The subtilisin-like protease furin regulates hemin-induced CD63 surface expression on platelets

Accumulation of free heme B in the plasma can be the result of severe hemolytic events, when the scavenger system for free hemoglobin and heme B is overwhelmed. Free heme B can be oxidized into toxic hemin, which has been proven to activate platelet degranulation and aggregation and promote thrombosis. In the present study we analyzed the effect of hemin on the activation-mediated lysosomal degranulation and CD63 surface expression on platelets using classic flow cytometry and fluorescence microscopy techniques. Classical platelet activators were used as control to distinguish the novel effects of hemin from known activation pathways. CD63 is a tetraspanin protein, also known as lysosomal-associated membrane protein 3 or LAMP-3. In resting platelets CD63 is located within the membrane of delta granules and lysosomes of platelet, from where it is integrated into the platelet outer membrane upon stimulation. We were able to show that hemin like the endogenous platelet activators ADP, collagen or thrombin does provoke CD63 re-localization. Interestingly, only hemin-induced CD63 externalization is dependent on the subtilisin-like pro-protein convertase furin as shown by inhibitor experiments. Furthermore, we were able to demonstrate that hemin induces lysosome secretion, a source of the hemin-mediated CD63 presentation. Again, only the hemin-induced lysosome degranulation is furin dependent. In summary we have shown that the pro-protein convertase furin plays an important role in hemin-mediated lysosomal degranulation and CD63 externalization.

Machine learning insights into thrombo-ischemic risks and bleeding events through platelet lysophospholipids and acylcarnitine species

Coronary artery disease (CAD) often leads to adverse events resulting in significant disease burdens. Underlying risk factors often remain inapparent prior to disease incidence and the cardiovascular (CV) risk is not exclusively explained by traditional risk factors. Platelets inherently promote atheroprogression and enhanced platelet functions and distinct platelet lipid species are associated with disease severity in patients with CAD. Lipidomics data were acquired using mass spectrometry and processed alongside clinical data applying machine learning to model estimates of an increased CV risk in a consecutive CAD cohort (n = 595). By training machine learning models on CV risk measurements, stratification of CAD patients resulted in a phenotyping of risk groups. We found that distinct platelet lipids are associated with an increased CV or bleeding risk and independently predict adverse events. Notably, the addition of platelet lipids to conventional risk factors resulted in an increased diagnostic accuracy of patients with adverse CV events. Thus, patients with aberrant platelet lipid signatures and platelet functions are at elevated risk to develop adverse CV events. Machine learning combining platelet lipidome data and common clinical parameters demonstrated an increased diagnostic value in patients with CAD and might improve early risk discrimination and classification for CV events.

Thrombus architecture is influenced by the antiplatelet loading treatment in patients with acute myocardial infarction

BACKGROUND

Intracoronary thrombus formation is a main cause of acute myocardial infarction triggered by platelet activation. However, there are no data on the impact of different treatment strategies with antiplatelet agents before percutaneous coronary intervention (PCI) on histological characteristics of thrombus formation.

OBJECTIVE

In this study, we investigate the impact of preinterventional administration of the P2Y12-inhibitors clopidogrel and prasugrel on thrombus composition, highlighting significant changes associated with the antiplatelet pre-treatment.

METHODS

We prospectively enrolled 104 consecutive patients with ST-segment elevation myocardial infarction (STEMI) undergoing immediate PCI and thrombus aspiration by immunohistochemical staining along with RNA-sequencing employing Nanostring analysis. Fifty-two patients were treated with either prasugrel loading (60 mg) or clopidogrel loading (600 mg) prior to PCI, respectively.

RESULTS

In Patients with STEMI, intracoronary thrombus architecture was significantly altered between patients pre-treated with prasugrel when compared to clopidogrel. Fibrin content of thrombi was significantly decreased (41.8 % versus 66.7 %, p = 0.009) after pre-treatment with prasugrel compared to clopidogrel. Furthermore, levels of MPO positive cells in intracoronary thrombi were significantly decreased in patients with prasugrel pre-treatment (90.5 versus 201.1, p = 0.014) indicating an association of antiplatelet pre-treatment and the inflammatory responses during thrombus formation. Most strikingly, we observed significant differences among both pre-treatment groups regarding altered RNA expression and signaling pathways of thrombo-inflammatory processes within the thrombotic material, which were independently associated with antiplatelet strategies.

CONCLUSIONS

Our study elucidates the impact of antiplatelet pre-treatment on thrombus remodeling and architecture, thereby lowering the risk of recurrent adverse cardiovascular events in prasugrel-treated patients.

Translating genomic tools to Raman spectroscopy analysis enables high-dimensional tissue characterization on molecular resolution

Spatial transcriptomics of histological sections have revolutionized research in life sciences and enabled unprecedented insights into genetic processes involved in tissue reorganization. However, in contrast to genomic analysis, the actual biomolecular composition of the sample has fallen behind, leaving a gap of potentially highly valuable information. Raman microspectroscopy provides untargeted spatiomolecular information at high resolution, capable of filling this gap. In this study we demonstrate spatially resolved Raman "spectromics" to reveal homogeneity, heterogeneity and dynamics of cell matrix on molecular levels by repurposing state-of-the-art bioinformatic analysis tools commonly used for transcriptomic analyses. By exploring sections of murine myocardial infarction and cardiac hypertrophy, we identify myocardial subclusters when spatially approaching the pathology, and define the surrounding metabolic and cellular (immune-) landscape. Our innovative, label-free, non-invasive "spectromics" approach could therefore open perspectives for a profound characterization of histological samples, while additionally allowing the combination with consecutive downstream analyses of the very same specimen.

