The role of platelet factor 4 in platelet aggregation induced by the antibodies implicated in heparin-induced thrombocytopenia

Nanoparticles Bind to Endothelial Cells in Injured Blood Vessels via a Transient Protein Corona

Nanoparticles travel through blood vessels to reach disease sites, but the local environment they encounter may affect their surface chemistry and cellular interactions. Here, we found that as nanoparticles transit through injured blood vessels they may interact with a highly localized concentration of platelet factor 4 proteins released from activated platelets. The platelet factor 4 binds to the nanoparticle surface and interacts with heparan sulfate proteoglycans on endothelial cells, and induces uptake. Understanding nanoparticle interactions with blood proteins and endothelial cells during circulation is critical to optimizing their design for diseased tissue targeting and delivery.

Oral squamous cell carcinoma patients can be differentiated from healthy individuals with label-free serum proteomics

Background:

No blood biomarkers to detect early oral cavity squamous cell carcinoma (OSCC) without clinical signs exist – diagnosis is solely based on histology of a visible tumour. Most OSCC patients are diagnosed at advanced stage, which leads to significant morbidity and poor survival. Our aim was to find the serum screening or detection biomarkers in OSCC.

Methods:

Serum samples from patients with OSCC treated at the Department of Otorhinolaryngology – Head and Neck Surgery, Helsinki University Hospital (Finland) were collected. Age- and gender-matched healthy individuals served as controls. Quantitative label-free proteomics in high definition MS^E mode(HDMS^E) was performed on 13 patients and 12 healthy samples. Various statistical analyses were performed on quantitative proteomics data to obtain the most influential proteins, which classify the patients vs healthy samples.

Results:

In quantitative proteomic analysis (HDMS^E), 388 proteins were quantified in our pilot study. A complete separation between cases and controls was seen in supervised and unsupervised classification techniques such as orthogonal projections on latent structure-discriminant analysis (OPLS-DA) and self-organising maps. Using OPLS-DA S-plot, we identified a set of eight proteins that completely separated OSCC patients from healthy individuals.

Conclusions:

Although the tumour stages varied from I to IVa, these potential biomarkers were able to identify all OSCCs demonstrating their sensitivity to detect tumours of all stages. We are the first to suggest a set of serum biomarkers in our pilot study to be evaluated further as a diagnostic panel to detect preclinical OSCC in risk patients.

Role of platelet chemokines, PF-4 and CTAP-III, in cancer biology

With the recent addition of anti-angiogenic agents to cancer treatment, the angiogenesis regulators in platelets are gaining importance. Platelet factor 4 (PF-4/CXCL4) and Connective tissue activating peptide III (CTAP-III) are two platelet-associated chemokines that modulate tumor angiogenesis, inflammation within the tumor microenvironment, and in turn tumor growth. Here, we review the role of PF-4 and CTAP-III in the regulation of tumor angiogenesis; the results of clinical trial using recombinant PF-4 (rPF-4); and the use of PF-4 and CTAP-III as cancer biomarkers.

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.

β2 Glycoprotein I (β2GPI) binds platelet factor 4 (PF4): implications for the pathogenesis of antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune thrombophilia characterized by arterial/venous thrombosis and/or pregnancy morbidity in the presence of antiphospholipid antibodies that mainly recognize β2 glycoprotein I (β2GPI). To investigate potential platelet ligands of β2GPI, platelet membrane proteins from healthy persons and patients with APS were passed through a β2GPI-affinity column. By using mass spectrometry, platelet factor 4 (PF4) appeared as the dominant β2GPI binding protein. PF4 could bind in vitro, with high-affinity, recombinant β2GPI, and the binding was abrogated by soluble β2GPI. Coprecipitation experiments further confirmed this interaction. In silico molecular docking showed that PF4 tetramers can bind 2 β2GPI molecules simultaneously. Size exclusion chromatography confirmed that anti-β2GPI antibodies selectively interact with complexes composed of (β2GPI)2–(PF4)4. In addition, as shown by the β2GPI antigenicity evaluation, the reactivity of APS sera was higher against PF4–β2GPI complex than against β2GPI alone. On complex formation, anti-β2GPI–β2GPI–PF4 significantly induced platelet p38MAPK phosphorylation and TXB2 production, mainly through F(ab′)2 fragments of antibodies. In summary, this study makes evident that β2GPI forms stable complexes with PF4, leading to the stabilization of β2GPI dimeric structure that facilitates the antibody recognition. This interaction can probably be involved in the procoagulant tendency of APS.

