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Background: Myocardial injury, defined by elevated troponin levels, is associated with adverse outcome in patients with coronavirus disease 2019 (COVID-19). The frequency of cardiac injury remains highly uncertain and confounded in current publications; myocarditis is one of several mechanisms that have been proposed. Methods: We prospectively assessed patients with myocardial injury hospitalized for COVID-19 using transthoracic echocardiography, cardiac magnetic resonance imaging, and endomyocardial biopsy. Results: Eighteen patients with COVID-19 and myocardial injury were included in this study. Echocardiography revealed normal to mildly reduced left ventricular ejection fraction of 52.5% (46.5%–60.5%) but moderately to severely reduced left ventricular global longitudinal strain of −11.2% (−7.6% to −15.1%). Cardiac magnetic resonance showed any myocardial tissue injury defined by elevated T1, extracellular volume, or late gadolinium enhancement with a nonischemic pattern in 16 patients (83.3%). Seven patients (38.9%) demonstrated myocardial edema in addition to tissue injury fulfilling the Lake-Louise criteria for myocarditis. Combining cardiac magnetic resonance with speckle tracking echocardiography demonstrated functional or morphological cardiac changes in 100% of investigated patients. Endomyocardial biopsy was conducted in 5 patients and revealed enhanced macrophage numbers in all 5 patients in addition to lymphocytic myocarditis in 1 patient. SARS-CoV-2 RNA was not detected in any biopsy by quantitative real-time polymerase chain reaction. Finally, follow-up measurements of left ventricular global longitudinal strain revealed significant improvement after a median of 52.0 days (−11.2% [−9.2% to −14.7%] versus −15.6% [−12.5% to −19.6%] at follow-up; P =0.041). Conclusions: In this small cohort of COVID-19 patients with elevated troponin levels, myocardial injury was evidenced by reduced echocardiographic left ventricular strain, myocarditis patterns on cardiac magnetic resonance, and enhanced macrophage numbers but not predominantly lymphocytic myocarditis in endomyocardial biopsies.

Background: Even among biomarker-negative patients undergoing elective percutaneous coronary intervention (PCI), periprocedural thrombotic and bleeding complications can lead to increased morbidity and mortality. Whether stronger platelet inhibition by an intensified oral loading strategy (ILS) before PCI impacts on outcomes among these patients in contemporary practice remains unclear. Methods: This multicenter, randomized, assessor-blinded trial tested the hypothesis that in elective PCI prasugrel 60 mg (ILS) is superior to standard loading strategy with clopidogrel 600 mg regarding a composite primary end point of all-cause death, any myocardial infarction, definite/probable stent thrombosis, stroke, or urgent vessel revascularization. After PCI, all patients were on clopidogrel 75 mg/day and aspirin. The trial was terminated prematurely because of slower-than-expected recruitment and funding discontinuation. Results: Of 781 patients included in the final analysis, 382 were assigned to ILS and 399 to standard loading strategy. At 30 days, the primary end point occurred in 66 patients (17.3%) assigned to ILS and 74 patients (18.6%) assigned to standard loading strategy (odds ratio, 0.92 [95% CI, 0.63–1.32]; P =0.64). Any myocardial infarction and Bleeding Academic Research Consortium ≥2 bleeding rates were similar among ILS and standard loading strategy groups 16.2% versus 17.5%, odds ratio, 0.91 (95% CI, 0.62–1.32), P =0.62 and 4.2% versus 4.8%, odds ratio 0.87 (95% CI, 0.44–1.73), P =0.70, respectively. Conclusions: In biomarker-negative stable and unstable angina patients undergoing elective PCI, the trial did not find a conclusive difference in efficacy or safety. This observation should be interpreted in the context of wide CIs and premature termination of the trial. Registration: URL: https://www.clinicaltrials.gov . Unique identifier: NCT02548611.

