903-8 Mitogenic Effect of Thromboxane A2and Its Synergistic Interaction with Serotonin on Smooth Muscle Cell Proliferation is Reversed by Ridogrel

BackgroundThromboxane A2(TxA2) and serotonin (5HT) released from aggregating platelets are known mitogens for vascular smooth muscle cells (SMC). Recently we reported that TxA2and 5HT act synergistically in inducing proliferation of SMC and may contribute to the development of restenosis following vascular injury.PurposeIn this study, we examined whether ridogrel (a TxA2synthase inhibitor/receptor antagonist) can inhibit the TxA2induced SMC proliferation both in the presence and absence of 5HT.MethodsCanine aortic primary SMC were preincubated with either 30 μg/ml of Ridogrel in phosphate buffered saline (PBS) or equal volume of PBS, as control, for 2 hrs in serum free medium. Increasing concentrations of U46619 (a TxA2mimetic) with or without 5HT were then added and 3H-thymidine incorporated into DNA of the SMC was measured.ResultsControl (PBS) 5HT Concentration(μM)Rido9rel 30 μg/ml 5HT Concentration(μM)05500550TxA20 nM100236±37222±568±4306±3212±13TxA27.5 nM100±1394±201131±9784±8294±27*249±6*TxA275 nmM173±29541±691369±14674±117*283±24*279±17*TxA2750 nM282±8795±221569±10376±27*285±28*274±21*Values are % of control: Control=100% =9023±621 cpm/106cells. n =3*p<0.001 compared to corresponding PBS treated controlsThe data show that unlike the PBS treated controls, ridogrel reversed both the mitogenic effect of TxA2on SMC as well as its synergistic interaction with 5HT in inducing cellular proliferation.ConclusionThe data indicate the specificity of the interaction of TxA2with 5HT in inducing SMC proliferation. This suggests a potential role forthe combined use of TxA2synthase inhibitor/receptor antagonist and 5HT receptor antagonist for inhibiting SMC proliferation at sites of vascular injury

A perspective on the potential problems with aspirin as an antithrombotic agent: a comparison of studies in an animal model with clinical trials

AbstractAspirin is the most widely prescribed agent to reduce the platelet-mediated contributions to atherosclerosis, coronary thrombosis and restenosis after angioplasty. While aspirin treatment has led to significant reductions in morbidity and mortality in many clinical trials, there are several scenarios in which aspirin may fail to provide a full antithrombotic benefit. The cyclic flow model of experimental coronary thrombosis suggests that elevations of plasma catecholamines, high shear forces acting on the platelets in the stenosed lumen and the presence of multiple, input stimuli can activate platelets through different mechanisms that may lead to thrombosis despite aspirin therapy. Aspirin therapy is limited because it only blocks some of the input stimuli, leaving aspirin-independent pathways through which coronary thrombosis can be precipitated. These include thrombin and thrombogenic arterial wall substrates such as tissue factor. New agents that block the adenosine diphosphate (ADP) receptor, or regulate platelet free cytosolic calcium, such as direct nitric oxide donors, may be more potent overall than aspirin. Agents that block the platelet integrin GPIIb-IIIa receptor inhibit the binding of fibrinogen to platelets regardless of which input stimuli activate the platelet and, thus, as demonstrated in the cyclic flow model, would be much more potent than aspirin as an antithrombotic agent. The cyclic flow model has been useful in predicting which agents are likely to be of benefit in clinical trials

Knockdown of plakophilin 2 downregulates MIR-184 through CpG hypermethylation and suppression of the E2F1 pathway and leads to enhanced adipogenesis in vitro

Rationale: PKP2, encoding plakophilin 2 (PKP2), is the most common causal gene for arrhythmogenic cardiomyopathy. Objective: To characterize miRNA expression profile in PKP2-deficient cells. Methods and results: Control and PKP2-knockdown HL-1 (HL-1(Pkp2-shRNA)) cells were screened for 750 miRNAs using low-density microfluidic panels. Fifty-nine miRNAs were differentially expressed. MiR-184 was the most downregulated miRNA. Expression of miR-184 in the heart and cardiac myocyte was developmentally downregulated and was low in mature myocytes. MicroRNA-184 was predominantly expressed in cardiac mesenchymal progenitor cells. Knockdown of Pkp2 in cardiac mesenchymal progenitor cells also reduced miR-184 levels. Expression of miR-184 was transcriptionally regulated by the E2F1 pathway, which was suppressed in PKP2-deficient cells. Activation of E2F1, on overexpression of its activator CCND1 (cyclin D1) or knockdown of its inhibitor retinoblastoma 1, partially rescued miR-184 levels. In addition, DNA methyltransferase-1 was recruited to the promoter region of miR-184, and the CpG sites at the upstream region of miR-184 were hypermethylated. Treatment with 5-aza-2'-deoxycytidine, a demethylation agent, and knockdown of DNA methyltransferase-1 partially rescued miR-184 level. Pathway analysis of paired miR-184:mRNA targets identified cell proliferation, differentiation, and death as the main affected biological processes. Knockdown of miR-184 in HL-1 cells and mesenchymal progenitor cells induced and, conversely, its overexpression attenuated adipogenesis. Conclusions: PKP2 deficiency leads to suppression of the E2F1 pathway and hypermethylation of the CpG sites at miR-184 promoter, resulting in downregulation of miR-184 levels. Suppression of miR-184 enhances and its activation attenuates adipogenesis in vitro. Thus, miR-184 contributes to the pathogenesis of adipogenesis in PKP2-deficient cells

Detecting thermal discrepancies in vessel walls

An infrared, heat-sensing catheter particularly useful for identifying potentially fatal arterial plaques in patients with disease of the coronary or other arteries and its use are detailed. In one embodiment, an infrared fiberoptic system (with or without ultrasound) is employed at the tip of the catheter to locate inflamed, heat-producing, atherosclerotic plaque, which is at greater risk for rupture, fissure, or ulceration, and consequent thrombosis and occlusion of the artery. In another embodiment, a catheter with an infrared detector (with or without ultrasound) employed at its tip will likewise locate inflamed heat-producing atherosclerotic plaque. The devices and methods of the invention may be used to detect abscesses, infection, and cancerous regions by the heat such regions differentially display over the ambient temperature of immediately adjacent tissues. The methods and devices of the invention may also be used to detect regions of cooler than ambient tissue in a vessel or organ which indicate cell death, thrombosis, cell death, hemorrhage, calcium or cholesterol accumulations, or foreign materials

In vivo measurement of myocardial mass using nuclear magnetic resonance imaging

To examine the accuracy of nuclear magnetic resonance imaging in measuring left ventricular mass, measurements of left ventricular mass made using this technique were compared with left ventricular weight in 10 mongrel dogs. Left ventricular myocardial volume was measured from five short-axis ehd-diastolic images that spanned the left ventricle. Left ventricular mass was calculated from left ventricular myocardial volume and compared with the left ventricular weight determined after formalin immersion-fixation.Linear regression analysis yielded the following relation in grams: left ventricular mass determined using nuclear magnetic resonance imaging = (0.94) (left ventricular weight) + 9.1 (r = 0.98, SEE = 6.1 g). The small overestimation of left ventricular weight by nuclear magnetic resonance imaging was judged to be secondary to both difficulty with proper border definition and partial volume effects. Hence, this imaging technique can be used to obtain accurate measurements of left ventricular mass in dogs in vivo