Low Concentrations Of Heparin Research Articles

Flow cytometry vs conventional methods for the evaluation of anti-PF4/heparin antibodies: a single center study.

Aim: Heparin-induced thrombocytopenia (HIT) is a rare, life-threatening, immune-mediated adverse effect of heparin administration. This study compares frequently used laboratory assays in terms of their effectiveness in HIT diagnosis. Materials & methods: Fifty patients with suspected HIT were tested by gel immunoassay and solid phase PF4/heparin antibody ELISA. On positive results, platelet activation markers P-selectin and Annexin V were assayed using flow cytometry. Results: Thirty/50 patients were negative for both immunoassays. Flow cytometry was performed in the 20 immunoassay positive patients. Platelet activation was observed in 7/20 in the presence of low heparin concentration (0.2IU/ml). Conclusion: The results are in accordance with the currently available literature and flow cytometry seems a promising alternative in HIT laboratory investigation.

Heparin binding proteins on monocyte cell surfaces regulates pre-inflammatory responses in diabetes.

Many diabetic complications, such as renal and cardiovascular disease, share a common association with extensive and chronic inflammation due to infiltration by activated leukocytes that originate from the bone marrow (BM). Our previous study demonstrated that macrophage progenitor cells that divided in hyperglycemia induced intracellular synthesis of hyaluronan and became pro-inflammatory macrophages (Mpi), and that the presence of low concentrations of heparin (~50 nM) prevented the intracellular HA synthesis and promoted the formation of tissue repair macrophages (Mtr). However, the molecular mechanism underlying heparin's role is still unknown. This study showed that heparin can be internalized by dividing monocyte progenitor cells. Further, there are two most abundant heparin binding proteins, alpha-enolase (ENO-1) and cofilin-1, identified on monocyte cell surfaces. In addition to their conventional roles inside of cells, ENO-1 and cofilin-1 can be found on cell surfaces and are also involved in autoimmune diseases. Thus, this study provides new insight into heparin's role in regulating monocyte and macrophage function.

"Autoimmune HIT", a Potential Diagnostic Artifact Due to Remnant Heparin in HIT Samples, Is Not Associated with More Severe Outcomes

In recent years, there has been increasing use of the term "autoimmune" heparin-induced thrombocytopenia (HIT) to describe patients with HIT antibodies that activate platelets in the absence of exogenous heparin (i.e., the "zero heparin" serotonin release assay, SRA), with the proposed implication that such patients present with more severe phenotypes. Platelet activation in the SRA in the absence of exogenous heparin is likely a real phenomenon in rare/infrequent patients who did not receive proximate heparin therapy (Spontaneous HIT) and in patients who develop HIT after heparin treatment has ceased (delayed-onset HIT). However, in other patients deemed to have "autoimmune" HIT based on reactivity in the "zero heparin" SRA, we hypothesized that platelet reactivity in this SRA test system might result from remnant heparin in the patient's diagnostic blood sample. To further complicate the interpretation of autoimmune HIT testing, there is a lack of rigorous data demonstrating a correlation between this diagnosis and disease severity. This study was undertaken to evaluate the technical validity and clinical relevance of an autoimmune HIT diagnosis. First, thirty "real-world" diagnostic HIT patient samples were subjected to anti-Xa testing. Remarkably, fourteen of the 30 samples (47%) had detectable heparin, with a range of 0.11-0.55 IU/mL for thirteen samples, while one sample had heparin <0.1 IU/mL (data not shown due to Abstract 2-figure panel limit). Next, to determine the extent to which low concentrations of unfractionated or low molecular weight heparin spiked into patient samples impact reactivity in the SRA, spiked samples were tested in the "conventional" low dose heparin (0.1 IU/ml) SRA and the "zero heparin" SRA (autoimmune HIT test). Fig 1A demonstrates that even ultra-low concentrations of unfractionated heparin (0.06 IU/mL) spiked into the sample facilitate serotonin release in the "zero heparin" SRA. On the other hand, the conventional SRA was not impacted by heparin spiked into samples unless concentrations were 5 IU/mL or higher, several-fold greater than what would be seen in patient samples. Similarly, LMWH induced platelet reactivity in the zero heparin SRA at concentrations between 0.25-1.0 IU/mL, while there was no effect on the conventional SRA at these concentrations (data not shown). As proof-of-concept that low levels of heparin mediate reactivity in a zero-heparin functional test, a HIT patient sample devoid of heparin was spiked with 0.05 IU/ml of heparin and evaluated with and without digestion with heparinase I. Heparin-spiked samples induced platelet activation in a zero-heparin functional assay which was abrogated upon heparinase I digestion (data not shown). Together, these results are consistent with the hypothesis that at least some cases of "autoimmune HIT" are labeled as such due to residual heparin present in patient samples rather than due to the presence of a qualitatively different ("autoimmune") HIT antibody. To evaluate the clinical relevance of an "autoimmune" HIT diagnosis, platelet nadir and the presence of thrombosis were interrogated as markers of disease severity in a cohort of 48 HIT patient samples with unknown heparin levels. Thirty-six patients were positive in the zero heparin SRA ("Autoimmune HIT" cohort; >50% serotonin release), while 12 were negative ("Classical HIT" cohort; positive in the conventional SRA, but <50% serotonin release in the zero heparin SRA). Fig 1B demonstrates that there was no difference in platelet nadir between the two groups (p=0.562); further, there were no differences between these groups in rates of confirmed thrombosis/skin necrosis and acute system reactions (p=0.324; data not shown). In summary, "autoimmune HIT" diagnostic testing (zero-heparin SRA) should not be performed until samples are confirmed to be devoid of heparin, and rigorous large-scale studies are needed to evaluate whether results of validly-conducted autoimmune HIT tests correlate with disease severity. Figure 1. (A) Low concentrations of spiked heparin in a HIT patient sample facilitates platelet activation in the "autoimmune" HIT test (zero-heparin SRA; red line) but does not affect the conventional SRA (black line). (B) Platelet nadir was similar between "autoimmune" (n=36) and conventional HIT (n=12) cohorts. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Vaccine induced thrombotic thrombocytopenia: development and reactivity of anti-platelet factor 4 antibodies and immune pathogenic mechanisms

