Early pharmacologic intervention and plaque stability in acute coronary syndromes

Pigment epithelium-derived factor (PEDF) prevents platelet activation and aggregation in diabetic rats by blocking deleterious effects of advanced glycation end products (AGEs)

BACKGROUND

Alteration of platelet function contributes to microthrombus formation and may play an important role in the pathogenesis of diabetic vascular complications. In addition, there is a growing body of evidence that oxidative stress generation is involved in platelet activation and aggregation in vivo. Since we have recently found that pigment epithelium-derived factor (PEDF) inhibits thrombus formation in rats through its anti-oxidative properties, we investigated here whether PEDF prevented platelet activation and aggregation in diabetic or advanced glycation end products (AGEs)-injected rats.

METHODS AND RESULTS

Experimental diabetes was induced by injecting streptozotocin to Sprague-Dawley rats. Diabetic or non-diabetic Sprague-Dawley rats were injected intravenously with or without 1 mg AGEs-bovine serum albumin or non-glycated bovine serum albumin in the presence or absence of 10 microg PEDF everyday. Administration of PEDF or pyridoxal phosphate, an inhibitor of AGEs formation, inhibited platelet P-selectin expression and aggregation by suppressing NADPH oxidase-driven superoxide generation, and subsequently ameliorated a shortened tail vein bleeding time in diabetic rats. Further, intravenous administration of AGEs to normal rats mimicked the effects of diabetes on platelet activation and bleeding time, which were also blocked by simultaneous administration of PEDF.

CONCLUSIONS

These results demonstrated for the first time that PEDF inhibited platelet activation and aggregation in diabetic rats through its anti-oxidative properties. Our present study suggests that PEDF may play a protective role against diabetic vascular complications by attenuating the deleterious effects of AGEs on platelets.

Pigment epithelium-derived factor (PEDF) administration inhibits occlusive thrombus formation in rats: A possible participation of reduced intraplatelet PEDF in thrombosis of acute coronary syndromes

OBJECTIVES

Although remarkable therapeutic advances in the treatment of acute coronary syndromes (ACS) have been made with anti-platelet therapy, the therapeutic options may be limited by considerable side effects. Pigment epithelium-derived factor (PEDF) has anti-oxidative properties and may play a protective role against atherosclerosis. In this study, we investigated whether PEDF prevented occlusive thrombus formation in rats.

METHODS AND RESULTS

Occlusive thrombus formation was induced by treating rats with ligation and cuff placement at the left common carotid artery. Intravenous injection of PEDF dose-dependently inhibited thrombus formation and blocked the increase in immunoreactivity of P-selectin, a marker of platelet activation, NADPH oxidase activity and superoxide generation in thrombi. In vitro, PEDF significantly decreased collagen-induced reactive oxygen species generation in platelets and subsequently suppressed the platelet activation and aggregation. Plasma and intraplatelet levels of PEDF in the coronary circulation in patients with ACS were significantly lower than those in age- and gender-matched controls without coronary artery disease.

CONCLUSIONS

These results demonstrated that PEDF administration could inhibit occlusive thrombus formation by blocking the platelet activation and aggregation through its anti-oxidative properties. Our present study suggests that pharmacological up-regulation or substitution of PEDF may offer a promising strategy for the treatment of arterial thrombosis.

Time as a Variable With Niacin Extended‐Release/Lovastatin vs. Atorvastatin and Simvastatin

Time may be an important variable when evaluating the efficacy of lipid-altering drugs. In this analysis of the Advicor Versus Other Cholesterol-Modulating Agents Trial Evaluation, niacin extended-release/lovastatin 1000/40 mg was as effective as atorvastatin 10 mg and more effective than simvastatin (both 10 mg and 20 mg) in achieving low-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol treatment goals. The titration schedule for this study included the initiation of niacin-extended release/lovastatin 500/20 mg once a day for 4 weeks, titrated to the starting dose of 1000/40 mg after 4 weeks, and then titrated to the final dose of 2000/40 mg. The titration schedule for both atorvastatin and simvastatin was 10 mg per day for 8 weeks and then titrated to 40 mg per day. Using this schedule, 50% of niacin extended-release/lovastatin and atorvastatin patients reached low-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol treatment goals within approximately 7 weeks, compared with simvastatin, in which 50% reached both treatment goals in 13-14 weeks. These time differences may have potential clinical relevance in reducing coronary heart disease risk.

