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Divalent magnesium restores cytoskeletal storage lesions in cold-stored platelet concentrates
(2022)
Cold storage of platelet concentrates (PC) has become attractive due to the reduced risk of bacterial proliferation, but in vivo circulation time of cold-stored platelets is reduced. Ca2+ release from storage organelles and higher activity of Ca2+ pumps at temperatures < 15 °C triggers cytoskeleton changes. This is suppressed by Mg2+ addition, avoiding a shift in Ca2+ hemostasis and cytoskeletal alterations. We report on the impact of 2–10 mM Mg2+ on cytoskeleton alterations of platelets from PC stored at room temperature (RT) or 4 °C in additive solution (PAS), 30% plasma. Deformation of platelets was assessed by real-time deformability cytometry (RT-DC), a method for biomechanical cell characterization. Deformation was strongly affected by storage at 4 °C and preserved by Mg2+ addition ≥ 4 mM Mg2+ (mean ± SD of median deformation 4 °C vs. 4 °C + 10 mM Mg2+ 0.073 ± 0.021 vs. 0.118 ± 0.023, p < 0.01; n = 6, day 7). These results were confirmed by immunofluorescence microscopy, showing that Mg2+ ≥ 4 mM prevents 4 °C storage induced cytoskeletal structure lesion. Standard in vitro platelet function tests showed minor differences between RT and cold-stored platelets. Hypotonic shock response was not significantly different between RT stored (56.38 ± 29.36%) and cold-stored platelets with (55.22 ± 11.16%) or without magnesium (45.65 ± 11.59%; p = 0.042, all n = 6, day 1). CD62P expression and platelet aggregation response were similar between RT and 4 °C stored platelets, with minor changes in the presence of higher Mg2+ concentrations. In conclusion, increasing Mg2+ up to 10 mM in PAS counteracts 4 °C storage lesions in platelets, maintains platelet cytoskeletal integrity and biomechanical properties comparable to RT stored platelets.
For the last two decades, heparins have been widely used as anticoagulants. Besides
numerous advantages, up to 5% patients with heparin administration suffer from a major adverse
drug effect known as heparin-induced thrombocytopenia (HIT). This typical HIT can result in deep
vein thrombosis, pulmonary embolism, occlusion of a limb artery, acute myocardial infarct, stroke, and
a systemic reaction or skin necrosis. The basis of HIT may lead to clinical insights. Recent studies using
single-molecule force spectroscopy (SMFS)-based atomic force microscopy revealed detailed binding
mechanisms of the interactions between platelet factor 4 (PF4) and heparins of different lengths in
typical HIT. Especially, SMFS results allowed identifying a new mechanism of the autoimmune HIT
caused by a subset of human-derived antibodies in patients without heparin exposure. The findings
proved that not only heparin but also a subset of antibodies induce thrombocytopenia. In this review,
the role of SMFS in unraveling a major adverse drug effect and insights into molecular mechanisms
inducing thrombocytopenia by both heparins and antibodies will be discussed.
Background: Hyperthyroidism is known to induce a hypercoagulable state. It stimulates plasma levels of procoagulative factors and reduces fibrinolytic activity. So far most of the data have been derived from patients with endogenous hyperthyroidism with a wide variability in the underlying pathogenesis and severity of the disease. Objectives: In this study we experimentally induced thyrotoxicosis in healthy volunteers to explore the effects of thyroxine excess on the plasma proteome. Using a shotgun proteomics approach, the abundance of plasma proteins was monitored before, during and after thyrotoxicosis. Methods: Sixteen healthy male subjects were sampled at baseline, 4 and 8 weeks under 250 µg/day thyroxine p.o., as well as 4 and 8 weeks after stopping the application. Plasma proteins were analyzed after depletion of 6 high-abundance proteins (MARS6) by LC-ESI-MS/MS mass spectrometry. Mass spectrometric raw data were processed using a label-free, intensity-based workflow. Subsequently, the linear dependence between protein abundances and fT<sub>4</sub> levels were calculated using a Pearson correlation. Results: All subjects developed biochemical thyrotoxicosis, and this effect was reversed within the first 4 weeks of follow-up. None of the volunteers noticed any subjective symptoms. Levels of 10 proteins involved in the coagulation cascade specifically correlated with fT<sub>4</sub>, supporting an influence of thyroid hormone levels on blood coagulation even at nonpathological levels. Conclusions: The results suggest that experimental thyrotoxicosis exerts selective and specific thyroxine-induced effects on coagulation markers. Our study design allows assessment of thyroid hormone effects on plasma protein levels without secondary effects of other diseases or therapies.