In ultrarare cases, patients vaccinated with DNA adenovirus vector vaccine against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), develop a vaccine-induced immune thrombotic thrombocytopenia (VITT), with a high incidence of fatal cases. The causative agent is the development of platelet factor 4 (PF4)-dependent antibodies that resemble heparin-induced thrombocytopenia (HIT) complication, although many differences can be noticed in clinical presentation, antibody reactivity, involved epitopes on the PF4 protein, and pathological mechanisms. From the literature review, and the experience of HIT and testing a few plasmas from patients with VITT, this review analyzes the possible mechanisms, which show the strong immunoglobulin G (IgG) antibody reactivity to PF4 alone, in the absence of heparin, and to a lesser extend to stoichiometric complexes of PF4 and heparin (H-PF4). In addition, much lower heparin concentrations are required for inhibiting antibody binding to PF4. These concentrations are much lower than those required for disrupting the stoichiometric H-PF4 complexes. This confirms that IgG antibodies responsible for HIT bind preferentially to PF4, to epitopes that are readily masked by low concentrations of heparin. These antibodies are at a much higher concentration than the current ones observed for HIT, keeping a strong reactivity even for plasma dilutions as high as 1/500 to 1/5,000, whilst the current dilution for testing heparin-dependent antibodies in HIT is 1/100. Although VITT anti-PF4 antibodies can be detected with the current anti-H-PF4 enzyme-linked immunosorbent assays (ELISAs) designed for HIT, some assays have low sensitivity or are unreactive, like lateral immunofiltration methods or chemiluminescent automated assays. The preferred method should concern the use of capture assays using PF4 coated solid surfaces. This report proposes that the immune response is only targeted to the binding domain of PF4 with the hexons present on the adenovirus vector, through an epitope spreading mechanism, without any exposure of neo-epitopes on PF4 protein.

The Deglycosylated Form of 1E12, a Monoclonal Anti-PF4 IgG, Strongly Inhibits Antibody-Triggered Cellular Activation in Vaccine-Induced Thrombotic Thrombocytopenia, and Is a Potential New Treatment for Vιττ