Objective— Cancer patients are at high risk of developing deep venous thrombosis (DVT) and venous thromboembolism, a leading cause of mortality in this population. However, it is largely unclear how malignant tumors drive the prothrombotic cascade culminating in DVT. Approach and Results— Here, we addressed the pathophysiology of malignant DVT compared with nonmalignant DVT and focused on the role of tumor microvesicles as potential targets to prevent cancer-associated DVT. We show that microvesicles released by pancreatic adenocarcinoma cells (pancreatic tumor–derived microvesicles [pcMV]) boost thrombus formation in a model of flow restriction of the mouse vena cava. This depends on the synergistic activation of coagulation by pcMV and host tissue factor. Unlike nonmalignant DVT, which is initiated and propagated by innate immune cells, thrombosis triggered by pcMV was largely independent of myeloid leukocytes or platelets. Instead, we identified externalization of the phospholipid phosphatidylethanolamine as a major mechanism controlling the prothrombotic activity of pcMV. Disrupting phosphatidylethanolamine-dependent activation of factor X suppressed pcMV-induced DVT without causing changes in hemostasis. Conclusions— Together, we show here that the pathophysiology of pcMV-associated experimental DVT differs markedly from innate immune cell–promoted nonmalignant DVT and is therefore amenable to distinct antithrombotic strategies. Targeting phosphatidylethanolamine on tumor microvesicles could be a new strategy for prevention of cancer-associated DVT without causing bleeding complications.

Objectives: The aim of this study was to determine the diagnostic accuracy of grating-based phase-contrast computed tomography (gb-PCCT) to classify and quantify coronary vessel characteristics in comparison with optical coherence tomography (OCT) and histopathology in an ex vivo setting. Materials and Methods: After excision from 5 heart specimens, 15 human coronary arteries underwent gb-PCCT examination using an experimental imaging setup consisting of a rotating molybdenum anode x-ray tube, a Talbot-Lau grating interferometer, and a single photon counting detector. Subsequently, all vessels were imaged by OCT and histopathologically processed. Optical coherence tomography, gb-PCCT, and histopathology images were manually matched using anatomical landmarks. Optical coherence tomography and gb-PCCT were reviewed by 2 independent observers blinded to histopathology. Vessel, lumen, and plaque area were measured, and plaque characteristics (lipid rich, calcified, and fibrous) were determined for each section. Measures of diagnostic accuracy were derived, applying histopathology as the standard of reference. Results: Of a total of 286 assessed cross sections, 241 corresponding sections were included in the statistical analysis. Quantitative measures derived from gb-PCCT were significantly higher than from OCT (P = 0.85 for gb-PCCT and >= 0.61 for OCT, respectively). Results of Bland-Altman analysis demonstrated smaller mean differences between OCT and histopathology than for gb-PCCT and histopathology. Limits of agreement were narrower for gb-PCCT with regard to lumen area, for OCT with regard to plaque area, and were comparable with regard to vessel area. Based on histopathology, 228/241 (94.6%) sections were classified as fibrous, calcified, or lipid rich. The diagnostic accuracy of gb-PCCT was excellent for the detection of all plaque components (sensitivity, >= 0.95;specificity, >= 0.94), whereas the results for OCT showed sensitivities of >= 0.73 and specificities of >= 0.66. Conclusions: In this ex vivo setting, gb-PCCT provides excellent results in the assessment of coronary atherosclerotic plaque characteristics and vessel dimensions in comparison to OCT and histopathology. Thus, the technique may serve as adjunct nondestructive modality for advanced plaque characterization in an experimental setting.

Objectives: The feasibility and hemodynamic effects of isoflurane sedation in cardiogenic shock in the presence of venoarterial extracorporeal membrane oxygenation treatment are currently unknown. Design: Retrospective single-center study. Setting: Cardiac ICU of Munich university hospital. Patients/Subjects: Cardiogenic shock patients with venoarterial extracorporeal membrane oxygenation treatment under sedation with volatile isoflurane between November 2018 and October 2019 have been enrolled in this study and were matched by propensity score in a 1:1 ratio with IV sedated patients treated between January 2013 and November 2018 from the cardiogenic shock registry of the university hospital of Munich. Measurements and Main Results: Isoflurane sedation was used in 32 patients with cardiogenic shock and venoarterial extracorporeal membrane oxygenation treatment. The mean age of conventionally sedated patients was 58.4 ± 13.8 years and 56.3 ± 11.5 years for patients with isoflurane sedation (p = 0.51). Administration of isoflurane was associated with lower IV sedative drug use during venoarterial extracorporeal membrane oxygenation treatment (86% vs 32%; p = 0.01). Mean systolic arterial pressure was similar (94.3 ± 12.6 vs 92.9 ± 10.5 mm Hg; p = 0.65), but mean heart rate was significantly higher in the conventional sedation group, when compared with the isoflurane group (85.2 ± 20.5 vs 74.7 ± 15.0 beats/min; p = 0.02). Catecholamine doses, venoarterial extracorporeal membrane oxygenation blood and gas flow, ventilation time (304 ± 143 vs 398 ± 272 hr; p = 0.16), bleeding complications bleeding academic research consortium 3a or higher (59.3% vs 65.3%; p = 0.76), and 30-day mortality (59.2% vs 63.4%, p = 0.80) were similar in both groups. The overall sedation costs per patient were significantly lower in the conventional group, when compared with the isoflurane group (537 ± 624 vs 1280 ± 837 €; p < 0.001). Conclusions: Volatile sedation with isoflurane is feasible—albeit at higher costs—in patients with cardiogenic shock and venoarterial extracorporeal membrane oxygenation treatment and was not associated with higher catecholamine dosage or extracorporeal membrane oxygenation flow rate compared with IV sedation.