Since its introduction in 2006, the NOD/scid mouse model has greatly contributed to the understanding of the pathomechanisms of antibody-mediated thrombocytopenia. This progress has however been hampered by inter-laboratory differences. With this work, we make several suggestions to minimise these differences:
We suggest that human platelets (blood group 0) be injected into the mice (age- and sex-matched, 8-16 weeks) via the tail vein. For antibody injection, scientists may choose between intraperitoneal and tail vein injection, each of which has strengths and drawbacks. In case of low antibody titer or low avidity antibodies, preincubation of the platelets with the patient serum prior to injection promotes platelet elimination where standard protocols fail. For subsequent sample preparation, we found that newly-launched ready-to-use kits present a good alternative to classical density gradient centrifugation by reducing man-hours and turnover time without affecting the quality of flow cytometry analysis.
In a second part, we used the revised mouse model to study anti-CD36 mediated thrombocytopenia in vivo. Anti-CD36 antibodies have been suggested as frequent case for FNAIT in Asia. The mechanisms behind this remain partly unclear. After injecting anti-CD36 monoclonal antibody or anti-CD36 patient immunoglobulin into the system, circulating human platelets were rapidly cleared. Interestingly, the polyclonal patient immunoglobulins used were not uniform in their anti-platelet reactivity. On further examination, we found that the anti-CD36 antibodies induce platelet activation and aggregation, which we were able to inhibit by the addition of an Fcγ-receptor blocking agent. This suggests a possible role for Fcγ-receptor in the activation and elimination process.
As our results from the experiments on the role of complement in the elimination process are however ambiguous, further studies are needed. The clinical relevance of anti-CD36 antibody-mediated platelet activation and aggregation for the high abortion rates in affected women has yet to be evaluated.
Platelet factor 4 (PF4, synonym: CXCL4) is an evolutionary old chemokine with proposed roles in hemostasis and antimicrobial defense. In addition, PF4 has attracted considerable attention as a crucial mediator of one of the most prothrombotic adverse drug effects affecting blood cells, heparin-induced thrombocytopenia (HIT). Interest in PF4 substantially increased in 2021 when it was identified as the target antigen in the life-threatening adverse effect, vaccine-induced immune thrombotic thrombocytopenia (VITT). We address the concept that a major biological function of PF4—a strongly cationic chemokine—is to bind to negatively-charged prokaryotic microorganisms, resulting in structural changes in PF4 that trigger a danger signal recognized by the adaptive immune system. Application of biophysical tools has provided substantial insights into the molecular mechanisms by which PF4 becomes immunogenic, providing insights into a new mechanism of autoimmunity. Binding of autoantibodies with high affinity induces conformational change(s) in the endogenous protein, which are then recognized as foreign antigen, as exemplified by the prothrombotic disorders, autoimmune HIT and VITT. The final part of our review summarizes current assays for HIT and VITT, explaining how structural aspects of anti-PF4 pathobiology relate to assay design and performance characteristics. Currently, functional (platelet activation) assays using washed platelets detect HIT antibodies when heparin is added, and VITT antibodies when PF4 is added. Solid-phase PF4-dependent immunoassays using microtiter plates are sensitive for both HIT and VITT antibodies, while rapid immunoassays, in which the PF4/heparin antigen is coated on beads, are sensitive and specific for HIT, but not for VITT antibodies.
