SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Fibrin

171

Fibrin polymerization is a necessary part of hemostasis but clots can obstruct blood vessels and cause heart attacks and strokes. The polymerization reactions are specific and controlled, involving strong knob-into-hole interactions to convert soluble fibrinogen into insoluble fibrin. It has long been assumed that clots and thrombi are stable structures until proteolytic digestion. On the contrary, using the technique of fluorescence recovery after photobleaching, we demonstrate here that there is turnover of fibrin in an uncrosslinked clot. A peptide representing the knobs involved in fibrin polymerization can compete for the holes and dissolve a preformed fibrin clot, or increase the fraction of soluble oligomers, with striking rearrangements in clot structure. These results imply that in vivo clots or thrombi are more dynamic structures than previously believed that may be remodeled as a result of local environmental conditions, may account for some embolization, and suggest a target for therapeutic intervention.

Concepts: Stroke, Polymer chemistry, Monomer, Hemostasis, Coagulation, Thrombus, Protein, Fibrin

152

Diabetes mellitus (DM) is an extremely common disorder which carries a risk of vascular impairment. DM type 2 (DM2) can be characterized by the dysfunction of haemostasis manifesting by stimulated coagulation process, disorder of platelet function and decreased fibrinolytic activity. These all are the reasons why DM2 is the most common acquired thrombophilia. Endothelial dysfunction along with platelet hyperactivity are unquestionably involved in the hyperactivation of platelets and clotting factors in DM. As a natural consequence of continuous investigation, many markers of endothelial dysfunction and diabetic thrombocytopathy have been identified and considered for implementation in clinical practice. Endothelial function can be assessed by the evaluation of endothelial markers, circulating molecules synthesised in various amounts by the endothelium. These markers precede the signs of evident microangiopathy. Platelets have an ethiopathogenic relation to the microangiopathy in DM. Their increased activity was confirmed in both types of DM. Predictors of endothelial and platelet disorder could improve the screening of individuals at increased risk, thus leading to the early diagnosis, appropriate treatment, as well as to the effective prevention of the complications of DM2. In the article we deal with the mechanisms involved in the pathogenesis of endothelial and platelet functional abnormalities, endothelial and platelet markers of DM2 considered for implementation in clinical practice and possibilities of their detection.

Concepts: Diabetes mellitus, Thrombotic thrombocytopenic purpura, Fibrin, Blood, Hemostasis, Endothelium, Platelet, Coagulation

33

Blood clotting is a precise cascade engineered to form a clot with temporal and spatial control. Current control of blood clotting is achieved predominantly by anticoagulants and thus inherently one-sided. Here we use a pair of nanorods (NRs) to provide a two-way switch for the blood clotting cascade by utilizing their ability to selectively release species on their surface under two different laser excitations. We selectively trigger release of a thrombin binding aptamer from one nanorod, inhibiting blood clotting and resulting in increased clotting time. We then release the complementary DNA as an antidote from the other NR, reversing the effect of the aptamer and restoring blood clotting. Thus, the nanorod pair acts as an on/off switch. One challenge for nanobiotechnology is the bio-nano interface, where coronas of weakly adsorbed proteins can obscure biomolecular function. We exploit these adsorbed proteins to increase aptamer and antidote loading on the nanorods.

Concepts: Tenase, Fibrin, Thrombus, Heparin, Platelet, Warfarin, Blood, Coagulation

29

The growing utilisation of indwelling pleural catheters (IPCs) has put forward a new era in the management of recurrent symptomatic pleural effusions. IPC use is safe compared to talc pleurodesis, though complications can occur. Pleural infection affects <5% of patients, and is usually responsive to antibiotic treatment without requiring catheter removal or surgery. Pleural loculations develop over time, limiting drainage in 10% of patients, which can be improved with intrapleural fibrinolytic therapy. Catheter tract metastasis can occur with most tumours but is more common in mesothelioma. The metastases usually respond to analgaesics and/or external radiotherapy. Long-term intermittent drainage of exudative effusions or chylothorax can potentially lead to loss of nutrients, though no data exist on any clinical impact. Fibrin clots within the catheter lumen can result in blockage. Chest pain following IPC insertion is often mild, and adjustments in analgaesics and drainage practice are usually all that are required. As clinical experience with the use of IPC accumulates, the profile and natural course of complications are increasingly described. We aim to summarise the available literature on IPC-related complications and the evidence to support specific strategies.

