Expression and translation of the COX-1b gene in human cells--no evidence of generation of COX-1b protein.

Cyclooxygenase 1b (COX-1b) is a splice variant of COX-1, containing a retained intron 1 within the signal peptide sequence. COX-1b mRNA is found in many species, but the existence of a functionally active protein, which is possibly related to different species-dependent lengths of intron 1, is controversially discussed. The human intron 1 comprises 94 bp, and the resulting frameshift at the intron 1-exon 2 junction creates a premature stop codon. Nevertheless, full-length human COX-1b protein expression, including translated intron 1 and the signal peptide, has been reported and was explained by a frameshift repair. In this study, the fate of COX-1b mRNA in a human overexpression system is analyzed. Independent of the hypothetical frameshift repair mechanism, the splicing of the COX-1b intron 1, resulting in COX-1 mRNA and removal of the signal peptide during protein maturation, with subsequent generation of a COX-1 protein is demonstrated.

Adolescent ischemic stroke associated with anabolic steroid and cannabis abuse.

We report on a 16-year-old body builder who suffered from an acute ischemic stroke. In the urine, cannabis metabolites as well as metabolites of the oral androgenic-anabolic steroid methandrostenolone were detected, both known to be associated with stroke events. This report highlights the role of cannabis and steroid abuse that induce strokes in the absence of arteriopathy, cardioembolism or thrombophilia. Owing to new upcoming socio-behavioral aspects of late childhood and early adolescent life, this formally rare abuse of cannabis and/or anabolic steroids as well as their associations with strokes becomes more current than ever.

Crossed cerebellar diaschisis after status epilepticus in a young child.

We report on a 3.8-year-old girl who was born preterm. Due to a posthemorrhagic hydrocephalus she had a ventriculoperitoneal shunt. Magnetic resonance imaging (MRI) showed mild atrophy of the left cerebellum. She was found unresponsive in a febrile state. After the application of midazolam she regained consciousness. There were no epileptic discharges on electroencephalogram. MRI with diffusion-weighted sequences showed areas of hyperintensity in the right cerebrum. After the patient deteriorated again, MRI showed signs of increased intracranial pressure and high signal intensity throughout the right cerebral and left cerebellar hemispheres, suggesting crossed cerebellar diaschisis (CCD) most likely resulting from a nonconvulsive status epilepticus (SE). A follow-up MRI showed progressive brain atrophy. CCD after SE might be caused by cortical excitatory input through the cortico-pontine-cerebellar pathway. Alternatively, the cerebral edema in SE may decrease neuronal cell activity in the contralateral cerebellar hemisphere. The unilateral cerebellar atrophy before the onset of CCD might be attributed to impaired neuronal connections after peripartal cerebral injury. This case presents a young child with a combination of two CCDs, at first due to perinatal brain injury, and at second to SE. MRI with diffusion-weighted sequences can detect CCD at an early stage.

Determination of thromboxane formation, soluble CD40L release and thrombopoietin clearance in apheresis platelet concentrates.

All deleterious changes in platelet morphology, structure and function that occur in platelet concentrates (PC) during storage are titled as the 'platelet storage lesion'. No single in vitro test currently available is sufficient in assessing these changes of platelet quality. The release of soluble CD40 Ligand (sCD40L), the formation of thromboxane (TXB2) and the thrombopoietin (TPO) clearance reflect different aspects of platelet metabolism and activitiy, and were used to examine platelet quality in apheresis platelet products. At days 1, 3 and 5, in single-donor apheresis platelet products (n = 10) under routine storage conditions, sCD40L (measured by ELISA) and TXB2 (measured by RIA) were determined after platelet stimulation (recalcification and clot formation). TPO (measured by ELISA) was determined after an incubation time of 5 h at 37°C with platelet-rich plasma (adjusted initial TPO concentration of about 500 pg/mL). Results were related to a therapeutic unit (TU = 2 × 10(11) platelets). Immediately after platelet preparation, sCD40L release was 41 ± 7.6 ng/TU, TXB2 formation 1688 ± 374 ng/TU and TPO clearance 1.22 ± 0.32 ng/h/TU. At days 1, 3 and 5, sCD40L was reduced to 89 ± 7%, 71 ± 12% and 57 ± 9%, TXB2 release to 91 ± 6%, 74 ± 12% and 58 ± 9% and TPO clearance to 90 ± 15%, 84 ± 5% and 79 ± 10% of the respective control values. In conclusion, in single-donor apheresis PC, sCD40L release and TXB2 formation as well as TPO clearance by the platelets were dependent on storage duration and reduced to about 60% to 80% of the respective control values after a storage period for 5 days. These findings are in line with literature data, indicating that a loss of platelet functionality of about 30% will occur after 5 days of storage.

