Adsorption and coagulability of fibrinogen on atheromatous lipid surfaces

Molecular Basis for Surface-Initiated Non-Thrombin-Generated Clot Formation Following Viral Infection

In this paper, we propose a model that connects two standard inflammatory responses to viral infection, namely, elevation of fibrinogen and the lipid drop shower, to the initiation of non-thrombin-generated clot formation. In order to understand the molecular basis for the formation of non-thrombin-generated clots following viral infection, human epithelial and Madin-Darby Canine Kidney (MDCK, epithelial) cells were infected with H1N1, OC43, and adenovirus, and conditioned media was collected, which was later used to treat human umbilical vein endothelial cells and human lung microvascular endothelial cells. After direct infection or after exposure to conditioned media from infected cells, tissue surfaces of both epithelial and endothelial cells, exposed to 8 mg/mL fibrinogen, were observed to initiate fibrillogenesis in the absence of thrombin. No fibers were observed after direct viral exposure of the endothelium or when the epithelium cells were exposed to SARS-CoV-2 isolated spike proteins. Heating the conditioned media to 60 °C had no effect on fibrillogenesis, indicating that the effect was not enzymatic but rather associated with relatively thermally stable inflammatory factors released soon after viral infection. Spontaneous fibrillogenesis had previously been reported and interpreted as being due to the release of the alpha C domains due to strong interactions of the interior of the fibrinogen molecule in contact with hydrophobic material surfaces rather than cleavage of the fibrinopeptides. Contact angle goniometry and immunohistochemistry were used to demonstrate that the lipids produced within the epithelium and released in the conditioned media, probably after the death of infected epithelial cells, formed a hydrophobic residue responsible for fibrillogenesis. Hence, the standard inflammatory response constitutes the ideal conditions for surface-initiated clot formation.

Pneumolysin/Plasma Protein Adsorption, Bacterial Adherence, and Cell Adhesion Characteristics of a Cell-Membrane-Mimicking Polymer System

This study delivers the first report on a cell-membrane-mimicking polymer system, poly[oxy(4-(13-cholenoatenonyl)-1,2,3-triazoyl-1-methyl)ethylene-random-oxy(4-(13-phosphorylcholinenonyl)-1,2,3-triazoyl-1-methyl)ethylene] (PGA-Chol_mPC_n) films in various compositions in terms of physicochemical properties, protein adsorptions, bacterial adherences, and human cell adhesions. Higher Chol-containing PGA-Chol_mPC_n in a self-assembled multi-bilayer membrane structure is confirmed to show excellently high affinity to pneumolysin (a cytolysin) and its C-terminal fragment (domain 4) but substantially suppressed affinity to the N-terminal fragment (domains 1-3) and further to plasma proteins. Furthermore, the adherences of pathogenic bacteria are increased favorably; however, the adhesion and proliferation of a human HEp-2 cell line are hindered severely. In contrast, higher-PC-containing PGA-Chol_mPC_n membranes promote HEp-2 cell adhesion and proliferation but significantly suppress the adsorptions of pneumolysin and its fragments and plasma proteins as well as bacterial adherence. The results collectively confirm that PGA-Chol_mPC_n can yield a membrane platform enriched with hydrophobic Chol and hydrophilic and zwitterionic PC moieties in any desired compositions, providing highly selective and sensitive physicochemical characters and biocompatibilities which are demanded for applications in various fields including biomedicine, cosmetics, and environmentally friendly consumer products.