Rationale: Platelets are known to play a crucial role in hemostasis. Sphingosine kinases (Sphk) 1 and 2 catalyze the conversion of sphingosine to the bioactive metabolite sphingosine 1-phosphate (S1P). Although platelets are able to secrete S1P on activation, little is known about a potential intrinsic effect of S1P on platelet function. Objective: To investigate the role of Sphk1- and Sphk2-derived S1P in the regulation of platelet function. Methods and Results: We found a 100-fold reduction in intracellular S1P levels in platelets derived from Sphk2 −/− mutants compared with Sphk1 −/− or wild-type mice, as analyzed by mass spectrometry. Sphk2 −/− platelets also failed to secrete S1P on stimulation. Blood from Sphk2-deficient mice showed decreased aggregation after protease-activated receptor 4-peptide and adenosine diphosphate stimulation in vitro, as assessed by whole blood impedance aggregometry. We revealed that S1P controls platelet aggregation via the sphingosine 1-phosphate receptor 1 through modulation of protease-activated receptor 4-peptide and adenosine diphosphate–induced platelet activation. Finally, we show by intravital microscopy that defective platelet aggregation in Sphk2-deficient mice translates into reduced arterial thrombus stability in vivo. Conclusions: We demonstrate that Sphk2 is the major Sphk isoform responsible for the generation of S1P in platelets and plays a pivotal intrinsic role in the control of platelet activation. Correspondingly, Sphk2-deficient mice are protected from arterial thrombosis after vascular injury, but have normal bleeding times. Targeting this pathway could therefore present a new therapeutic strategy to prevent thrombosis.

Supplemental Digital Content is available in the text., Objectives: Improvements in cannula removal techniques, and in particular a standardized decannulation technique with a suitable closure device, are needed to further improve patients’ outcomes after percutaneous cannulation. The decannulation techniques described so far are neither sufficiently standardized nor proven enough to be used in the large group of venoarterial extracorporeal membrane oxygenation patients. To meet this challenge, we have established a highly standardized and safe decannulation technique based on the Perclose ProGlide closure system (Abbott Vascular, Lake Bluff, IL). Design: Establishment of a highly standardized and safe decannulation technique based on the Perclose ProGlide closure system, which is described in detail with comprehensive instructions for the executive clinician and first application in the context of a pilot study. Measurements and Main Results: So far our technique has already been used successfully in seven patients since January 2019 as a standard procedure on our ICU with only one minor complication occurred after the first procedure, that is, a small pseudoaneurysm likely originating from antegrade perfusion puncture site which was sealed by thrombin injection. Conclusions: Our crossed ProGlide technique using a hemostasis valve Y connector ensuring no blood loss seems to be a very promising decannulation technique.

Objective— Fractalkine (FKN) activates a G αi protein–coupled signaling pathway similar to the one activated by ADP via P2Y 12 , which is the drug target of clopidogrel. FKN levels are increased under several disease conditions associated with impaired clopidogrel responsiveness. Methods and Results— Blood samples were obtained from healthy volunteers and from 40 patients under chronic clopidogrel treatment. FKN reduced prostaglandin E1–induced vasodilator-stimulated phosphoprotein phosphorylation by ≈25% ( P 12 . In vitro, FKN increased platelet reactivity index in clopidogrel-treated patients indicating potential activation of downstream targets of P2Y 12 . When stratifying patients by their FKN levels, patients within the highest quartile of FKN (2042±25 pg/mL) had the weakest response to clopidogrel (platelet reactivity index, 68±4%), and patients within the lowest quartile (479±50 pg/mL) had the strongest response (platelet reactivity index, 48±7%; P =0.0106). FKN by itself induced phosphoinositide 3-kinase activation leading to Akt phosphorylation at Ser 473 ( P Conclusion— In addition to desensitizing platelets to prostaglandin E1 via G αi , FKN induces phosphoinositide 3-kinase–dependent Akt phosphorylation via a G βγ protein similar to ADP signaling through P2Y 12 . FKN increased the platelet ADP response in clopidogrel-treated patients. Once released from an atherosclerotic lesion, this mechanism could contribute locally to impaired clopidogrel responsiveness at the vulnerable plaque.