Interventional Removal of LV Thrombus in a Patient With Cardiogenic Shock and Transitory Ischemic Attack

We discuss a 38-year-old bodybuilder who had cardiogenic shock and multiorgan failure. The patient developed significant speech disorders resulting from thromboembolism of a huge, volatile left ventricular thrombus. Because of inoperability and the threat of severe ischemic stroke, the thrombus was removed with a snare and application of a cerebral embolic protection device. (Level of Difficulty: Advanced.).

The Subtilisin-Like Protease Furin Regulates Hemin-Dependent Ectodomain Shedding of Glycoprotein VI

INTRODUCTION

 Hemolysis results in release of free hemoglobin and hemin liberation from erythrocytes. Hemin has been described to induce platelet activation and to trigger thrombosis.

METHODS

 We evaluated the effect of hemin on platelet function and surface expression of the platelet collagen receptor glycoprotein VI (GPVI). Isolated platelets were stimulated with increasing concentrations of hemin.

RESULTS

 We found that hemin strongly enhanced platelet activation, aggregation, and aggregate formation on immobilized collagen under flow. In contrast, we found that surface expression of GPVI was significantly reduced upon hemin stimulation with high hemin concentrations indicating that hemin-induced loss of surface GPVI does not hinder platelet aggregation. Loss of hemin-induced surface expression of GPVI was caused by shedding of the ectodomain of GPVI as verified by immunoblotting and is independent of the GPVI or CLEC-2 mediated ITAM (immunoreceptor-tyrosine-based-activation-motif) signaling pathway as inhibitor studies revealed. Hemin-induced GPVI shedding was independent of metalloproteinases such as ADAM10 or ADAM17, which were previously described to regulate GPVI degradation. Similarly, concentration-dependent shedding of CD62P was also induced by hemin. Unexpectedly, we found that the subtilisin-like proprotein convertase furin controls hemin-dependent GPVI shedding as shown by inhibitor studies using the specific furin inhibitors SSM3 and Hexa-D-arginine. In the presence of SSM3 and Hexa-D-arginine, hemin-associated GPVI degradation was substantially reduced. Further, SSM3 inhibited hemin-induced but not CRP-XL-induced platelet aggregation and thrombus formation, indicating that furin controls specifically hemin-associated platelet functions.

CONCLUSION

 In summary, we describe a novel mechanism of hemin-dependent GPVI shedding and platelet function mediated by furin.

Deceleration capacity of heart rate predicts 1-year mortality in patients undergoing transcatheter edge-to-edge mitral valve repair

BACKGROUND

Risk stratification for transcatheter procedures in patients with severe mitral regurgitation is challenging. Deceleration capacity (DC) has already proven to be a reliable risk predictor in patients undergoing transcatheter aortic valve implantation. We hypothesized, that DC provides prognostic value in patients undergoing transcatheter edge-to-edge mitral valve repair (TEER).

METHODS

We retrospectively analyzed electrocardiogram signals from 106 patients undergoing TEER at the University Hospital of Tübingen. All patients received continuous heart-rate monitoring to assess DC following the procedure. One-year all-cause mortality was defined as the primary end point.

RESULTS

Sixteen patients (15.1%) died within 1 year. The DC in nonsurvivors was significantly reduced compared to survivors (5.1 ± 3.0 vs. 3.0 ± 1.6 ms, p = 0.002). A higher EuroSCORE II and impaired left ventricular function were furthermore associated with poor outcome. In Cox regression analyses, a DC < 4.5 ms was found a strong predictor of 1-year mortality (hazard ratio: 0.10, 95% confidence interval: 0.13-0.79, p = 0.029). Finally, a significant negative correlation was found between DC and residual mitral regurgitation after TEER (r = -0.41, p < 0.001).

CONCLUSION

In patients with severe mitral regurgitation undergoing TEER, DC may serve as a new predictor of follow-up mortality.

Recovery of systemic hyperinflammation in patients with severe SARS-CoV-2 infection

INTRODUCTION

Patients with cardiovascular disease (CVD) and acute SARS-CoV-2 infection might show an altered immune response during COVID-19.

MATERIAL AND METHODS

Twenty-three patients with CVD and SARS-CoV-2 infection were prospectively enrolled and received a cardiological assessment at study entry and during follow-up visit. Inclusion criteria of our study were age older than 18 years, presence of CVD, and acute SARS-CoV-2 infection. The median age of the patient cohort was 69 (IQR 55-79) years. 12 (52.2%) patients were men. Peripheral monocytes and chemokine/cytokine profiles were analysed.

RESULTS

Numbers of classical and non-classical monocytes were significantly decreased during acute SARS-CoV-2 infection compared to 3-month recovery. While classical monocytes reached the expected level in peripheral blood after 3 months, the number of non-classical monocytes remained significantly reduced.

DISCUSSION

All three monocyte subsets exhibited changes of established adhesion and activation markers. Interestingly, they also expressed higher levels of pro-inflammatory cytokines like macrophage migration inhibitory factor (MIF) at the time of recovery, although MIF was only slightly increased during the acute phase.

CONCLUSION

Changes of monocyte phenotypes and increased MIF expression after 3-month recovery from acute SARS-CoV-2 infection may indicate persistent, possibly long-lasting, pro-inflammatory monocyte function in CVD patients.

Myocardial Abscess After Myocarditis: Advantages of Multimodal Imaging Detecting the Rare Case of Fungal Abscess

We discuss the rare case of a myocardial abscess of the left ventricle in a 42-year-old man on immunosuppressive therapy after fulminant myocarditis. Multimodal imaging detected the myocardial abscess along with other septic emboli caused by infection with aspergillus fumigatus, which could be treated effectively with antimycotic strategies. (Level of Difficulty: Intermediate.).

COVID-19 versus seasonal influenza: myocardial injury and prognostic importance

Background

Acute myocardial injury is associated with poor prognosis in respiratory tract infections. We aimed to highlight the differences in prevalence of myocardial injury and its impact on prognosis in patients with COVID-19 compared to those with seasonal influenza.

