutation in the Gla domain provides new insight into the interaction between protein C and endothelial protein C receptor.

Interaction of the gamma-carboxyglutamic acid (Gla) domain of protein C with endothelial protein C receptor (EPCR) is a critical step for efficient activation of protein C, though interactions by mutants in the Gla domain of protein C with EPCR have been rarely evaluated. We identified a 44-year-old Japanese woman with a history of recurrent thromboembolism as an inherited missense mutation, the first such case reported in Japan, which involved a protein C Gla 25 mutation. Total protein C antigen and Gla protein C antigen levels in the proband were normal. Protein C activity measured with an anticoagulant assay was reduced, whereas that measured with an amidolytic assay was normal. She was therefore phenotypically diagnosed as type IIb protein C deficiency. Direct sequencing of the PCR fragments revealed a heterozygous G to A transition at nucleotide position 1462 in exon 3, which predicted an amino acid substitution of Glu 25 by Lys. Her mother and one son were also heterozygous for this mutation. A molecular dynamics simulation of Gla 25-->Lys/EPCR complex in water suggested that the affinity between the molecules was decreased compared to the wild type Gla domain/EPCR complex. Since Gla 25 has been shown to play an important role in protein C function, not only in membrane phospholipid binding but also in binding to EPCR, our findings provide new insight into the mechanism by which the Glu 25-->Lys mutation induces type IIb protein C deficiency in individuals.

New insights into the protein C pathway: potential implications for the biological activities of drotrecogin alfa (activated).

It has been hypothesized that the protein C pathway is a pivotal link between the inflammation and coagulation cascades. The demonstration that a survival benefit is associated with administration of drotrecogin alfa (activated) (recombinant human activated protein C [APC]) in severe sepsis patients has provided new insights into the protein C pathway. APC was originally identified based on its antithrombotic properties, which result from the inhibition of activated Factors V and VIII. In the early 1990s, any potential anti-inflammatory properties of APC were thought to relate primarily to its inhibition of thrombin generation. However, the mid-1990s saw the identification of the endothelial protein C receptor (EPCR), which has subsequently been shown to be neither endothelial specific nor protein C specific, but has a primary function as a cofactor for enhancing the generation of APC or behaving as an APC receptor. Thus, the potential biologic activities of APC can be classed into two categories related either to the limiting of thrombin generation or to cellular effects initiated by binding to the EPCR. Intracellular signaling initiated by binding of APC to its receptor appears to be mediated by interaction with an adjacent protease-activated receptor (PAR), or by indirect activation of the sphingosine 1-phosphate pathway. Based mostly on in vitro studies, binding of APC to its receptor on endothelial cells leads to a decrease in thrombin-induced endothelial permeability injury, while such binding on blood cells, epithelial cells, and neurons has been shown to inhibit chemotaxis, be anti-apoptotic, and be neuroprotective, respectively. In the Recombinant Human Activated Protein C Worldwide Evaluation in Severe Sepsis (PROWESS) study, drotrecogin alfa (activated) was associated with improved cardiovascular function, respiratory function, and a prevention of hematologic dysfunction. This article discusses the way in which the interactions of APC may alter the microcirculation.

A protein C deficiency exacerbates inflammatory and hypotensive responses in mice during polymicrobial sepsis in a cecal ligation and puncture model.

During the systemic inflammatory state induced by sepsis, the potential for coagulopathy exists because of up-regulation of natural procoagulants and anti-fibrinolytics, and down-regulation of natural anti-coagulants, with protein C (PC) being a critical example of the latter case. PC functions as an anti-coagulant, profibrinolytic, and anti-inflammatory agent, and, thus, its administration or deficiency may affect the course and outcome of sepsis in patients. In this study, a cecal ligation and puncture model of septic peritonitis was applied to wild-type mice and littermates with a targeted heterozygous deficiency of PC (PC(+/-)) to characterize the importance of a PC-deficiency on polymicrobial sepsis. An enhanced mortality rate was found to accompany a PC deficiency. Plasma cytokines, as well as organ-specific expression of cytokine transcripts, were elevated in PC(+/-) mice. No signs of severe disseminated intravascular coagulation (DIC) were observed in wild-type or PC(+/-) mice, as indicated by an increase in fibrinogen levels and the invariability of platelet counts after cecal ligation and puncture. Consumption of coagulation factors was similar in both genotypes and a decrease in the PC mRNA and protein levels was more prominent in PC(+/-) mice. Renal and organ muscle damage was enhanced in PC(+/-) mice, as shown by increases in plasma blood urea nitrogen, creatinine, and creatinine kinase. Hypotension and bradycardia were more enhanced in PC(+/-) mice than in wild-type mice, thus provoking a more severe septic shock response. Thus, the hemodynamic role of PC during sepsis is of critical importance to the outcome of the disease.

