Fibrinogen: Structure, abnormalities and laboratory assays

Fibrinogen is the primary precursor protein for the fibrin clot, which is the final target of blood clotting. It is also an acute phase reactant that can vary under physiologic and inflammatory conditions. Disorders in fibrinogen concentration and/or function have been variably linked to the risk of bleeding and/or thrombosis. Fibrinogen assays are commonly used in the management of bleeding as well as the treatment of thrombosis. This chapter examines the structure of fibrinogen, its role in hemostasis as well as in bleeding abnormalities and measurement thereof with respect to clinical management.

Thrombin generation potential is increased in patients with autoimmune inflammatory myopathies

PURPOSE

Dermatomyositis and polymyositis (DM/PM) are rare autoimmune inflammatory myopathies, characterized by an increased risk of cardiovascular and thromboembolic events, likely related to the prothrombotic plasma properties. The aim of this study was to assess the in vitro thrombin generation profile as a biomarker of plasma procoagulant properties in DM/PM patients.

METHODS

In 58 clinically stable DM/PM patients and 67 controls matched for sex, age, body mass index, we measured plasma thrombin generation potential using the Calibrated Automated Thrombinography (CAT) and analyzed its relationship with clinical disease characteristics, including autoantibodies profile.

RESULTS

Patients with DM/PM had a 21% increase in endogenous thrombin potential (ETP), 36% higher peak thrombin concentration, and 11% faster thrombin generation, compared to controls (p ​< ​0.001, all, also after adjustment for potential confounders). Interestingly, although both diseases did not differ in thrombin generation potential, heterogenous variables predicted elevated ETPs in both of them. In DM, that was higher fibrinogen, C-reactive protein, and total cholesterol, whereas in PM, presence of arthritis and increased blood platelet count. Surprisingly, thrombin formation capacity remained in a robust inverse relationship with serum troponin (r ​= ​-0.67, p ​< ​0.001) in the patient group.

CONCLUSIONS

DM/PM patients are characterized by an increased thrombin generation potential, suggesting prothrombotic plasma properties in both diseases. However, more studies are needed to verify its rationale and role in DM/PM clinical course and unfavorable clinical outcomes.

Tetramethylpyrazine Retards the Progression and Fibrogenesis of Endometriosis

The development of more efficacious, non-hormonal therapeutics for endometriosis is still an unmet medical need begging to be fulfilled. Growing evidence indicates that endometriotic lesions are wounds undergoing repeated tissue injury and repair, and, as such, platelets play an important role in lesional progression. Tetramethylpyrazine (TMP), a compound derived from a herb that has been used for thousands of years to combat “blood stasis” in traditional Chinese medicine, is a prescription drug in China for the treatment of cerebrovascular disorders. We tested the hypothesis that TMP can decelerate lesional progression through arresting epithelial-mesenchymal transition (EMT), fibroblast-to-myofibroblast transdifferentiation (FMT), and fibrogenesis. We found in our in vitro experiments that TMP treatment suppresses platelet-induced EMT, FMT, cellular contractility, and collagen production in a concentration-dependent manner. We also showed that in a mouse model of endometriosis, treatment with TMP significantly reduced lesion weight and the extent of lesional fibrosis and improved hyperalgesia, mostly likely through the reduction of lesional aggregation of platelets and the lesional expression of markers of EMT, FMT, and fibrogenesis. In light of our results and in view of its excellent safety profiles, TMP appears to be a promising drug candidate for treating endometriosis.

High Interleukin-6 Plasma Concentration upon Admission Is Predictive of Massive Transfusion in Severely Injured Patients

Severe bleeding remains a prominent cause of early in-hospital mortality in major trauma patients. Thus, prompt prediction of patients at risk of massive transfusion (MT) is crucial. We investigated the ability of the inflammatory marker interleukin (IL)-6 to forecast MT in severely injured trauma patients. IL-6 plasma levels were measured upon admission. Receiver operating characteristic curves (ROCs) were calculated, and sensitivity and specificity were determined. In this retrospective study, a total of 468 predominantly male (77.8%) patients, with a median injury severity score (ISS) of 25 (17–34), were included. The Youden index for the prediction of MT within 6 and 24 h was 351 pg/mL. Patients were dichotomized into two groups: (i) low-IL-6 < 350 pg/mL and (ii) high-IL-6 ≥ 350 pg/mL. IL-6 ≥ 350 pg/mL was associated with a lower prothrombin time index, a higher activated partial thromboplastin time, and a lower fibrinogen concentration compared with IL-6 < 350 pg/mL (p <0.0001 for all). Thromboelastometric parameters were significantly different between groups (p <0.03 in all). More patients in the high-IL-6 group received MT (p <0.0001). The ROCs revealed an area under the curve of 0.76 vs. 0.82 for the high-IL-6 group for receiving MT in the first 6 and 24 h. IL-6 ≥ 350 pg/mL predicted MT within 6 and 24 h with a sensitivity of 45% and 58%, respectively, and a specificity of 89%. IL-6 ≥ 350 pg/mL appears to be a reasonable early predictor for coagulopathy and MT within the first 6 and 24 h intervals. Large-scale prospective studies are warranted to confirm these findings.