Human vascular smooth muscle cells express functionally active endothelial cell protein C receptor.

The endothelial cell protein C receptor (EPCR) is expressed on endothelial cells and regulates the protein C anticoagulant pathway via the thrombin-thrombomodulin complex. Independent of its anticoagulant activity, activated protein C (APC) can directly signal to endothelial cells and upregulate antiapoptotic and antiinflammatory genes. Here we show that vascular smooth muscle cells (SMCs) also express EPCR. EPCR protein on SMCs was detected by flow cytometry and Western blotting. EPCR mRNA was identified by quantitative RT-PCR. To examine the functionality of EPCR, intracellular signaling in APC-stimulated SMCs was analyzed by determination of intracellular free calcium transients using confocal laser scanning microscopy. Phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK-1/2) was detected by immunoblotting. APC-induced ERK-1/2 phosphorylation was inhibited by an anti-EPCR antibody and by a cleavage site blocking anti-PAR-1 antibody, indicating that binding of APC to EPCR and cleavage of protease-activated receptor-1 (PAR-1) were involved. APC elicited an increase in [(3)H]-thymidine incorporation. The mitogenic effect of APC was significantly enhanced in the presence of thrombin. EPCR expression was also detected in SMCs in the fibrous cap of human carotid artery plaques. The present data demonstrate functionally active EPCR in SMCs and suggest that EPCR-bound APC might modulate PAR-1-mediated responses of SMCs to vascular injury.

Complete downmodulation of P-selectin glycoprotein ligand in monocytes undergoing apoptosis.

OBJECTIVE: Apoptotic monocytes release membrane microparticles which may play a major role in thrombogenicity through a P-selectin glycoprotein ligand (PGSL-1)-mediated mechanism. We have studied systematically the regulation of PSGL-1 expression and function in apoptotic monocytic cells. METHODS AND RESULTS: PSGL-1 expression (flow cytometry, immunofluorescence microscopy, immunoblot) was virtually abolished in apoptotic monocytes by proteolytic shedding. This was accompanied by a complete loss of PSGL-1-mediated platelet-leukocyte (flow cytometry) and leukocyte-endothelial cell (parallel plate flow chamber) interactions. Systematic screening of protease inhibitors combined with knock-out and siRNA experiments characterized the PSGL-1-cleaving enzyme as an N-ethylmaleimide-inhibitable metalloproteinase of the ADAM family. CONCLUSIONS: Downmodulation of PGSL-1 in apoptotic monocytes may prevent ectopic cell clearance in the peripheral vasculature to reduce local inflammatory and proliferative responses. Depletion of PSGL-1 expression on apoptotic microparticles may also act as a molecular switch to modulate their thrombogenic activity.

Membrane environment rather than tissue factor expression determines thrombin formation triggered by monocytic cells undergoing apoptosis.

Monocyte apoptosis is an important determinant of atherothrombosis. Two major mechanisms for apoptosis-associated thrombogenicity have been described: exposure of negatively charged membrane phospholipids and up-regulation of tissue factor (TF). However, the relative importance of these mechanisms is unclear. Thus, procoagulant functions (thrombin generation) of apoptotic (staurosporine, 2 muM, 24 h) U937 cells versus cell-derived microparticles (MPs) were studied. In apoptotic U937 cells, a significant increase in TF mRNA (real-time PCR), surface expression of TF (flow cytometry), and total cellular amount of TF (Western blotting) was observed. Control cells only minimally triggered thrombin generation (endogenous thrombin potential), and apoptotic cells were highly procoagulant. However, addition of negatively charged membranes completely restored the thrombin generation capacity of control U937 cells to the levels of apoptotic cells. MPs (defined as CD45(+) particles of subcellular size), derived from apoptotic U937 cells, were highly procoagulant but did not exhibit an increased TF expression or annexin V binding. Taken together, our data support the concept that the membrane environment, independent of TF expression, determines the extent of thrombin formation triggered by apoptosis of monocytic cells. Externalization of negatively charged phospholipids represents the most important mechanisms for whole cells. Additional yet unknown mechanisms appear to be involved in the procoagulant actions of MPs derived from apoptotic monocytes.

Preliminary evidence for a matrix metalloproteinase-2 (MMP-2)-dependent shedding of soluble CD40 ligand (sCD40L) from activated platelets.