Background: We assessed the effect of the uniform donor questionnaire (UDQ) on deferral rates in first-time and repeat donors. We focused on the introduced question about unprotected sexual contact with a new partner. Another goal was a stratified comparison of the deferral rates of the donor questionnaire (DQ) and UDQ. Methods: Data on donors and deferrals using the DQ and UDQ were collected at four blood establishments. The comparison included a 2-year period by questionnaire version. For the comparison of the questionnaires, an adjusted multinomial logistic regression was performed. Results: The analysis included 260,848 donations. First-time (FTD) and repeat donations (RD) showed higher deferral rates with the UDQ (FTD +5.4%, RD +1.4%). Deferral due to a new partner was 3.0% in first-time and 0.4% in repeat donors. The majority of these occurred in the youngest age groups. The most frequent deferral criterion was ‘disease' (5.1%). Conclusion: The regression revealed stronger predictors for deferral than the questionnaire version. Especially younger age carried a higher and independent risk for deferral. The additional deferrals of mainly young first-time donors due to a new sexual partner may identify those donors with potential heterosexual risk behavior who would otherwise not be identified.
Vaccine-induced immune thrombotic thrombocytopenia (VITT) and cerebral venous sinus thrombosis (CVST) have been recently described as rare complications following vaccination against SARS-CoV-2 with vector vaccines. We report a case of a young woman who presented with VITT and cerebral CVST 7 days following vaccination with ChAdOx1 nCov-19 (AstraZeneca). While the initial MRI was considered void of pathological findings, MRI 3 days later revealed extensive CVST of the transversal and sigmoidal sinus with intracerebral haemorrhage. Diagnostic tests including a platelet-factor-4-induced platelet activation assay confirmed the diagnosis of VITT. Treatment with intravenous immunoglobulins and argatroban resulted in a normalisation of platelet counts and remission of CVST.
Abstract
Background
Toxins are key virulence determinants of pathogens and can impair the function of host immune cells, including platelets. Insights into pathogen toxin interference with platelets will be pivotal to improve treatment of patients with bacterial bloodstream infections.
Materials and Methods
In this study, we deciphered the effects of Staphylococcus aureus toxins α‐hemolysin, LukAB, LukDE, and LukSF on human platelets and compared the effects with the pore forming toxin pneumolysin of Streptococcus pneumoniae. Activation of platelets and loss of platelet function were investigated by flow cytometry, aggregometry, platelet viability, fluorescence microscopy, and intracellular calcium release. Thrombus formation was assessed in whole blood.
Results
α‐hemolysin (Hla) is known to be a pore‐forming toxin. Hla‐induced calcium influx initially activates platelets as indicated by CD62P and αIIbβ3 integrin activation, but also induces finally alterations in the phenotype of platelets. In contrast to Hla and pneumolysin, S. aureus bicomponent pore‐forming leukocidins LukAB, LukED, and LukSF do not bind to platelets and had no significant effect on platelet activation and viability. The presence of small amounts of Hla (0.2 µg/ml) in whole blood abrogates thrombus formation indicating that in systemic infections with S. aureus the stability of formed thrombi is impaired. Damage of platelets by Hla was not neutralized by intravenous immune globulins.
Conclusion
Our findings might be of clinical relevance for S. aureus induced endocarditis. Stabilizing the aortic‐valve thrombi by inhibiting Hla‐induced impairment of platelets might reduce the risk for septic (micro‐)embolization.
