Albumin-IgG complexes in human serum and plasma that inhibit blood platelet adhesion

Parameter Estimation of Platelets Deposition: Approximate Bayesian Computation With High Performance Computing

Cardio/cerebrovascular diseases (CVD) have become one of the major health issue in our societies. Recent studies show the existing clinical tests to detect CVD are ineffectual as they do not consider different stages of platelet activation or the molecular dynamics involved in platelet interactions. Further they are also incapable to consider inter-individual variability. A physical description of platelets deposition was introduced recently in Chopard et al. (2017), by integrating fundamental understandings of how platelets interact in a numerical model, parameterized by five parameters. These parameters specify the deposition process and are relevant for a biomedical understanding of the phenomena. One of the main intuition is that these parameters are precisely the information needed for a pathological test identifying CVD captured and that they capture the inter-individual variability. Following this intuition, here we devise a Bayesian inferential scheme for estimation of these parameters, using experimental observations, at different time intervals, on the average size of the aggregation clusters, their number per mm2, the number of platelets, and the ones activated per μℓ still in suspension. As the likelihood function of the numerical model is intractable due to the complex stochastic nature of the model, we use a likelihood-free inference scheme approximate Bayesian computation (ABC) to calibrate the parameters in a data-driven manner. As ABC requires the generation of many pseudo-data by expensive simulation runs, we use a high performance computing (HPC) framework for ABC to make the inference possible for this model. We consider a collective dataset of seven volunteers and use this inference scheme to get an approximate posterior distribution and the Bayes estimate of these five parameters. The mean posterior prediction of platelet deposition pattern matches the experimental dataset closely with a tight posterior prediction error margin, justifying our main intuition and providing a methodology to infer these parameters given patient data. The present approach can be used to build a new generation of personalized platelet functionality tests for CVD detection, using numerical modeling of platelet deposition, Bayesian uncertainty quantification, and High performance computing.

A physical description of the adhesion and aggregation of platelets

The early stages of clot formation in blood vessels involve platelet adhesion-aggregation. Although these mechanisms have been extensively studied, gaps in their understanding still persist. We have performed detailed in vitro experiments, using the well-known Impact-R device, and developed a numerical model to better describe and understand this phenomenon. Unlike previous studies, we took into account the differential role of pre-activated and non-activated platelets, as well as the three-dimensional nature of the aggregation process. Our investigation reveals that blood albumin is a major parameter limiting platelet aggregate formation in our experiment. Simulations are in very good agreement with observations and provide quantitative estimates of the adhesion and aggregation rates that are hard to measure experimentally. They also provide a value of the effective diffusion of platelets in blood subject to the shear rate produced by the Impact-R.

Serum IgG-like glycoferroprotein: identification of its final dissociation form of thermostable protein coupled with albumin

Human serum IgG-like glycoferroprotein identical to ascitic IgG-like glycoferroprotein that binds labeled monoclonal antibodies to CA125 is a complex consisting of three proteins: IgG, human serum albumin, and unidentified thermostable protein. Final dissociation form of serum IgG-like glycoferroprotein also appears as a complex of three nonidentical polypeptides with a molecular weight of 55 kDa (PC55) migrating in the albumin zone of thermostable protein coupled with albumin and structures chemically identical to human serum albumin and IgG heavy chains. Under denaturing conditions of electrophoresis in polyacrylamide gel, IgG-like glycoferroprotein and PC55 have the same molecular weight (about 55 kDa), while under reducing conditions their weight is about 75 kDa. Transition form (form the lower to the higher molecular weight) appears as an oblique (at about ≈ 30°) protein band creating a ladder string effect. Ladder string effect was reproduced with thermostable protein coupled with albumin, PC55, IgG-like glycoferroprotein, with all commercially available human and bovine albumins, rat albumin as well as with heated and renatured albumins and can serve as electrophoretic identification sign for thermostable protein coupled with albumin. Renatured after boiling (100°C for 15 min) bovine albumin under reducing conditions appeared as bow string twisted in helix, that raises molecule in 2.5 turns from ≈ 2 to ≈ 75 kDa. These data attest to the existence of an albumin double and to its possible double structure.

