Modification of atherosclerosis by agents that do not lower cholesterol

Therapeutic potential of nitric oxide donors in the prevention and treatment of atherosclerosis

Well-known risk factors for atherosclerosis include hypercholesterolaemia, hypertension, diabetes, and smoking. These conditions are associated with endothelial dysfunction, which itself is associated with reduced endothelial generation of nitric oxide (NO). This is an overview of the implications of NO generation in atherosclerosis and of the potential therapeutic benefit of drugs which donate NO, such as organic nitrates, nicorandil, and sydnonimines, or those which increase the availability of endogenous NO, such as statins, angiotensin-converting enzyme inhibitors, L-arginine, and tetrahydrobiopterin.

Beta-blockers for heart failure: why, which, when, and where

Beta-blockers are a highly effective treatment for patients with all grades of heart failure secondary to LV systolic dysfunction. Beta-blockers are best deployed as a form of tertiary prevention in heart failure but have a very limited role for the treatment of a heart failure crisis. Physicians and patients need to understand the time course of the effects of beta-blocker therapy. The initial effects are often neutral or adverse, though the benefits, at least of carvedilol, may be apparent within days in patients with severe heart failure. Benefits accumulate gradually over a period of weeks to months. Some patience, perseverance, and education are required in order to allow patients to reap the full benefits of beta-blocker therapy for this malignant disease. Initiation of treatment early in the course of the disease maximizes the effectiveness and acceptance of therapy. Trials are under way to determine whether the benefits of beta-blockers extend to patients over 80 years of age and to those with preserved LV systolic function. It is likely that important differences exist between beta-blockers in terms of their clinical benefit, though whether differences exist between the agents that have been reported to be effective so far awaits the outcome of a large clinical trial. It is unclear whether the target doses of beta-blockers currently recommended are optimal.

What is the optimal medical management of ischemic heart failure?

Ischemic heart disease is an important and common contributor to the development of heart failure. Theoretically, all patients with heart failure may benefit from treatment designed to retard progressive ventricular dysfunction and arrhythmias. Patients with ischemic heart disease may also theoretically benefit from the relief of ischemia, the prevention of coronary occlusion, and revascularization. However, there is little evidence to show that the presence or absence of coronary disease modifies the benefits of effective treatments such as angiotensin-converting enzyme inhibitors and beta-blockers. Moreover, there is no evidence that treatment directed specifically at myocardial ischemia or coronary disease alters outcome in patients with heart failure. Treatments aimed at relieving painless myocardial ischemia have not been shown to alter prognosis. Lipid-lowering therapy is theoretically attractive for patients with heart failure and coronary disease; however, theoretical concerns also exist about the safety of such agents, and patients with heart failure have been excluded from large outcome studies very effectively. Some agents, such as aspirin, designed to reduce the risk of coronary occlusion seem ineffective or harmful in patients with heart failure, although warfarin may be safe and possibly effective. There is no evidence yet that revascularization improves prognosis in patients with heart failure, even in patients who are shown to have extensive myocardial hibernation. On current evidence, revascularization should be reserved for the relief of angina. Large-scale, randomized controlled trials are currently underway that are investigating the role of specific treatments targeted at coronary syndromes. The Carvedilol Hibernation Reversible Ischemia Trial: Marker of Success study is investigating the effects of carvedilol in a large cohort of patients with and without hibernating myocardium. The Warfarin and Antiplatelet Therapy in Chronic Heart Failure study is comparing the efficacy of aspirin, clopidogrel, and warfarin. The Heart Revascularization Trial-United Kingdom study is assessing the effect of revascularization on mortality in patients with heart failure and myocardial hibernation. Smaller scale studies are assessing the safety and efficacy of statin therapy in patients with heart failure. Only once the outcomes to these and other planned trials are known can the medical community know how best to treat their patients.

What is the optimal medical management of ischaemic heart failure?