In-hospital initiation of statin therapy in acute coronary syndromes: maximizing the early and long-term benefits

Patients with acute coronary syndrome (ACS) are at high risk for recurrent coronary events, sudden death, and all-cause mortality. Conventional revascularization therapies reduce the risk of further ischemia but do not affect the underlying atherosclerotic disease. Statins have a proven record in the secondary prevention of coronary heart disease. Furthermore, statins have been shown to exert varying degrees of pleiotropic effects, which may stabilize vulnerable atherosclerotic plaques. A compelling body of evidence from randomized controlled trials demonstrates that high-dose, potent statin therapy initiated immediately after an acute coronary event can significantly reduce early as well as longer-term morbidity and mortality. Furthermore, high-dose, potent statin therapy displays a reasonable safety profile. National guidelines now recommend that in patients with ACS, statin therapy should be initiated in hospital prior to discharge, irrespective of baseline low-density lipoprotein cholesterol levels, to improve clinical outcomes. Every effort should be made to ensure all eligible patients with ACS are initiated and maintained on statin therapy.

Evaluating Cardiovascular Pathophysiology and Anatomy in Atherosclerosis

The process of atherosclerosis begins with endothelial dysfunction from impaired bioavailability of NO and progresses through multiple stages of plaque development. Impaired endothelial function decreases NO and increases oxidized macromolecules such as low-density lipoprotein cholesterol. Oxidized low-density lipoprotein cholesterol accumulates in subendothelial space, forming plaques that may eventually compromise the lumen. Acute coronary events result from plaque rupture and consequent thrombus formation and abrupt occlusion of the vessel lumen. New diagnostic methods such as flow-mediated dilation of the brachial artery can detect endothelial dysfunction, and intravascular ultrasound can detect early plaque formation in the arterial wall. These techniques may provide a means to identify patients at risk for adverse cardiovascular outcomes, thereby enabling physicians to potentially prevent adverse events by early initiation of lipid-lowering therapy.

Synergism of aspirin and heparin with a low-frequency non-invasive ultrasound system for augmentation of in-vitro clot lysis

BACKGROUND

Aspirin, glycoprotein IIb/IIIa inhibitors and heparin are routinely used in acute coronary syndromes. Previously we showed that there is synergism between ultrasound and heparin and tirofiban in augmenting blood clot disruption. However, there is a little data on a possible synergism of low-frequency ultrasound with aspirin for in-vitro clot dissolution, and especially on the combination of aspirin with heparin and/or glycoprotein IIb/IIIa inhibitors.

MATERIALS AND METHODS

Human blood clots (n = 320) were incubated for 10 or 20 minutes in saline containing aspirin alone or combined with heparin and/or tirofiban and/or eptifibatide. Clots were randomly treated with low-frequency ultrasound (27.3 kHz) or incubation only. The percent clot weight loss and the incremental effect of ultrasound were calculated.

RESULTS

The most significant incremental effect of ultrasound on clot weight reduction was detected with aspirin alone (5.2 +/- 2.3% and 5.2 +/- 2.6% after 10' and 20', p = 0.04 and p = 0.06, respectively) and in combination with heparin (8.8 +/- 2.5% and 11.5 +/- 2.7% after 10' and 20', p = 0.01 and p = 0.0001, respectively). The greatest absolute magnitude of clot weight reduction was observed with ultrasound combined with aspirin and heparin (48.5 +/- 9.5% after 20'). The addition of tirofiban or eptifibatide to aspirin, heparin and ultrasound did not increase clot lysis. However, eptifibatide had significantly better synergism than tirofiban (p = 0.025 and p = 0.015, after 10 and 20 minutes, respectively).