Structure and Function of Trypsin-Loaded Fibrinolytic Liposomes

Protease encapsulation and its targeted release in thrombi may contribute to the reduction of haemorrhagic complications of thrombolysis. We aimed to prepare sterically stabilized trypsin-loaded liposomes (SSL_T) and characterize their structure and fibrinolytic efficiency. Hydrogenated soybean phosphatidylcholine-based SSL_T were prepared and their structure was studied by transmission electron microscopy combined with freeze fracture (FF-TEM), Fourier transform infrared spectroscopy (FT-IR), and small-angle X-ray scattering (SAXS). Fibrinolytic activity was examined at 45, 37, or 24°C on fibrin or plasma clots with turbidimetric and permeation-driven lysis assays. Trypsin was shown to be attached to the inner surface of vesicles (SAXS and FF-TEM) close to the lipid hydrophilic/hydrophobic interface (FT-IR). The thermosensitivity of SSL_T was evidenced by enhanced fibrinolysis at 45°C: time to reduce the maximal turbidity to 20% decreased by 8.6% compared to 37°C and fibrin degradation product concentration in the permeation lysis assay was 2-fold to 5-fold higher than that at 24°C. SSL_T exerted its fibrinolytic action on fibrin clots under both static and dynamic conditions, whereas plasma clot dissolution was observed only in the permeation-driven assay. The improved fibrinolytic efficiency of SSL_T under dynamic conditions suggests that they may serve as a novel therapeutic candidate for dissolution of intravascular thrombi, which are typically exposed to permeation forces.

Association of the −262C/T polymorphism in the catalase gene promoter with carotid atherosclerosis in Slovenian patients with type 2 diabetes

Genetic variations of the antioxidant enzymes may influence the susceptibility to oxidative stress and consequently the development and progression of diabetic complications. The aim of the current study was to test the association between the −262C/T polymorphism in the catalase gene promoter and carotid atherosclerosis in Slovenian patients with type 2 diabetes. Two-hundred and eighty six diabetics and 150 healthy controls were enrolled in the study. Carotid atherosclerosis was quantified ultrasonographiocally by carotid intima-media thickness (CITM), plaque score and plaque type. Genotypes were determined using the real-time PCR. Fibrinogen concentration showed a borderline statistically significant difference due to catalase genotypes (p=0,05). No difference in clinical characteristics, CIMT, plaque stability or plaque score was observed. Logistic regression model adjusted for age, gender, smoking, BMI, lipid parameters and duration of hypertension and diabetes showed significant association of T allele and lower risk for higher plaque score (OR=0,25; p=0,025). No association with CIMT>1mm and unstable plaques was observed. T allele of −262C/T is associated with lower risk for higher plaque score but it did not affect clinical parameters, CIMT and plaque stability. Whether this polymorphism can be used as a genetic marker for advanced carotid atherosclerosis in diabetic patients needs to be evaluated in the future.

Longitudinal assessment of fibrinogen in relation to subclinical cardiovascular disease: the CARDIA study

OBJECTIVE

To examine the strength of the associations of fibrinogen with subclinical atherosclerosis in healthy persons.

METHODS

A population-based, prospective, observational study of black and white men and women (Coronary Artery Risk Development in Young Adults [CARDIA]). Fibrinogen levels were measured at year 7 (ages 25-37, n = 2969), and again at year 20 (ages 38-50, n = 2832). Measures of subclinical atherosclerosis (coronary artery calcification [CAC] and carotid intimal-medial thickness [CIMT]) were recorded at year 20.

RESULTS

Over the 13-year study interval (1992-1993 to 2005-2006), fibrinogen rose from a mean of 3.32 to 4.05 g L(-1). After adjusting for age, gender and race, fibrinogen was positively associated with greater incidence of CAC and increased CIMT cross-sectionally as well as after 13 years of follow-up (all P-trend < 0.001). After further adjustment for field center, BMI, smoking, education, systolic blood pressure, diabetes, antihypertensive medication use, total and HDL cholesterol, and CRP, significant positive relationships between fibrinogen and incidence of CAC remained for the total cohort longitudinally (P-trend = 0.037), but not cross-sectionally (P-trend = 0.147).

CONCLUSION

This 13-year study demonstrates that higher levels of fibrinogen during young adulthood are positively associated with incidence of CAC and increased CIMT in middle-age, but the strength of the association declines with increasing age.

