Protein S and protein C Biochemistry, physiology, and clinical manifestation of deficiencies

Data-independent LC-MS/MS analysis of ME/CFS plasma reveals a dysregulated coagulation system, endothelial dysfunction, downregulation of complement machinery

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating chronic condition that is characterized by unresolved fatigue, post-exertion symptom exacerbation (PESE), cognitive dysfunction, orthostatic intolerance, and other symptoms. ME/CFS lacks established clinical biomarkers and requires further elucidation of disease mechanisms. A growing number of studies demonstrate signs of hematological and cardiovascular pathology in ME/CFS cohorts, including hyperactivated platelets, endothelial dysfunction, vascular dysregulation, and anomalous clotting processes. To build on these findings, and to identify potential biomarkers that can be related to pathophysiology, we measured differences in protein expression in platelet-poor plasma (PPP) samples from 15 ME/CFS study participants and 10 controls not previously infected with SARS-CoV-2, using DIA LC-MS/MS. We identified 24 proteins that are significantly increased in the ME/CFS group compared to the controls, and 21 proteins that are significantly downregulated. Proteins related to clotting processes - thrombospondin-1 (important in platelet activation), platelet factor 4, and protein S - were differentially expressed in the ME/CFS group, suggestive of a dysregulated coagulation system and abnormal endothelial function. Complement machinery was also significantly downregulated, including C9 which forms part of the membrane attack complex. Additionally, we identified a significant upregulation of lactotransferrin, protein S100-A9, and an immunoglobulin variant. The findings from this experiment further implicate the coagulation and immune system in ME/CFS, and bring to attention the pathology of or imposed on the endothelium. This study highlights potential systems and proteins that require further research with regards to their contribution to the pathogenesis of ME/CFS, symptom manifestation, and biomarker potential, and also gives insight into the hematological and cardiovascular risk for ME/CFS individuals affected by diabetes mellitus.

A Comprehensive Review of Risk Factors and Thrombophilia Evaluation in Venous Thromboembolism

Venous thromboembolism (VTE), which encompasses deep vein thrombosis (DVT) and pulmonary embolism (PE), is a significant cause of morbidity and mortality worldwide. There are many factors, both acquired and inherited, known to increase the risk of VTE. Most of these result in increased risk via several common mechanisms including circulatory stasis, endothelial damage, or increased hypercoagulability. Overall, a risk factor can be identified in the majority of patients with VTE; however, not all risk factors carry the same predictive value. It is important for clinicians to understand the potency of each individual risk factor when managing patients who have a VTE or are at risk of developing VTE. With this, many providers consider performing a thrombophilia evaluation to further define a patient's risk. However, guidance on who to test and when to test is controversial and not always clear. This comprehensive review attempts to address these aspects/concerns by providing an overview of the multifaceted risk factors associated with VTE as well as examining the role of performing a thrombophilia evaluation, including the indications and timing of performing such an evaluation.

A Case of Type 2 Protein S Deficiency Presenting as Cerebral Venous Thrombosis (CVT) in an 18-Year-Old Female

Here, we report a case of cerebral venous thrombosis in an 18-year-old female. On evaluation, she was found to have type 2 protein S deficiency, which is the rarest form of protein S deficiency and is also known as a qualitative defect. Protein S is primarily synthesized by hepatocytes and undergoes vitamin K-dependent gamma-carboxylation. Mature protein S circulates in two states: free and bound to the complement component C4b-binding protein (C4b-BP). The free form of protein S acts as a cofactor for activated protein C. This case is unique as here, there is a qualitative effect that is responsible for the manifestations.

Atypical presentation of pulmonary embolism and deep vein thrombosis due to protein S deficiency in a young female with chest pain

Venous thromboembolism has many risk factors including protein S deficiency, which poses a significant diagnostic challenge as it presents with atypical complaints. A treatable yet potentially fatal condition, acute pulmonary embolism, is currently third most common cause of cardiovascular death. Clinicians should include pulmonary embolism as differential diagnosis in young adults with atypical symptoms with 2 D ECHO findings of the dilated right atrium, right ventricle, and elevated pulmonary artery pressure, and diagnosis is confirmed by computed tomography pulmonary angiography (CTPA). Anticoagulants including NOACs should be initiated promptly to improve the outcome for patients.