The Glasgow Prognostic Score and fibrinogen to albumin ratio as prognostic factors in hospitalized patients with COVID-19

Aim: This study aims to determine the prognostic value of the Glasgow Prognostic Score (GPS) and fibrinogen to albumin ratio (FAR) in patients with COVID-19.

Methods: Electronic database records of 400 patients with COVID-19 were retrospectively analyzed and the initial levels of CRP, albumin, fibrinogen values were recorded. The ground-glass opacities (GGO) and consolidations were evaluated on thorax CT. Hospital mortality and the need for intensive care unit (ICU) transfer were determined as adverse outcomes.

Results: It was determined that 345 patients (86.25%) were discharged while 31 patients (7.75%) were transferred to ICU in addition to 24 patients who died (6%). The rates of deaths and transfers to ICU were significantly increased in GPS 2 group compared to both GPS 0 and 1 groups. Additionally, increased FAR was observed in patients who died and transferred to ICU compared to the discharged patients. The FAR was significantly increased in patients with diffuse GGO. Logistic regression analysis indicated that FAR ≥144.59 and the presence of GPS 2 were independent predictors of the adverse outcomes in COVID-19 patients.

Conclusion: Our results demonstrated that the GPS and FAR could possess a predictive value for adverse outcomes in patients with COVID-19.

The short- and long-term associations of particulate matter with inflammation and blood coagulation markers: A meta-analysis

Inflammation and the coagulation cascade are considered to be the potential mechanisms of ambient particulate matter (PM) exposure-induced adverse cardiovascular events. Tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), interleukin-8 (IL-8), and fibrinogen are arguably the four most commonly assayed markers to reflect the relationships of PM with inflammation and blood coagulation. This review summarized and quantitatively analyzed the existing studies reporting short- and long-term associations of PM2.5(PM with an aerodynamic diameter ≤2.5 μm)/PM10 (PM with an aerodynamic diameter≤10 μm) with important inflammation and blood coagulation markers (TNF-α, IL-6, IL-8, fibrinogen). We reviewed relevant studies published up to July 2020, using three English databases (PubMed, Web of Science, Embase) and two Chinese databases (Wang-Fang, China National Knowledge Infrastructure). The OHAT tool, with some modification, was applied to evaluate risk of bias. Meta-analyses were conducted with random-effects models for calculating the pooled estimate of markers. To assess the potential effect modifiers and the source of heterogeneity, we conducted subgroup analyses and meta-regression analyses where appropriate. The assessment and correction of publication bias were based on Begg's and Egger's test and "trim-and-fill" analysis. We identified 44 eligible studies. For short-term PM exposure, the percent change of a 10 μg/m3 PM2.5 increase on TNF-α and fibrinogen was 3.51% (95% confidence interval (CI): 1.21%, 5.81%) and 0.54% (95% confidence interval (CI): 0.21%, 0.86%) respectively. We also found a significant short-term association between PM10 and fibrinogen (percent change = 0.17%, 95% CI: 0.04%, 0.29%). Overall analysis showed that long-term associations of fibrinogen with PM2.5 and PM10 were not significant. Subgroup analysis showed that long-term associations of fibrinogen with PM2.5 and PM10 were significant only found in studies conducted in Asia. Our findings support significant short-term associations of PM with TNF-α and fibrinogen. Future epidemiological studies should address the role long-term PM exposure plays in inflammation and blood coagulation markers level change.

Pravastatin Alleviates Radiation Proctitis by Regulating Thrombomodulin in Irradiated Endothelial Cells

Although radiotherapy plays a crucial in the management of pelvic tumors, its toxicity on surrounding healthy tissues such as the small intestine, colon, and rectum is one of the major limitations associated with its use. In particular, proctitis is a major clinical complication of pelvic radiotherapy. Recent evidence suggests that endothelial injury significantly affects the initiation of radiation-induced inflammation. The damaged endothelial cells accelerate immune cell recruitment by activating the expression of endothelial adhesive molecules, which participate in the development of tissue damage. Pravastatin, a cholesterol lowering drug, exerts persistent anti-inflammatory and anti-thrombotic effects on irradiated endothelial cells and inhibits the interaction of leukocytes and damaged endothelial cells. Here, we aimed to investigate the effects of pravastatin on radiation-induced endothelial damage in human umbilical vein endothelial cell and a murine proctitis model. Pravastatin attenuated epithelial damage and inflammatory response in irradiated colorectal lesions. In particular, pravastatin improved radiation-induced endothelial damage by regulating thrombomodulin (TM) expression. In addition, exogenous TM inhibited leukocyte adhesion to the irradiated endothelial cells. Thus, pravastatin can inhibit endothelial damage by inducing TM, thereby alleviating radiation proctitis. Therefore, we suggest that pharmacological modulation of endothelial TM may limit intestinal inflammation after irradiation.