Methods

This was a single-center prospective cohort study with a historical control group. 300 age-/sex-matched SARS-CoV-2 and seasonal influenza positive patients were enrolled. Myocardial injury was assessed by electrocardiogram (ECG), transthoracic echocardiography and biomarkers including high-sensitivity troponin-I. All patients were followed-up for 30 days after enrollment for all-cause mortalitiy, admission to the intensive care unit (ICU) and mechanical ventilation.

Results

Right ventricular distress was more common in COVID-19 whereas pathological ECG findings and impaired left ventricular function were more prevalent among influenza patients. COVID-19 patients suffered from a higher percentage of hypertension and dyslipidaemia. Contrary to COVID-19, pericardial effusion at admission was associated with poor outcome in the influenza group. Severe course of disease and respiratory failure resulted in significantly higher rates of ICU treatment and mechanical ventilation in COVID-19 patients. Although distribution of myocardial injury was similar, significantly fewer cardiac catheterizations were performed in COVID-19 patients. However, number of cardiac catheterizations was low in both groups. Finally, 30-day mortality was significantly higher in COVID-19 compared to influenza patients.

Conclusions

In adults requiring hospitalization due to COVID-19 or seasonal influenza, cardiovascular risk factors and signs of myocardial distress differ significantly. Furthermore, cardiovascular comorbidities may impair prognosis in COVID-19 patients to a higher degree than in their influenza counterparts.

Characterization of GPVI- or GPVI-CD39-Coated Nanoparticles and Their Impact on In Vitro Thrombus Formation

Traditional antithrombotic agents commonly share a therapy-limiting side effect, as they increase the overall systemic bleeding risk. A novel approach for targeted antithrombotic therapy is nanoparticles. In other therapeutic fields, nanoparticles have enabled site-specific delivery with low levels of toxicity and side effects. Here, we paired nanotechnology with an established dimeric glycoprotein VI-Fc (GPVI-Fc) and a GPVI-CD39 fusion protein, thereby combining site-specific delivery and new antithrombotic drugs. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles, NP-BSA, NP-GPVI and NP-GPVI-CD39 were characterized through electron microscopy, atomic force measurements and flow cytometry. Light transmission aggregometry enabled analysis of platelet aggregation. Thrombus formation was observed through flow chamber experiments. NP-GPVI and NP-GPVI-CD39 displayed a characteristic surface coating pattern. Fluorescence properties were identical amongst all samples. NP-GPVI and NP-GPVI-CD39 significantly impaired platelet aggregation. Thrombus formation was significantly impaired by NP-GPVI and was particularly impaired by NP-GPVI-CD39. The receptor-coated nanoparticles NP-GPVI and the bifunctional molecule NP-GPVI-CD39 demonstrated significant inhibition of in vitro thrombus formation. Consequently, the nanoparticle-mediated antithrombotic effect of GPVI-Fc, as well as GPVI-CD39, and an additive impact of CD39 was confirmed. In conclusion, NP-GPVI and NP-GPVI-CD39 may serve as a promising foundation for a novel therapeutic approach regarding targeted antithrombotic therapy.

Anti-platelet factor 4 antibodies causing VITT do not cross-react with SARS-CoV-2 spike protein

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a severe adverse effect of ChAdOx1 nCoV-19 COVID-19 vaccine (Vaxzevria) and Janssen Ad26.COV2.S COVID-19 vaccine, and it is associated with unusual thrombosis. VITT is caused by anti-platelet factor 4 (PF4) antibodies activating platelets through their FcγRIIa receptors. Antibodies that activate platelets through FcγRIIa receptors have also been identified in patients with COVID-19. These findings raise concern that vaccination-induced antibodies against anti-SARS-CoV-2 spike protein cause thrombosis by cross-reacting with PF4. Immunogenic epitopes of PF4 and SARS-CoV-2 spike protein were compared using in silico prediction tools and 3D modeling. The SARS-CoV-2 spike protein and PF4 share at least 1 similar epitope. Reactivity of purified anti-PF4 antibodies from patients with VITT was tested against recombinant SARS-CoV-2 spike protein. However, none of the affinity-purified anti-PF4 antibodies from 14 patients with VITT cross-reacted with SARS-CoV-2 spike protein. Sera from 222 polymerase chain reaction-confirmed patients with COVID-19 from 5 European centers were tested by PF4-heparin enzyme-linked immunosorbent assays and PF4-dependent platelet activation assays. We found anti-PF4 antibodies in sera from 19 (8.6%) of 222 patients with COVID-19. However, only 4 showed weak to moderate platelet activation in the presence of PF4, and none of those patients developed thrombotic complications. Among 10 (4.5%) of 222 patients who had COVID-19 with thrombosis, none showed PF4-dependent platelet-activating antibodies. In conclusion, antibodies against PF4 induced by vaccination do not cross-react with the SARS-CoV-2 spike protein, indicating that the intended vaccine-induced immune response against SARS-CoV-2 spike protein is not the trigger of VITT. PF4-reactive antibodies found in patients with COVID-19 in this study were not associated with thrombotic complications.

Platelet Activation and Plasma Levels of Furin Are Associated With Prognosis of Patients With Coronary Artery Disease and COVID-19

[Figure: see text].

Numbers and phenotype of non-classical CD14dimCD16+ monocytes are predictors of adverse clinical outcome in patients with coronary artery disease and severe SARS-CoV-2 infection

AIMS

To elucidate the prognostic role of monocytes in the immune response of patients with coronary artery disease (CAD) at risk for life-threatening heart and lung injury as major complications of SARS-CoV-2 infection.