Thrombin spatial distribution determines protein C activation during hemostasis and thrombosis

Rebalancing the hemostatic system by targeting endogenous anticoagulant pathways, like the protein C (PC) system, is being tested as a means of improving hemostasis in patients with hemophilia. Recent intravital studies of hemostasis demonstrated that, in some vascular contexts, thrombin activity is sequestered in the extravascular compartment. These findings raise important questions about the context-dependent contribution of activated PC (APC) to the hemostatic response, because PC activation occurs on the surface of endothelial cells. We used a combination of pharmacologic, genetic, imaging, and computational approaches to examine the relationships among thrombin spatial distribution, PC activation, and APC anticoagulant function. We found that inhibition of APC activity, in mice either harboring the factor V Leiden mutation or infused with an APC-blocking antibody, significantly enhanced fibrin formation and platelet activation in a microvascular injury model, consistent with the role of APC as an anticoagulant. In contrast, inhibition of APC activity had no effect on hemostasis after penetrating injury of the mouse jugular vein. Computational studies showed that differences in blood velocity, injury size, and vessel geometry determine the localization of thrombin generation and, consequently, the extent of PC activation. Computational predictions were tested in vivo and showed that when thrombin generation occurred intravascularly, without penetration of the vessel wall, inhibition of APC significantly increased fibrin formation in the jugular vein. Together, these studies show the importance of thrombin spatial distribution in determining PC activation during hemostasis and thrombosis.

Right neck venous thrombosis following ovarian hyperstimulation syndrome in a patient with protein S deficiency: A case report and review of literature

OBJECTIVE

The risk of venous thromboembolism in pregnancies increased in ovarian hyperstimulation syndrome (OHSS) after assisted reproductive technologies (ART). We present a rare case with protein S deficiency receiving ART treatment with OHSS, following right neck venous thromboembolism.

CASE REPORT

A 34-year-old women with primary infertility underwent IVF treatment and presented with OHSS. However, thromboembolism in the right jugular and subclavian veins was diagnosed at eight weeks of gestation. She was continuously treated with low molecular weight heparin (LMWH) since eight weeks of gestation and the diagnosis of protein S deficiency was made. Due to placenta previa with massive bleeding, she gave live birth to two healthy babies via cesarean section at 34 weeks of gestation.

CONCLUSION

Thromboembolism is one of life-threatening complications among women with OHSS. Although inherited thrombophilia is rare diseases, thrombophilia workup may be taken into consideration for women with thrombotic events.

Impact of erythrocytapheresis on natural anticoagulant levels in children with sickle cell disease: A pilot study

Venous thromboembolism (VTE) is being increasingly recognized in children with sickle cell disease (SCD). In a retrospective cohort study, we identified bilateral central venous catheter (CVC) placement as an independent risk factor for VTE. At our institution, the only indication for bilateral CVC placement in children with SCD is erythrocytapheresis. To investigate the impact of erythrocytapheresis on coagulation, we measured levels of natural anticoagulants in 11 patients with SCD on chronic erythrocytapheresis, immediately before and after apheresis. We demonstrated a statistically significant reduction in most parameters. Additional studies are needed to further investigate the exact etiology and clinical impact of this acute decrease.

Regulation of human platelet aggregation by genetically modified pig endothelial cells and thrombin inhibition

BACKGROUND

Coagulation disorders remain barriers to successful pig-to-primate organ xenotransplantation. In vitro, we investigated the impact of pig genetic modifications on human platelet aggregation in response to pig aortic endothelial cells (pAEC).