Sepsis: Inflammation Is a Necessary Evil

Sepsis is one of the leading causes of deaths world-wide and yet there are no therapies available other than ICU treatment. The patient outcome is determined by a complex interplay between the pro and anti-inflammatory responses of the body i.e., a homeostatic balance between these two competing events to be achieved for the patient’s recovery. The initial attempts on drug development mainly focused on controlling inflammation, however, without any tangible outcome. This was despite most deaths occurring during the immune paralysis stage of this biphasic disease. Recently, the focus has been shifting to understand immune paralysis (caused by apoptosis and by anti-inflammatory cytokines) to develop therapeutic drugs. In this review we put forth an argument for a proper understanding of the molecular basis of inflammation as well as apoptosis for developing an effective therapy.

The multifaceted role of fibrinogen in tissue injury and inflammation

The canonical role of the hemostatic and fibrinolytic systems is to maintain vascular integrity. Perturbations in either system can prompt primary pathological end points of hemorrhage or thrombosis with vessel occlusion. However, fibrin(ogen) and proteases controlling its deposition and clearance, including (pro)thrombin and plasmin(ogen), have powerful roles in driving acute and reparative inflammatory pathways that affect the spectrum of tissue injury, remodeling, and repair. Indeed, fibrin(ogen) deposits are a near-universal feature of tissue injury, regardless of the nature of the inciting event, including injuries driven by mechanical insult, infection, or immunological derangements. Fibrin can modify multiple aspects of inflammatory cell function by engaging leukocytes through a variety of cellular receptors and mechanisms. Studies on the role of coagulation system activation and fibrin(ogen) deposition in models of inflammatory disease and tissue injury have revealed points of commonality, as well as context-dependent contributions of coagulation and fibrinolytic factors. However, there remains a critical need to define the precise temporal and spatial mechanisms by which fibrinogen-directed inflammatory events may dictate the severity of tissue injury and coordinate the remodeling and repair events essential to restore normal organ function. Current research trends suggest that future studies will give way to the identification of novel hemostatic factor-targeted therapies for a range of tissue injuries and disease.

Pro-Thrombotic Activity of Blood Platelets in Multiple Sclerosis

The available data, including experimental studies, clearly indicate an excessive intravascular activation of circulating platelets in multiple sclerosis (MS) and their hyper-responsiveness to a variety of physiological activators. Platelet activation is manifested as an increased adhesion and aggregation and is accompanied by the formation of pro-thrombotic microparticles. Activated blood platelets also show an expression of specific membrane receptors, synthesis many of biomediators, and generation of reactive oxygen species. Epidemiological studies confirm the high risk of stroke or myocardial infarction in MS that are ischemic incidents, strictly associated with incorrect platelet functions and their over pro-thrombotic activity. Chronic inflammation and high activity of pro-oxidative processes in the course of MS are the main factors identified as the cause of excessive platelet activation. The primary biological function of platelets is to support vascular integrity, but the importance of platelets in inflammatory diseases is also well documented. The pro-thrombotic activity of platelets and their inflammatory properties play a part in the pathophysiology of MS. The analysis of platelet function capability in MS could provide useful information for studying the pathogenesis of this disease. Due to the complexity of pathological processes in MS, medication must be multifaceted and blood platelets can probably be identified as new targets for therapy in the future.

Thrombomodulin regulates monocye differentiation via PKCδ and ERK1/2 pathway in vitro and in atherosclerotic artery

Thrombomodulin (TM) modulates the activation of protein C and coagulation. Additionally, TM regulates monocyte migration and inflammation. However, its role on monocyte differentiation is still unknown. We investigated the effects of TM on monocyte differentiation. First, we found that TM was increased when THP-1 cells were treated with phorbol-12-myristate-13-acetate (PMA). Overexpression of TM enhanced the macrophage markers, CD14 and CD68 expression in PMA-induced THP-1. TM siRNA depressed the PMA-induced increase of p21^Cip1/WAF1 via ERK1/2-NF-kB p65 signaling. TM regulated cytoskeletal reorganization via its interaction with paxillin, cofilin, LIMK1, and PYK2. In addition, PMA-induced p21^Cip1/WAF1 expression, CD14-positive cell labeling intensity and ERK1/2 phosphorylation were markedly inhibited when protein kinase C-δ (PKCδ) was knocked down. We identified that TM directly interacts with PKCδ. PKCδ was highly expressed in human atherosclerotic arteries and colocalized with TM in CD68-positive infiltrated macrophages of plaques, indicating that the coordination between TM and PKCδ in macrophages participated in atherogenesis. TM may act as a scaffold for PKCδ docking, which keeps PKCδ in the region close to the monocyte membrane to promote the activation of ERK1/2. Taken together, our findings suggest that TM-PKCδ interaction may contribute to cardiovascular disorders by affecting monocye differentiation, which may develop future therapeutic applications.