METHODS AND RESULTS

From February to April 2020, we prospectively studied a cohort of 96 participants comprising 47 consecutive patients with CAD and acute SARS-CoV-2 infection (CAD + SARS-CoV-2), 19 CAD patients without infections, and 30 healthy controls. Clinical assessment included blood sampling, echocardiography, and electrocardiography within 12 h of admission. Respiratory failure was stratified by the Horovitz Index (HI) as moderately/severely impaired when HI ≤200 mmHg. The clinical endpoint (EP) was defined as HI ≤200 mmHg with subsequent mechanical ventilation within a follow-up of 30 days. The numbers of CD14dimCD16+ non-classical monocytes in peripheral blood were remarkably low in CAD + SARS-CoV-2 compared with CAD patients without infection and healthy controls (P < 0.0001). Moreover, these CD14dimCD16 monocytes showed decreased expression of established markers of adhesion, migration, and T-cell activation (CD54, CD62L, CX3CR1, CD80, and HLA-DR). Decreased numbers of CD14dimCD16+ monocytes were associated with the occurrence of EP. Kaplan-Meier curves illustrate that CAD + SARS-CoV-2 patients with numbers below the median of CD14dimCD16+ monocytes (median 1443 cells/mL) reached EP significantly more often compared to patients with numbers above the median (log-rank 5.03, P = 0.025).

CONCLUSION

Decreased numbers of CD14dimCD16+ monocytes are associated with rapidly progressive respiratory failure in CAD + SARS-CoV-2 patients. Intensified risk assessments comprising monocyte sub- and phenotypes may help to identify patients at risk for respiratory failure.

2424Long-term outcome of patients with biopsy-proven viral myocarditis: 12-year results from a late gadolinium enhancement cardiac magnetic resonance study

Purpose

Myocarditis is a common cardiac disease that is associated with significant mortality as demonstrated by several studies. Late gadolinium enhancement (LGE) by cardiac magnetic resonance imaging (CMR) is a valuable tool for risk stratification of patients with suspected myocarditis. Previous studies using CMR-LGE have reported a good negative predictive value over follow-up periods of 4–6 years, while its positive predictive value was only modest. However, there is a lack of data regarding the long-term prognosis (>10 years) of these patients. This study reports an extended long-term follow-up of a large cohort of patients with biopsy-proven viral myocarditis.

Methods

At initial presentation, all patients underwent endomyocardial biopsy and CMR for the work-up of suspected myocarditis or unclear cardiomyopathy and had evidence of virus in PCR analyses. The primary endpoints were: all-cause death, cardiac death, and the occurrence of sudden cardiac death (SCD).

Results

183 patients with biopsy-proven viral myocarditis were followed for a median of 11.5 years. At baseline, patients were 52 years old, 31% were females, and the median ejection fraction was moderately reduced (44%). Initial CMR assessment revealed LGE in 101 (55%) patients, while 82 (45%) patients had LGE-negative CMR. During the follow-up period, the following endpoints occurred in the overall cohort: all-cause death (n=71, 39%), cardiac death (n=50, 27%) and SCD (n=20, 11%). Most importantly, only a single LGE-negative patient experienced a SCD during this 12-year follow-up, while all other SCDs occurred in patients with LGE-positive CMR (1% vs. 19%, p<0.001). Consequently, the negative predictive value (NPV) of normal CMR-LGE regarding SCD was 98%. In addition, cardiac mortality (12% vs. 40%, p<0.001, NPV=88%) and all-cause mortality (20% vs. 54%, p<0.001, NPV=79%) were significantly lower in patients without LGE.

Conclusion

This cohort of biopsy-proven viral myocarditis demonstrates substantial mortality (39% in 11.5 years). However, absence of LGE on CMR was associated with favorable prognosis. This was applicable regarding all-cause and cardiac mortality, but most importantly with regard to SCD with a NPV of 98% over almost 12 years median follow-up.

Acknowledgement/Funding

This work was funded by the Robert-Bosch-Stiftung, Stuttgart, Germany and the Berthold-Leibinger-Stiftung, Ditzingen, Germany.

Antisense-mediated exon skipping: a therapeutic strategy for titin-based dilated cardiomyopathy

Frameshift mutations in the TTN gene encoding titin are a major cause for inherited forms of dilated cardiomyopathy (DCM), a heart disease characterized by ventricular dilatation, systolic dysfunction, and progressive heart failure. To date, there are no specific treatment options for DCM patients but heart transplantation. Here, we show the beneficial potential of reframing titin transcripts by antisense oligonucleotide (AON)-mediated exon skipping in human and murine models of DCM carrying a previously identified autosomal-dominant frameshift mutation in titin exon 326. Correction of TTN reading frame in patient-specific cardiomyocytes derived from induced pluripotent stem cells rescued defective myofibril assembly and stability and normalized the sarcomeric protein expression. AON treatment in Ttn knock-in mice improved sarcomere formation and contractile performance in homozygous embryos and prevented the development of the DCM phenotype in heterozygous animals. These results demonstrate that disruption of the titin reading frame due to a truncating DCM mutation can be restored by exon skipping in both patient cardiomyocytes in vitro and mouse heart in vivo, indicating RNA-based strategies as a potential treatment option for DCM.

Is the diagnostic yield of myocardial stress perfusion MRI impaired by three-vessel coronary artery disease?

BACKGROUND

Three-vessel coronary artery disease (CAD) comes along with globally reduced myocardial perfusion potentially restricting the demarcation of regional hypoperfusion in stress perfusion cardiac magnetic resonance imaging (MRI).

PURPOSE

To evaluate whether stress perfusion cardiac MRI is capable of detecting myocardial hypoperfusion in patients with 3-vessel CAD reliably.

MATERIAL AND METHODS

Two hundred and five patients with symptoms of CAD were included. The examination protocol comprised imaging of myocardial perfusion at stress (0.14 mg/kg/min adenosine for 4 min) using a 2D saturation recovery gradient echo sequence after administration of gadobutrol (0.1 mmol/kg body weight). Perfusion sequences were assessed qualitatively by two experienced observers. Coronary angiography served as standard of reference.