Protamine is administered as protamine sulfate to reverse the anticoagulant effect of heparin following cardiopulmonary bypass surgery. Immunogenicity of protamine has been recognized for decades in several patient groups including vasectomized men, diabetic patients on protamine-containing insulin and patients undergoing cardiopulmonary bypass surgery. Anti-protamine/heparin antibodies are a newly described class of heparin-dependent antibodies found in about 30% of patients exposed to protamine and heparin during cardiac surgery. A subset of seropositive patients especially who tested positive for platelet-activating anti-protamine/heparin immunoglobulin G (IgG) antibodies before surgery have prolonged postoperative thrombocytopenia with an increased risk for arterial occlusions. Studies presented in this thesis shed light on potential approaches that may prevent antibody-mediated platelet activation by anti-protamine/heparin antibodies. Two approaches are presented in this thesis, partially desulfated heparin (ODSH) and low molecular weight protamine (LMWP). Our studies demonstrated the ability of ODSH to inhibit anti-protamine/heparin antibody-mediated platelet destruction in the NOD/SCID mouse model by: i) reduction of antibody binding to preformed protamine/heparin complexes, as shown by enzyme immunoassay, ii) interfering with the binding of protamine/heparin complexes to platelets as shown by flow cytometry and fluorescence microscopy, and iii) inhibition of antibody-mediated platelet activation. Interestingly, ODSH was also able to block ongoing platelet destruction by displacing pre-bound complexes from the platelet surface. In addition, our data suggest the use of synthesized LMWP as a substitute for protamine in heparin reversal. The in vitro investigations showed that synthesized LMWP efficiently neutralizes heparin using the activated partial thromboplastin time. Anti-protamine/heparin antibodies have low binding properties to LMWP/heparin complexes as indicated in enzyme immunoassay. The ability of platelet-activating anti-protamine/heparin antibodies to induce platelet activation in the functional assay was significantly reduced in the presence of LMWP/heparin compared to protamine/heparin complexes. Owing to findings obtained in our studies, both approaches might be a promising future option to reduce anti-protamine/heparin antibody-mediated adverse effects.
Background: Patients with mucin-producing adenocarcinoma have an increased risk for venous and arterial thrombosis. When these patients present with thrombocytopenia, disseminated intravascular coagulopathy (DIC) is often the underlying cause. Case Report: We report 2 patients who were admitted due to bleeding symptoms of unknown cause, in whom further workup revealed adenocarcinoma-induced DIC. Conclusion: In elderly patients presenting with signs of DIC, such as reduced fibrinogen levels, elevated prothrombin time, elevated D-dimer, and thrombocytopenia, without any obvious reason (e.g., sepsis), adenocarcinoma-associated coagulopathy should be considered as the underlying cause. Paradoxically, in these patients bleeding symptoms improve when the patient is sufficiently anti-coagulated with low molecular weight heparin. Treatment of the underlying disease is of central importance in controlling acute or chronic DIC associated with malignant diseases and chemotherapy should be started as soon as possible.
Background
Signs of an inflammatory process have been described in major depression.
Methods
In a double-blind, randomized study of celecoxib or placebo add-on to reboxetine in 40 depressed patients, celecoxib treatment has beneficial effects. In order to evaluate the tryptophan/kynurenine metabolism and to identify predictors for remission, tryptophan (TRP), kynurenine (KYN), kynurenic acid (KYNA), and quinolinic acid (QUIN) were estimated in the serum of 32 patients before and after treatment and in a group of 20 healthy controls.
Results
KYN levels were significantly lower in patients (p = 0.008), and the QUIN/KYN ratios were significantly higher (p = 0.028). At baseline, the higher KYN/TRP ratio was predictive for remission during celecoxib add-on treatment (p = 0.04) as well as for remission in the overall patient group (p = 0.01). In the placebo group, remitters showed a higher KYNA/QUIN ratio (p = 0.032). In the overall group, remitters showed lower KYNA/KYN (p = 0.035) and QUIN/KYN (p = 0.011) ratios. The lower the formation of downstream metabolites, especially QUIN, the better the treatment outcome.
Conclusion
The high KYN/TRP ratio predicted remission after treatment with celecoxib in this small sample of depressed patients. Eventually, the KYN/TRP ratio might be a marker for those patients, which benefit from an additional anti-inflammatory treatment.
Vector-based SARS-CoV-2 vaccines have been associated with vaccine- induced thrombosis with thrombocytopenia syndrome (VITT/TTS), but the causative factors are still unresolved. We comprehensively analyzed the ChAdOx1 nCoV-19 (AstraZeneca) and Ad26.COV2.S (Johnson and Johnson) vaccines. ChAdOx1 nCoV-19 contains significant amounts of host cell protein impurities, including functionally active proteasomes, and adenoviral proteins. A much smaller amount of impurities was found in Ad26.COV2.S. Platelet factor 4 formed complexes with ChAdOx1 nCoV-19 constituents, but not with purified virions from ChAdOx1 nCoV-19 or with Ad26.COV2.S. Vascular hyperpermeability was induced by ChAdOx nCoV-19 but not by Ad26.COV2.S. These differences in impurities together with EDTAinduced capillary leakage might contribute to the higher incidence rate of VITT associated with ChAdOx1 nCoV-19 compared to Ad26.COV2.S.