Concepts: Oncology, Pneumothorax, Fibrin, Pleurodesis, Foley catheter, Catheter, Cancer, Pleural effusion

29

Background: Trauma is a global disease with over 2.5 million deaths annually from haemorrhage and coagulopathy. Overt hyperfibrinolysis is rare in trauma and associated with massive fatal injuries. Paradoxically, clinical trials suggest a much broader indication for antifibrinolytics. Objective: To determine the incidence and magnitude of fibrinolytic activation in trauma patients and its relationship to clot lysis as measured by thromboelastometry. Methods: Prospective cohort study of 303 consecutive trauma patients admitted between January 2007 and June 2009. Blood was drawn on arrival for thromboelastometry (TEM) and coagulation assays. Follow-up was until hospital discharge or death. TEM hyperfibrinolysis was defined as maximum clot lysis (ML) >15%. Fibrinolytic Activation (FA) measured by plasmin-antiplasmin complex (PAP) and D-dimer levels. Data were collected on demographics, mechanism, severity of injury and baseline vital signs. Outcome Measure(s): 28-day mortality. Secondary: 28-day ventilator-free days and 24-hour transfusion requirement. Results: Only 5% of patients had severe fibrinolysis on TEM, but 57% of patients had evidence of ‘moderate’ fibrinolysis with PAP levels elevated over twice normal (>1500μg/L) without lysis on TEM. TEM only detected clot lysis when PAP levels were increased 30 times normal (p<0.001) and antiplasmin levels were less than 75% of normal. Patients with FA had increased 28-day mortality compared with no FA (12% vs 1%, p<0.001), fewer ventilator-free days and longer hospital stay. Conclusions: FA occurs in the majority of trauma patients and the magnitude of FA correlates with poor clinical outcome. This was not detected by conventional thromboelastometry, an insensitive measure of endogenous fibrinolytic activity. © 2012 International Society on Thrombosis and Haemostasis.

Concepts: Alpha 2-antiplasmin, Fibrin, Plasmin, Pulmonary embolism, Thrombus, Thromboelastometry, Fibrinolysis, Coagulation

28

The mechanism action of the polyphenol-rich extracts from berries of Aronia melanocarpa (black chokeberry) and from grape seeds in the defence against homocysteine (Hcy) and its derivatives action in blood platelets is still unknown. In this study, the influence of the aronia extract and grape seeds extract (GSE) on the platelet adhesion to collagen and fibrinogen and the platelet aggregation during a model of hyperhomocysteinemia was investigated. The aim of our study in vitro was also to investigate superoxide anion radicals (O 2 (-•) ) production after incubation of platelets with Hcy, HTL and the aronia extract and GSE during a model of hyperhomocysteinemia (induced by reduced form of homocysteine at final dose of 100 μM) and the most reactive form of Hcy-its cyclic thioester, homocysteine thiolactone (HTL, 1 μM). Moreover, the additional aim of our study was also to establish and compare the influence of the aronia extract, GSE and resveratrol (3,4',5-trihydroxystilben), a phenolic compound, which has been supposed to be beneficial for the prevention of cardiovascular events, on selected steps of platelet activation.

Concepts: Black chokeberry, Berries, Fibrin, Aronia, Blood, Platelet

28

Thrombin is a serine protease that cleaves the peptide bonds in proteins located on the carboxyl side of arginine. Thrombin plays a central role in thromboembolic diseases, which are the major cause of mortality. The aim of the study was to estimate the effects of plant extracts on proteolytic properties of thrombin. Thrombin was incubated with polyphenol-rich extracts from berries of Aronia melanocarpa or seeds of Vitis vinifera (0.5, 5, 50 µg/mL) and with polyphenols ((+)-catechin, (-)-epicatechin, gallic acid, chlorogenic acid, procyanidin B1, cyanidin, cyanidin 3-glucoside, quercetin). The in vitro experiments showed that both extracts in all used concentrations inhibited proteolytic activity of thrombin observed as inhibition of thrombin-induced fibrinogen polymerization, stabilized fibrin formation, and platelet aggregation. Moreover, thrombin amidolytic activity was inhibited by polyphenols belonging to the flavonoid class. Results presented in this study indicate that polyphenol-rich extracts from berries of A. melanocarpa and seeds of V. vinifera may become promising dietary supplements in the prevention of thrombotic states. Copyright © 2012 John Wiley & Sons, Ltd.