Platelets are the major source of soluble CD40 ligand (sCD40L) in the blood. It has been demonstrated that CD40L is cleaved from the surface of activated platelets to release sCD40L. However, the enzyme involved in sCD40L shedding has not been identified yet. Using a panel of pharmacological inhibitors of serine, cysteine, aspartate, or metalloproteinases, preliminary evidence is presented for the hypothesis that matrix metalloproteinase-2 (MMP-2) might be the protease, primarily responsible for CD40L cleavage from platelet surface.

Impaired interaction between platelets and endothelial progenitor cells in diabetic patients.

This editorial focuses on new data on the role of platelets of the recruitment of endothelial progenitor cells to sites of vascular lesion and their differentiation into endothelium. Questions of further research are raised.

Cholesterol enhances thrombin-induced release of fibroblast growth factor-2 in human vascular smooth muscle cells.

OBJECTIVE: The mitogenic response to the G protein-coupled receptor agonist thrombin in human vascular smooth muscle cells (SMCs) depends on release of fibroblast growth factor-2 (FGF-2). Yet, intracellular mechanisms triggering FGF-2 release are unknown. The present study investigates possible effects of cholesterol enrichment and depletion, which have been shown to influence FGF-2-dependent signaling and SMC mitogenesis, on thrombin-induced FGF-2 release. METHODS AND RESULTS: Cultured human aortic and saphenous vein SMCs were enriched with cholesterol by using a cyclodextrin-cholesterol complex. Cholesterol accumulation was determined by a fluorometric assay. ELISA, Western blotting, and RT-PCR were used for quantification of FGF-2 levels. DNA synthesis was determined by [3H]-thymidine incorporation, proliferation by cell counting. Stimulation of SMCs with thrombin (30 nmol/L) resulted in release of FGF-2 into the pericellular space within 10 minutes. Preincubation with cyclodextrin-cholesterol caused accumulation of cellular cholesterol, increased thrombin-induced FGF-2 release, and stimulated FGF-2 de novo synthesis. Thrombin-induced DNA synthesis and proliferation were enhanced in cholesterol-rich SMCs. This effect was inhibited by FGF-2-neutralizing antibodies. CONCLUSIONS: Enhanced cellular cholesterol stimulates thrombin-induced release of FGF-2 and increases the mitogenic response toward thrombin in human SMCs. This mechanism might also be relevant for thrombin-induced mitogenesis in hypercholesterolemia in vivo.

Differential effects of factor IIa inhibitors on the endogenous thrombin potential.

Calibrated automated thrombin generation measurement in clotting plasma (endogenous thrombin potential, ETP) is being used increasingly to monitor the effects of anticoagulant drugs. Calibrated automated thrombography measures the concentration of thrombin in clotting plasma by monitoring the cleavage of a fluorogenic substrate (Z-Gly-Gly-Arg-7-amino-4-methylcoumarin) and comparing it with a constant known thrombin activity in a parallel nonclotting sample. This study compared the concentration-dependent effects of different factor IIa inhibitors on the ETP. In accordance with a theoretical prediction, the monovalent factor IIa inhibitors melagatran and argatroban reduced peak thrombin concentrations without a marked effect on the lag time of thrombin generation. However, both bivalent factor IIa inhibitors lepirudin and bivalirudin markedly prolonged the lag time of thrombin generation and thus behaved like "super" factor Xa inhibitors according to the theoretical model. These findings have important consequences for therapeutic drug monitoring using thrombin generation assays. For monitoring of hirudins, the lag time of thrombin generation seems to be a very sensitive parameter. In contrast, for monitoring of argatroban, the evaluation of the ETP seems to be useful.

Aspirin "resistance".

Recent clinical studies have shown that the expected antiplatelet effect of aspirin is not always achieved. From the laboratory point of view, resistance to aspirin is the inability to achieve the expected inhibition of platelet cyclooxygenase-(COX-)1 with prevention of platelet thromboxane (TX) A2 formation. The failure to prevent atherothrombotic events (treatment failure) must be distinguished from aspirin resistance. Nevertheless, different definitions of aspirin resistance complicate the assessment of published data, a problem aggravated by discordant results of the available diagnostic laboratory techniques.The pharmacological mechanisms of aspirin resistance are not completely understood. Potential causes include pharmacokinetic and pharmacodynamic issues, such as reduced bioavailability, increased platelet turnover, interactions with nonsteroidal anti-inflammatory drugs, comorbidities (hypercholesterolemia or diabetes mellitus), alternative pathways of platelet activation, and genetic polymorphisms. Clinical trials demonstrated a negative impact of aspirin resistance on the clinical outcome: an about fourfold increased risk of major atherothrombotic events has been found in aspirin nonresponders suffering from vascular disease.An individualized antiplatelet therapy with aspirin will have to consider the possibility of aspirin resistance. Thus, standardized and inexpensive diagnostic assays are needed. The identification of aspirin-resistant patients is essential to individually tailor antiplatelet treatment. For example, increasing the dosage of aspirin or alternative antiplatelet drugs are potential therapeutic concepts, but these require careful future investigation.