[Resistance to curative treatment by unfractionned heparin]

Unfractionated heparin has been used as antithrombotic therapy for many years. Its main effect is attributed to the activation of antithrombin (AT), the heparin/AT complex inactivating both factor IIa (thrombin) and factor Xa. Resistance to unfractionated heparin with clinical or biological expression is uncommon. The occurrence of venous or arterial thrombosis or the extension of thrombosis in a patient receiving unfractionated heparin, should always raise suspicion of either AT deficiency or type 2 heparin-induced thrombocytopenia (HIT type 2). HIT type 2 is not a true heparin resistance but an immune complication that requires heparin discontinuation and the use of alternative anticoagulants. Biological heparin resistance is suspected in the presence of a normal or not prolonged activated partial thromboplastin time despite the administration of increasing dose of heparin. Measurement of anti-Xa activity is useful to adjust heparin treatment. Isolated biological heparin resistance is encountered in several physiological and pathological situations including inflammatory and infectious disorders, pregnancy and thrombocytosis. It also occurs in acquired antithrombin deficiency of nephrotic syndrome, l-asparaginase treatment or cardiopulmonary bypass. Biological heparin resistance is relatively common, but clinically significant resistance to heparin is rare and should always raise suspicion of either AT deficiency or type 2 heparin-induced thrombocytopenia.

Prevalence of heparin-induced antibodies in patients with chronic renal failure undergoing hemodialysis

Heparin-induced thrombocytopenia (HIT) type II is a serious complication of heparin therapy. It presents initially as thrombocytopenia, and is associated with thrombosis in 20-50% of the cases. HIT is related to the presence of heparin-induced antibodies (HIA), which show specificity for the PF4-heparin (PF4-H) complex. The FcgammaRIIa receptor has been suggested to participate in the pathogenic mechanism of HIA. Since patients undergoing chronic hemodialysis (HD) are exposed repeatedly to heparin, we studied the prevalence of HIA and their eventual relationship with thrombocytopenia and/or thrombosis, and the possible participation of the FcgammaRIIa polymorphism. We studied 207 patients with chronic renal failure (CRF) undergoing HD. As a control we included 130 blood donors and 28 patients with CRF without HD. The HIA patients were studied with the use of a PF4-H ELISA. Additionally, in some positive cases for the previous test, a 14C- serotonin release assay (14C-SRA) was performed. The polymorphism FcgammaRIIa H/R131 was studied by polymerase chain reaction (PCR) with allele-specific primers. Thirty-seven patients (17.9%) undergoing HD presented with HIA. The majority of these antibodies were IgG, IgM, and IgA. The HIA investigated presented specificity against the PF4-H complex, but not against PF4 alone (P<0.001). Twelve out of 22 (54.5%) PF4-H antibodies were positive when tested with the 14C-SRA. The distribution of the FcgammaRIIa polymorphism in patients and healthy controls was 42.6% and 41.6% for H/H131, 41% and 48.9% for the H/R131 isoform, and 16.4% and 9.5% for the R/R131 isoform, respectively. No statistically significant difference in the FcgammaRIIa isoform distribution was found. Twenty-nine out of 156 patients (18.5%) presented thrombocytopenia, and 21/207 (12.4%) had thrombosis of the native vein arterio-venous fistula (AVF). We did not find any statistically significant between HIA and thrombocytopenia or thrombosis. An important proportion of patients with CRF undergoing HD developed HIA, but these cases were not associated with thrombocytopenia or thrombosis of AVF. The frequency of the FcgammaRIIa polymorphism did not statistically differ between HIT type II and normal controls.