Background— The Bleeding Academic Research Consortium (BARC) has recently proposed a unified definition of bleeding in patients receiving antithrombotic therapy. We investigated the relationship between bleeding events as defined by BARC and 1-year mortality in patients undergoing percutaneous coronary intervention (PCI) and assessed whether the BARC bleeding definition is superior to existing bleeding definitions in regard to mortality prediction in patients after PCI procedures. Methods and Results— This study represents a patient-level pooled analysis of 12 459 patients recruited in 6 randomized trials of patients undergoing PCI. Bleeding events were assessed with the use of BARC, Thrombolysis in Myocardial Infarction (TIMI), and Randomized Evaluation in PCI Linking Angiomax to Reduced Clinical Events (REPLACE-2) trial criteria. The primary outcome was 1-year mortality. Bleeding occurred in 1233 patients (9.9%) according to BARC (679 patients or 5.4% with BARC class ≥2 bleeding), in 374 patients (3.0%) according to TIMI, and in 491 patients (3.9%) according to REPLACE-2 criteria. There were 340 deaths (2.7%) over the first year after PCI. BARC class ≥2 bleeding was associated with a significant increase in 1-year mortality (adjusted hazard ratio 2.72; 95% confidence interval, 2.03–3.63). The predictivity of a multivariable model for 1-year mortality was significantly improved after inclusion of bleeding defined according to BARC to an extent comparable to that provided by TIMI and REPLACE-2 criteria. Conclusions— The present study demonstrated a close association between bleeding events defined according to BARC and 1-year mortality after PCI.

Background— Erythropoietin improves myocardial function in experimental models of myocardial infarction. The aim of the present study was to determine the value of erythropoietin in patients with acute ST-elevation myocardial infarction. Methods and Results— This randomized, double-blind study included 138 patients admitted with acute ST-elevation myocardial infarction and treated with primary percutaneous coronary intervention. Patients were randomly assigned to receive epoetin-β (3.33×104 U, n=68) or placebo (n=70) immediately and at 24 and 48 hours after percutaneous coronary intervention. The primary end point was left ventricular ejection fraction after 6 months measured by MRI. Other end points included infarct size at 5 days and 6 months. Clinical adverse events (death, recurrent myocardial infarction, stroke, and infarct-related artery revascularization) were investigated at 30 days and 6 months. Left ventricular ejection fraction at 6-month follow-up was 52.0±9.1% in the erythropoietin group compared with 51.8±9.3% in the placebo group ( P =0.92). Five days after percutaneous coronary intervention, left ventricular ejection fraction was 49.4±8.0% in the erythropoietin group and 50.8±7.3% in the placebo group ( P =0.32); infarct size was 26.8±20.9% and 28.3±24.4% ( P =0.76) and decreased to 17.3±14.3% and 20.9±16.4% at 6-month follow-up ( P =0.27). The cumulative 6-month incidence of death, recurrent myocardial infarction, stroke or target vessel revascularization was 13.2% in the erythropoietin group and 5.7% in the placebo group (hazard ratio, 2.36; 95% confidence interval, 0.73 to 7.66; P =0.15). Conclusions— In patients with acute ST-elevation myocardial infarction treated with primary percutaneous coronary intervention, erythropoietin treatment did not improve left ventricular ejection fraction or reduce infarct size but may increase clinical adverse events. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT00390832.

Objective— Angiographic indexes of restenosis after coronary stent placement in patients show a bimodal pattern suggesting the existence of two populations with different risk of restenosis. This is reflected in the arterial remodeling response of inbred mouse strains arguing for a genetic control of the mechanisms leading to lumen narrowing. As bone marrow–derived cells (BMCs) contribute to vascular healing after arterial injury, we investigated the role of BMCs in the genetic control of restenosis. Methods and Results— 129X1/SvJ mice developed significantly more neointima and late lumen loss compared to C57BL/6 mice. Gene expression analysis of intimal tissue revealed major differences in the expression of inflammatory and hematopoietic stem and progenitor cell–associated genes in response to arterial injury. In 129X1/SvJ mice stronger mobilization of lin − sca-1 + CXCR4 + cells was observed after vascular injury. Bone marrow transplantation identified the extent of neointima formation as clearly dependent on the genetic background of BMCs (ie, mice with 129X1/SvJ BMCs developed more intimal hyperplasia). The inflammatory response and the recruitment of BMCs to the site of arterial injury were significantly increased in mice with 129X1/SvJ BMCs. Conclusions— The genetically controlled mechanisms leading to lumen narrowing in vascular remodeling are dependent on mobilization and recruitment capacities of particular BMCs.