Methods to evaluate the pharmacology of oral antiplatelet drugs.

Principally, there are two reasons why the pharmacological response to antiplatelet drugs should be measured: on the one hand, an insufficient inhibition of platelet function may result in atherothrombotic complications; on the other hand, an excessive inhibition of platelet function may lead to bleeding complications. The clinical importance to measure the effects of antiplatelet drugs is demonstrated by increasingly growing evidence for an association of resistance to antiplatelet drugs with thromboembolic events. It is often claimed that there is no generally accepted definition of "resistance" and, instead, there is an ongoing semantic discussion about the correct term to be used to describe this phenomenon. From the pharmacological point of view, there is only one acceptable definition of "resistance" to antiplatelet drugs: the term "resistance" should be used when a drug is unable to hit its pharmacological target. Thus, laboratory methods used to evaluate the effects of antiplatelet drugs should be designed to measure the direct pharmacodynamic effect of a drug, rather than the consequences for global platelet function. Based on physiological/pathophysiological, pharmacological, and practical considerations, the authors propose the following assays to be used to measure the effects of oral antiplatelet drugs: for the detection of aspirin actions, thromboxane or arachidonic acid-induced responses (light aggregometry, whole-blood aggregometry) should be measured; for the detection of clopidogrel actions, VASP (vasodilator-stimulated phosphoprotein) phosphorylation (flow cytometry) or ADP-(adenosine diphosphate-)induced responses (light aggregometry, whole-blood aggregometry, possibly also flow cytometry) should be measured.

[Platelet function analysis with point-of-care methods]. / Messung der Thrombozytenfunktion mit Point-of-Care-Methoden.

BACKGROUND: More and more patients are treated with antiplatelet drugs today. In this context a sufficient inhibition of platelet aggregation, on the one hand, is of essential importance to the efficiency of prophylaxis of myocardial and cerebral infarction and to avoiding thrombosis of drug-eluting stents. On the other hand, this medication can result in an increased risk of perioperative bleeding. In both situations control of the efficiency of therapy or rather the assessment of the impairment of hemostasis is of vital importance. METHODS: Platelet function analyzer (PFA-100), multiple platelet function analyzer (Multiplate), and rotational thrombelastometry (ROTEM) are reliable and easy to use point-of-care (POC) devices. Since these three analyzers monitor different aspects of platelet function and have different limitations, the selection of the right test system depends on the right question. RESULTS: PFA-100 enables a sensitive detection of von Willebrand's syndrome. Multiplate is apt to control efficiency of platelet inhibiton with acetylsalicylic acid, clopidogrel and glycoprotein IIb/IIIa receptor antagonists. ROTEM analysis offers the opportunity to assess hemostasis as a holistic system. Thereby, ROTEM analysis particularly detects hyperfibrinolysis, heparin effects, and fibrinogen-platelet interaction. CONCLUSION: Due to their easy handling the described POC devices are applicable to perioperative coagulation management as well as during and after coronary intervention or to monitoring of platelet function in cardiologic practice. They enable a quick assessment of platelet function and an individually guided therapy.

Alternatively spliced human tissue factor (asHTF) is not pro-coagulant.

It has been proposed that alternatively-spliced human tissue factor (asHTF) is pro-coagulant. We have evaluated the function of asHTF in a mammalian expression system. Full-length human tissue factor (HTF) and asHTF were cloned from smooth muscle cells and over-expressed in HEK293 cells. As expected, a marked pro-coagulant activity (FX activation, thrombin generation) was observed on the surface, in lysates, and on microparticles from HTF transfected cells. In contrast, no pro-coagulant activity of asHTF was observed.

Alternative splicing of platelet cyclooxygenase-2 mRNA in patients after coronary artery bypass grafting.