METHODS

In comparison to human (h)AEC and wild-type (WT) pAEC, the expression of human complement- (CD46, CD55) or coagulation (thrombomodulin [TBM], endothelial protein C receptor [EPCR]) -regulatory proteins on pAEC from WT or α1,3-galactosyltransferase gene-knockout (GTKO) pigs was studied by flow cytometry. Using platelet-aggregometry, human whole blood platelet aggregation was evaluated after co-incubation with various AEC. Further, the inhibitory effect on aggregation of heparin, low molecular weight heparin, and hirudin was assessed.

RESULTS

Heparin, low molecular weight heparin and hirudin almost completely prevented platelet aggregation induced by WT pAEC. The level of expression of human CD46, CD55, TBM and EPCR on pAEC was comparable to that on hAEC. Platelet aggregation induced by all genetically modified pAEC was significantly less (P < 0.05) than that by WT pAEC (which was 54%). GTKO/CD46/TBM pAEC induced the least platelet aggregation (27%)-a reduction of almost 50%-but this remained significantly greater (P < 0.01) than aggregation induced by hAEC (4%). There was significant positive correlation between reduction of aggregation and TBM or EPCR expression on pAEC (r = 0.89 and r = 0.86, respectively; P < 0.05). Platelet aggregation induced by GTKO/CD46/TBM pAEC in the presence of hirudin (1 IU/ml) was comparable to platelet aggregation induced by hAEC.

CONCLUSIONS

Genetic modification of pAEC is associated with significant reduction of human platelet aggregation in vitro. With concomitant thrombin inhibition, platelet aggregation was comparable to that stimulated by hAEC.

Low borderline plasma levels of antithrombin, protein C and protein S are risk factors for venous thromboembolism

BACKGROUND

Inherited deficiencies of antithrombin (AT), protein C (PC) and protein S (PS) are risk factors for venous thromboembolism (VTE). They are usually defined by laboratory cut-offs (in our setting 81, 70 and 63 IU dL(-1), respectively), which give only a rough idea of the VTE risk associated with plasma levels of these proteins.

OBJECTIVES

 We investigated whether the risk of VTE associated with the plasma deficiencies of AT, PC or PS has a dose-response effect, and whether low borderline levels of these proteins are associated with an increased risk of VTE, both in the whole study population and separately in carriers of either factor V Leiden or G20210A prothrombin gene mutation.

PATIENTS/METHODS

A case-control study of 1401 patients with a first objectively-documented VTE and 1847 healthy controls has been carried out.

RESULTS

A dose-response effect on the VTE risk was observed for all the three anticoagulant proteins. Compared with individuals with AT, PC or PS levels > 100 IU/dL, the adjusted odds ratio (95% CI) of VTE was 2.00 (1.44-2.78) for AT levels between 76 and 85 IUdL(-1) , 2.21 (1.54-3.18) and 1.84 (1.31-2.59) for PC and PS levels between 61 and 75 IUdL(-1) . The risk of unprovoked VTE in factor V Leiden or prothrombin G20210A carriers appears 2 to 3-fold increased when levels of AT or PS are low borderline.

CONCLUSIONS

 Low borderline plasma levels of AT, PC and PS are associated with a 2-fold increased risk of VTE and should be considered in the assessment of the individual VTE risk.

Inhibition of APC anticoagulant activity on oxidized phospholipid by anti-{beta}2-glycoprotein I monoclonal antibodies

Activated protein C (APC) anticoagulant activity and the ability to be inhibited by auto-antibodies associated with thrombosis are strongly augmented by the presence of phosphatidylethanolamine (PE) and phospholipid oxidation. beta(2)-glycoprotein I (beta(2)-GPI) is a major antigen for antiphospholipid antibodies present in patients with the antiphospholipid syndrome. We therefore investigated whether anti-beta(2)-GPI monoclonal antibodies (mAbs) could inhibit APC with similar membrane specificity. Five mouse mAbs that reacted with different epitopes on beta(2)-GPI were examined. Each inhibited the PE-, phospholipid oxidation-dependent enhancement of APC anticoagulant activity and required antibody divalency. A chimeric APC that retains anticoagulant activity but is relatively unaffected by protein S, PE, or oxidation was not inhibited by the antibodies. In purified systems, anti-beta(2)-GPI mAb inhibition of factor Va inactivation was greater in the presence of protein S and required beta(2)-GPI. Surprisingly, although the mAbs did increase beta(2)-GPI affinity for membranes, PE and oxidation had little influence on the affinity of the beta(2)-GPI antibody complex for the membrane vesicles. We conclude that antibodies to beta(2)-GPI inhibit APC function specifically and contribute to a hypercoaguable state by disrupting specific protein-protein interactions induced by oxidation of PE-containing membranes.