A 2014 Update on Coagulation Management for Cardiopulmonary Bypass

Coagulopathy after cardiac surgery with cardiopulmonary bypass is a serious complication that may result in massive bleeding requiring transfusion of significant amounts of blood products, plasma, and platelets. In addition to increased patient morbidity and mortality it is associated with longer hospital stay and increased resource utilization. The current review discusses aspects in cardiopulmonary bypass–induced coagulopathy with emphasis on point-of-care testing and individualized “goal-directed” therapy in patients who develop excessive bleeding after cardiac surgery.

Therapeutic effects of Shenfu Injection on post-cardiac arrest syndrome

Survival rates after cardiac arrest have not changed substantially over the past 5 decades. Postcardiac arrest (CA) syndrome (PCAS) is the primary reason for the high mortality rate after successful restoration of spontaneous circulation (ROSC). Intravenous administration of Shenfu Injection (, SFI) may attenuate post-CA myocardial dysfunction and cerebral injury, inhibit systemic ischemia/reperfusion responses, and treat underlying diseases. In this article, we reviewed the therapeutic effects of SFI in PCAS. SFI might be useful in the treatment of PCAS, incorporating the multi-link and multi-target advantages of Chinese medicine into PCAS management. Further experimental and clinical research to verify the therapeutic effects of SFI in PCAS is required.

Coagulation and the fibrin network in rheumatic disease: a role beyond haemostasis

Activation of the immune system has been increasingly recognised to be associated with procoagulatory status in patients with inflammatory rheumatic disease. Changes in endothelial cell and platelet activation, blood flow, expression and activity of different coagulation factors, and impaired fibrinolysis serve as pathophysiological basis for enhanced risk of venous thromboembolism in inflammatory rheumatic diseases, such as rheumatoid arthritis (RA), connective tissue diseases and vasculitides. Recent studies identifying mechanisms for a functional role of coagulation factors beyond haemostasis have provided examples of interesting links between the coagulation system and innate immune activation. Furthermore, citrullinated fibrinogen is an important and early autoantigen in patients with RA carrying the HLA-DRβ1 shared epitope allele, which demonstrates an adaptive immune response to a coagulation factor in an inflammatory rheumatic disease. Additional studies have provided strong evidence that a multitude of different components of the haemostatic system (such as thrombin, fibrinogen, coagulation factor XIII and factors of the fibrinolytic system) are relevant mediators of inflammatory processes as well as of inflammatory control. Understanding the interactions between coagulation and the immune system in inflammatory rheumatic diseases will not only improve our knowledge of disease mechanisms, but could also permit the development of innovative therapeutic interventions.

Protective cross talk between activated protein C and TNF signaling in vascular endothelial cells: implication of EPCR, noncanonical NF-κB, and ERK1/2 MAP kinases

Activated protein C (APC) is a natural anticoagulant protease that displays cytoprotective and antiinflammatory activities and has been demonstrated to reduce mortality of patients with severe sepsis. However, APC signaling is not fully understood. This study further investigated the antiinflammatory effects of APC in vascular endothelial cells (EC) and examined the cross talk between APC and TNF signaling. Analysis of the regulatory mechanisms mediated by APC on vascular human EC shows that APC impairs TNF signaling by triggering a preemptive activation of intracellular pathways. We found that APC signaling causes a moderate but significant induction of cell adhesion molecules (CAMs) including VCAM-1 at mRNA and protein levels. Activation of the noncanonical NF-κB and ERK1/2 are both pivotal to APC signaling leading to VCAM-1 expression. APC upregulates TNF receptor-associated factor 2 (TRAF2) and phosphorylates NF-κB p65 at Ser276 and Ser536 independently of IκB degradation. The ultimate protective antiinflammatory effect of APC in response to TNF is associated with a sustained activation of ERK1/2 and Akt while phosphorylation of NF-κB p65 is precluded. Inhibitors of ERK (PD98059 and U0126) abolish the antiinflammatory signal mediated by APC. Blocking antibodies and silencing assays also suggest that, in EC, protease-activated receptor 1 and endothelial protein C receptor (EPCR) both conduct ERK activation and VCAM-1 induction in response to APC. To conclude, APC protects EC by attenuating CAM expression during inflammation. APC engages a regulatory cross talk involving EPCR, ERK, and NF-κB that impairs TNF signaling.