Ischaemic heart disease is probably the most important cause of heart failure. All patients with heart failure may benefit from treatment designed to retard progressive ventricular dysfunction and arrhythmias. Patients with heart failure due to ischaemic heart disease may also, theoretically, benefit from treatments designed to relieve ischaemia and prevent coronary occlusion and from revascularisation. However, there is little evidence to show that effective treatments, such as angiotensin converting enzyme (ACE) inhibitors and beta-blockers, exert different effects in patients with heart failure with or without coronary disease. Moreover, there is no evidence that treatment directed specifically at myocardial ischaemia, whether or not symptomatic, or coronary disease alters outcome in patients with heart failure. Some agents, such as aspirin, designed to reduce the risk of coronary occlusion appear ineffective or harmful in patients with heart failure. There is no evidence, yet, that revascularisation improves prognosis in patients with heart failure, even in patients who are demonstrated to have extensive myocardial hibernation. On current evidence, revascularisation should be reserved for the relief of angina. Large-scale, randomised controlled trials are currently underway investigating the role of specific treatments targeted at coronary syndromes in patients who have heart failure. The CHRISTMAS study is investigating the effects of carvedilol in a large cohort of patients with and without hibernating myocardium. The WATCH study is comparing the efficacy of aspirin, clopidogrel and warfarin. The HEART-UK study is assessing the effect of revascularisation on mortality in patients with heart failure and myocardial hibernation. Smaller scale studies are currently assessing the safety and efficacy of statin therapy in patients with heart failure. Only when the results of these and other studies are known will it be possible to come to firm conclusions about whether patients with heart failure and coronary disease should be treated differently from other patients with heart failure due to left ventricular systolic dysfunction.

Thinness and weight loss: beneficial or detrimental to longevity?

This review examined the hypotheses that 1) low body mass index (BMI) is optimal for longevity and 2) weight loss reduces mortality rates. The preponderance of epidemiological evidence fails to support either of these hypotheses. Indeed, a number of studies show that thinness and weight loss (regardless of initial BMI) are associated with increased mortality rates. These findings cannot be attributed to smoking status or to weight loss resulting from subclinical disease. The effect of intentional weight loss on mortality rates depends upon health status. For overweight individuals in good health, there is no compelling evidence to show that mortality rates are reduced with weight loss. Even among overweight persons with one or more obesity-related health conditions, specific weight loss recommendations may be unnecessary: 1) the reduction in mortality rate associated with intentional weight loss is independent of the amount of weight loss, 2) the reductions in all-cause mortality rate associated with increased physical activity and fitness (23-44%), independent of changes in body weight, are greater than that reported for intentional weight loss (approximately 20%), and 3) many obesity-related health conditions (e.g., hypertension, dyslipidemias, insulin resistance, glucose intolerance) can be ameliorated independently of weight loss. In view of the potential risks associated with weight loss and weight cycling, it is suggested that public health may be better served by placing greater emphasis on lifestyle changes and less attention to weight loss per se.

Antiatherosclerotic activity of drugs in relation to nitric oxide function

Many studies have shown that loss of endothelium-derived nitric oxide is a major factor of ischemic episodes in patients with coronary artery disease and there is increasing evidence to suggest that nitric oxide might exert antiatherosclerotic actions. Based on these concepts, the results of animal studies on the effects of lipid lowering drugs, antioxidants, angiotensin converting enzyme inhibitors, Ca2+ channel blockers, estrogens and agents which modulate nitric oxide bioavailability are presented and compared to the results of patient studies and clinical trials. In spite of encouraging results obtained with antioxidants in animals, clinical trials could only show a clear positive effect of vitamin E treatment on the outcome of cardiovascular disease. Angiotensin converting enzyme inhibitors can ameliorate endothelial dysfunction in coronary heart disease, but their impact on disease progression remains unclear. There is evidence that estrogen replacement therapy in post-menopausal women may increase the bioavailability of nitric oxide. Finally, improved endothelial function and plaque stability clearly contribute to the clinical benefits of lipid lowering interventions, statins in particular. Taken together, these studies lend support to the concept that improving endothelial function and nitric oxide release might serve as valuable elements in the prevention or therapy of cardiovascular disease.

Heart failure due to ischaemic heart disease: epidemiology, pathophysiology and progression

Ischaemic heart disease is the most common underlying cause of heart failure in industrialised countries. Its manifestations are protean with myocardial infarction being only one important facet. The prognosis of patients with heart failure due to ischaemic heart disease also appears to be worse than that associated with many other aetiologies. The presence of ischaemic heart disease may influence both the efficacy and choice of treatment. Agents such as digoxin and amlodipine appear less effective in patients with ischaemic heart disease while ACE inhibitors and beta-blockers appear as or more effective in patients with ischaemic heart disease. Many have expressed an opinion about how coronary disease should be managed in the patient with heart failure supported by little or no evidence. There are major theoretical and practical concerns about the use of anti-coagulant, anti-platelet and statin therapy in patients with heart failure as well as major theoretical benefits. Only randomised controlled trials will resolve these issues. The same may be said of revascularisation. Fortunately trials addressing all these areas are under way. This should put the management of coronary disease in patients with heart failure on a firm evidence-based footing.