Objective— Thrombus formation after atherosclerotic plaque rupture critically involves the platelet collagen receptor glycoprotein (GP) VI. We investigated the impact of EXP3179, an active metabolite of the angiotensin II type 1 (AT 1 )-receptor antagonist Losartan (LOS) on GPVI-dependent platelet activation. Methods and Results— EXP3179 and LOS but not EXP3174—the major AT 1 -receptor blocking metabolite of LOS—dose-dependently inhibited collagen-I ( P P P P P P P P Conclusion— EXP3179 acts as a specific inhibitor of the platelet collagen receptor GPVI independent of AT 1 -receptor antagonism. Further investigations may clarify its individual potential as a novel pharmacological approach to specifically inhibit atherothrombotic events by GPVI-receptor blockade.

Objective— The chemokine fractalkine activates platelets and induces leukocyte adhesion to the endothelium. Expression of fractalkine and its receptor, CX 3 CR1, is elevated in coronary artery disease. We assessed the effects of fractalkine on vascular function in isolated rat aorta. Methods and Results— CX 3 CR1 expression was demonstrated in rat aortic endothelial and smooth muscle cells by immunohistochemistry, Western blot, and polymerase chain reaction (PCR). Fractalkine (up to 1 μg/mL) did not directly induce contractile or relaxant responses when applied to rat aortic rings in organ baths. Short-term incubation with fractalkine (1 μg/mL) for 5 minutes did not affect vascular reactivity. Pretreatment of isolated rat aortic rings with fractalkine for 2 hours impaired acetylcholine-induced nitric oxide (NO)-mediated relaxation after preconstriction with phenylephrine in a concentration-dependent manner. The concentration response to the NO donor DEA-NONOate was significantly shifted to the right. The radical scavenger tiron normalized the attenuated acetylcholine-induced relaxation after fractalkine incubation. Aortic superoxide formation was enhanced by fractalkine, which was inhibited by diphenyleneiodonium but not by inhibitors of xanthine oxidase or NO synthase. Conclusion— In addition to its role as a chemokine and adhesion molecule, fractalkine induces vascular dysfunction by stimulating vascular reactive oxygen species resulting in reduced NO bioavailability.

Vessel maturation involves recruitment of mural cells. Laminar shear stress is a major trigger for vessel maturation. However, the molecular mechanisms by which shear stress affects recruitment of pericytes are unclear. MicroRNAs are small non-coding RNAs, which post-transcriptionally control gene expression. Since shear stress regulates various miRs, we hypothesize that flow-induced miRs inhibit repulsive cues and facilitate mural cell coverage. Laminar shear stress for 72h induces the up-regulation of miR-27b (2.8±0.24-fold vs static, p To determine whether miR-27b controls pericyte recruitment, we tested the effect of endothelial miR-27b on adhesion of pericytes. Overexpression of miR-27b increased the adhesion of pericytes (p Taken together, our data demonstrate that shear stress regulate miR-27b, which targets Ang2 and semaphorins, thereby controlling pericyte adhesion and coverage in vitro and in vivo.

Objective— Monocyte recruitment into the subendothelium is a crucial step in atherogenesis. Chlamydia pneumoniae resides in circulating monocytes and in the atherosclerotic vascular wall. However, the role of C pneumoniae for monocyte recruitment is unknown. The aim of this study was to examine the impact of C pneumoniae on monocyte adhesion and migration. Methods and Results— C pneumoniae –infected, fluorescence-labeled mouse macrophages (ANA-1) were injected intravenously into noninfected, healthy mice. In vivo videomicroscopy showed increased rolling and firm adhesion to the carotid artery compared with noninfected macrophages. In vitro, C pneumoniae infection (yielding 25% to 35% infected monocytes) increased adhesion of human monocytes or MonoMac6 cells to human umbilical vein endothelial cells and improved cell migration through endothelial-like ECV604 cells. Cell adhesion was inhibited by antibody blockade of very late antigen-4, lymphocyte function-associated antigen-1, macrophage antigen-1, or urokinase receptor, which were found upregulated or activated on C pneumoniae infection (flow cytometry). In contrast, C trachomatis did not induce monocyte adhesion at comparable infection rates (25% to 35%), indicating a unique activation pathway for C pneumoniae . Polymyxin B did not affect C pneumoniae –induced adhesion, excluding a relevant role of lipopolysaccharide in this process. Conclusions— These data indicate that C pneumoniae can direct monocytes to predilection sites of nonatherosclerotic vessel walls in vivo by activation of the integrin adhesion receptor system.