The development of inflammatory joint disease is attenuated in mice expressing the anticoagulant prothrombin mutant W215A/E217A

Thrombin is a positive mediator of thrombus formation through the proteolytic activation of protease-activated receptors (PARs), fibrinogen, factor XI (fXI), and other substrates, and a negative regulator through activation of protein C, a natural anticoagulant with anti-inflammatory/cytoprotective properties. Protease-engineering studies have established that 2 active-site substitutions, W215A and E217A (fII(WE)), result in dramatically reduced catalytic efficiency with procoagulant substrates while largely preserving thrombomodulin (TM)-dependent protein C activation. To explore the hypothesis that a prothrombin variant favoring antithrombotic pathways would be compatible with development but limit inflammatory processes in vivo, we generated mice carrying the fII(WE) mutations within the endogenous prothrombin gene. Unlike fII-null embryos, fII(WE/WE) mice uniformly developed to term. Nevertheless, these mice ultimately succumbed to spontaneous bleeding events shortly after birth. Heterozygous fII(WT/WE) mice were viable and fertile despite a shift toward an antithrombotic phenotype exemplified by prolonged tail-bleeding times and times-to-occlusion after FeCl₃ vessel injury. More interestingly, prothrombin(WE) expression significantly ameliorated the development of inflammatory joint disease in mice challenged with collagen-induced arthritis (CIA). The administration of active recombinant thrombin(WE) also suppressed the development of CIA in wild-type mice. These studies provide a proof-of-principle that pro/thrombin variants engineered with altered substrate specificity may offer therapeutic opportunities for limiting inflammatory disease processes.

Liposomal Formulations of Thrombomodulin Increase Engraftment after Intraportal Islet Transplantation

Early destruction of donor islet grafts due to an instant blood-mediated inflammatory reaction (IBMIR) remains a major obstacle in islet transplantation. Thrombomodulin plays an important role in limiting coagulation and inflammatory events through a variety of effects. In this study, we investigated the ability of thrombomodulin (TM), when reconstituted as a liposomal formulation, to enhance early syngeneic islet engraftment by minimizing or abrogating the IBMIR. Administration of TM significantly improved early engraftment of syngeneic islets after intraportal transplantation in diabetic mice. In the absence of treatment, conversion to euglycemia was observed among 46.6% (7/15) of recipients. In contrast, administration of TM led to euglycemia in 93.3% (14/15) of recipients ( p = 0.0142). Recipients that received TM exhibited a lower incidence of primary nonfunction and better glucose control over a 30-day period after transplantation. Fibrin deposition ( p < 0.05), neutrophil infiltration ( p < 0.05), expression of TNF-α and IL-β mRNA ( p < 0.05), as well as NF-κB activity ( p < 0.05) were significantly reduced in the liver of islet recipients having been treated with liposomal TM. These data demonstrate that TM significantly improves early syngeneic islet engraftment through effects that target both coagulation and inflammatory pathways.

Improving the outcome of in-hospital cardiac arrest: the importance of being EARNEST

Cardiopulmonary resuscitation techniques were introduced more than 50 years ago, yet the rate of survival from cardiac arrest, particularly in the hospital setting, remains dismally low. This article reviews the prevalence, etiology, and outcome of in-hospital cardiac arrest, with a focus on the determinants of outcome that are amenable to improvement. These include principally components of basic life support that may be supported by either prompting or mechanical assistance (eg, chest compression, ventilation, and defibrillation). Also reviewed are preevent and postevent effectors such as medical staff skills and recognition of impending arrest, induction of mild hypothermia, and stabilization after return of spontaneous circulation.

Lectin-like domain of thrombomodulin binds to its specific ligand Lewis Y antigen and neutralizes lipopolysaccharide-induced inflammatory response

Thrombomodulin (TM), a widely expressing glycoprotein originally identified in vascular endothelium, is an important cofactor in the protein C anticoagulant system. TM appears to exhibit anti-inflammatory ability through both protein C-dependent and -independent pathways. We presently have demonstrated that recombinant N-terminal lectinlike domain of TM (rTMD1) functions as a protective agent against sepsis caused by Gram-negative bacterial infections. rTMD1 caused agglutination of Escherichia coli and Klebsiella pneumoniae and enhanced the macrophage phagocytosis of these Gram-negative bacteria. Moreover, rTMD1 bound to the Klebsiella pneumoniae and lipopolysaccharide (LPS) by specifically interacting with Lewis Y antigen. rTMD1 inhibited LPS-induced inflammatory mediator production via interference with CD14 and LPS binding. Furthermore, rTMD1 modulated LPS-induced mitogen-activated protein kinase and nuclear factor-kappaB signaling pathway activations and inducible nitric oxide synthase expression in macrophages. Administration of rTMD1 protected the host by suppressing inflammatory responses induced by LPS and Gram-negative bacteria, and enhanced LPS and bacterial clearance in sepsis. Thus, rTMD1 can be used to defend against bacterial infection and inhibit LPS-induced inflammatory responses, suggesting that rTMD1 may be valuable in the treatment of severe inflammation in sepsis, especially in Gram-negative bacterial infections.