Stability and state of aggregation of aqueous fibrinogen and dipalmitoylphosphatidylcholine lipid vesicles

The stability and state of aggregation of aqueous fibrinogen (FB) and dipalmitoylphosphatidylcholine (DPPC) vesicles in water or buffer at 25 degrees C were studied with dynamic light scattering (DLS), UV-vis spectroturbidimetry (ST), and cryo-transmission electron microscopy (cryo-TEM). In water, when 1000 ppm (0.10 wt %) DPPC dispersions were prepared with a protocol including extensive sonication, they contained mostly vesicles and were quite clear, transparent, and stable for at least 30 days. FB mixtures with water (0.075 wt %) were quite unstable and biphasic. They formed large aggregates which eventually precipitated. The addition of DPPC vesicles into these unstable FB dispersions reversed FB aggregation and precipitation and produced stable translucent microdispersions. The inferred lipid/protein aggregates were limited in size, with average diameters ranging from 200 to 300 nm. In buffer, DPPC dispersions were also clear and quite stable, with average dispersed particles diameter of ca. 90 nm. FB dissolved in aqueous buffer and formed transparent and stable solutions. Adding salt to an aggregated FB dispersion in water reversed the aggregation. FB aggregated and redissolved in the presence of the citrate and after the citrate was removed. There was no effect of citrate (present in FB initially) in the FB aggregation or redissolution. FB molecules in buffer form dimers or higher aggregates. Their average aggregation number is 2, determined with Rayleigh scattering analysis of turbidity data. The average hydrodynamic diameter of FB solutions from DLS was 30 nm. Mixing a stable FB solution in buffer and a stable DPPC dispersion in buffer produced highly unstable mixtures, in which large aggregates precipitated. These results have implications in understanding the interactions of lipids and proteins in many biological applications and food processing applications.

Phospholipid barrier to fibrinolysis: role for the anionic polar head charge and the gel phase crystalline structure

The massive presence of phospholipids is demonstrated in frozen sections of human arterial thrombi. Purified platelet phospholipids and synthetic phospholipids retard in vitro tissue-type plasminogen activator (tPA)-induced fibrinolysis through effects on plasminogen activation and plasmin function. The inhibition of plasminogen activation on the surface of fibrin correlates with the fraction of anionic phospholipid. The phospholipids decrease the amount of tPA penetrating into the clot by 75% and the depth of the reactive surface layer occupied by the activator by up to 30%, whereas for plasmin both of these parameters decrease by approximately 50%. The phospholipids are not only a diffusion barrier, they also bind the components of the fibrinolytic system. Isothermal titration calorimetry shows binding characterized with dissociation constants in the range 0.35-7.64 microm for plasmin and tPA (lower values with more negative phospholipids). The interactions are endothermic and thermodynamically driven by an increase in entropy, probably caused by the rearrangements in the ordered gel structure of the phospholipids (in line with the stronger inhibition at gel phase temperatures compared with liquid crystalline phase temperatures). These findings show a phospholipid barrier, which should be overcome during lysis of arterial thrombi.

Fibrinogen-coated chylomicrons in gastrointestinal lymph: a new rationale regarding the arterial deposition of postprandial lipids

The recent discovery that fibrinogen binds to chylomicrons in gastrointestinal lymph has prompted a new rationale regarding the arterial deposition of postprandial lipids, i.e., dietary fat. According to this new rationale, fibrinogen bound to chylomicrons in the gastrointestinal lymph renders those lipid particles and/or their remnants an adhesive potential, even before the particles reach the arterial system. It is proposed that such an adhesive potential, if realized in the vicinity of the arterial wall, can contribute to the nucleation and growth of atherosclerotic plaques, especially during and immediately following a fat-rich meal. Arguments in support of this proposal are made based on the proximity of the lymph outflow tract to the arteries most susceptible to atherosclerosis, and on the tissue distributions and activities of heparin, diamine oxidase, and lipoprotein lipase. This new rationale reconciles existing theories on atherosclerosis, and it also suggests novel means by which to prevent/treat the disease.

Fibrinogen in rat gastrointestinal lymph before, during and after intraduodenal administration of emulsified triglyceride: fibrinogen bound to chylomicrons in gastrointestinal lymph is functional

Samples of gastrointestinal lymph were collected from fasted, male, Sprague-Dawley rats before, during and after intraduodenal administration of either a phospholipid-stabilized, triglyceride-rich emulsion or the dextrose-saline diluent of the emulsion. In lipid-treated rats, the triglyceride, total protein, and functional fibrinogen contents of lymph increased significantly during the 4 h of continuous lipid infusion, with all analytes returning to near baseline values by 20 h later. Levels of the same analytes changed little, if at all, in control animals. As assessed using immunoblotting, chylomicrons in gastrointestinal lymph are coated with fibrinogen. Fibrinogen-coated chylomicrons readily incorporate into solution phase clots and, in the presence of thrombin, adhere in heparin-preventable fashion to each other and to other fibrinogen-coated surfaces. Taken together, these data indicate that lipid feeding creates in gastrointestinal lymph a condition that is conducive temporally to the physical association of fibrinogen with newly ingested lipids before they reach the circulatory system.