RESULTS

Sensitivity and specificity for hemodynamically relevant stenoses in patients with 0-, 1-, 2-, 3-vessel coronary artery disease were 100%/91%, 91%/73%, 90%/71%, 92%/64%; positive/negative predictive value, 67%/100%, 91%/73%, 83%/81%, 93%/58%; diagnostic accuracy, 93%/87%/83%/87%, respectively. The negative predictive value in patients with 3-vessel CAD was lower than in patients with 0- and 2-vessel CAD and the specificity lower than in patients with no CAD whereas the positive predictive value was higher than in patients with no CAD. The other proportions did not differ significantly between the groups.

CONCLUSION

The diagnostic value of stress perfusion cardiac MRI in patients with 3-vessel CAD is comparable to results in patients with 1- or 2-vessel CAD. In the rare event that stress perfusion images do not depict regional hypoperfusion in patients with severe 3-vessel CAD, myocardial ischemia could be identified by reduced semi-quantitative perfusion parameters.

Massive haemoptysis in an intravenous drug user with infective tricuspid valve endocarditis

Major causes of morbidity in intravenous drug users are infections. In infective endocarditis, the tricuspid valve is mainly involved. Masses can cause septic embolisms and, in rare cases, they are associated with mycotic aneurysms of pulmonary arteries that lead to severe haemorrhage. We report the case of a young woman with a history of intravenous drug abuse and prolonged infective tricuspid valve endocarditis. Initially, echocardiography showed large masses on the anterior leaflet of the tricuspid valve and severe tricuspid regurgitation; blood cultures revealed staphylococcus and streptococcus species. Eight months after initial diagnosis, she presented with severe haemoptysis and fever. CT revealed a ruptured mycotic aneurysm of the right pulmonary artery. Lobectomy was performed immediately. Postoperatively, the patient fully recovered. After continued antibiotic treatment, follow-up examinations showed negative echocardiographic findings and blood cultures results.

Hemostasis in Danio rerio: is the zebrafish a useful model for platelet research?

New scientific models have been established in the past few years to identify novel factors of hemostasis and thrombosis and to analyze their function in greater detail. One fairly new animal model is the zebrafish, Danio rerio, which shares most of the central factors of platelet adhesion, activation, aggregation and release reaction with humans. Examples include GPIIb-IIIa, many other integrins, coagulation factors, inflammatory and cytokine-like proteins as well as arachidonic acid metabolism enzymes. Yet the zebrafish genome has undergone a teleost-specific genome duplication, causing the existence of duplicated paralogues in some instances, and a few genes have not been identified in the zebrafish genome. Taken together the high fecundity of the zebrafish, the possibility to observe transparent developing embryos in real time, the availability of a large number of mutants and transgenics as well as the possibility to knock down gene function by microinjection of morpholino antisense oligonucleotides and the similarity of the hemostatic system are important assets of the zebrafish, promising that it will be an attractive model to study thrombocyte function, thrombosis and hemostasis. This review provides an overview of the central factors of thrombocyte function identified so far in the zebrafish genome and a compilation of methods and tools available for the study of thrombocyte development and function in zebrafish.

Magnetic resonance myocardial perfusion imaging-First experience at 3.0T

OBJECTIVE

MR myocardial perfusion imaging (MRMPI) is an established technique for the evaluation of the hemodynamical relevance of coronary artery disease. Perfusion imaging at 3.0T provides certain advantages compared to 1.5T. Aim of this study was to evaluate myocardial MR perfusion imaging at 3.0T.

MATERIALS AND METHODS

Twelve patients with stable Angina pectoris and known or suspected coronary artery disease were examined at 3.0T. Myocardial perfusion was assessed using a saturation recovery gradient echo 2D sequence (TR 1.9ms, TE 1.0ms, FA 12 degrees ) with 0.05mmol Gd-DTPA per kg body weight at stress during injection of 140microg adenosine/kg body weight/min and at rest in short axis orientation. Perfusion analysis was based on a least square fit of the signal/time curve (peak signal intensity, slope). Perfusion series were assessed by two independent observers. Reference for the presence of relevant coronary artery stenoses was invasive coronary angiography. Two experienced observers evaluated the coronary angiograms in biplane projections for the presence and grade of stenoses. Results were compared with the MR perfusion analysis.

RESULTS

All MR examinations could be safely performed and yielded high image quality. In eight patients stress-induced hypoperfusion was detected (stenosis >70% in coronary angiography). In four patients myocardial hypoperfusion was ruled out (stenosis <70%). The myocardial perfusion reserve index was significantly reduced in hypoperfused myocardium with 1.9+/-1.6 compared to 2.5+/-1.6 in regularly perfused myocardium (p<0.05). In coronary angiography, eight patients were found to suffer from coronary artery disease, whereas in four patients coronary artery disease was ruled out.

CONCLUSION

Our initial results show that MRMPI at 3.0T provides reliably high-image quality and diagnostic accuracy.

Animal serum-free culture conditions for isolation and expansion of multipotent mesenchymal stromal cells from human BM

BACKGROUND

Multipotent mesenchymal stromal cells (MSC) have become important tools in regenerative and transplantation medicine. Rapidly increasing numbers of patients are receiving in vitro-expanded MSC. Culture conditions typically include FSC because human serum does not fully support growth of human MSC in vitro (MSC(FCS)). Concerns regarding BSE, other infectious complications and host immune reactions have fueled investigation of alternative culture supplements.

METHODS

As PDGF has long been identified as a growth factor for MSC, we tested media supplementation with platelet lysate for support of MSC proliferation.