▪IntroductionVaccine-induced thrombotic thrombocytopenia (VITT) is a severe complication of recombinant adenoviral vector vaccines used to prevent COVID-19, likely due to anti-platelet factor 4 (PF4) IgG antibodies. The specificity and platelet-activating activity of VITT antibodies strikingly resemble that of antibodies detected in “autoimmune” heparin-induced thrombocytopenia (HIT), but their features remain poorly characterized. In particular, a better knowledge of these antibodies should help to understand the mechanisms leading to hypercoagulability and the particular thrombotic events observed in VITT, but rarely in typical HIT. We have recently developed a chimeric IgG1 anti-PF4 antibody, 1E12, which strongly mimics “autoimmune” HIT antibodies in terms of specificity and cellular effects. Therefore, we assessed whether 1E12 could mimic VITT antibodies. We then evaluated the capability of DG-1E12, a deglycosylated form of 1E12 unable to bind FcγR, to inhibit cellular activation induced by VITT antibodies.Methods and ResultsUsing a PF4-sensitized serotonin release assay (PF4-SRA) (Vayne C, New Engl J Med, 2021), we demonstrated that 1E12 (5 and 10 μg/mL) strongly activated platelets, with a pattern similar to that obtained with human VITT samples (n=7), i.e. in a PF4-dependent manner and without heparin. This platelet activation was inhibited by low heparin concentration (0.5 IU/mL), an effect also observed with VITT samples. Serotonin release induced by 1E12 was also fully inhibited by IV-3, a monoclonal antibody blocking FcγRIIa, or by IdeS, a bacterial protease that cleaves IgG and strongly inhibits the binding of IgG antibodies to FcγRIIa. This inhibitory effect of IV-3 and IdeS strongly supports that interactions between pathogenic anti-PF4 IgG and FcγRIIa play a central role in VITT.Incubation of 1E12 or VITT samples with isolated neutrophils (PMN) and platelets with PF4 (10 µg/mL) strongly induced DNA release and NETosis, supporting that PMN are involved in the processes leading to thrombosis in VITT. Furthermore, when whole blood from healthy donors incubated with 1E12 or VITT plasma was perfused in capillaries coated with von Willebrand Factor, numerous large platelet/leukocyte aggregates containing fibrin(ogen) were formed.To investigate whether 1E12 and VITT antibodies recognize overlapping epitopes on PF4, we then performed competitive assays with a deglycosylated form of 1E12 (DG-1E12), still able to bind PF4 but not to interact with Fcγ receptors. In PF4-SRA, pre-incubation of DG-1E12 (50 µg/mL) dramatically reduced platelet activation induced by VITT antibodies, which was fully abrogated for 9 of the 14 VITT samples tested. Additional experiments using a whole blood PF4-enhanced flow cytometry assay recently designed for VITT diagnosis (Handtke et al, Blood 2021), confirmed that DG-1E12 fully prevented platelet activation induced by VITT antibodies. Moreover, when platelets and neutrophils were pre-incubated with DG-1E12 (100 µg/mL), NETosis and thus DNA release, nuclear rounding, and DNA decondensation induced by VITT antibodies were completely inhibited. Finally, DG-1E12 (100 µg/mL) also fully abolished VITT antibody-mediated thrombus formation in whole blood in vitro under vein flow conditions. Comparatively, DG-1E12 did not inhibit ALB6, a murine monoclonal anti-CD9 antibody, which also strongly activates platelets in a FcγRIIa-dependent manner.ConclusionsOur results show that 1E12 exhibits features similar to those of human VITT antibodies in terms of specificity, affinity and cellular effects, and could therefore be used as a model antibody to study the pathophysiology of VITT. Our data also demonstrate that DG-1E12 prevents blood cell activation and thrombus formation induced by VITT antibodies, likely due to the competitive effect of its Fab fragment on antibody binding to PF4. DG-1E12 may allow the development of a new drug neutralizing the pathogenic effect of autoimmune anti-PF4 antibodies, such as those associated with VITT. DisclosuresThiele: Bristol Myers Squibb: Honoraria, Other; Pfizer: Honoraria, Other; Bayer: Honoraria; Chugai Pharma: Honoraria, Other; Novo Nordisk: Other; Novartis: Honoraria; Daichii Sankyo: Other. Pouplard: Stago: Research Funding. Greinacher: Macopharma: Honoraria; Biomarin/Prosensa: Other, Research Funding; Sagent: Other, Research Funding; Rovi: Other, Research Funding; Gore inc.: Other, Research Funding; Bayer Healthcare: Other, Research Funding; Paringenix: Other, Research Funding; BMS: Honoraria, Other, Research Funding; MSD: Honoraria, Other, Research Funding; Boehringer Ingelheim: Honoraria, Other, Research Funding; Aspen: Honoraria, Other, Research Funding; Portola: Other; Ergomed: Other; Instrument Laboratory: Honoraria; Chromatec: Honoraria. Gruel: Stago: Other: symposium fees, Research Funding. Rollin: Stago: Research Funding.

An ex vivo comparison of partial thromboplastin time and activated clotting time for heparin anticoagulation in an ovine model.

Sheep are a primary model of mechanical circulatory support (MCS) with heparin anticoagulation therapy frequently being monitored by activated clotting time (ACT) due to ease and cost. In patients undergoing long-term heparin therapy, other anticoagulation monitoring strategies, such as activated partial thromboplastin time (aPTT), have proven to be more reliable indicators for the adequacy of anticoagulation, frequently determined by heparin concentration. As there is a paucity of similar studies in sheep, we sought to investigate the correlation between heparin concentration and ACT and aPTT using whole sheep blood in an ex vivo model. Fresh whole blood was serially drawn from an adult female Dorset-hybrid sheep and aliquots were placed into tubes containing heparin saline solutions with concentrations ranging from 0 to 7.81 U heparin per mL of whole blood. ACT and aPTT values were measured on each of the samples. The experiment was performed four times with the same animal. A simple linear regression was performed to determine correlation, and subgroup analysis was performed on low versus high heparin concentrations typically seen in human patients on long-term MCS, such as extracorporeal membrane oxygenation (ECMO), versus cardiopulmonary bypass, respectively. aPTT measurements versus the heparin concentration had an R2 =0.7295. ACT measurements versus the heparin concentration had a R2 =0.4628. aPTT measurements versus the ACT measurements had a R2 =0.2974. The strength of the correlation between aPTT and heparin concentration increased at low heparin concentrations (R2 =0.8392). aPTT had a more reliable correlation to heparin concentration and thus anticoagulation level than ACT. This was particularly true at lower heparin concentrations, similar to ranges seen for patients on ECMO. The correlation between aPTT and ACT values was poor. Further in vivo studies should be performed to confirm our results.