Alternative mRNA is favored by the A3 haplotype of the EPCR gene PROCR and generates a novel soluble form of EPCR in plasma

The endothelial cell protein C receptor also exists in soluble form in plasma (sEPCR), resulting from ADAM17 cleavage. Elevated sEPCR levels are observed in subjects carrying the A3 haplotype, which is characterized by a Ser219Gly substitution in the transmembrane domain, rendering the receptor more sensitive to cleavage. Because sEPCR production is not completely blocked by metalloprotease inhibition, we looked for another mechanism. Comparing mRNA expression patterns and levels in A3 and non-A3 cells from 32 human umbilical cord veins, we detected a truncated mRNA in addition to the full-length mRNA. This truncated mRNA was 16 times more abundant in A3 human umbilical vein endothelial cells than in non-A3 human umbilical vein endothelial cells and encoded a protein lacking the transmembrane domain. We stably expressed a recombinant form of this protein (rEPCRisoform) and a protein mimicking the plasma sEPCR (rEPCRsol). Functional studies of the purified recombinant proteins revealed that the rEPCRisoform bound to recombinant protein C with similar affinity than rEPCRsol and that it also inhibited the anticoagulant activity of APC. Trace amounts of the EPCR isoform were found in the plasma of A3 subjects. These results suggest that the sEPCRisoform could contribute to the regulatory effect of sEPCR in plasma.

Influence of Gender on Outcome of Severe Sepsis

Whether gender influences the outcome of severe sepsis remains a matter of debate. Because many confounding variables may affect observed associations between gender and mortality, high-quality statistical analyses are essential to carefully adjust the two groups of patients. About 55% to 65% of patients with sepsis have chronic co-morbidities associated with immune dysfunction (e.g., chronic renal failure, diabetes mellitus, human immunodeficiency virus [HIV] infection, and alcohol abuse), which increase the susceptibility to sepsis [1]. Genetic polymorphisms that affect the susceptibility to infection and/or the severity of the systemic response to infection [2] may lead to variability among individuals and between males and females [3]. Access to healthcare, another determinant of the incidence and outcome of sepsis, varies according to age, ethnic group, and gender, although a recent study conducted in the USA found only relatively small quality-of-care differences between males and females or across income groups compared to the gap for each subgroup between observed and desirable quality of health care [4]. Here, we review the data on the existence of, and reasons for, associations between gender and outcome of severe sepsis (Fig. 1).

Kruppel-like factor 2 as a novel mediator of statin effects in endothelial cells

BACKGROUND

Although 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) are known to modulate endothelial function, the transcriptional mechanisms underlying these effects are incompletely understood. We hypothesized that Lung-Kruppel-like factor (LKLF/KLF2), a novel and potent regulator of endothelial gene expression, may mediate the downstream effects of statins. Here we report that statin-induced expression of endothelial NO synthase (eNOS) and thrombomodulin is KLF2 dependent.

METHODS AND RESULTS

KLF2 mRNA was induced by treatment with multiple statins in a concentration-dependent manner. Multiple lines of evidence suggest that this induction is dependent on inhibition of the Rho pathway and requires de novo transcription. Furthermore, promoter deletion and mutational analyses suggest that mevastatin induced KLF2 promoter activity through a single myocyte enhancer factor binding site. Finally, small-interfering RNA-mediated knockdown of KLF2 strongly attenuated the ability of mevastatin to increase eNOS and thrombomodulin accumulation in endothelial cells.

CONCLUSIONS

Taken together, these observations indicate that statin-dependent induction of eNOS and thrombomodulin requires KLF2 and thereby provides a novel molecular target for modulating endothelial function in vascular disease.

Estrogenic regulation of tissue factor and tissue factor pathway inhibitor in platelets

Oral estrogen treatment increases thrombotic risk. Tissue factor (TF), tissue factor pathway inhibitor (TFPI), and platelet interaction with leukocytes are important determinants of thrombogenesis. Therefore, the present study was designed to define and compare platelet TF and TFPI mRNA and adhesion protein expression in platelets derived from animals treated with different types of oral estrogens. Ovariectomized pigs were treated with 17beta-estradiol (2 mg/day), conjugated equine estrogen (CEE; 0.625 mg/day), or raloxifene (60 mg/day) for 4 wk. Compared with intact animals, ovariectomy and treatment differentially affected populations of leukocytes: neutrophils decreased whereas lymphocytes increased significantly 4 wk after ovariectomy and with 17beta-estradiol and CEE treatments; eosinophils increased only with 17beta-estradiol treatment. Content of TF protein increased in platelets from 17beta-estradiol- and raloxifene-treated pigs, whereas TF mRNA was detected only in platelets from 17beta-estradiol- and CEE treated pigs. TFPI mRNA increased in platelets after ovariectomy and estrogen treatment. Only a trace of TFPI protein was detected, but a higher-molecular-mass protein was observed in all treatment groups. Expression of CD40 and CD40 ligand increased with ovariectomy and decreased with 17beta-estradiol and CEE treatments more than with raloxifene. The ratio of activated to basal P-selectin expression decreased with ovariectomy and increased with raloxifene treatments. These results suggest that estrogenic formulations may affect individual thrombotic risk by different mechanisms that regulate TF and platelet-leukocytic interactions. These studies provide the rationale for evaluation of interactions among platelets and TF and TFPI expression on thrombin generation during estrogen treatment in humans.

