Role of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitors, angiotensin-converting enzyme inhibitors, cyclooxygenase-2 inhibitors, and aspirin in anti-inflammatory and immunomodulatory treatment of cardiovascular diseases

Role of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Inhibitors, Angiotensin-Converting Enzyme Inhibitors, Cyclooxygenase-2 Inhibitors, and Aspirin in Anti-Inflammatory and Immunomodulatory Treatment of Cardiovascular Diseases Bernhard Schieffer,

MD,

and Helmut Drexler,

MD

The immunologic response in atherosclerosis involves not only intrinsic cells of the artery wall, but also circulating leukocytes, lymphocytes, and macrophages. Interaction of various arms of the immune response modulates plaque development and stability, and it is conceivable that immunologic effects of some cardiovascular therapies may contribute to their mechanism of benefit. The preponderance of data has accrued with the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins). Statin effects, such as inhibition of T cell activation, tissue factor expression, or reduction of platelet hyperreactivity, may elicit beneficial effects in vitro and in vivo in patients with coronary artery disease. Moreover, aspirin may limit oxidation of lipoproteins and fibrinogen, and it may inhibit cytokine-induced nitric oxide synthase II expression. The hypothesis that

selective inhibition of cyclooxygenase-2 (COX-2) may increase risk of myocardial infarction is controversial and may also be of questionable clinical significance. Finally, angiotensin-converting enzyme (ACE) inhibitors not only reduce proinflammatory mediators, such as interleukin-6, but also enhance the concentration of anti-inflammatory cytokines, such as interleukin-10. Because ACE is expressed at the shoulder region of atherosclerotic plaques, and ACE activity is enhanced in unstable plaques, ACE inhibition may also contribute to plaque stability. This article reviews the potential immunomodulatory potencies of aspirin, COX-2 inhibitors, statins, and ACE inhibitors as established pharmacotherapy in patients with coronary artery disease. 䊚2003 by Excerpta Medica, Inc. Am J Cardiol 2003;91(suppl):12H–18H

therosclerosis is a chronic inflammatory disease that is initiated and perpetuated by cross-talk A between shared pathways of adaptive and innate im-

cular biomechanics and oxidative stress. This combined immune/inflammatory response involves endothelial and smooth muscle cells and the accumulation of lipids and fibrous materials in atheromatous plaques of the vessel wall. Moreover, this inflammatory response involves not only intrinsic cells of the artery wall but also requires the recruitment of circulating leukocytes, lymphocytes, and macrophages into the vessel wall (Figure 1). Because plaque composition and vulnerability have emerged as more critical determinants of plaque rupture than the degree of luminal stenosis, the interaction of various arms of the immune response predicts the perpetuation of atherosclerosis and the stability of atherosclerotic plaques (Figure 1). In the future, enhanced understanding of these processes may provide new targets for pharmacologic treatment. Suppressing ⱖ1 components of the immune or inflammatory systems may contribute to reduction in cardiovascular risk. Therefore, the present review will discuss the potential immunomodulatory potencies of aspirin, cyclooxygenase-2 (COX-2) inhibitors, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins), and angiotensin-converting enzyme (ACE) inhibitors as established pharmacotherapy in patients with coronary artery disease.

munity. First, components of the innate immunity (phagocytic leukocytes, activated complement, and proinflammatory cytokines) are rapidly mobilized. Later on, adaptive immunity (involving T cells, antibody formation, and immunoregulatory cytokines) modulates disease activity and progression. Immune processes can further influence the balance between cell proliferation and apoptosis, between synthetic and degradative processes (ie, matrix metalloproteases and their tissue inhibitors), and between prothrombotic and antithrombotic processes. Risk factors such as lipoproteins and their oxidized products modulate aspects of immune response, whereas risk factors such as hypertension and cigarette smoking modulate vasFrom the Department of Cardiology and Angiology, Medizinische Hochschule, Hannover, Germany. This work was supported by a grant from the Leducq Foundation and by Grant No. SFB566/B9 from the Deutsche Forschungsgemeinschaft. Address for reprints: Bernhard Schieffer, MD, Department of Cardiology and Angiology, Medizinische Hochschule Hannover, Carl Neuberg Strasse 1, 30625 Hannover, Germany. E-mail: [email protected].

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©2003 by Excerpta Medica, Inc. All rights reserved.

0002-9149/03/$ – see front matter doi:10.1016/S0002-9149(03)00429-6

FIGURE 1. Immunomodulatory effects of chemokines, cytokines, and angiotensin II, the effector peptide of the renin-angiotensin system. MMP ⴝ matrix metalloproteinases; TIMP ⴝ tissue inhibitor of metalloproteinase.