A Point-of-Care Quartz Biosensor Chip for Detection of PF4/Heparin Complexes

BACKGROUNDOur recent studies indicate that circulating PF4/heparin complexes activate complement and contribute to a subsequent immune response seen in heparin-induced thrombocytopenia (HIT) (Khandelwal, Blood 2016). We undertook studies to develop a sensitive assay for measuring circulating PF4/heparin. To do so, we utilize a quartz crystal microbalance (QCM) device, which is a piezoelectric acoustic resonator that detects decreases in the resonance frequency of the quartz crystal due to the increased mass caused by molecules binding to the electrode surface. We hypothesize that a novel label-free QCM biosensor functionalized with PF4/heparin capture antibodies can provide for robust quantitative antigen detection and physical characterization of antigen-antibody interactions. METHODSWe formed a mixed self-assembled monolayer by using thiol-functionalized polyethylene glycols (PEGs) with -OH and biotin terminated head-groups on gold electrodes of quartz biosensor (Nelson; Langmuir 2001). PEG-backfilling of this surface provided protein non-fouling effects (1% BSA adsorbed only 10 ng/cm2), while biotin end-groups enabled close to full surface coverage of streptavidin (180 ng/cm2). This surface became our platform to immobilize biotinylated KKO (anti-PF4/heparin IgG2Κb monoclonal antibody, developed in Arepally Lab) and TRA (isotype IgG2Κb control antibody; developed in Arepally Lab).To characterize the sensor's detection ability, we flowed recombinant PF4 (provided by M. Poncz, Children's Hospital of Philadelphia) with a range of heparin (Elkins-Sinn, NJ) concentrations. The solutions are introduced to the biosensors 10 minutes after mixing the heparin and flowed through the system until the frequency readout stabilized. We determined the amount of captured PF4/heparin complexes and the layer thickness by monitoring the sensor's resonance frequency shifts and acoustic dissipation.The surface distribution of PF4/heparin complexes on KKO-functionalized surfaces was imaged by tapping-mode atomic force microscopy (AFM). The imaging results are used to verify layer thickness calculated by acoustic modeling of the QCM signal. RESULTSIn initial experiments, KKO showed no changes in the presence of buffer or PF4 alone. However, when PF4 (10 μg/ml) was infused with increasing amounts of heparin (0.2, 1 or 10 U/ml) significant binding was detected starting at 0.2 U/ml heparin (Figure A). The acoustic modeling of the KKO-bound PF4 complexes with 0.2 U/ml heparin suggested that the macromolecular complexes were nearly 25 nm high. These results are consistent with the neutralization model for the role of PF4 in heparin-induced thrombocytopenia, in which the amount of PF4/ heparin complexes peaks at a specific molar ratio of PF4:heparin (Kowalska; Thrombosis Research 2010). Comparatively, almost no binding occurred when the quartz crystal was functionalized with TRA. This result not only demonstrates the protein non-fouling capacity of the PEG backfilling of the surface, but also shows the specificity of the surface-immobilized assay.To gauge the sensitivity of the QCM biosensor to lower concentrations of PF4 and heparin that may be found in vivo, we tested 1µg/mL PF4 with lower heparin concentrations (0.02-0.05 U/ml). As shown in Figure B, a nearly linear KKO binding response was observed in this range capable of distinguishing heparin concentrations that differed by as little as 0.01 U/ml. The highest adsorption was observed at heparin concentration of 0.02 U/ml with associated atomic force microscopy (AFM) images again showing spherical particles with 25 nm diameter on the KKO immobilized surface. CONCLUSIONSHighly specific binding to PF4 complexes demonstrates the sensitivity of the QCM platform and its ability to distinguish differences between heparin concentrations of even 0.01 U/ml. Since QCM is a mass-sensing biosensor, it has a unique sensitivity advantage while sensing high molecular weight macromolecular complexes. This, combined with possible miniaturization of the sensor and integration with lab-on-a-chip systems, creates the potential for point-of-care bed-side detection of PF4/heparin. [Display omitted] DisclosuresArepally:Biokit: Patents & Royalties.