A novel splice acceptor site mutation of protein S gene in affected individuals with type I protein S deficiency: allelic exclusion of the mutant gene

Sequencing studies of the protein S gene (PROS1) in a Japanese patient suffering from recurrent thrombosis revealed the following. The proband and his first daughter, but not the second daughter, were having the type I protein S (PS) deficiency due to a novel point mutation from A to G at the intronic acceptor splice site in intron 13 of the PROS1. In the affected daughter, exclusion of the aberrant allele was assessed by the BstX1 dimorphism of PROS1 at Pro626 (CCG/CCA). The reduced PS activities in the proband and his first daughter were apparently due to defective production of mRNA from the mutant allele.

Lipid oxidation enhances the function of activated protein C

Although lipid oxidation products are usually associated with tissue injury, it is now recognized that they can also contribute to cell activation and elicit anti-inflammatory lipid mediators. In this study, we report that membrane phospholipid oxidation can modulate the hemostatic balance. Oxidation of natural phospholipids results in an increased ability of the membrane surface to support the function of the natural anticoagulant, activated protein C (APC), without significantly altering the ability to support thrombin generation. Lipid oxidation also potentiated the ability of protein S to enhance APC-mediated factor Va inactivation. Phosphatidylethanolamine, phosphatidylserine, and polyunsaturation of the fatty acids were all required for the oxidation-dependent enhancement of APC function. A subgroup of thrombotic patients with anti-phospholipid antibodies specifically blocked the oxidation-dependent enhancement of APC function. Since leukocytes are recruited and activated at the thrombus or sites of vessel injury, our findings suggest that after the initial thrombus formation, lipid oxidation can remodel the membrane surface resulting in increased anticoagulant function, thereby reducing the thrombogenicity of the thrombus or injured vessel surface. Anti-phospholipid antibodies that block this process would therefore be expected to contribute to thrombus growth and disease.

Possible involvement of cytokines in diffuse intravascular coagulation and thrombosis

Recently, basic and clinical advances have provided insights into the molecular events that link inflammation with blood coagulation and thrombosis. At least in cell culture, the inflammatory cytokines, especially tumour necrosis factor alpha (TNF) and interleukin 1-beta (IL-1), are major mediators that can elicit changes in cell phenotype. With respect to coagulation, one of the clot-promoting and one of the inhibitory pathways seem especially prone to modulation by these cytokines. Whenever Tissue Factor contacts the blood, coagulation is initiated rapidly. These cytokines can elicit Tissue Factor production on endothelium and monocytes. Thus, the cytokines elaborate Tissue Factor formation intravascularly. This contrasts with the normal situation in which Tissue Factor is located exclusively in the extravascular space, largely on fibroblasts, where it is expressed constitutively. Furthermore, cytokines, especially interleukin 6 (IL-6), can stimulate new platelet formation, and the new platelets responding to IL-6 have increased sensitivity to thrombin activation and increased procoagulant activity. Regulating the clotting process are a large number of anticoagulant and fibrinolytic mechanisms. The three major anticoagulant mechanisms appear to involve antithrombin-heparin, Tissue Factor pathway inhibitor (TFPI) and the Protein C pathway. Of these, the Protein C pathway appears to be the primary target for cytokine action. The Protein C pathway is initiated when thrombin binds to thrombomodulin (TM). TM is expressed constitutively on endothelium. In tissue culture, TNF, IL-1 or endotoxin lead to a slow loss of TM and endothelial cell Protein C receptor (EPCR) from the cell surface. In addition, Protein S levels decrease in patients with disseminated intravascular coagulation (DIC). Taken together, these results suggest that cytokines should elicit massive thrombotic responses when administered systemically. At near toxic levels, TNF fails to elicit an overt DIC or thrombotic response in patients, although sensitive markers of coagulation do detect changes in coagulation in response to TNF. In baboons, very high levels of TNF also fail to elicit fibrinogen or platelet consumption. However, if the Protein C pathway is blocked, these cytokines can elicit either DIC or deep-vein thrombosis, depending on the conditions. Thrombus formation is potently potentiated by impeding flow and/or by catheterization. DIC is facilitated by providing membrane surfaces, possibly mimicking complement mediated platelet activation/damage that occurs in shock. Thus, available evidence suggests important roles for inflammatory cytokines in DIC and thrombosis, but they seem insufficient by themselves to elicit overt thrombotic responses without secondary stimuli. Current data suggest that anti-inflammatory drugs are a viable candidate to blocking DIC or thrombosis without impairing the haemostatic balance.