Effect of lercanidipine and its (R)-enantiomer on atherosclerotic lesions induced in hypercholesterolemic rabbits

The in vivo antiatherogenic activity of the calcium antagonist lercanidipine and its (R)-enantiomer was investigated in two different types of atherosclerotic lesions (hyperplastic and fatty-streak lesions) in rabbits. Lercanidipine (0.3, 1, and 3 mg kg(-1) week(-1)) as well as its (R)-enantiomer at 3 mg kg(-1) week(-1) were given by subcutaneous injection for 10 weeks to White New Zealand rabbits, with cholesterol feeding beginning at week 2. The hyperplastic lesion was obtained by positioning a hollow silastic collar around one carotid artery, while aortic fatty streak lesions were induced by cholesterol feeding. In untreated animals (n=5), 14 days after collar positioning an intimal hyperplasia was clearly detectable: the arteries without collar showed a intima/media (I/M) ratio of 0.03+/-0.02, whereas in carotids with a collar the ratio was 2+/-0.42. In lercanidipine-treated animals a significant and dose-dependent effect on intimal hyperplasia was observed. I/M ratios were 0.73+/-0.4, 0.42+/-0.1, 0.32+/-0.1 for 0.3, 1, and 3 mg kg(-1) week(-1), respectively (P<0.05). The lercanidipine enantiomer (3 mg kg(-1) week(-1)) was as effective as the racemate (0.41+/-0.11). Proliferation of smooth muscle cells, assessed by incorporation of BrdU into DNA, was reduced by about 50%, 70%, 85%, and 80% by lercanidipine (0.3, 1, and 3 mg kg(-1) week(-1)) and its (R)-enantiomer, respectively. The area of fatty-streaks in the aorta (n = 11-15) was significantly reduced by lercanidipine (3 mg kg(-1) week(-1), 16% vs 27%, P<0.05), a trend was observed also with lower doses. When different segments of the aorta were considered (arch, thoracic, abdominal) a significant and dose-dependent effect in the thoracic and abdominal aorta was observed also at lower doses. The (R)-enantiomer was as effective as lercanidipine. These results suggest a direct antiatherosclerotic effect of lercanidipine, independent of modulation of risk factors such as hypercholesterolemia and/or hypertension as demonstrated by the absence of stereoselectivity.

Concentration of endogenous tPA antigen in coronary artery disease: relation to thrombotic events, aspirin treatment, hyperlipidemia, and multivessel disease

Tissue plasminogen activator (tPA) is the major plasminogen activator responsible for dissolving blood clots found in blood vessels. However, elevated concentrations of tPA antigen were found to be related to adverse events in patients with coronary artery disease (CAD). Considerable controversy about the significance of these results exists. The goal of this cross-sectional study was to identify independent determinants for tPA antigen concentrations in patients with CAD, to possibly clarify the above paradoxical relationship. The baseline tPA antigen concentrations of 366 patients with angiographic evidence of coronary sclerosis were determined. Univariate analysis showed that age (P=0.013), angiographic extent of disease (P<0.001), presence of angina at rest (P<0.001), diabetes mellitus (P=0.004), hypercholesterolemia (P=0. 045), hypertriglyceridemia (P=0.015), and chronic intake of nitrates (P<0.001) were significantly and positively related to tPA antigen concentration, while the chronic intake of aspirin was inversely related to tPA antigen (P<0.001). In addition, plasminogen activator inhibitor type 1 (PAI-1) activity was found to be significantly and positively associated with tPA antigen concentration (P<0.001). A multivariate analysis identified chronic low-dose aspirin therapy (P<0.001), PAI-1 activity (P<0.001), hypertriglyceridemia (P=0.005), the type of angina (P=0.026), multivessel disease (P=0.041), and hypercholesterolemia (P=0.043) as significant and independent determinants of tPA antigen. While hypertriglyceridemia and hypercholesterolemia both are related to the underlying disease, the type of angina and the number of involved vessels are linked to the severity and extent of disease, and all of them are indicators of a prothrombotic state found during the progression of CAD. In contrary, low-dose aspirin rather would decrease the likelihood of thrombotic events. The relation of tPA antigen to PAI-1 activity furthermore underlines the relation between tPA antigen concentration and a prothrombotic state. Therefore, the positive or-in case of aspirin therapy-negative correlation of these parameters with tPA antigen concentration would indicate that thrombus formation and simultaneous endothelial cell activation might be major determinants for tPA antigen concentration in CAD.