The α-defensins stimulate proteoglycan-dependent catabolism of low-density lipoprotein by vascular cells: a new class of inflammatory apolipoprotein and a possible contributor to atherogenesis

AbstractInflammation may contribute to the pathogenesis of atherosclerosis. On the basis of previous reports that human atherosclerotic lesions contain α-defensins, a class of cationic proteins released by activated neutrophils, the study was designed to ask whether defensins modulate the binding and catabolism of low-density lipoprotein (LDL) by human vascular cells. The results of the study demonstrated that defensin stimulated the binding of 125I-LDL to cultured human umbilical vein endothelial cells, smooth muscle cells, and fibroblasts approximately 5-fold in a dose-dependent and saturable manner. Defensin and LDL formed stable complexes in solution and on cell surfaces. Stimulation of LDL binding by defensin was not inhibited by antibodies against the LDL-receptor (LDL-R), or by recombinant receptor-associated protein, which blocks binding of ligands to the α2-macroglobulin receptor/LDL-R–related protein and other LDL-R family members. Furthermore, defensin stimulated the binding, endocytosis, and degradation of LDL by fibroblasts lacking LDL-R. Stimulation of LDL degradation by defensin was inhibited approximately 75% by low concentrations of heparin (0.2 units/mL) and was similarly reduced in CHO cells lacking heparan-sulfate–containing proteoglycans. The effect of defensin was substantially increased in cells overexpressing the core protein of the syndecan-1 heparan sulfate proteoglycan. The α-defensins released from activated neutrophils may provide a link between inflammation and atherosclerosis by changing the pattern of LDL catabolism from LDL-R to the less efficient LDL-R–independent, proteoglycan-dependent pathway.

Indeterminate Serotonin Release Assays Are Associated with a High Mortality Rate

INTRODUCTION: The serotonin release assay (SRA) is considered the gold standard for diagnosis of heparin-induced thrombocytopenia (HIT). While the SRA holds high sensitivity and specificity when results are definitive, up to 10% of samples from patients with suspected HIT yield "indeterminate" results. In classic HIT, the SRA typically reveals high levels of serotonin release when serum is mixed with low concentrations of heparin and low levels of serotonin release when serum is mixed with high concentrations of heparin. Results are considered "indeterminate" when high levels of serotonin release are seen at both low and high concentrations of heparin, indicating a failure of high-dose heparin to saturate the heparin binding sites of PF4 molecules and inhibit platelet activation. Explanations for indeterminate assays include the presence of heparin-binding proteins that interfere with the assay, high titers of HLA class I alloantibodies, or immune complexes. Since the diagnosis of HIT carries such significance and has so many ramifications, an indeterminate SRA may leave therapeutic indecision. The etiologies, platelet trends, clinical course and outcomes of patients that receive indeterminate SRA results are not well-understood. We conducted a retrospective review of 2,056 patients that underwent SRA testing as part of their evaluation for HIT. METHODS: Using the electronic medical record data extraction software Clinical Looking Glass, we identified patients that underwent SRA testing between 1/1/2014 and 12/31/2018. SRA results were considered "indeterminate" when serotonin release exceeded 19% at all heparin dilutions (0.1 U/mL, 0.5 U/mL and 10 U/mL). We conducted a retrospective chart review to study the clinical course among patients who had "indeterminate" SRA results, the trends in platelet count, the timing of platelet drops and the physician response to this result. Statistical analysis was performed using chi-square testing for categorical variables. RESULTS: We identified 2,056 patients that underwent SRA testing between 2014 and 2019. Of these, 90 patients (4.4%) had "positive" SRA results and 1,814 patients (88.2%) had "negative" SRA results. Among the 152 patients (7.4%) with "indeterminate" SRA results, the mean 4T score was just 2.9, corresponding to a HIT probability of &amp;lt;5%. One-hundred and twenty of these 152 patients (78.9%) had heparin-PF4 antibody testing with optical densities below 0.60 OD, while only 4 of 152 patients (2.6%) had optical densities above 2.00 OD. Seventy eight of 152 patients (51.3%) either continued or were re-exposed to heparin after the indeterminate SRA result, and in 71 of 78 cases (91.0%), the platelet count stabilized or improved despite heparin exposure. In the remaining 7 cases, no acute VTE were found and no diagnosis of HIT was made. Four of the 71 patients (5.6%) that continued or were re-exposed to heparin were noted to have an acute VTE. A significantly higher portion of patients with an indeterminate SRA died during admission compared to those with a positive or negative SRA (49.3% vs. 21.1% and 27.2%, p &amp;lt;2.4 x10-10). The prevalence of thrombocytopenia &amp;lt;50,000 was substantially higher in patients with an indeterminate or positive SRA, compared to those with a negative SRA (39.5% and 40.0% vs. 27.5%, p &amp;lt;4.0 x 10-4). Re-exposure or continuation of heparin did not affect mortality; patients that were given heparin after an indeterminate SRA had a 47.4% mortality, compared to 51.4% in those given no more heparin (p = 0.63). Table 1 summarizes these findings. CONCLUSIONS: This is the largest study to date looking at patients with indeterminate SRA testing results, in which platelets exhibit high levels of serotonin release at both low and high heparin concentrations. Our data suggest 1) the majority of patients with indeterminate SRAs likely did not have HIT, 2) as evidenced by the low 4T scores and heparin-PF4 antibody levels, an indeterminate SRA suggests thrombocytopenia related to in-vivo platelet activation, and 3) an indeterminate SRA is associated with increased mortality. SRA results warrant a case-by-case assessment of the clinical picture in order to avoid unnecessary cessation of heparin products. Further studies exploring the mechanism leading to high serotonin release at both low and high heparin concentrations, causing an "indeterminate" SRA result, are warranted. Disclosures No relevant conflicts of interest to declare.