A Mutation of the Active Protein S Gene Leading to an EGF1-Lacking Protein in a Family With Qualitative (Type II) Deficiency

The genomic analysis of a 70-year-old man with recurrent deep venous thrombosis having a protein S (PS)-deficient phenotype corresponding to both type III and type II evidenced two different mutations: a +5 g→a mutation in the donor splice site of intron e (ivs e) and a ser 460 to Pro mutation. The propositus' son, who had a type II PS deficiency phenotype, only bore the ivs e +5 g→a mutation. The study of platelet PS mRNA prepared from this subject showed that the ivs e, +5 g→a mutation led to the generation of two abnormal transcripts, one lacking exon 5 and the other lacking exons 5 and 6. The presence of an additional PS band with a decreased molecular mass on immunoblots performed in reducing conditions suggested the presence of truncated PS lacking EGF1 (encoded by exon 5). Two monoclonal antibodies (MoAbs) were used to further characterize the nonfunctional plasma PS. Comparison of PS levels measured with each of these MoAbs and PS levels in conventional assays was consistent with the presence of an abnormal inactive protein in the plasma of both patients bearing the ivs e, +5 g→a mutation, suggesting that variant PS lacking EGF1 is secreted but is devoid of activated protein C cofactor activity.

A Mutation of the Active Protein S Gene Leading to an EGF1-Lacking Protein in a Family With Qualitative (Type II) Deficiency

The genomic analysis of a 70-year-old man with recurrent deep venous thrombosis having a protein S (PS)-deficient phenotype corresponding to both type III and type II evidenced two different mutations: a +5 g→a mutation in the donor splice site of intron e (ivs e) and a ser 460 to Pro mutation. The propositus' son, who had a type II PS deficiency phenotype, only bore the ivs e +5 g→a mutation. The study of platelet PS mRNA prepared from this subject showed that the ivs e, +5 g→a mutation led to the generation of two abnormal transcripts, one lacking exon 5 and the other lacking exons 5 and 6. The presence of an additional PS band with a decreased molecular mass on immunoblots performed in reducing conditions suggested the presence of truncated PS lacking EGF1 (encoded by exon 5). Two monoclonal antibodies (MoAbs) were used to further characterize the nonfunctional plasma PS. Comparison of PS levels measured with each of these MoAbs and PS levels in conventional assays was consistent with the presence of an abnormal inactive protein in the plasma of both patients bearing the ivs e, +5 g→a mutation, suggesting that variant PS lacking EGF1 is secreted but is devoid of activated protein C cofactor activity.

Xenogeneic endothelial cells activate human prothrombin

BACKGROUND

Delayed xenograft rejection is characterized by platelet activation and fibrin deposition and is thought to occur independently of complement activation. We have therefore investigated the potential for xenogeneic endothelial cells (EC) to regulate the conversion of prothrombin to thrombin, a central component of the final common pathway of coagulation and an important platelet agonist.