Direct vascular effects of HMG-CoA reductase inhibitors

Several studies have demonstrated that any beneficial effect of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) on coronary events are linked to their hypocholesterolemic properties. However, since mevalonic acid (MVA), the product of the enzyme reaction, is the precursor of numerous metabolites, inhibition of HMG-CoA reductase has the potential to result in pleiotropic effects. MVA and other intermediates of cholesterol synthesis (isoprenoids) are necessary for cell proliferation and other important cell functions, hence effects other than cholesterol reduction may help to explain the antiatherosclerotic properties of statins. Recently, we provided in vitro evidence that fluvastatin, simvastatin, lovastatin, cerivastatin, but not pravastatin, dose-dependently decrease smooth muscle cells (SMC) migration and proliferation, independently of their ability to reduce plasma cholesterol. Moreover, statins are able to reduce the in vitro cholesterol accumulation in macrophages, by blocking cholesterol esterification and endocytosis of modified lipoproteins. This in vitro inhibition was completely prevented by the addition of mevalonate and partially by all-trans farnesol and all-trans geranylgeraniol, confirming the specific role of isoprenoid metabolites--probably through a prenylated protein(s)--in regulating these cellular events. The inhibitory effect of lipophilic statins on SMC proliferation has been recently shown in different models of proliferating cells such as cultured arterial myocytes and rapidly proliferating carotid and femoral intimal lesions in rabbits. Finally, ex vivo studies recently showed that sera from fluvastatin-treated patients interfere with smooth muscle cell proliferation. These results suggest that HMG-CoA reductase inhibitors exert a direct antiatherosclerotic effect in the arterial wall, beyond their effects on plasma lipids, that could translate into a more significant prevention of cardiovascular disease.

Impact of a combination of a calcium antagonist and a beta-blocker on cell- and copper-mediated oxidation of LDL and on the accumulation and efflux of cholesterol in human macrophages and murine J774 cells

Calcium antagonists and beta-blockers may retard or inhibit atherogenesis. In the absence of data pertaining to the potential cardioprotective action of an association of such agents, we have investigated the impact of nifedipine and atenolol, alone or in combination, on the capacity of monocyte-macrophages (ex vivo) and copper ions (in vitro) to oxidize LDL and on intracellular metabolism and efflux of free and esterified forms of cholesterol in human macrophages and foam cells. At concentrations up to 100 micromol/L, atenolol had no effect on the oxidative resistance of LDL; on the contrary, nifedipine displayed a significant dose-dependent capacity to protect LDL during copper-mediated oxidation (100 micromol/L; P<.001). Using a DPPH radical generating system, nifedipine was shown to exert free radical-trapping activity (molar ratio of scavenging activity, nifedipine:alpha-tocopherol, 1:114). The addition of atenolol to nifedipine was without effect on the antioxidant activity of the calcium antagonist. In experiments in which oxidative modification was mediated by monocyte-macrophages, nifedipine but not atenolol conserved its antioxidant capacity. Furthermore, we demonstrated that association of atenolol with nifedipine did not modify the antioxidant properties of nifedipine itself. Using a human monocyte-derived macrophage culture system, nifedipine, atenolol, or a combination of the two drugs was ineffective in inhibiting foam cell formation induced by acetylated LDL or oxidized LDL. However, atenolol (100 micromol/L) increased cellular accumulation of cholesteryl ester (+17%; P<.05), whereas nifedipine (100 micromol/L) decreased total cholesterol (-37.4%; P<.05) accumulation induced by acetylated LDL in the mouse macrophage cell line J774. A combination of the two drugs neutralized these antagonistic effects. None of these results were reproduced during the oxidized LDL-induced transformation of murine J774 cells into foam cells. Furthermore, cholesterol efflux from preloaded human macrophages was equally unaffected by the addition of the drugs alone or in combination. It therefore seems unlikely that the beneficial effect of atenolol on coronary heart disease is mediated by changes in either LDL oxidizability or cholesterol metabolism in human macrophages and foam cells. Our findings with nifedipine suggest, however, that this calcium antagonist may potentially exert antiatherosclerotic properties via a reduction of the oxidative modification of LDL, thereby affecting a reduction in foam cell formation and in the pathophysiological cellular activities of oxidized lipids, rather than by inducing a direct reduction in cholesterol accumulation in human foam cells of macrophage origin.