IMMUNOMODULATORY POTENCIES OF ASPIRIN Salicylates in the form of willow bark have been used as an analgesic and antipyretic drugs since the time of Hippocrates, but their antiplatelet and antiinflammatory potency was not detected until the mid 20th century.1,2 Aspirin exerts its effect primarily by interfering with the biosynthesis of cyclic prostanoids (ie, thromboxane A2, prostacyclin, and other prostaglandins [PGs]).3 These proinflammatory and proaggregatory prostanoids are generated by the enzymatically catalyzed oxidation of arachidonic acid, which is itself derived from membrane phospholipids. Arachidonic acid is metabolized by the enzyme PGH synthase (also known as COX), which, through its COX and peroxidase activities, results in the production of PGG2 and PGH2, respectively.4,5 PGH2 is then modified by specific synthases to PGD2, PGE2, PGF2, PGI2 (prostacyclin), and thromboxane A2, all of which mediate specific cellular functions. The 2 COX isoforms (COX-1 and COX-2), characterized by a single amino acid substitution in the catalytic site of the enzyme, have been identified. Whereas COX-1 is constitutively expressed in most cells and induces the synthesis of homeostatic PGs responsible for normal cellular functions, COX-2 is rapidly induced by inflammatory stimuli and growth factors.6,7 COX-2 activation results in the production of PGs that contribute to the inflammatory response. Aspirin exerts its primary antithrombotic effects through the inhibition of COX by the irreversible acetylation of a specific serine moiety (serine 530 of COX-1 and serine 516 of COX-2) and is 170-fold more potent in inhibiting COX-1 than COX-2.8,9 In the presence of aspirin, neither affected isoform is capable of converting arachidonic acid to PGH2, a necessary step in the production of prostanoids.10 –12 COX-1 is completely inactivated, and COX-2 converts arachidonic acid not to PGH2 but to 15-R-hydroxyeicosatetraenoic acid. The resultant decreased

production of PGs and thromboxane A2 likely accounts for the antiaggregatory and anti-inflammatory effects of aspirin.13 However, additional mechanisms for platelet inhibition by aspirin have been proposed, which include (1) inhibition of platelet activation by neutrophils, an effect that appears to be mediated by a nitric oxide/cyclic guanosine monophosphate– dependent process; or (2) inhibition of prostacyclin synthesis in endothelial cells, which enhances nitric oxide production. Moreover, other mechanisms may contribute to the clinical benefits and anti-inflammatory potency of aspirin in the treatment of cardiovascular disorders. Aspirin may help to decrease the progression of atherosclerosis by protecting low-density lipoprotein from oxidative modification and also by improving endothelial function in atherosclerotic vessels.14 Furthermore, aspirin has been shown to inhibit cytokine-dependent induction of nitric oxide synthase II gene expression, perhaps through a mechanism involving nuclear factor-␬B activation, an effect that may decrease nitrosative stress that accompanies cytokine elaboration.14 –20 Aspirin can also directly scavenge hydroxyl radicals to form the 2,3- and 2,5-dihydroxybenzoate derivatives, which themselves do the following: (1) serve as markers of oxidative stress, (2) quench oxy-radical flux, and (3) acetylate amino groups of lysine residues in proteins, which prevents their oxidation.21,22 This antioxidant effect on proteins may be important in limiting both lipoprotein and fibrinogen oxidation; in the latter case, oxidation enhances fibrin formation, and lysine acetylation enhances fibrinolysis.23,24 Thus, aspirin is likely to reduce the inflammatory response in patients with coronary artery disease in a dose-dependent manner. In this regard, 2 large-scale randomized trials of aspirin for the primary prevention of cardiovascular events (the Physicians’ Health Study25 and the British Physicians’ Study26) showed no significant differences in the incidence of myocardial infarction, but they showed a significant increase

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in disabling strokes.25–28 Combined analyses of these results demonstrated a significant 33% treatment-related reduction in nonfatal myocardial infarction but still failed to show a decrease in mortality. These beneficial effects are currently linked to suppression of thromboxane A2– dependent platelet aggregation.29 This in turn reflects permanent loss of the cyclooxygenase activity of platelet PG G/H synthase, through acetylation of serine 530.30