[Protein C system and thrombosis diseases]. / Sistema proteina C i trombozy.

The mechanism of protein C system functioning and role of its components in the regulation of the coagulation and the fibrinolysis was considered in the review. There are also new data about the anticoagulation, profibrinolysis and antiinflammatory functions of protein C system. Activated protein C is inhibited by the protein C inhibitor, alpha 1-antitripsin, and inhibitor of tissue activator plasminogen-1. Hereditary or acquired deficiency of protein C, protein S and thrombomodulin lead to thrombotic diseases. Injection of exogenous recombinant protein C or activated protein C into the blood increases the anticoagulant activity of the blood and produced the antithrombotic effect.

Laboratory issues in diagnosing abnormalities of protein C, thrombomodulin, and endothelial cell protein C receptor.

OBJECTIVE: To review the current understanding of the pathophysiology of protein C deficiency and its role in congenital thrombophilia. Recommendations for diagnostic testing for protein C function and concentration, derived from the medical literature and consensus opinions of recognized experts in the field, are included, specifying whom, how, and when to test. The role of related proteins, such as thrombomodulin and endothelial protein C receptor, is also reviewed. Data Sources.-Review of the published medical literature. DATA EXTRACTION AND SYNTHESIS: A summary of the medical literature and proposed testing recommendations were prepared and presented at the College of American Pathologists Conference XXXVI: Diagnostic Issues in Thrombophilia. After discussion at the conference, consensus recommendations presented in this manuscript were accepted after a two-thirds majority vote by the participants. CONCLUSIONS: Protein C deficiency is an uncommon genetic abnormality that may be a contributing cause of thrombophilia, often in conjunction with other genetic or acquired risk factors. When assay of protein C plasma levels is included in the laboratory evaluation of thrombophilia, a functional amidolytic protein C assay should be used for initial testing. The diagnosis of protein C deficiency should be established only after other acquired causes of protein C deficiency are excluded. A low protein C level should be confirmed with a subsequent assay on a new specimen. Antigenic protein C assays may be of benefit in subclassification of the type of protein C deficiency. The role of thrombomodulin and endothelial cell protein C receptor in thrombosis has yet to be clearly established, and diagnostic testing is not recommended at this time.

Assessing the relative importance of the biophysical properties of amino acid substitutions associated with human genetic disease.

The inclusion of a mutation in a pathology-based database such as the Human Gene Mutation Database (HGMD) is a two-stage process: first, the mutation must occur at the DNA level, then it must cause a clinically detectable disease state. The likelihood of the latter step, termed the relative clinical observation likelihood (RCOL), can be regarded as a function of the structural/functional consequences of a mutation at the protein level. Following this paradigm, we modeled in silico all amino acid replacements that could potentially have arisen from an inherited single base pair substitution in five human genes encoding arylsulphatase A (ARSA), antithrombin III (SERPINC1), protein C (PROC), phenylalanine hydroxylase (PAH), and transthyretin (TTR). These proteins were chosen on the basis of 1) the availability of a crystallographic structure, and 2) a sufficiently large number of amino acid replacements being logged in HGMD. A total of 9,795 possible mutant structures were modeled and 20 different biophysical parameters assessed. Together with the HGMD-derived spectra of clinically detected mutations, these data allowed maximum likelihood estimation of RCOL profiles for the 20 parameters studied. Nine parameters (including energy difference between wild-type and mutant structures, accessibility of the mutated residue, and distance from the binding/active site) exhibited statistically significant variability in their RCOL profiles, indicating that mutation-associated changes affected protein function. As yet, however, a biological meaning could only be attributed to the RCOL profiles of solvent accessibility and, for three proteins, local energy change, disturbed geometry, and distance from the active center. The limited ability of the biophysical properties of mutations to explain clinical consequences is probably due to our current lack of understanding as to which amino acid residues are critical for protein folding. However, since the proteins examined here were unrelated, and our findings consistent, it may nevertheless prove possible to extrapolate to other proteins whose dysfunction underlies inherited disease.

Type-I protein-C deficiency caused by disruption of a hepatocyte nuclear factor (HNF)-6/HNF-1 binding site in the human protein-C gene promoter.

The level and tissue specificity of eukaryotic gene transcription is determined by the binding of specific transcription factors to DNA sequence elements located around the transcription start site. The availability and activity of specific transcription factors depends on a variety of developmental and environmental cues and, therefore, varies from cell type to cell type. For instance, liver tissue, the principal site of expression of the coagulation inhibitor protein C, expresses a heterogeneous group of transcription factors called hepatocyte nuclear factors (HNFs). Some of these HNFs are essential players in protein-C gene expression. This review discusses the significance of HNF-1 and HNF-6 in regulating the transcription of the protein-C gene and gives directions for future research.