Homocysteine--an atherogenic and a thrombogenic factor?

A recent study found that hyperhomocysteinemia is associated with an increased risk of extracranial carotid artery stenosis, while another study demonstrated that hyperhomocysteinemia is a common risk factor for recurrent venous thrombosis. It seems as if an elevated circulating homocysteine is atherogenic as well as thrombogenic, possibly indicating extensive involvement of homocysteine in the pathogenesis of coronary heart disease.

Previous aspirin use may attenuate the severity of the manifestation of acute ischemic syndromes

BACKGROUND

The present study was designed to investigate whether the prior use of aspirin could influence the severity of the manifestation of acute coronary artery syndromes, given the well-documented observations that aspirin can prevent myocardial infarction, stroke, and death in cardiovascular disease.

METHODS AND RESULTS

A series of 539 consecutive patients admitted to the Coronary Care Unit of a General Hospital was carefully characterized in a study with an ambidirectional design, with regard to previous medical history, aspirin use, and subsequent hospital diagnosis. Among the 214 patients previously taking aspirin, the hospital diagnosis was myocardial infarction in 24% and unstable angina in 76% compared with 54% and 46%, respectively, among the 325 not taking aspirin (P < .0001), for a reduction in the odds ratio of myocardial infarction with aspirin of 72% (95% CI, 59% to 90%). The decrease in odds was homogeneous in all subsets studied and independent of age, sex, previous angina, or previous myocardial infarction. The myocardial infarction was of a Q-wave type in 62% of aspirin users compared with 76% of nonusers (P < .05). By multivariate analysis, previous aspirin use was a strong predictor of unstable angina versus myocardial infarction and the only independent predictor of non-Q-wave versus Q-wave myocardial infarction.

CONCLUSIONS

This study, thus, suggests a shift to less severe manifestation of acute coronary syndromes with aspirin use, implying that the failure of the drug in many patients with an acute coronary syndrome is only partial and that aspirin has the potential of attenuating the severity of the underlying acute thrombotic disease process.

New approaches to the prevention of atherosclerosis

In recent years, remarkable progress has been made in the prevention and treatment of atherosclerosis. However, much of the research has been devoted to the investigation of lipid metabolism and lipid-lowering drugs. This review highlights some recent topics in both experimental and clinical investigations, with emphasis on studies other than those on lipid-lowering drugs. These topics include oxidative modification of lipoproteins, hyperfibrinogenaemia, hyperhomocysteinaemia, female sex hormones and endothelium-derived relaxing factor (or nitric oxide). Some of these approaches have already been applied in the clinic.

Comparable beneficial effects of defibrotide and nifedipine in calcium induced atherosclerosis

The present study demonstrates the antiatherosclerotic property of Defibrotide (DFT) in an experimental model in which the pathology is secondary to calcium deposition in the vessel wall and various organs. Rats were treated by gavage for 21 consecutive days with Vitamin D3 and/or, twice a day, with DFT or Nifedipine (N). The calcium contents of aorta, heart and kidney were determined by atomic absorption spectrometry. Specimens of these tissues were examined histologically. DFT or N administered alone did not modify the calcium contents of aorta, heart or kidney. On the contrary, Vitamin D3 caused a huge increase in the calcium concentration in the aorta and in the kidney, whereas the heart content was only double that of control animals. In rats treated with Vitamin D3, contemporaneous administration of DFT or N sharply and highly significantly reduced the aorta calcium concentration and there were less striking, although still significant, reductions in the other two tissues. Histological examination paralleled these data; the effect of DFT or N in reducing the mineralization of aorta and heart was very evident, and more pronounced for DFT. These results confirm that DFT, even though not belonging to the class of the calcium antagonists, has comparable antiatherosclerotic properties, possibly due to its endothelial protective efficacy, as evidenced by the lesser amount of calcium in the aortic tissue.