RESULTS

We found that primary cultures of BM-derived MSC can be established with animal serum-free media containing fresh frozen plasma and platelets (MSC(FFPP)). Moreover, MSC(FFPP) showed vigorous proliferation that was superior to classical culture conditions containing FCS. MSC(FFPP) morphology was equivalent to MSC(FCS), and MSC(FFPP) expressed CD73, CD90, CD105, CD106, CD146 and HLA-ABC while being negative for CD34, CD45 and surface HLA-DR, as expected. In addition to being phenotypically identical, MSC(FFPP) could efficiently differentiate into adipocytes and osteoblasts. In terms of immune regulatory properties, MSC(FFPP) were indistinguishable from MSC(FCS). Proliferation of PBMC induced by IL-2 in combination with OKT-3 or by PHA was inhibited in the presence of MSC(FFPP).

DISCUSSION

Taken together, FCS can be replaced safely by FFPP in cultures of MSC for clinical purposes.

Transcatheter occlusion of a large intercostal side-branch of left internal mammary artery bypass with detachable platinum coils

Intercostal branches of the internal mammary artery (IMA) are usually tied off during IMA-bypass surgery. Some side-branches may be missed, however, due to anatomical variants or during minimal invasive procedures with limitation of the surgeon's ability to ligate proximal branches. There are a number of reports in the literature describing interventional closure of side-branches using Gianturco coils. Following embolization or malposition, however, these coils may be extremely difficult to retrieve from coronary arteries. We report about interventional embolization of a IMA side-branch with detachable micro-coils in a patient with symptomatic coronary steal. Detachable coils are safer than Gianturco coils and are an effective method to abolish symptomatic coronary steal due to unligated intercostal branches of the IMA graft.

Platelet-leukocyte aggregates during hemodialysis: effect of membrane type

Hemodialysis is associated with the formation of platelet-leukocyte aggregates. Whether this phenomenon is hemodialysis (HD) membrane dependent is unclear. To evaluate this process, we examined respectively platelet activation (anti-CD41, anti-CD62, and antifibrinogen monoclonal antibodies [MoAb] binding), leukocyte activation (CD11b expression), and the appearance of platelet specific antigens on leukocytes as an index of platelet-leukocyte aggregation during HD using 3 different membrane materials, Cuprophan, Hemophan, and polysulfone. Flow cytometric techniques and specific MoAb were used. All parameters were assayed 5 min after initiation of HD to avoid the confounding variable of leukopenia and resultant cell subpopulation analysis. Platelet activation (anti-CD62 and antifibrinogen binding) occurred only with Cuprophan. All 3 membranes induced equivalent increases in CD11b expression on neutrophils and similarly increased the binding of anti-CD41 to neutrophils, reflecting an increment in the formation of platelet neutrophil aggregates. However, only Cuprophan induced an increase in anti-CD62 binding to neutrophils, suggesting that the aggregated platelets linked to neutrophils were activated. Increased anti-CD41 binding by monocytes was similarly observed with all 3 membranes. However, only polysulfone induced an increase in CD11b expression and fibrinogen binding to monocytes. We conclude that while the formation of platelet leukocyte aggregates appears to be a universal phenomenon in HD occurring with a variety of membrane types, subtypes of this phenomenon consisting of activated platelets and fibrinogen binding may be membrane dependent. This phenomenon may serve as a new biocompatibility parameter and may shed light on some of the biologic consequences of hemodialysis.

Effects of ATP on ligand recognition of platelet fibrinogen receptor on GPIIb-IIIa

The recent discovery of 8-azido-ATP binding sites on the platelet fibrinogen receptor glycoprotein complex GPIIb-IIIa suggests that extracellular ATP may directly modulate function of GPIIb-IIIa. In this study we investigated the effect of ATP on ligand binding to GPIIb-IIIa. Fibrinogen-mediated aggregation of washed platelets was inhibited by ATP and 8-azido-ATP in a dose-dependent manner, independent of the agonist (thrombin, collagen, epinephrine, phorbol 12-myristate 13-acetate) used to induce platelet activation. In addition, 8-azido-ATP and ATP inhibited binding of 125I-labeled fibrinogen to thrombin- and phorbol ester-activated platelets. Interaction of nonstimulated platelets with solid-phase fibrinogen was also reduced by 8-azido-ATP and ATP. Moreover, fibrinogen mimetic peptide-induced conformational change of GPIIb-IIIa on resting platelets was reduced in the presence of both nucleotides. Finally, photoincorporation of 8-azido-[gamma-32P]ATP into GPIIb-IIIa was suppressed by GRGDSP but not by the biologically inactive GRGESP peptide. Thus interaction of ATP with 8-azido-ATP binding sites present on GPIIb-IIIa modulate receptor function, which may play a role in regulation of in vivo platelet aggregation.

Platelet-leukocyte aggregation during hemodialysis

Hemodialysis is associated with simultaneous changes in leukocytes and platelets, but it is unclear whether these alterations affect the interactions between these cell types. To evaluate this process, we examined the appearance of platelet specific antigens (CD41) on leukocytes as an index of platelet-leukocyte aggregation during hemodialysis using three different synthetic membranes. Patients with end-stage renal disease (ESRD) on long-term hemodialysis treatment were enrolled. Flow cytometric techniques and platelet specific monoclonal antibodies (MoAb) that recognize the glycoprotein complex on resting and activated platelets (anti-CD41), the activated GPIIb-IIIa complex receptor (anti-LIBS1), and the p selectin GMP140, that is exposed on platelet plasma membrane after activation and platelet degranulation (anti-CD62), were used. Subjects with ESRD had a lower predialysis platelet surface expression of CD41 and LIBS1 compared to normal controls, but unchanged CD62 expression. In parallel, patients with ESRD manifested a uniformly reduced platelet-leukocyte microaggregates predialysis compared to normal controls. When examined across the dialyzer, however, an increase in platelet-neutrophil and platelet-monocyte microaggregates was observed with all three synthetic membranes at both 15 and 30 minutes after initiation of dialysis. This phenomenon could be duplicated in vitro by physiologic concentrations of the platelet specific agonist ADP, but not by the complement factors C3a or C5a. We conclude that platelet-leukocyte aggregates occur during dialysis likely related to a primary platelet activation mechanism. This phenomenon may serve as a new biocompatibility parameter and may shed light on some of the biologic consequences of hemodialysis.