Platelet adhesion and spreading at the sites of vascular injury is vital to hemostasis. As an integral part of the innate immune system, platelets interact with opsonized bacterial pathogens through FcγRIIA and contribute to host defense. As mechanoscavangers, platelets actively migrate and capture bacteria via cytoskeleton-rich, dynamic structures, such as filopodia and lamellipodia. However, the role of human platelet FcγRIIA in cytoskeleton-dependent interaction with opsonized bacteria is not well understood. To decipher this, we used a reductionist approach with well-defined micropatterns functionalized with immunoglobulins mimicking immune complexes at planar interfaces and bacteriamimetic microbeads. By specifically blocking of FcγRIIA and selective disruption of the platelet cytoskeleton, we show that both functional FcγRIIA and cytoskeleton are necessary for human platelet adhesion and haptotaxis. The direct link between FcγRIIA and the cytoskeleton is further explored by single-particle tracking. We then demonstrate the relevance of cytoskeleton-dependent differential mobilities of FcγRIIA on bacteria opsonized with the chemokine platelet factor 4 (PF4) and patient-derived anti-PF4/polyanion IgG. Our data suggest that efficient capture of opsonized bacteria during host-defense is governed by mobility dynamics of FcγRIIA on filopodia and lamellipodia, and the cytoskeleton plays an essential role in platelet morphodynamics at biological interfaces that display immune complexes.
Inherited platelet disorders affecting the human platelet cytoskeleton result in increased bleeding risk. However, deciphering their impact on cytoskeleton-dependent intrinsic biomechanics of platelets remains challenging and represents an unmet need from a diagnostic and prognostic perspective. It is currently unclear whether ex vivo anticoagulants used during collection of peripheral blood impact the mechanophenotype of cellular components of blood. Using unbiased, high-throughput functional mechanophenotyping of single human platelets by real-time deformability cytometry, we found that ex vivo anticoagulants are a critical pre-analytical variable that differentially influences platelet deformation, their size, and functional response to agonists by altering the cytoskeleton. We applied our findings to characterize the functional mechanophenotype of platelets from a patient with Myosin Heavy Chain 9 (MYH9) related macrothrombocytopenia. Our data suggest that platelets from MYH9 p.E1841K mutation in humans affecting platelet non-muscle myosin heavy chain IIa (NMMHC-IIA) are biomechanically less deformable in comparison to platelets from healthy individuals.
Background
Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a prothrombotic, heparin-induced thrombocytopenia (HIT)-mimicking, adverse reaction caused by platelet-activating anti-platelet factor 4 (PF4) antibodies that occurs rarely after adenovirus vector-based COVID-19 vaccination. Strength of PF4-dependent enzyme immunoassay (EIA) reactivity—judged by optical density (OD) measurements—strongly predicts platelet-activating properties of HIT antibodies in a functional test. Whether a similar relationship holds for VITT antibodies is unknown.
Objectives
To evaluate probability for positive platelet activation testing for VITT antibodies based upon EIA OD reactivity; and to investigate simple approaches to minimize false-negative platelet activation testing for VITT.
Methods
All samples referred for VITT testing were systematically evaluated by semiquantitative in-house PF4/heparin-EIA (OD readings) and PF4-induced platelet activation (PIPA) testing within a cohort study. EIA-positive sera testing PIPA-negative were retested following 1/4 to 1/10 dilution. Logistic regression was performed to predict the probability of a positive PIPA per magnitude of EIA reactivity.
Results
Greater EIA ODs in sera from patients with suspected VITT correlated strongly with greater likelihood of PIPA reactivity. Of 61 sera (with OD values >1.0) testing negative in the PIPA, a high proportion (27/61, 44.3%) became PIPA positive when tested at 1/4 to 1/10 dilution.