CONCLUSIONS

Aspirin alone or in combination with heparin results in significant augmentation of clot lysis and is synergistic with application of low-frequency ultrasound for 10 and 20 minutes only. These results may have important implications for a possible use of low-frequency ultrasound in treatment algorithms of acute coronary syndromes.

Dyslipidemia, statins, and venous thromboembolism: a potential risk factor and a potential treatment

The optimal drug for the prevention of venous thromboembolism is one that is efficacious, associated with minimal bleeding risk, and easy to administer. Statins fulfill the latter two criteria, but their efficacy remains unproved. By examining the association between dyslipidemia and venous thromboembolism, as well as the evidence that statins might prevent venous thromboembolism, there may be a new rationale for the use of this class of drugs. There may be a common link between arterial and venous thrombosis. Dyslipidemia may be one of the many systemic factors associated not only with arterial thrombosis, but with venous thromboembolism as well. This may occur through the effects of circulating lipid molecules on the vascular endothelium, platelet function, and coagulation factors. By impeding these mechanisms, statins may be protective against venous thrombosis, but epidemiologic studies are few in number, and no randomized clinical trials have been conducted. Better epidemiologic evidence is required to establish whether dyslipidemia is a risk factor for venous thromboembolism. If future observational studies can demonstrate that statins are associated with a lower risk of venous thromboembolism, then consideration should be given to conducting a randomized clinical trial comparing statins with placebo for the prevention of venous thromboembolism. Until then, the efficacy of statins for the prevention or treatment of venous thromboembolism remains uncertain.

Barriers to preventive interventions for coronary heart disease

Many barriers exist to the delivery of preventive services by cardiologists and other physicians. Appropriate training and the development of supportive infrastructures can effectively overcome these barriers. In addition, institutional priorities must change to encourage such efforts. Cardiologists must continue to recognize the importance of risk-factor modification, and training programs in cardiology should teach appropriate counseling techniques, the use of risk-factor-lowering pharmacologic agents, and the manner in which cardiologists should interface with dietitians and other ancillary personnel [77]. In addition, it is important to recognize and teach, both didactically and by example, that counseling patients and carrying out long-term preventive interventions can be as gratifying and interesting as performing dramatic procedures that, although valuable and rewarding, take place at a very late point in the patient's clinical course, a point that might have been averted by greater attention to risk-factor modification. Increasingly, the public and governmental agencies are becoming involved in encouraging such an approach [66], and health care provider groups [78] and organizations [67] are also facilitating the development of a more comprehensive approach to the delivery of preventive intervention [79].

Pharmacologic plaque passivation for the reduction of recurrent cardiac events in acute coronary syndromes

Acute coronary syndrome (ACS) is often associated with the rupture of vulnerable atherosclerotic plaque, coronary thrombus formation, and abrupt limitation of blood flow, leading to adverse outcomes. Passivation of vulnerable plaque represents a therapeutic concept that has the potential to prevent or limit the magnitude of a new rupture in order to reduce the recurrence or severity of events. Plaque passivation can be defined as a process by which the structure or content of the atherosclerotic plaque is changed to reduce the risk of subsequent rupture and thrombosis. This may be achieved by using strategies that address different components of the plaque or the endothelium. The following factors can affect the susceptibility of plaque to rupture: macrophage infiltration; accumulation of inflammatory cells; paracrine secretion of enzymes that may cause degradation of the fibrous cap of coronary plaque; shear stress; circadian rhythm variation in stress hormone release; and infectious agents. The use of pharmacologic agents to reduce plaque vulnerability by passivation has been explored. Clinical studies demonstrate that lipid-modifying agents (e.g., statins), antiplatelet agents (acetylsalicylic acid, thienopyridines, thianopyridines, glycoprotein IIb/IIIa inhibitors), and antithrombotic agents (unfractionated heparin and low-molecular-weight heparin) can reduce the occurrence of acute coronary events in ACS patients. In addition, angiographic studies suggest that statins may also promote regression of atherosclerosis. Angiotensin-converting enzyme inhibitors, niacin, and calcium antagonists may also contribute to plaque passivation. This article reviews atherosclerotic plaque development and vulnerability and discusses some clinical studies highlighting the role of plaque passivation in the management of ACS patients.