Single-donor platelet concentrates: changes of surface glycoproteins during storage

Storage of single-donor platelet concentrates is currently limited to 5 days. During this period, however, numerous morphologic and biochemical changes have been observed. These changes result in functional impairment of stored platelets. The present study describes increased binding of a monoclonal antibody against GMP 140 on the surface of stored single-donor platelets revealing an activation process. In contrast, binding of monoclonal antibodies directed against glycoprotein complex (GP) IIb-IIIa and ligand-induced binding site (LIBS1) is slightly diminished during storage. When platelets are stimulated with ADP GMP 140, GP IIb-IIIa, and LIBS1 are expressed to a higher extent than on the surface on nonstimulated platelets. The quantity exposed, however, depends upon the storage time. It is significantly reduced when platelets are stored for longer than 1-2 days. The present data indicate that storage of single-donor platelet concentrates affects fibrinogen binding, cell to cell cohesion, and release reaction. The results are in good agreement with conventional aggregation and in vitro bleeding time measurements.

Impaired function of platelet membrane glycoprotein IIb-IIIa in end-stage renal disease

Impaired platelet function and a bleeding tendency are well-recognized complications of chronic renal failure. Because the fibrinogen receptor GPIIb-IIIa plays a central role in platelet aggregation and adhesion to the subendothelium, it was reasoned that a defect in this receptor may underlie the impaired platelet function in uremia. To test this hypothesis, the function of this receptor in the platelets of 11 uremic patients was studied. Aggregation studies were performed with flow cytometric techniques with anti-GPIIb-IIIa conformation-specific monoclonal antibodies (mAb) (anti-LIBS1 and anti-PMI-1). Antifibrinogen and antithrombospondin mAb were used to characterize fibrinogen binding to GPIIb-IIIa and the release of alpha-granules, respectively. Platelets from patients with chronic renal failure showed significantly decreased binding of conformation-dependent anti-LIBS1 mAb after ADP, phorbol myristate acetate, or RGD-peptide stimulation compared with normal controls, suggesting a defect related to the ability of the fibrinogen receptor to undergo a conformational change. Moreover, antifibrinogen and antithrombospondin binding to activated platelets were reduced in uremic patients, implying impairment of both ligand-binding and alpha-granule release. Hemodialysis partially restored GPIIb-IIIa function, which may account for the observed effects of this therapy in restoring platelet aggregation. These findings indicate that platelets of patients with chronic renal failure reveal an aggregation defect at least partially due to an intrinsic GPIIb-IIIa dysfunction and the presence of a putative uremic toxin that inhibits fibrinogen binding to GPIIb-IIIa.

Flow-cytometric analysis of mepacrine-labelled platelets in patients with end-stage renal failure

Platelet dysfunction and increased bleeding tendency has been the most consistently described haemostatic abnormality in patients with renal failure. Besides abnormalities in platelet membrane glycoproteins, a reduced amount of platelet-dense granule content has been demonstrated in patients with end-stage renal failure (ESRD) indicating an acquired storage pool deficiency (SPD) present in uraemia. To study dense granules, platelets were labelled with mepacrine, a fluorescent probe which is specifically incorporated into dense bodies. MepaPlatelets of 13 patients with ESRD and of 11 healthy controls were studied. The results showed that mepacrine-labelled platelets of patients with ESRD reveal a significantly (p < 0.05) reduced fluorescence compared to the control group. This implies a reduced number or content of dense granules present in ESRD platelets. Thus, the current data indicate that ESRD is associated with an acquired platelet SPD which may be a useful and rapid method for screening patients with suspected acquired or inherited SPD.

Characterization of a gain of function mutation of integrin alpha IIb beta 3 (platelet glycoprotein IIb-IIIa)

Integrin alpha IIb beta 3 (platelet glycoprotein IIb-IIIa) is a prototype of integrins involved in cellular adhesive functions. As part of a structure-function analysis of this molecule, we constructed a mutant, designated alpha IIb beta 3 (beta 1-2), by replacing 6 amino acids within a putative ligand binding domain of the beta 3 subunit with sequences derived from beta 1. The alteration did not affect the capacity of beta 3(beta 1-2) to combine with transfected alpha IIb, nor did it cause it to combine with endogenous alpha 5. Integrin alpha IIb beta 3(beta 1-2) was in a "resting" state on Chinese hamster ovary cells as judged by minimal binding of an activation-specific anti-alpha IIb beta 3, PAC1. Nevertheless, cells expressing alpha IIb beta 3(beta 1-2) spontaneously bound fibrinogen with low affinity (Ka = (4.85 +/- 0.84) x 10(6) M-1). Activation with an anti-beta 3 antibody (monoclonal antibody 62) resulted in a 10-fold increase in fibrinogen binding affinity (Ka = (4.55 +/- 0.77) x 10(7) M-1), which was 3-fold greater than fibrinogen binding to activated wild type alpha IIb beta 3 (Ka = (1.66 +/- 0.33) x 10(7) M-1, F = 7.46, p = 0.008). The mutant receptor also bound fibrinogen mimetic peptide ligands with enhanced affinity as measured by the conformation-specific antibody, anti-LIBS1. This indicates that the increased affinity for fibrinogen was caused by enhanced interaction of alpha IIb beta 3(beta 1-2) with known recognition sequences in fibrinogen. Thus, this gain of function mutant augments ligand binding function, supporting a role for this region of the beta subunit in ligand binding to integrins.