METHODS AND RESULTS

Quiescent porcine aortic EC (PAEC) were found to convert high levels of human prothrombin to thrombin (0.234+/-0.019 IU/ml) when compared with human aortic EC (0.017+/-0 IU/ml, 30-min time point, chromogenic assay; P<0.001). PAEC activation by human complement resulted in comparable levels of thrombin generation. Prothrombin conversion by PAEC as determined by generation of F1+2 (1.909+/-0.119 nmol/L) and formation of thrombin-antithrombin III complexes (125.611+/-6.373 microg/L) was significantly greater than the matched human aortic EC values (F1+2: 1.539+/-0.03 nmol/L, P<0.001; thrombin-antithrombin III: 1.833+/-0.104 microg/L, P<0.001). Sequential analysis of prothrombin activation by PAEC indicated generation of the intermediate meizothrombin followed by autolytically accelerated thrombin formation. Subsequent experiments established important cross-species' incompatibilities with respect to porcine thrombomodulin interaction with human thrombin and protein C in that PAEC had a reduced capacity to generate activated human protein C in vitro.

CONCLUSION

These observations indicate a potentially important molecular barrier involving blood coagulation that may impact on the planned clinical application of porcine transgenic organs.

ProC® Global: the first functional screening assay for the complete protein C pathway

In clinical practice, venous thromboembolic complications are much more frequent than bleeding disorders. In fact, disturbances within the protein C pathway due to coagulation factor V (FV) Leiden mutation and deficiency of protein C or protein S are the most frequent abnormalities in hereditary thrombophilia. Furthermore, acquired dysfunctions of the protein C system may predispose the single individual to an increased thrombotic risk. A routine-suited screening assay that would allow the monitoring of the proper interplay of factors in the protein C pathway could add an important factor to the basic coagulation profile. This consists of the prothrombin time and of the activated partial thromboplastin time, which currently allow only a screening for increased risk for bleeding but not for venous thromboembolism. A new functional screening test for the protein C system such as the presented ProC® Global should therefore facilitate detection of FV Leiden as well as deficiency of protein C and protein S. The results of the present evaluation indicate that ProC Global is highly sensitive to activated protein C resistance/FV Leiden (100%) and protein C deficiency (90%) and sensitive to protein S deficiency (63%). Furthermore, the assay gives a quantitative measure of the net potential of the protein C pathway in relation to the intrinsic procoagulant system. The use of this assay for a prospective assessment of thromboembolic risk is the subject of current studies.

Loss of ATP diphosphohydrolase activity with endothelial cell activation

Quiescent endothelial cells (EC) regulate blood flow and prevent intravascular thrombosis. This latter effect is mediated in a number of ways, including expression by EC of thrombomodulin and heparan sulfate, both of which are lost from the EC surface as part of the activation response to proinflammatory cytokines. Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature. An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis. We describe here that the antithrombotic effects of the ATPDase, like heparan sulfate and thrombomodulin, are lost after EC activation, both in vitro and in vivo. Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.

Coagulation assay with improved specificity to factor V mutants insensitive to activated protein C