Generation of hematopoietic repopulating cells from human embryonic stem cells independent of ectopic HOXB4 expression

Despite the need for alternative sources of human hematopoietic stem cells (HSCs), the functional capacity of hematopoietic cells generated from human embryonic stem cells (hESCs) has yet to be evaluated and compared with adult sources. Here, we report that somatic and hESC-derived hematopoietic cells have similar phenotype and in vitro clonogenic progenitor activity. However, in contrast with somatic cells, hESC-derived hematopoietic cells failed to reconstitute intravenously transplanted recipient mice because of cellular aggregation causing fatal emboli formation. Direct femoral injection allowed recipient survival and resulted in multilineage hematopoietic repopulation, providing direct evidence of HSC function. However, hESC-derived HSCs had limited proliferative and migratory capacity compared with somatic HSCs that correlated with a distinct gene expression pattern of hESC-derived hematopoietic cells that included homeobox (HOX) A and B gene clusters. Ectopic expression of HOXB4 had no effect on repopulating capacity of hESC-derived cells. We suggest that limitations in the ability of hESC-derived HSCs to activate a molecular program similar to somatic HSCs may contribute to their atypical in vivo behavior. Our study demonstrates that HSCs can be derived from hESCs and provides an in vivo system and molecular foundation to evaluate strategies for the generation of clinically transplantable HSC from hESC lines.

A differentiated approach to assess the diagnostic usefulness of a rapid particle gel immunoassay for the detection of antibodies against heparin-platelet factor 4 in cardiac surgery patients

Enzyme-linked immunosorbent assay (ELISA) methods have shown to be of a low specificity for confirming heparin-induced thrombocytopenia (HIT) in cardiac surgery patients. In other patient collectives, a new antigen test [ID-HPF4 Particle Gel Immuno Assay (PaGIA); Diamed, Cressier sur Morat, Switzerland] was recently reported to exhibit a better specificity than the ELISA. Since a more specific test would serve as a useful tool when diagnosing HIT, a prospective study was carried out to elucidate the specificity and diagnostic usefulness of PaGIA in cardiac surgical patients. As assessed in cardiac surgery patients without HIT, the proportion of PaGIA-positive samples was lowest at baseline (16%; 13/74), increasing to 31% (19/61) at postoperative days 5-9 (P = 0.06) and 69% (29/42) at postoperative days 10-18 (P < 0.001 versus postoperative days 5-9). The respective proportions in an ELISA (HPF4 ELISA; Stago, Asnières sur Seine, France) were lower. Because the prevalence of antibody positivity increases during the postoperative course, a differentiated mathematical model was used to assess predictive values and likelihood ratios (LR) of the PaGIA at three different phases of hospitalization. Calculating LR revealed -LR to be 0.07 at baseline, 0.09 during postoperative days 5-9, and 0.19 during postoperative days 10-18, while +LR were 5.9 at baseline, 3.0 during postoperative days 5-9, and 1.4 during postoperative days 10-18. Thus, in cardiac surgery patients, the PaGIA can be regarded as a useful tool in excluding rapid onset and typical onset of HIT, and further provides valuable information in the confirmation of rapid onset of HIT. Using a differentiated approach for calculation of predictive values and LR, the present study demonstrates that PaGIA, despite a lower specificity than the employed ELISA, in some situations is a valuable tool when diagnosing HIT in cardiac surgery patients.

Insights from mouse models of heparin-induced thrombocytopenia and thrombosis

Heparin-induced thrombocytopenia/thrombosis (HIT/T) is the most frequent cause of drug-induced antibody-mediated thrombocytopenia, a common cause of life-and limb-threatening platelet activation and thrombosis. Although antibodies to heparin-platelet factor 4 (PF4) complexes are found in essentially all patients with HIT/T, it is unclear how antibody formation is initiated, why only a small subset of these antibodies cause disease, or the mechanism by which they initiate thrombosis. The recent development of a transgenic mouse model of HIT/T showed, for the first time in vivo, that heparin, PF4, antibodies to the heparin-PF4 complex, and Fc gamma RIIA are necessary and sufficient to recapitulate the severe thrombocytopenia and thrombosis seen in patients. This model can be expanded to systematically study individual factors important to HIT/T development in vivo, to determine their contribution to the spectrum of human disease. Several recent papers have examined the role of other contributors, such as monocyte tissue factor, endothelial cell activation, and leukocyte-platelet aggregates in the pathogenesis of the disease. Mouse models will provide a means to test new diagnostic and therapeutic approaches.