Background— CD40L-CD40 interactions induce inflammatory signals in cells of the vascular wall. We evaluated the effects of glycoprotein (GP) IIb/IIIa (α IIb β 3 ) engagement that occurs during platelet-endothelium interactions on CD40L surface exposure on platelets and initiation of proteolytic activity in human umbilical vein endothelial cells (HUVECs). Methods and Results— Transient (60-minute) adhesion of thrombin-prestimulated platelets enhanced HUVEC expression of urokinase-type plasminogen activator receptor and membrane type-1 matrix metalloproteinase (MT1-MMP) (reverse transcriptase–polymerase chain reaction, flow cytometry) and secretion of urokinase-type plasminogen activator, tissue-type plasminogen activator, and MMP-1 (ELISA) and induced proteolytic activity via MMP-2 and MMP-9 (gelatin zymography). These effects were abrogated by hindrance of physical platelet-endothelial contacts using transwell systems or inhibited by GRGDSP, mAbs anti–GP IIb/IIIa (7E3), anti-α v β 3 (LM609), or anti-CD40L (TRAP1). In addition, MMP-2 and MMP-9 were inhibited by specific GP IIb/IIIa antagonists tirofiban, lamifiban, or integrelin. On endothelial cells, induction of proteolytic activity by activated platelets was mimicked by CD40 engagement using soluble CD40L but not affected by antibody clustering of α v β 3 . On platelets, CD40L and CD62P exposure was enhanced on adhesion to HUVECs or immobilized fibrinogen and was abrogated by GRGDSP or LM609. In suspension, cross-linking of GP IIb/IIIa by fibrinogen plus secondary mAb upregulated CD40L surface exposure. Consistently, bivalent mAb 7E3 upregulated CD40L, whereas ligation of GP IIb/IIIa by soluble fibrinogen alone or monovalent Fab-fragment c7E3 had no effect. Conclusions— Platelet adhesion via GP IIb/IIIa upregulates CD40L and CD62P surface exposure. Proteolytic activity of HUVEC is induced by the concerted action of β 3 -integrin–mediated platelet adhesion and subsequent CD40L-induced signals in HUVECs. Effective anti–GP IIb/IIIa or anti-CD40L strategies might, therefore, contribute to plaque stabilization.

Background Although hepatic ischemia-reperfusion (I/R) injury can be reduced by cooling of the ischemic organ, a systematic in vivo analysis of the influence of organ temperature in I/R injury is missing. The aim of this study was to systematically investigate the impact of defined temperatures of the ischemic liver tissue on microvascular I/R injury. Methods Ischemia of the left liver lobe was induced in C57BL/6 mice for 90 min. The ischemic lobe was placed in a polyethylene well and the temperature was adjusted to 37 degrees C, 26 degrees C, 15 degrees C, and 4 degrees C by superfusion with cooled/warmed saline solution. The ischemia groups (n=7 each) were compared with a sham-operated group (n=7). The sinusoidal perfusion index and the number of leukocytes firmly adherent to the endothelium of postsinusoidal venules were assessed using intravital fluorescence microscopy at 30 min, 120 min, and 240 min of reperfusion, respectively. At the end of the experiment, serum activities of the liver enzymes aspartate aminotransferase/alanine aminotransferase were determined, and tissue specimens were examined by electron microscopy. Results Core body temperature did not differ significantly between the groups. In the 37 degrees C group, the sinusoidal perfusion index was significantly reduced and the number of adherent leukocytes was significantly increased compared with the sham group. In all hypothermia groups, however, the microcirculatory parameters did not differ from the sham group. Serum activities of aspartate aminotransferase/alanine aminotransferase were significantly increased and hepatocellular integrity was severely affected in the 37 degrees C group as compared with all other groups. Conclusions These findings demonstrate that in the mouse liver the known protective effect of hypothermia is already encountered at 26 degrees C. Further reduction of temperature did not generate additional protection from I/R injury.