Kruppel-like factor 2 (KLF2) regulates endothelial thrombotic function

The vascular endothelium maintains blood fluidity by inhibiting blood coagulation, inhibiting platelet aggregation, and promoting fibrinolysis. Endothelial cells lose these nonthrombogenic properties on exposure to proinflammatory stimuli. We recently identified the Kruppel-like factor KLF2 as a novel regulator of endothelial proinflammatory activation. Here it is found that KLF2 differentially regulates key factors involved in maintaining an antithrombotic endothelial surface. Overexpression of KLF2 strongly induced thrombomodulin (TM) and endothelial nitric oxide synthase (eNOS) expression and reduced plasminogen activator inhibitor-1 (PAI-1) expression. Furthermore, overexpression of KLF2 inhibited the cytokine-mediated induction of tissue factor (TF). In contrast, siRNA mediated knockdown of KLF2 reduced antithrombotic gene expression while inducing the expression of pro-coagulant factors. The functional importance of KLF2 was verified by in vitro clotting assays. By comparison to control infected cells, KLF2 overexpression increased blood clotting time as well as flow rates under basal and inflammatory conditions. In contrast, siRNA-mediated knockdown of KLF2 reduced blood clotting time and flow rates. These observations identify KLF2 as a novel transcriptional regulator of endothelial thrombotic function. The full text of this article is available online at http://circres.ahajournals.org.

Thrombomodulin-protein C-EPCR system: integrated to regulate coagulation and inflammation

Late in the 18th century, William Hewson recognized that the formation of a clot is characteristic of many febrile, inflammatory diseases (Owen C. A History of Blood Coagulation. Rochester, Minnesota: Mayo Foundation; 2001). Since that time, there has been steady progress in our understanding of coagulation and inflammation, but it is only in the past few decades that the molecular mechanisms linking these 2 biologic systems have started to be delineated. Most of these can be traced to the vasculature, where the systems most intimately interact. Thrombomodulin (TM), a cell surface-expressed glycoprotein, predominantly synthesized by vascular endothelial cells, is a critical cofactor for thrombin-mediated activation of protein C (PC), an event further amplified by the endothelial cell protein C receptor (EPCR). Activated PC (APC), in turn, is best known for its natural anticoagulant properties. Recent evidence has revealed that TM, APC, and EPCR have activities that impact not only on coagulation but also on inflammation, fibrinolysis, and cell proliferation. This review highlights recent insights into the diverse functions of this complex multimolecular system and how its components are integrated to maintain homeostasis under hypercoagulable and/or proinflammatory stress conditions. Overall, the described advances underscore the usefulness of elucidating the relevant molecular pathways that link both systems for the development of novel therapeutic and diagnostic targets for a wide range of inflammatory diseases.

Activated protein C in sepsis: emerging insights regarding its mechanism of action and clinical effectiveness

PURPOSE OF REVIEW

Dysregulation of endogenous coagulant and anticoagulant systems is now believed to play an important role in the pathogenesis of sepsis and septic shock. Reductions in host activated protein C levels and resultant microvascular thrombosis provided a basis for the use of recombinant human activated protein C in sepsis. Although controversial, the findings from an initial phase III trial testing this agent resulted in its approval for use in patients with severe sepsis and high risk of death. This review highlights emerging insights into the biology of protein C and activated protein C in sepsis, summarizes additional analysis growing out of the phase III trial testing recombinant human activated protein C, and assesses the cost-effectiveness that the clinical use of the agent has had thus far.

RECENT FINDINGS

Binding of activated protein C to the endothelial cell protein C receptor is recognized to result in a growing number of actions including increased activity of activated protein C itself and inhibition of both nuclear factor-kappaB, a central regulator in the host inflammatory response, and apoptosis. Additional analysis of the original phase III trial testing recombinant human activated protein C appears to emphasize one of the US Food and Drug Administration's original concerns regarding an association between severity of sepsis and this agent's effects. Postmarketing analysis and growing experience with other anticoagulant agents and corticosteroids in sepsis raise questions regarding the ultimate cost-effectiveness of activated protein C.

SUMMARY

The protein C pathway is important both to coagulant and inflammatory pathways during sepsis. Based on emerging investigations, its actions appear to be increasingly complex ones. Despite potentially promising results in an initial phase III trial, the role of recombinant human activated protein C in the treatment of septic patients must continue to be evaluated.