Conclusions
VITT serology resembles HIT in that greater EIA OD reactivity predicts higher probability of positive testing for platelet-activating antibodies. Unlike the situation with HIT antibodies, however, diluting putative VITT serum increases probability of a positive platelet activation assay, suggesting that optimal complex formation depends on the stoichiometric ratio of PF4 and anti-PF4 VITT antibodies.
Background: Securing future blood supply is a major issue of transfusion safety. In this prospective 10-year longitudinal study we enrolled all blood donation services and hospitals of the federal state Mecklenburg-Western Pomerania. Methods and Results: From 2005 to 2015 (time period with major demographic effects), whole blood donation numbers declined by 18%. In male donors this paralleled the demographic change, while donation rates of females declined 12.4% more than expected from demography. In parallel, red cell transfusion rates/1,000 population decreased from 2005 to 2015 from 56 to 51 (-8.4%), primarily due to less transfusions in patients >60 years. However, the transfusion demand declined much less than blood donation numbers: -13.5% versus -18%, and the population >65 years (highest transfusion demand) will further increase. The key question is whether the decline in transfusion demand observed over the previous years will further continue, hereby compensating for reduced blood donation numbers due to the demographic change. The population structure of Mecklenburg-Western Pomerania reflects all Eastern German federal states, while the Western German federal states will reach similar ratios of age groups 18-64 years / ≥65 years about 10 years later. Conclusions: Regular monitoring of age- and sex-specific donation and transfusion data is urgently required to allow transfusion services strategic planning for securing future blood supply.
Platelets transfusion is a safe process, but during or after the process, the recipient may experience an adverse reaction and occasionally a serious adverse reaction (SAR). In this review, we focus on the inflammatory potential of platelet components (PCs) and their involvement in SARs. Recent evidence has highlighted a central role for platelets in the host inflammatory and immune responses. Blood platelets are involved in inflammation and various other aspects of innate immunity through the release of a plethora of immunomodulatory cytokines, chemokines, and associated molecules, collectively termed biological response modifiers that behave like ligands for endothelial and leukocyte receptors and for platelets themselves. The involvement of PCs in SARs—particularly on a critically ill patient’s context—could be related, at least in part, to the inflammatory functions of platelets, acquired during storage lesions. Moreover, we focus on causal link between platelet activation and immune-mediated disorders (transfusion-associated immunomodulation, platelets, polyanions, and bacterial defense and alloimmunization). This is linked to the platelets’ propensity to be activated even in the absence of deliberate stimuli and to the occurrence of time-dependent storage lesions.
‘Chameleonic' Serological Findings Leading to Life-Threatening Hemolytic Transfusion Reactions
(2015)
Background: The phenomena of co-incidence of transfusion-induced allo- and autoantibodies, blockage and/or loss of red blood cell (RBC) antigens are conspicuous and may result in confusion and misdiagnosis. Case Report: A 67-year-old female was transferred to the intensive care unit due to hemolysis which developed 2 days following transfusion of three Rh(D)-negative RBC units in the presence of strongly reactive autoantibodies. Standard serological testing and genotyping were performed. Upon arrival, the patient was typed as Ccddee. Her hemolysis was decompensated, and an immediate blood transfusion was required. In addition, direct and indirect antiglobulin tests (DAT and IAT) as well as the eluate were strongly positive. Emergency transfusion of Rh(D)-negative RBCs resulted in increased hemolysis and renal failure. An exhaustive testing revealed anti-D, anti-c, CCddee phenotype and CCD.ee genotype. Three units of cryopreserved CCddee RBCs were transfused, and the patient's condition immediately improved. The discrepancy between Rh-D phenotyping and genotyping was likely caused by masking of the D-epitopes by the autoantibodies. In fact, further enquiry revealed that the patient had been phenotyped as Rh(D)-positive 6 months ago and had been transfused at that time following hip surgery. Conclusion: The phenomena of transfusion-induced autoantibodies, masked alloantibodies, antigen blockage and/or loss are rare but important features which should be considered in patients presenting with autoimmune hemolytic anemia and/or hemolytic transfusion reactions.