The role of endothelin (ET)-1 as a mediator of small intestinal mucosal perfusion failure and tissue damage was investigated in the rat using intravital fluorescence videomicroscopy. The effects of intravenous infusion of ET-1 (3 nmol/kg) on functional capillary density, mucosal thickness, and the degree of mucosal damage were evaluated. Administration of ET-1 caused pronounced mucosal injury with a significant reduction of mucosal thickness compared with vehicle-treated control animals. Concomitantly, villous functional capillary density was markedly reduced 30 and 90 min after the infusion of ET-1. ET(A) receptor blockade by pretreatment with BQ 610 or with the novel ET(A) receptor antagonist ETR-P1/FL peptide prevented ET-1 induced capillary perfusion failure and mucosal damage. In contrast, the ET(B) receptor antagonist IRL 1038 was not effective. These results indicate that, acting via the ET(A) receptor, elevated levels of circulating ET-1 under various pathophysiological conditions, such as septic or hemorrhagic shock, might impair nutritive perfusion of the intestinal mucosa and contribute to tissue injury.

We thank Drs Vranckx and Valgimigli for their interest in our article1 related to validation of the Bleeding Academic Research Consortium (BARC) definition of bleeding in patients with coronary artery disease undergoing percutaneous coronary intervention.2 In the article, and in this response, we share the same opinion with Drs Vranckx and Valgimigli regarding the need to validate the BARC-proposed bleeding definition criteria in prospective studies. Although compiled and proposed by a highly experienced group of researchers in investigating bleeding complications (as an end point in various trials …

Background: Platelets play a key role in haemostasis and in the pathophysiology of various diseases including arterial thrombosis. Glycoprotein (GP)VI, the major platelet collagen receptor, mediates platelet activation and firm adhesion to collagen structures exposed at sites of vascular injury. Here, we determined the effects of specific activation of GPVI on the human platelet proteome by two-dimensional differential in-gel electrophoresis (2D-DIGE) and mass spectrometry. Methods and Results: Platelets from healthy human donors were isolated and purified. Platelets were stimulated with an activating monoclonal antibody specific for GPVI, or control IgG. Platelet proteins were subjected to 2D-DIGE with extensive software-assisted image analysis. Subsequent identification of the differentially abundant proteins was carried out by MALDI TOF/TOF MS and LC ESI-MS/MS. We identified 8 differentially regulated proteins associated with cell signaling, metabolism, organization and rearrangement of the cytoskeleton, and membrane trafficking. Differentially abundant proteins included pleckstrin, beta-centractin, src substrate cortactin, charged multivesicular body protein 3, aldose reductase and protein disulfide isomerase-associated 3 precursor. Conclusion: Specific platelet activation via GPVI results in the differential regulation of several proteins. The results provide further insight into the mechanisms that underlie platelet activation through the GPVI receptor, which may help to identify novel pharmacological targets.

Background: Pathological fibrin formation is a predominant cause for arterial thrombosis, triggering myocardial infarction and stroke. Tissue factor (TF), which is expressed by vascular endothelium and cell-derived microparticles, is a central trigger of intravascular fibrin generation. In intact blood vessels, TF is only minimally active, and the coagulation system is down-regulated. In contrast, TF is rapidly stimulated following endothelial disruption. However, the molecular mechanisms that trigger fibrin formation via regulation of TF activation are largely undefined. Methods and Results: Here, we have identified a novel pathway that leads to TF activation in vitro and contributes to intravascular coagulation in vivo. We show that the protein disulfide isomerase (PDI) induces disulfide formation of the Cys186/Cys209 pair located in the extracellular domain of TF. In vitro, PDI-mediated disulfide formation led to profound activation of TF. In vivo, we found that PDI is not present in the intact vessel wall, but becomes abundantly expressed following vessel damage. We show that injured smooth muscle cells and adherent/activated platelets are the major cellular sources of PDI at sites of vascular injury. We then assessed fibrin formation following injury of the common carotid artery using intravital microscopy. We observed that PDI-blockade strongly reduced fibrin formation by approximately 45– 60%. Likewise, intravenous infusion of PDI significantly enhanced TF-dependent fibrin formation. Together, this implies that PDI initiates coagulation in vitro and also during arterial thrombosis in vivo. Notably, PDI did not act on platelets to trigger intravascular coagulation. Correspondingly, PDI blockade also inhibited fibrin formation, when platelet adhesion was prevented using a function-blocking anti-GPVI antibody. Conclusion: These findings reveal for the first time in vivo that the thiol isomerase PDI is a major molecular trigger of blood coagulation, which is exposed after vessel injury and converts TF into its functionally active form. Hence, PDI represents a promising novel target for the treatment of pathologic fibrin formation in patients with thrombotic disorders.