Heparinized chitosan/hydroxyapatite scaffolds stimulate angiogenesis

Formation of blood vessels during bone regeneration represents a major challenge for tissue engineered constructs. Poor revascularization can lead to scaffold failure and consequently, leads to non-healing fracture. Heparin is known to bind with angiogenic growth factors influencing the process of new blood vessels formation. There are several problems associated with the use of growth factors in clinic such as low stability, uncontrolled delivery to the site, and high price. The aim of the present study was to explore the potential of heparin to produce pro-angiogenic bone regeneration materials. Chitosan/hydroxyapatite freeze-gelled scaffolds were prepared and loaded with heparin. Different concentrations of heparin were successfully loaded onto the scaffolds, its release from the scaffold was analysed by toluidine blue assay and their angiogenic effect was evaluated by chorioallantoic membrane (CAM) assay to determine the optimal concentration of heparin to induce a proangiogenic effect. It was noted that low heparin concentrations exhibited a positive effect, with approximately 28 μg per scaffold indicating a significant increment in blood vessels. The synthesized materials showed no cytotoxic effects when evaluated by using U2OS cell line.

Preclinical safety and efficacy evaluation of the Pipeline Vantage Embolization Device with Shield Technology

BackgroundThe Pipeline Vantage Embolization Device with Shield Technology is a next generation flow diverter developed to improve aneurysm occlusion and implant endothelialization in addition to lowering thrombogenicity. We report here...

Single conical track-etched nanopore for a free-label detection of OSCS contaminants in heparin

The heparin contamination by oversulfated chondroitin (OSCS) was at the origin of one major sanitary problem of last decade. Here we propose a novel strategy to detect OSCS from heparin solution based on conical nanopore functionalized with poly-L-lysine deposition to ensure its re-usability. This sensor is an excellent to detect low heparin concentration (from 25 ng/ml to 3 μg/ml) using the modification of ionic current rectification. It also allows following the kinetic of heparin degradation by heparinase with a good correlation with results obtained by classical methods. The sensor is sensitive to the inhibition of heparinase by OSCS until a concentration of 200 pg/ml representing 0.01% in weight in a heparin. This resolution is one order of magnitude lower than the one obtained by chromatography. For the first time, it was reached without fluorescence labeling.

Heparin affects cytosolic glucose responses of hyperglycemic dividing mesangial cells

Mesangial expansion underlies diabetic nephropathy, leading to sclerosis and renal failure. The glycosaminoglycan heparin inhibits mesangial cell growth, but the molecular mechanism is unclear. Here, rat mesangial cells (RMCs) were growth-arrested in the G0/G1 phase of cell division, stimulated to divide in normal glucose (5.6 mm) or high glucose (25.6 mm) with or without heparin, and analyzed for glucose uptake. We observed that RMCs entering the G1 phase in normal glucose with or without heparin rapidly cease glucose uptake. RMCs entering G1 in high glucose sustained glucose uptake for the first 3 h, and high-glucose exposure of RMCs only in the first 8 h of G1 induced the formation of an extracellular monocyte-adhesive hyaluronan matrix after cell division was completed. Moreover, a low heparin concentration under high-glucose conditions blocked glucose uptake by 1 h into G1 Of note, glucose transporter 4 (glut4) localized on the RMC surface at G0/G1 and was internalized into G1 cells under normal glucose conditions with or without heparin within 30 min. We also noted that, under high-glucose conditions, glut4 remained on the RMC surface for at least 2 h into G1 and was internalized by 4 h without heparin and within 1 h with heparin. These results provide evidence that the influx of glucose in hyperglycemic dividing RMCs initiates intermediate glucose metabolism, leading to increased cytosolic UDP sugars, and induces abnormal intracellular hyaluronan synthesis during the S phase of cell division.

Heparin-dependent aggregation of hen egg white lysozyme reveals two distinct mechanisms of amyloid fibrillation

Heparin, a biopolymer possessing high negative charge density, is known to accelerate amyloid fibrillation by various proteins. Using hen egg white lysozyme, we studied the effects of heparin on protein aggregation at low pH, raised temperature, and applied ultrasonic irradiation, conditions under which amyloid fibrillation was promoted. Heparin exhibited complex bimodal concentration-dependent effects, either accelerating or inhibiting fibrillation at pH 2.0 and 60 °C. At concentrations lower than 20 μg/ml, heparin accelerated fibrillation through transient formation of hetero-oligomeric aggregates. Between 0.1 and 10 mg/ml, heparin rapidly induced amorphous heteroaggregation with little to no accompanying fibril formation. Above 10 mg/ml, heparin again induced fibrillation after a long lag time preceded by oligomeric aggregate formation. Compared with studies performed using monovalent and divalent anions, the results suggest two distinct mechanisms of heparin-induced fibrillation. At low heparin concentrations, initial hen egg white lysozyme cluster formation and subsequent fibrillation is promoted by counter ion binding and screening of repulsive charges. At high heparin concentrations, fibrillation is caused by a combination of salting out and macromolecular crowding effects probably independent of protein net charge. Both fibrillation mechanisms compete against amorphous aggregation, producing a complex heparin concentration-dependent phase diagram. Moreover, the results suggest an active role for amorphous oligomeric aggregates in triggering fibrillation, whereby breakdown of supersaturation takes place through heterogeneous nucleation of amyloid on amorphous aggregates.