Recently, we cloned from platelet mRNA a novel cyclooxygenase (COX)-2 splice variant, designated COX-2a, which is characterized by a partial deletion of exon 5. Preliminary studies of mRNA distribution of COX-2 isoforms in platelets from coronary artery bypass grafting (CABG) patients showed a variable increase in COX-2a mRNA expression after cardiac surgery. Thus, we assessed whether this variant may play a functional role in these patients. We report a marked (about 200-fold) increase in the expression of COX-2a mRNA after CABG. Evidence is presented that ribosomal frame-shifting may correct the coding sequence resulting in the expression of a full-length COX-2a protein. In addition, a reading frame-corrected COX-2a mutant (COX-2a delta G) was generated by site-directed mutagenesis and expressed in COS-7 cells using an adenoviral expression system. However, COX-2a protein was not active in terms of prostaglandin formation. Thus, alternative mRNA splicing might represent an intriguing posttranscriptional mechanism to oppose a transcriptional activation of the COX-2 gene. Evolutionary, this mechanism may prevent COX-2-dependent thromboxane synthesis in the platelet, which would potentiate the likelihood of thrombosis; pharmacologically, this mechanism would prevent an aspirin-insensitive pathway of thromboxane formation.

Regulation of thrombomodulin expression in human vascular smooth muscle cells by COX-2-derived prostaglandins.

There is concern that cyclooxygenase (COX)-2 inhibitors may promote atherothrombosis by inhibiting vascular formation of prostacyclin (PGI2) and an increased thrombotic risk of COX-2 inhibitors has been reported. It is widely accepted that the prothrombotic effects of COX-2 inhibitors can be explained by the removal of platelet-inhibitory PGI2. Using microarray chip technology, we have previously demonstrated that thrombomodulin (TM) mRNA is upregulated in cultured human coronary artery smooth muscle cells by the stable prostacyclin mimetic iloprost. This study is the first to demonstrate a stimulation of the expression of functionally active thrombomodulin in human smooth muscle cells by prostaglandins, endogenously formed via the COX-2 pathway. Because TM is an important inhibitor of blood coagulation, these findings provide a novel platelet-independent mechanism to explain the prothrombotic effects of COX-2 inhibitors. The full text of this article is available online at http://circres.ahajournals.org.

ICAM-1 and p38 MAPK mediate fibrinogen-induced migration of human vascular smooth muscle cells.

Fibrinogen deposition in the vessel wall represents an independent atherogenic risk factor. In Boyden-chamber assays, fibrinogen concentration-dependently (1-100 microM) induced migration of human vascular smooth muscle cells (SMC). This was inhibited by antibodies to intercellular adhesion molecule-1 (ICAM-1, 10 microg/ml), and by inhibitors of PI3-kinase (LY294002, 10 microM) and MAPK (mitogen-activated protein kinase) p38 (SB203580, 10 microM). The MEK (MAP kinase kinase) inhibitor PD98059 (10 muM) and the GPIIb/IIIa antagonist abciximab (10 mug/ml) had no effect. ICAM-1 antibodies inhibited fibrinogen-induced Akt and p38 phosphorylation. Thus fibrinogen stimulates human SMC migration through binding to ICAM-1 and activation of Akt and p38.

Rapid release of active tissue factor from human arterial smooth muscle cells under flow conditions.

Circulating tissue factor (TF) is an important determinant of coronary thrombosis. Among other cell types, such as monocytes, vascular smooth muscle cells (SMCs) are capable of releasing TF. When studied under static conditions, SMCs do release TF, but this process is slow and, thus, cannot explain the elevated levels of circulating TF, as observed in patients with acute coronary syndromes. The present study demonstrates that cultured human mammary artery SMCs very rapidly (minutes) release active, microparticle-bound TF when exposed to flow conditions. There was a clear log-linear correlation between the shear rate (range 10 s(-1) to 1500 s(-1)) and the procoagulant activity of SMC perfusates. Flow-dependent release of TF was transient (10 minutes) and did not measurably reduce cell surface TF content. Interestingly, a time-dependent (t(1/2) 30 minutes) re-exposure of releasable TF was detected after a no-flow period. These data demonstrate that SMCs may become a pathophysiologically relevant source of TF that can be rapidly released into the circulation in situations in which endothelial damage occurs and SMCs come into a close contact with the flowing blood.

Does a coxib-associated thrombotic risk limit the clinical use of the compounds as analgesic, antiinflammatory drugs? Arguments against.

The issue of the risk-benefit assessment of cyclooxygenase-2 (COX-2) inhibitors, as compared to traditional non-steroidal anti-inflammatory drugs (tNSAIDs), is far from being resolved. These compounds need to be carefully re-evaluated in order to avoid hasty conclusions, as it happened when COX-2 inhibitors were introduced into clinical practice. Several arguments support the concept, that COX-2 inhibitors remain a valuable therapeutic option at least for selected patients.