Background: Arterial (AT) and venous thromboses (VT) are the major causes of morbidity in industrialized countries. While the critical contribution of platelets to AT has been recognized, the molecular and cellular mechanisms that trigger the development of VT are not yet fully understood. Methods: We established a novel model of VT, where thrombus formation occurs after venous stasis in the absence of mechanical endothelial injury. In contrast to published models, our approach closely resembles the triggers that lead to VT in humans. The molecular and cellular events in VT were assessed using intravital and electron microscopy. In particular, we evaluated the differential contribution of platelets (pts) and leukocytes (lcs) to AT and VT. Results: We found that in AT pts adhere rapidly, whereas only few lcs are recruited. The loss of platelet P-Selectin reduced lc accumulation during AT, was associated with thrombus destabilization, but had no effect on pt adhesion/aggregation. The loss of GPIIb led to a complete lack of pt adhesion/aggregation in AT. While AT largely depends on pts, lc adhesion was the prominent initial phenomenon during VT and involved both P-selectin and Mac-1. P-Selectin−/− as well as Mac-1−/− mice showed a massive reduction in lc accumulation. The lack of P-Selectin was accompanied by a reduction of the thrombus size 48 hours after stasis and was only marginally reduced in Mac 1−/− mice, indicating that lc rolling is sufficient to promote VT. The expression of tissue factor by lcs played a pivotal role for VT. Accordingly, mice with reduced TF expression showed a dramatic reduction in venous thrombus size. In addition to TF-bearing lcs, pts were recruited to the vessel wall early in VT. Pt accumulation involved both the fibrinogen and the vWF receptor and was virtually abolished in mice lacking GPIIb or GPIbα. To our surprise, we observed that pts do not accumulate during VT but play a functional role. Reduced pt adhesion in mice lacking either GPIIb, GPIbα, or VWF was associated with a significant reduction in venous thrombus size. Conclusion: Together, we show that VT, unlike AT depends on the concerted action of both lcs and pts. Hence, targeting pt activation and adhesion might provide a promising strategy in the prophylaxis and treatment of VT.

The homing and differentiation mechanisms of endothelial progenitor cells (EPCs) at sites of vascular lesions are unclear. To investigate whether platelets play a role in the recruitment and differentiation of EPCs, we made use of a robust mouse embryonic EPC (eEPC) line that reliably differentiates to a mature endothelial phenotype. We found that platelets stimulate chemotaxis and migration of these murine eEPCs. Further, the substantial adhesion of murine eEPCs on immobilized platelets that occurs under dynamic flow conditions is inhibited by neutralizing anti–P-selectin glycoprotein ligand-1 and anti–VLA-4 (β 1 -integrin) monoclonal antibodies but not by anti-CD11b (a M -integrin; macrophage antigen-1). Coincubation of murine eEPCs with platelets for 5 days induced differentiation of EPCs to mature endothelial cells as verified by positive von Willebrand factor immunofluorescence and detection of Weibel Palade bodies through electron microscopy. We conclude that platelets may play a critical part in the capture and subsequent differentiation of murine eEPCs at sites of vascular lesions, revealing a possible new role of platelets in neoendothelization after vascular injury.

Abstract:— The possibility of evaluating the function of transgenes in platelets requires the generation of platelets from nucleated progenitor cells in vitro. In this article, we provide effective culture conditions for generating functional culture-derived (CD) human and mouse platelets from CD34 + progenitor cells that allow expression of any foreign protein of interest. We have evolved an effective cytokine cocktail (thrombopoietin, stem cell factor, interleukin [IL]-1β, IL-6) that induces a high yield of CD platelets and optimal shedding from cultivated megakaryocytes generated from CD34 + progenitor cells. CD platelets showed similar functional and morphological characteristics compared with isolated blood platelets, including surface expression of platelet antigens (CD41, CD42, CD62P), aggregation, release of granule constituents (P-selectin, platelet factor 4, serotonin). Moreover, transmission electron microscopy revealed the presence of typical α- and dense granules and dense tubular system in CD platelets. Additionally, we showed that stable transgene expression in CD platelets can be performed through infection of CD34 + progenitor cells using adenoviral vectors. Thus, we describe a methodology that enables studying functional consequences of transgenes of interest in the natural environment of platelets that may impose substantial impact on potential future platelet research and therapeutic target evaluation. The full text of this article is available online at http://circres.ahajournals.org.