Abstract 191: Immobilized ApoA-I and High Density Lipoproteins are Anti-thrombotic and Inhibit Smooth Muscle Cell Attachment and Proliferation

Aim: The clinical efficacy of current endovascular stents is limited by thrombosis and restenosis. Plasma activated coated stainless steel (PAC) is able to covalently bind proteins to stainless steel (SS) surfaces in their bioactive state. High density lipoproteins (HDL) and its main apolipoprotein constituent apoA-I regulate key biological processes involved in restenosis and thrombosis, highlighting their potential for immobilization on PAC stent surfaces. We hypothesized that covalently bound apoA-I or reconstituted HDL (rHDL) to PAC will retain its biological properties and improve stent patency. Methods and Results: Covalent binding of 125I labelled apoA-I and rHDL was increased on PAC compared to SS (p&lt;0.001). Thrombosis formation under static conditions was assessed by scanning electron microscopy. Thrombi were strikingly reduced on PAC and completely absent on PAC+apoA-I and PAC+rHDL, while extensive thrombi formed on all SS samples at all time points. Thrombus formation under flow conditions using a Chandler Loop (0.5U/ml heparin) showed PAC, PAC+apoA-I and PAC+rHDL had 98%, 97% and 94% lower thrombus weights, compared to SS samples, respectively (p&lt;0.05). Lower heparin concentrations (0.3U/ml) revealed that PAC+apoA-I and PAC+rHDL were superior to PAC alone in reducing thrombus weights (98% and 95%, respectively, p&lt;0.01). P-selectin protein expression was measured by ELISA in the plasma from the Chandler loop assay (0.3U/ml heparin). Plasma exposed to PAC+apoA-I had reduced p-selectin levels (32%) compared to the PAC control (p&lt;0.05). Immobilized apoA-I and rHDL on PAC reduced smooth muscle cell (SMC) attachment by 70% and 80%, respectively, p&lt;0.05. Conversely, endothelial cell (EC) attachment was increased by 36% on PAC+apoA-I (p&lt;0.05). Immobilized PAC+apoA-I and PAC+rHDL also reduced TNF-α-induced SMC proliferation (26% and 20% respectively), compared to the PAC control (p&lt;0.05). Conclusion: ApoA-I and rHDL covalently bind to PAC surfaces. Immobilized apoA-I and rHDL retain their anti-thrombotic properties, inhibit SMC attachment and proliferation, and increase EC attachment. This may represent a novel site-directed approach to increase stent patency.

Identification and characterization of chloroplast casein kinase II from Oryza sativa (rice).

Plastid casein kinase II is an important regulator of transcription, posttranscriptional processes, and, most likely, different metabolic functions in dicotyledonous species. Here we report the identification and characterization of pCKII from the monocotyledonous species Oryza sativa. OspCKII activity was enriched from isolated rice chloroplasts using heparin-Sepharose chromatography, in which it co-elutes with the transcriptionally active chromosome (TAC) and several ribosomal proteins. Inclusion mass scanning of the kinase-active fraction identified the gene model for OspCKII. Transient expression of GFP fused to the 184 N-terminal amino acids of the OspCKII sequence in rice confirmed the chloroplastic localization of the kinase. OspCKII activity shows the characteristic features of casein kinase II, such as the utilization of GTP as phosphate donor, inhibition by low concentrations of heparin and poly-lysine, and utilization of the canonical pCKII motif E-S-E-G-E in the model substrate RNP29. Phosphoproteome analysis of a protein extract from rice leaves combined with a meta-analysis with published phosphoproteomics data revealed differences in the target protein spectrum between rice and Arabidopsis. Consistently, several pCKII phosphorylation sites in dicotyledonous plants are not conserved in monocots and algae, suggesting that details of pCKII regulation in plastids have changed during evolution.