Ligand bridging mediates integrin alpha IIb beta 3 (platelet GPIIB-IIIA) dependent homotypic and heterotypic cell-cell interactions

The aggregation of cells bearing recombinant integrin alpha IIb beta 3 (platelet GPIIb-IIIa) has been analyzed by two-color flow cytometry. As in normal platelets, aggregation requires functional alpha IIb beta 3, "activation" of alpha IIb beta 3, and fibrinogen (fg) binding to alpha IIb beta 3. Cellular aggregation required that both interacting cells express functional alpha IIb beta 3, because a binding defective mutant, alpha IIb beta 3 (D119----Y), failed to support interaction with wild type alpha IIb beta 3-bearing cells. In addition, cells bearing resting alpha IIb beta 3 were incorporated into aggregates formed by cells bearing a constitutively active mutant, alpha IIb beta 3 (beta 1-2), indicating that only one of the cells in an interacting pair must be activated. Finally, heterotypic interactions occurred between cells bearing activated alpha IIb beta 3 and cells bearing alpha V beta 3, a fg-binding integrin present on endothelial and tumor cells. Thus, ligand bridging between fg-binding integrins represents a mechanism of cell-cell interaction, cells bearing resting alpha IIb beta 3 (e.g., resting platelets) may be incorporated into aggregates formed by cells bearing activated alpha IIb beta 3, and alpha IIb beta 3 mediates heterotypic interactions with cells bearing other fg receptors.

Effects of hemodialysis on platelet-derived thrombospondin

The effects on platelet-derived thrombospondin (TSP) of hemodialysis with a cellulose membrane were studied in patients during routine hemodialysis and in normal subjects using an ex vivo model. Plasma and platelet-bound TSP were determined pre- and post-dialysis, in blood entering and leaving the dialyzer after 1, 3, 5, 15, and 30 minutes of dialysis, and in blood leaving the ex vivo module after 5, 10, 15, 20, and 25 minutes of perfusion. Plasma concentrations of beta-thromboglobulin (beta TG) and thromboxane B2 (TxB2), and platelet membrane expression of the alpha-granule protein GMP-140, were also measured. Significant increases in plasma concentrations of TSP and beta TG occurred between the inlet and outlet of the dialyzer after 5, 15, and 30 minutes of dialysis, accompanied by a slow, but significant, increase in their arterial plasma concentrations. In contrast, initiation of dialysis was associated with an immediate increase in plasma TxB2 concentration between the inlet and outlet of the dialyzer and an abrupt increase in arterial plasma TxB2 concentration which plateaued at 250% of the pre-dialysis value after five minutes. Transit of platelets through the dialyzer had no effect on platelet-membrane-associated TSP or GMP-140. Plasma TSP and beta TG concentrations at the outlet of the ex vivo module also increased significantly during perfusion, but plasma TSP concentrations were twofold greater than those during hemodialysis. In vitro stimulation of platelets with thrombin and immunoblotting studies of platelet release proteins showed reduced TSP release by platelets of hemodialysis patients.(ABSTRACT TRUNCATED AT 250 WORDS)

[Serum level of digoxin-like immunoreactive substances in newborn infants in the first two weeks of life, in umbilical cord blood and in pregnant patients at the time of labor]

A digoxin-like immunoreactivity (DLIS) was measured by two routinely used clinical digoxin-immunoassays (radio- and enzymeimmunoassay) in cord blood of 255 newborns, in sera of their mothers at birth and in sera of 211 newborns during the first two postpartal weeks. The highest DLIS levels were found in serum of neonates at the first day of life (median: 0.23 ng/ml, 25% and 75% percentile: 0.19 and 0.28 ng/ml) and in cord blood (median: 0.21 ng/ml, 25% and 75% percentile: 0.19 and 0.24 ng/ml); maternal serum was shown to have three times less DLIS (median: 0.08 ng/ml, 25% and 75% percentile: 0.05 and 0.10 ng/ml). There was no significant correlation between DLIS concentrations in serum of newborns, cord blood or pregnants. The DLIS serum levels of preterms with birthweight less than 2500 g and gestational age less than 37 weeks were significantly lower than those of normal neonates at term (p less than 0.01); concomitantly the lowest DLIS levels were found in maternal serum of preterms (p less than 0.01). These observations strongly suggest rather a DLIS origin in the newborn than in the mother. During the first two postpartal weeks the DLIS concentration of a vast majority of the 211 newborns (91%) decreased continuously to one half of the starting value. Within the second postpartal week preterms were found to have a significantly delayed decrease in the DLIS serum levels (p less than 0.01). Small for date newborns showed no difference in their postpartal DLIS time course compared to normal neonates.(ABSTRACT TRUNCATED AT 250 WORDS)

The isolation and reconstitution of the ADP/ATP carrier from wild-type Saccharomyces cerevisiae. Identification of primarily one type (AAC-2)

Methods for isolation of the ADP/ATP carrier (AAC) from yeast (Saccharomyces cerevisiae) are described which allow separation of the carrier from the initially copurified porin which poses a specific problem in yeast. The procedure varies according to whether one wishes to obtain a stable CAT-AAC complex, the free and active AAC for reconstitution, or the SDS-denatured pure AAC peptide. CNBr cleavage of AAC enabled us to differentiate clearly between isogenes AAC-1 and AAC-2 recently found in yeast, due to the exclusive occurrence of a methionine (M-115) residue at the end of the first domain in AAC-2. Thus the AAC isolated from wild-type yeast is primarily or exclusively AAC-2. The isolated AAC is active in ADP/ATP exchange in reconstituted liposomes with a Vmax of 1100 mumol/min per g protein and Km = 15 microM for ADP, and a Vmax of 900 mumol/min per g protein and Km = 9 microM for ATP.