Reactivity of human platelets with immobilized fibrinogen is dictated by the chemical character of the surface

Quiescent platelets readily adhere to surface-immobilized fibrinogen. In contrast, platelets exposed to soluble fibrinogen do not demonstrate such activity. As part of an effort to characterize this phenomenon, a solid-phase reagent was prepared by adsorbing human fibrinogen to polystyrene-divinylbenzene microparticles. Using a suspension of human platelets, phase-contrast microscopy was used to quantitate directly platelets bound to fibrinogen-coated beads. This method is fast, straightforward, and requires minimal amounts of reagents and sample. An existing turbidimetric assay was modified to monitor optically the rate and extent of platelet-fibrinogen binding. When platelet-rich plasma was added to a stirred suspension of fibrinogen-coated beads, the rate of aggregation was related directly to the concentration of fibrinogen on the bead surface. This response could not be mitigated by the thrombin inhibitor, hirudin, indicating that any thrombin generated in the reaction has no role in bead aggregation. Conversely, the alpha(IIb)beta(3) antagonist, abciximab (ReoPro), completely prevented aggregation, implicating specific fibrinogen-alpha(IIb)beta(3) interactions as responsible for the observed effect. Beads coated with either albumin or a densely packed, pure film of the neutral phospholipid, phosphatidylcholine (lecithin), do not aggregate under identical conditions, nor do fibrinogen-coated beads aggregate when platelet-depleted plasma is added. When fibrinogen was coated to beads as a mixed film with lecithin, a striking increase in reactivity toward platelets was demonstrated, compared to unmodified beads. These studies indicate that the observed adhesion of platelets to beads is a direct result of platelet-fibrinogen interactions and platelets respond differently to fibrinogen when presented as a mixed film with lipid, compared to the protein alone at an interface.

Thermally Induced Transient Activity Changes of Plasmin Adsorbed onto Bare and Fibrinogen-Modified Graphite and Glassy Carbon Surfaces

The occurrence of a thermally induced first-order transition affecting the amidolytic activity of plasmin adsorbed onto bare and protein-modified graphite and glassy carbon was demonstrated in the 10-45 degrees C temperature range in the presence of a chromogenic substrate. Modification of the surfaces was achieved upon spontaneous adsorption of plasmin to surfaces bearing a coating of fibrinogen, whether electrochemically oxidized or not. The amount of fibrinogen adsorbed at graphite was determined by ELISA. The kinetics of the transition was characterized by its starting temperature (T(c)), which was between 14 and 19 degrees C, the first-order rate constant, and the activation energy E(a) deduced from Arrhenius plots. Results showed the absence of a correlation between T(c), E(a), and contact angle variations. It is therefore likely that these variables address separate steps in a complex pathway of reactions undergone by plasmin under mild thermal constraints. Copyright 2001 Academic Press.

Albumin-binding surfaces: in vitro activity

Immobilized monoclonal antibodies (Mabs) have been used to attract specific molecules to a solid surface from complex mixtures such as blood, plasma or serum, thereby directing the response to the modified substrate, a key goal in rational biomaterial design. The nature of the Mab dictated the nature of the response: anti-albumin antibodies were used to prevent cell and platelet adhesion in vitro, whilst anti-fibronectin Mabs promoted attachment. Patterned surfaces could be formed, bearing Mabs that generated adhesive and non-adhesive regions. Fibrinogen adsorption from plasma showed a Vroman peak on unmodified control polymer, which was reduced by 64% in the presence of surface-bound anti-albumin Mab. Immobilization of a control Mab reduced fibrinogen adsorption only slightly, implying an albumin-mediated effect. In static tests, platelet adhesion from human platelet rich plasma was significantly reduced by the immobilization of anti-HSA Mab when compared to the untreated FEP surface (p < 0.0001). This effect was also seen with citrated blood flowing through Mab-treated polyurethane tubing at a shear rate of 132 s(-1) (p=0.034). Since platelets and proteins (as blood, plasma or serum) were introduced to the surface simultaneously, the generation of a defined protein film must have been sufficiently rapid as to shape the platelet or cell response.