Protein S: A conduit between anticoagulation and inflammation

OBJECTIVE

To review the multifaceted roles of the anticoagulant protein S, facilitating a better comprehension of this protein's role in anticoagulation and inflammation pathways and the crosstalk between these pathologic states.

DATA SOURCES AND STUDY SELECTION

Original research and review articles published in English pertaining to protein S, sourced from PubMed, during the last 30 yrs.

DATA EXTRACTION AND SYNTHESIS

The protein C anticoagulant pathway is an essential mechanism for attenuating thrombin generation by the membrane-bound procoagulant complexes, tenase and prothrombinase. Protein S is a nonenzymatic protein. In the absence of activated protein C, it demonstrates anticoagulant activity; in the presence of activated protein C, it functions as a cofactor for activated protein C-dependent proteolytic inactivation of the coagulation cofactors factor Va and factor VIIIa. However, in plasma, these anticoagulant activities are limited by the concentration of free protein S (approximately 40% of the total protein S plasma concentration). The remaining protein S (approximately 60%) is found in a high-affinity, calcium-stabilized complex with C4b-binding protein, which renders this fraction devoid of anticoagulant function. Several recent investigations have attributed novel activated protein C-independent functions of protein S to the association of protein S with C4b-binding protein, thus establishing the importance of this fraction of plasma protein S.

CONCLUSIONS

Together, these data support a role for protein S in both anticoagulation and inflammation, facilitating a better understanding of the need for both free and C4b-binding protein-bound protein S. Although these physiologic roles are truly dichotomous in terms of functional end point, mechanistically, both involve high-affinity membrane binding to phosphatidylserine-bearing surfaces. This binding is mediated by the n-terminal gamma-carboxyglutamic acid-rich domain of this protein.

[Physiopathology of severe sepsis]

Regarding the definition. Severe sepsis associates an explosive inflammatory reaction and organ failure. It is secondary to bacterial, fungal or viral infection. It can be at the origin of acute circulatory failure (state of septic shock). Response of the organism to infection. The presence of certain components of the membrane of pathogenic agents induces the release of various mediators in cascade, notably cytokines. Toll-like receptors (10 cloned in humans) intervene in the detection of microbes and in the inherent and subsequently adaptive immune response. Immune paralysis. The release of pro-inflammatory mediators characterizes the initial phase of sepsis. Persistence of the latter provokes acquired immunodepression, related to an anti-inflammatory profile, and hence to a delayed decrease in hypersensitivity, an incapacity to cope with the infection and the onset of nosocomial infections. The role of the mediators. During sepsis, the cytokines are predominantly pro-inflammatory (TNF-alpha and notably IL-1beta) whereas others, produced concomitantly or subsequently, are predominantly anti-inflammatory (IL-10 in particular). In fact, the majority of the cytokines have multiple and intrinsic effects, they mediate immune defense but also pathological manifestations. Many other mediators intervene: coagulation or complement systems, contact system, breakdown products of the phospholipid membrane, arachidonic acid metabolites, free radicals and nitrous oxide. Endocrine and metabolic dysregulations. The concept of relative adrenal insufficiency and peripheral syndrome of resistance to glycocorticosteroids have led to hormone replacement therapy during septic shock. Acute insulin resistance has also been described. The role of the endothelium and coagulation. The endothelium plays a key part in the onset of vascular insufficiency during sepsis due to abnormalities in vasomotricity and thrombomodulation. The anticoagulant regulating system is perturbed; there is a decrease in protein C with inactivation of its active form, which has pro-fibrinolytic properties, and a decrease in antithrombin III. Regarding myocardial dysfunction During septic shock there is often severe left ventricular systolic dysfunction, sometimes also involving the right ventricle, largely under-diagnosed despite its severe prognosis, and associated with reduced or even collapsed heart rate.

The blood coagulation system as a molecular machine

The human blood coagulation system comprises a series of linked glycoproteins that upon activation induce the generation of downstream enzymes ultimately forming fibrin. This process is primarily important to arrest bleeding (hemostasis). Hemostasis is a typical example of a molecular machine, where the assembly of substrates, enzymes, protein cofactors and calcium ions on a phospholipid surface markedly accelerates the rate of coagulation. Excess, pathological, coagulation activity occurs in "thrombosis", the formation of an intravascular clot, which in the most dramatic form precipitates in the microvasculature as disseminated intravascular coagulation. Thrombosis occurs according to a biochemical machine model in the case of atherothrombosis on a ruptured atherosclerotic plaque, but may develop at a slower rate in venous thrombosis, illustrating that the coagulation machinery can act at different velocities. The separate coagulation enzymes are also important in other biological processes, including inflammation for which the rapid conversion of one coagulation factor by the other is not a prerequisite. The latter role of coagulation enzymes may be related to the old and probably maintained function of the coagulation machine in innate immunity.