The prevalence of a new hereditary defect in the protein C anticoagulant pathway, the factor V-Leiden, has been reported to range between 20% to 60% in familial thrombophilia. In addition to differences in patient groups, these very divergent numbers might also be due to the detection method applied. In most studies a modified APTT was used, where activated protein C (APC) is added simultaneously with the start of the clotting reaction. However, this method is also influenced by other factors like protein S, factor VIII or lupus anticoagulants. Furthermore, heparin or oral anticoagulant therapy might interfere. We tried to develop a coagulation assay dependent only on those mutant forms of factor V stable against proteolytic attack by APC. For this purpose, samples were first diluted with a factor V deficient plasma (f.V-dp). Then, coagulation was initiated either on the intrinsic pathway (APTT) or on the extrinsic pathway (PT) or, by directly activating factor X (RVVT). Additionally, APC was added, which prolongation of the clotting time. Deficiencies in protein S or the presence of factor V-Leiden resulted in a less pronounced clotting time prolongation. Titration of protein S-deficient plasma samples with f.V-dp diminished this effect. In contrast, in samples with factor V-Leiden the difference to the clotting time obtained with normal plasma even increased in the order APTT>>RVVT>PT. In the APTT-based method high concentrations of factor VIII shortened the clotting times, thus mimicking a factor V-Leiden defect. This could be compensated for up to 4 U/ml factor VIII by using a f.V-dp containing factor VIII at physiological concentration. Neither unfractionated nor LMW-heparin (up to 2 U/ml) interfered with the determination. In a brief investigation on 16 plasma samples from patients under oral anticoagulation 5 (30%) showed a similar behaviour as observed with normal plasma from factor V-Leiden carriers. These results let us suggest that by simply mixing the patient sample with a factor V-deficient plasma factor V-Leiden might be detected also in patients under oral anticoagulant therapy. Inherited disorders of protein C or protein S are well known as thrombotic risk factors (1). The recent investigations by Dahlbäck et al. (2) led to the discovery of a new hereditary defect in the protein C anticoagulant pathway: the factor V-Leiden (3). This mutation renders activated factor V stable against proteolytic attack by activated protein C (APC). The reports on the prevalence of this mutation in thrombophilic patients show a considerable variation between 21% (4) and 64% (5).(ABSTRACT TRUNCATED AT 400 WORDS)

Possible involvement of cytokines in diffuse intravascular coagulation and thrombosis

Inflammation and the cytokines clearly affect the coagulation system. Less clear are the specific influences of the coagulation system on inflammation. In this chapter only some of the coagulation systems affected by the cytokines are discussed, and the influences on the fibrinolytic system, which is also downregulated by selected cytokines are not mentioned; see Schneiderman and Loskutoff (1991) for a brief review. The major focus is on possible models by which inflammation and coagulation are linked, and examples where in vitro studies have led to correct in vivo predictions and where the results remain ambiguous. Finally, this chapter is clearly a biased perspective with the primary emphasis on the components and pathways with which the author has personal experience.

Paradoxical embolism as a cause of ischemic stroke of uncertain etiology. A transcranial Doppler sonographic study

BACKGROUND AND PURPOSE

This study was designed to test the hypothesis that paradoxical embolization would be a cause of embolic strokes and transient ischemic attacks in patients with stroke of uncertain etiology in all age groups.

METHODS

Thirty patients who had stroke of uncertain etiology were studied. They were divided into the following three groups: 13 patients with sudden onset (group A), 11 patients with subacute onset (group B), and 6 asymptomatic stroke patients (group C). Eleven patients with stroke of obvious etiology (group D) and 11 normal healthy volunteers (group E) were also studied as controls. In all patients transcranial Doppler sonography and contrast echocardiography were recorded simultaneously after intravenous injection of the contrast medium. Findings of positive patient foramen ovale in contrast echocardiography or "chirp" sounds in transcranial Doppler sonography were defined as positive for paradoxical contrast embolization. Radioisotope phlebography of the lower extremities and pulmonary scintigraphy, using technetium-99 macroaggregated albumin, were performed in all 17 patients who had positive findings of paradoxical contrast embolization and in 12 patients whose findings were negative.

RESULTS

Positive findings of paradoxical contrast embolization were found in 17 subjects by transcranial Doppler sonography but in only 8 on contrast echocardiography. These positive findings were detected more frequently in group A (77%) than in groups B, D, and E (9%, 18%, and 9%, respectively) (P < .05). In group C, 4 of 6 patients (67%) had positive findings. There were positive findings on both phlebography and pulmonary scintigraphy only in 6 group A patients, with positive findings of paradoxical contrast embolization.

CONCLUSIONS

Transcranial Doppler sonography is a sensitive detector of right-to-left shunts. Paradoxical cerebral embolization might be frequent in patients with stroke of unknown etiology, especially when the stroke is of sudden onset.