Ten-year follow-up results from the Goettingen Risk, Incidence and Prevalence Study (GRIPS). I. Risk factors for myocardial infarction in a cohort of 5790 men

Besides the accepted major risk factors for myocardial infarction (MI), cholesterol, hypertension and smoking, several other variables such as lipoproteins, apolipoproteins, fibrinogen and family history of MI, have been considered, but their usefulness as predictors of MI is controversially discussed. The Göttingen Risk Incidence and Prevalence Study (GRIPS) aimed to evaluate the independent impact of the latter in comparison to the established risk factors. GRIPS is a prospective cohort study, which included 5790 men, aged 40-59.9 years, without cardiovascular disease at baseline. Multivariate logistic regression models for the estimation of the MI risk based on the 10-year follow-up data from 97.4% of the study participants established LDL cholesterol as the strongest predictor of MI. It was followed by family history of MI, Lp(a), age, smoking, systolic blood pressure, HDL cholesterol (inversely related) and plasma glucose (P < 0.001). Apolipoprotein B as well as the ratios total/HDL cholesterol, LDL/HDL cholesterol and Apo B/AI were less effective predictors than LDL cholesterol and did not contribute independently to the estimation of MI risk. Similarly apoprotein AI was a weaker predictor of MI risk then HDL cholesterol. GRIPS is the first prospective cohort study which clearly justifies the key role of LDL cholesterol in preventive strategies. However, the data also give strong support for the additional consideration of other risk factors for a valid estimation of the MI risk for an individual subject.

Evidence for prothrombin production and thrombin expression by phorbol ester-treated THP-1 cells

With the addition of fibrinogen, fibrin clots form in serum-free culture medium recovered from phorbol ester-treated THP-1 cells. We attribute this coagulant activity to thrombin generated as a consequence of cell stimulation because the coagulant activity exists in serum-free culture medium from treated cells only, and it is inhibited by hirudin. The thrombin does not derive from a prothrombin/thrombin contaminant since no detectable prothrombin/thrombin preexists in either the serum-free culture medium or the fibrinogen preparations used for our experiments. We hypothesized that the thrombin is synthesized by the cells themselves. In support of this hypothesis, we found that prothrombin mRNA is expressed in THP-1 cells following their treatment with phorbol ester. Accompanying expression of this mRNA, prothrombin antigen becomes detectable in lysates of PMA-treated THP-1 cells, and thrombin antigen and activity become detectable in both lysates and culture medium of treated cells. These results are consistent with the notion that certain cells of myelomonocytic lineage are capable of synthesizing proteins relevant to coagulation.

Prognostic value of plasma fibrinogen concentration in patients with unstable angina and non-Q-wave myocardial infarction (TIMI IIIB Trial)

Inflammation may play an important role in acute coronary syndromes. We studied the prognostic value of fibrinogen, an acute-phase protein directly involved in thrombotic process, measured serially in 1,473 patients with unstable angina and non-Q-wave myocardial infarction participating in the Thrombolysis in Myocardial Infarction IIIB trial. Overall, no association was found between baseline (pretreatment) fibrinogen and in-hospital (< or = 10 days) myocardial infarction (p=0.70) and death (p=0.64); however, patients with spontaneous ischemia (p=0.004) and the combined unsatisfactory outcome of death, myocardial infarction, and spontaneous ischemia (p=0.003) had higher fibrinogen concentrations than those without these events. This association was confined to patients with unstable angina. A baseline fibrinogen concentration > or = 300 mg/dl was associated with a modest trend toward an increased risk of death, myocardial infarction, or spontaneous ischemia (odds ratio 1.61, 95% confidence interval 1.02 to 2.52; p=0.04). Elevation of fibrinogen, a readily measurable acute-phase protein, at the time of hospital admission is associated with coronary ischemic events and a poor clinical outcome in patients with unstable angina.