Concepts: Fibrin, Grape, Platelet, Aronia, Amino acid, Protease, Coagulation, Protein

28

Protein-surface interactions are crucial to the overall biocompatability of biomaterials, and are thought to be the impetus towards the adverse host responses such as blood coagulation and complement activation. Only a few studies hint at the ultra-low fouling potential of zwitterionic poly(carboxybetaine methacrylate) (PCBMA) grafted surfaces and, of those, very few systematically investigate their non-fouling behavior. In this work, single protein adsorption studies as well as protein adsorption from complex solutions (i.e. human plasma) were used to evaluate the non-fouling potential of PCBMA grafted silica wafers prepared by nitroxide-mediated free radical polymerization. PCBMAs used for surface grafting varied in charge separating spacer groups that influence the overall surface charges, and chain end-groups that influence the overall hydrophilicity, thereby, allows a better understanding of these effects towards the protein adsorption for these materials. In situ ellipsometry was used to quantify the adsorbed layer thickness and adsorption kinetics for the adsorption of four proteins from single protein buffer solutions, viz, lysozyme, α-lactalbumin, human serum albumin and fibrinogen. Total amount of protein adsorbed on surfaces differed as a function of surface properties and protein characteristics. Finally, immunoblots results showed that human plasma protein adsorption to these surfaces resulted, primarily, in the adsorption of human serum albumin, with total protein adsorbed amounts being the lowest for PCBMA-3 (TEMPO). It was apparent that surface charge and chain hydrophilicity directly influenced protein adsorption behavior of PCBMA systems and are promising materials for biomedical applications.

Concepts: Surface chemistry, Fibrin, Adsorption, Protein, Proteins, Polymer chemistry, Radical, Blood

28

One key for the successful integration of implants into the human body is the control of protein adsorption by adjusting surface properties at different length scales. This is particularly important for titanium oxide constituting one of the most common biomedical interfaces. As for titania (TiO(2)) the interface is largely defined by its crystal surface structure it is crucial to understand how the surface crystallinity affects the structure, properties and function of protein layers mediating the subsequent biological reaction. For rutile TiO(2) we demonstrate that the conformation and relative amount of human plasma fibrinogen (HPF) and the structure of adsorbed HPF layers depend on the crystal surface nanostructure by employing thermally etched multi-faceted TiO(2) surfaces. Thermal etching of polycrystalline TiO(2) facilitates a nanoscale crystal faceting and, thus, the creation of different surface nanostructures on a single specimen surface. Atomic force microscopy shows that HPF arranges into networks and thin globular layers on flat and irregular crystal grain surfaces, respectively. On a third, faceted category we observed an alternating conformation of HPF on neighboring facets. The bulk grain orientation obtained from electron back scatter diffraction and thermodynamic mechanisms of surface reconstruction during thermal etching suggest the grain and facet surface specific arrangement and relative amount of adsorbed proteins to depend on the associated on-site free crystal surface energy. Implications for potentially favorable TiO(2) crystal facets regarding the inflammatory response and hemostasis are discussed in view of an advanced surface design of future implants.

Concepts: C-reactive protein, Protein, Sculptured thin film, Nanostructure, Fibrin, Titanium dioxide, Adsorption, Facet

27

The factors that contribute to pulmonary embolism (PE), a potentially fatal complication of deep vein thrombosis (DVT), remain poorly understood. Whereas fibrin clot structure and functional properties have been implicated in the pathology of venous thromboembolism and the risk for cardiovascular complications, their significance in PE remain incomplete. Therefore we systematically compared and quantified clot formation and lysis time, plasminogen levels, viscoelastic properties, activated factor XIII crosslinking and fibrin clot structure in isolated DVT and PE subjects. Clots made from plasma of PE subjects showed faster clot lysis times with no differences in lag time, rate of clot formation or maximum absorbance of turbidity as compared to DVT. Differences in lysis times were not due to alterations in plasminogen levels. Compared with DVT, clots derived from PE subjects showed accelerated establishment of viscoelastic properties, documented by a decrease in lag time and an increase in the rate of viscoelastic property formation. The rate and extent of fibrin crosslinking by activated factor XIII were similar between clots from DVT and PE subjects. Evaluation by electron microscopy revealed that plasma fibrin clots from PE subjects exhibited lower fiber density compared to those from DVT subjects. These data suggest that clot structure and functional properties differ between DVT and PE subjects and provide insights into mechanisms that may regulate embolization.

Concepts: Deep vein, Fibrinolysis, Fibrin, Pulmonary embolism, Thrombus, Deep vein thrombosis, Hematology, Vein