P57 * STEM CELL PLASTICITY AND TUMORIGENISIS: REGULATORY ROLES OF HEPARAN SULPHATE IN THE CANCER STEM CELL NICHE

INTRODUCTION: During the past few years, stem cells have received attention as a system for research and cell-based therapies due to their unique ability for self-renewal. However, concerns have arisen from our current knowledge regarding what permits a safe use of stem cells in tissue engineering strategies. Uncontrolled stem cell expansion is a major cause of cancer and tissue degeneration. Sub- populations of cancer cells have been identified in tumours, leading to the cancer stem cell hypothesis, and the potential to target these cells for effective new anti-cancer therapies. METHOD: Systems to be studied will include the role of extracellular HS on neuroblastoma cell lines influence on the phenotype of cancer cell lines. The methods to be used will include: neuroblastoma cell culture; proliferation and differentiaton assays, Immunophenotyping by fluorescent activated cell sorting (FACS) analysis, chemical biology (HS saccharide libraries & synthetic compounds), glycoanalysis (glycan purification; HPLC/FPLC, and glycan analysis) to study changes in HS molecular phenotype with neuroblastoma cells. RESULTS: When we analysed heparin- treated SKNAS cells by flow cytometry to identify the CD44+ sub-population, we observed that low concentrations of heparin (10 ng/ml) reduced the proportion of CD44+ cells in culture. Conversely, treatment with a modified (desulphated) heparin, the F3 compound, known to have anti-metastatic activity have shown no significant effect. on the proportion of CD44+ cells in the SKNAS cell cultures. CONCLUSION:These results suggest that: a) heparinoid compounds may be effective in reducing the proportion of CSCs in a tumour; b) this effect may have some selectivity for to certain HS structures, since highly sulphated heparin displayed differentially activity compared to a low sulphated heparin derivative.

Real-time measurement of free thrombin: Evaluation of the usability of a new thrombin assay for coagulation monitoring during extracorporeal circulation

In patients undergoing cardiac surgery with heart-lung machine support, adequate anticoagulation to mitigate blood clotting caused by the artificial surfaces of the extracorporeal circulation (ECC) system is essential. These patients routinely receive heparin, whose effectiveness is monitored by measurements of the activated clotting time (ACT). However, ACT values only poorly correlate with the actual hemostatic status. The aim of our study was to evaluate the detection of free thrombin in heparinized human blood as a monitor of anticoagulation during ECC. Human whole blood was anticoagulated with different concentrations of heparin (0.75, 1, 2 or 3 IU/ml) and circulated in the Chandler-loop model for up to 240 min at 37 °C. Next to ACT, ECC-mediated changes in free active thrombin, prothrombin fragment 1+2 (F1+2) and thrombin-antithrombin-III (TAT) levels were measured before and during circulation. Platelet activation and cell count parameters were further investigated. Our study shows that detection of ECC-mediated changes in free thrombin is possible in blood anticoagulated with 0.75 or 1 IU/ml heparin, whereas no thrombin was detectable at higher heparin concentrations. Thrombin generation during 240 min of ECC is comparable to F 1+2 and TAT plasma levels during ECC. Thrombin is the key enzyme in the coagulation cascade and hence represents a promising marker for monitoring the coagulation status of patients. Although detection of free thrombin was not feasible at high heparin concentrations, the employed test represents an additional test to current laboratory methods investigating blood coagulation at low heparin concentrations.

Raman spectroscopy for clinical-level detection of heparin in serum by partial least-squares analysis

Heparin is the most widely used anti-coagulant for the prevention of blood clots in patients undergoing certain types of surgeries including open heart surgeries and dialysis. The precise monitoring of heparin amount in patients' blood is crucial for reducing the morbidity and mortality in surgical environments. Based upon these considerations, we have used Raman spectroscopy in conjunction with partial least squares (PLS) analysis to measure heparin concentration at clinical level which is less than 10 United States Pharmacopeia (USP) in serum. The PLS calibration model was constructed from the Raman spectra of different concentrations of heparin in serum. It showed a high coefficient of determination (R2>0.91) between the spectral data and heparin level in serum along with a low root mean square error of prediction ~4 USP/ml. It enabled the detection of extremely low concentrations of heparin in serum (~8 USP/ml) as desirable in clinical environment. The proposed optical method has the potential of being implemented as the point-of-care testing procedure during surgeries, where the interest is to rapidly monitor low concentrations of heparin in patient's blood.

Murine Monoclonal Antibody to Platelet Factor 4/Heparin Complexes as a Potential Reference Standard for Platelet Activation Assays in Heparin-Induced Thrombocytopenia

Quality control of the platelet activation assays to diagnose heparin-induced thrombocytopenia (HIT), (14)C-serotonin release assay (SRA) and platelet aggregation test (PAT) has yet to be established due to lack of reference standards and the difficulty of obtaining significant amounts of HIT antibodies from patients with HIT. We prepared a murine monoclonal antibody to human platelet factor 4 (hPF4)/heparin complexes (HIT-MoAb) and investigated the platelet activating action of HIT-MoAb by using SRA and PAT. The HIT-MoAb activated human platelets at low heparin concentration and the platelet activations were inhibited at high heparin concentration in both SRA and PAT. The HIT-MoAb produced a concentration-dependent effect. Moreover, the platelet activation at low heparin concentration was inhibited by anti-FcγRIIa antibody. These results indicated that HIT-MoAb has characteristics similar to human HIT antibodies regarding heparin-dependent platelet activation. Therefore, it is suggested that HIT-MoAb has the potential to be a positive control or reference standard in platelet activation assays.