Adhesion, activation, and aggregation of blood platelets and biofilm formation on the surfaces of titanium alloys Ti6Al4V and Ti6Al7Nb

Titanium alloys are still on the top list of fundamental materials intended for dental, orthopedics, neurological, and cardiovascular implantations. Recently, a special attention has been paid to vanadium-free titanium alloy, Ti6Al7Nb, that seems to represent higher biocompatibility than traditional Ti6Al4V alloy. Surprisingly, these data are not thoroughly elaborated in the literature; particularly there is a lack of comparative experiments conducted simultaneously and at the same conditions. Our study fills these shortcomings in the field of blood contact and microbiological colonization. To observe platelets adhesion and biofilm formation on the surfaces of compared titanium alloys, fluorescence microscope Olympus GX71 and scanning electron microscope HITACHI S-3000N were used. Additionally, flow cytometry analysis of platelets aggregation and activation in the whole blood after contact with sample surface, as an essential tool for biomaterial thrombocompatibility assessment, was proposed. As a result of our study it was demonstrated that polished surfaces of Ti6Al7Nb and Ti6Al4V alloys after contact with whole citrated blood and E. coli bacterial cells exhibit a considerable difference. Overall, it was established that Ti6Al4V has distinct tendency to higher thrombogenicity, more excessive bacterial biofilm formation and notable cytotoxic properties in comparison to Ti6Al7Nb. However, we suggest these studies should be extended for other types of cells and biological objects.

Passivating protein coatings for implantable glucose sensors: Evaluation of protein retention

The long-term function of implantable biosensors is limited by the foreign-body reaction (FBR). Since the acute phase of the FBR involves macrophage attachment mediated by adsorbed fibrinogen, preadsorption, and retention of other proteins might reduce the FBR. The retention of preadsorbed albumin, hemoglobin, von Willebrand's factor, and high-molecular-weight kininogen was therefore measured after exposure to plasma. The retention of preadsorbed proteins after incubation with monocyte cultures and implantation in rats was also measured. Fibrinogen adsorption from plasma to the preadsorbed surfaces was also measured. Hemoglobin adsorption was higher than that for other proteins, and it also had the greatest retention after exposure to blood plasma. When surfaces preadsorbed with hemoglobin were incubated with monocytes, more of the hemoglobin was displaced than that after incubation in plasma, while still more hemoglobin was displaced when the surfaces were implanted in vivo. Protein preadsorption on polystyrene greatly reduced fibrinogen adsorption. However, polyurethane surfaces used for glucose sensors had low fibrinogen adsorption compared with polystyrene, and this low level was not further reduced by preadsorption with other proteins. Preadsorbed proteins on polymers appear to be removed by passive exchange and/or displacement by plasma proteins and by proteases released by monocytes.

A synergistic effect of albumin and fibrinogen on immunoglobulin-induced red blood cell aggregation

Therapeutic administration of immunoglobulins (Ig) has the potential to precipitate thrombotic events. This phenomenon may be explained by red blood cell (RBC) aggregation, which can be potentiated by Ig. The contribution of plasma albumin and fibrinogen to Ig-induced RBC aggregation is unclear. We examined RBC aggregation in three settings: 1) patients receiving therapeutic infusions of Ig; 2) patients receiving plasma supplemented in vitro with Ig; and 3) patients receiving RBC suspensions in standard buffer with varying concentrations of albumin, Ig, and fibrinogen. Ig infusion augmented aggregation of RBCs from patients with normal or high plasma levels of albumin but decreased aggregation in those with lower plasma albumin concentrations. In vitro, RBC aggregation was significantly increased only when all three components, fibrinogen, albumin, and Ig, were present at or above normal concentrations in the suspension but was unaffected when any one of the components was absent from the suspension. Our results suggest a three-way interaction among fibrinogen, Ig, and albumin that synergistically induces RBC aggregation in plasma. Understanding these interactions may help predict clinically important phenomena related to RBC aggregation, such as thrombotic complications of Ig infusion.

Influence of endogenous albumin binding on blood-material interactions

A method has been developed to enhance the albumin affinity of a number of medical polymers, based on alkylation of the surface with straight-chain 16- or 18-carbon alkyl groups. This method has been demonstrated to induce the rapid binding of albumin from single and binary protein solutions, from plasma, and apparently, from whole blood. The bound albumin resists fluid shear or chemically induced desorption. Fibrinogen adsorption is inhibited in vitro and in vivo. Complement protein C3 activation from plasma is inhibited. Fibrin formation and platelet aggregation is inhibited in short-term in vivo experiments. Long-term catheter implant studies suggest that the C18 alkylation is more effective than most, if not all, currently available treatments for the retention of a clean, biocompatible, blood-contacting surface. No data have been obtained to date that conflict with the hypothesis that a renewable albumin layer, so formed, blocks the adsorption or conformational alteration of plasma proteins that otherwise might initiate or participate in various host defenses.

Albumin adsorption and retention on C18-alkyl-derivatized polyurethane vascular grafts

The short-term albumin affinity and thrombo-resistance of a polyether polyurethane vascular graft have been improved. The method is based on the C18 alkylation of the polymer. Thrombus formation by a planimetric technique and albumin retention on wire-reinforced polyurethane tubes, both C18 alkylated and untreated, were measured in short-term (4-h) exposure at femoral arterial sites in the dog. 125I-Albumin was preabsorbed on tubes and then exposed to blood for successive 2-h periods. Albumin uptake on alkylated tubes prior to blood exposure and retention following 2 h of blood exposure were significantly greater than on controls. Following a fast desorption phase in blood, the remaining albumin was more slowly desorbed from alkylated than from control tubes. Reincubation with albumin and blood reexposure produced a similar tendency, suggesting blood conditioning does not reduce the albumin affinity-enhancing property of C18 alkylation in the short term. Blood-preconditioning experiments suggested endogenous albumin has a high affinity for the C18-alkylated surface. Scanning electron microscopic examination showed thrombus and platelet densities were higher on control than on alkylated surfaces. These results suggest in vivo albumin affinity is increased for C18-alkylated polyurethane, which may be linked to decreased thrombus formation on these surfaces.

Inhibition of platelet-aggregating activity in thrombotic thrombocytopenic purpura plasma by normal adult immunoglobulin G

Plasma from patients with thrombotic thrombocytopenic purpura (TTP) caused the aggregation of autologous and homologous platelets, and effect which was inhibited by normal plasma. IgG purified from seven normal adults at a concentration of 0.7 mg/ml completely inhibited the platelet aggregation induced by plasma obtained from two TTP patients with active disease. The inhibition of platelet aggregation by human adult IgG was concentration dependent, and the inhibitory activity of human IgG was neutralized by rabbit antihuman IgG. Fab fragments inhibited the TTP plasma-induced platelet aggregation as well as intact IgG, whereas Fc fragments had no effect. Platelet aggregation caused by ADP, collagen, epinephrine, or thrombin was not affected by purified human IgG. The prior incubation of IgG with TTP plasma caused a significantly greater reduction of platelet aggregation by TTP plasma than that of IgG and platelet suspension, suggesting that the IgG inhibits TTP plasma-induced platelet aggregation through direct interaction with platelet aggregating factor in TTP plasma. IgG obtained initially from five infants and young children under the age of 4 yr did not possess any inhibitory activity. When one of the children reached 3 yr of age, his IgG inhibited the aggregation induced by one TTP plasma, but not that caused by another plasma. The IgG procured from the same boy at 4 yr of age inhibited the aggregation induced by both TTP plasmas. The IgG purified from the TTP plasma during active disease failed to inhibit the aggregation caused by the same plasma. After recovery, however, the IgG effectively inhibited aggregation. These observations suggest that platelet-aggregating factors present in the TTP plasma are heterogeneous in nature and that the IgG present in the normal adult plasma, which inhibits the TTP plasma-induced platelet aggregation, may be partially responsible for the success of plasma infusion therapy in TTP.