SELECTIVE INHIBITION OF CYCLOOXYGENASE COX is the key enzyme in the synthesis of PGs from arachidonic acid. A role for COX-2 was suggested in both inflammation and cell growth because stimuli (including proinflammatory cytokines and growth factors) enhance COX-2 expression. The discovery of COX-2 has enabled the design of drugs that reduce inflammation without removing the protective PGs generated via COX-1.12 These highly selective COX-2 inhibitors may not only be anti-inflammatory but may also be active in colon cancer and Alzheimer disease. However, first-generation selective COX-2 inhibitors came from animal models in which compounds were sought that were potent anti-inflammatory agents with minimal side effects on the stomach. Nimesulide, etodolac, and meloxicam were discovered, and all were selective for COX-2 rather than COX-1. Other anti-inflammatory COX-2 inhibitors are in clinical development or in phase 3 clinical trials for rheumatoid arthritis and osteoarthritis. Drugs like celecoxib and meloxicam are reported to be effective against inflammation and to cause no gastrointestinal or renal problems.31,32 Celecoxib and meloxicam are also effective analgesics for moderate-to-severe pain in humans after oral surgery. Moreover, the selective COX-2 inhibitors elicit effective antipyretic activity within the anti-inflammatory dose range in animal models. Concerns that selective COX-2 inhibitors may be prothrombotic and increase the risk of myocardial infarction12 are based largely on the unexpected finding in a study of the gastrointestinal tolerability of these drugs. Patients receiving rofecoxib had a higher rate of myocardial infarction compared with patients receiving naproxen. The results of this study and data obtained from a meta-analysis of aspirin primaryprevention trials suggest that differences in the rates of myocardial infarction between rofecoxib and naproxen may have been because of an unexpectedly low rate of myocardial infarction in patients receiving naproxen.33,34 However, the magnitude of this increase in risk, if real, is uncertain, but it is likely to be relatively small in patients for whom cardiovascular prophylaxis with aspirin is not indicated. Patients who require nonsteroidal anti-inflammatory therapy for arthritis and who are at high risk of cardiovascular disease should receive aspirin in conjunction with selective COX-2 inhibitor therapy to minimize the risk of gastrointestinal ulceration. In patients who do not require aspirin for the prevention of cardiovascular events, the lower risk of gastrointestinal ulceration 14H THE AMERICAN JOURNAL OF CARDIOLOGY姞

associated with COX-2 inhibitor therapy compared with nonselective nonsteroidal anti-inflammatory drugs would be expected to outweigh any increase in the risk of myocardial infarction, if risk exists. A study by Altman et al35 tested the hypothesis that the combination of meloxicam plus heparin and aspirin would be superior to heparin and aspirin alone. In an open-label, randomized, prospective, single-blind pilot study, patients with acute coronary syndromes without ST-segment elevation were randomized during their coronary care unit stay to either of the following groups: (1) aspirin plus heparin treatment, or (2) aspirin, heparin, and meloxicam. Patients then received aspirin or aspirin plus meloxicam for 30 days. During the coronary care unit stay, the primary outcomes variable of recurrent angina, myocardial infarction, or death was significantly lower in patients receiving meloxicam. The second composite variable of coronary revascularization procedures, myocardial infarction, and death was also significantly lower in meloxicam-treated patients. More interestingly, no adverse complications associated with the meloxicam treatment were observed. Thus, selective COX-2 inhibition by meloxicam in combination with heparin and aspirin was associated with significant reductions in adverse outcomes in patients with acute coronary syndromes without ST-segment elevation. However, additional larger trials are needed to confirm these findings. Finally, other possible and fatal side effects reported from animal studies show that COX-2 inhibitors might elicit defects in fetal development or suppress female fertility. Although it could be argued that most female patients with rheumatoid arthritis and cardiovascular events are postmenopausal and thus at no real risk, some evaluation of potential risk in other possible uses, such as postoperative analgesia and the prevention of cardiovascular events in premenopausal female patients, should be considered.

IMMUNOMODULATORY EFFECTS OF STATINS Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (statins) constitute the most powerful class of lipid-lowering drugs available. Statins exert their action by inhibiting conversion of 3-hydroxy-3-methylglutaryl coenzyme A into mevalonate, the rate-limiting step in cholesterol synthesis.36 However, statins additionally inhibit the synthesis of a variety of compounds, including isoprenoids derived from the mevalonate pathway, which are involved in a number of important biologic processes in all types of cells.37 Changes in the levels of these compounds could be responsible for the effects of statins beyond their lipid-lowering effects.38,39 During the past several years, additional actions of statins unrelated to cholesterol reduction have been identified, including anti-inflammatory and immunomodulatory properties. Because atherosclerosis is a form of inflammation and the immune system plays an important role in its pathogenesis, pleiotropic effects of statins may pro-

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vide a complementary explanation to their clinical benefit.40 Major histocompatibility complex class II (MHCII) molecules are directly involved in the activation of T lymphocytes and in the control of the immune response. Whereas only a limited number of specialized cell types express MHC-II constitutively, numerous other cells become MHC-II positive upon induction by interferon-␥.41 Statins act as direct inhibitors of induction of MHC-II expression by interferon-␥ and thus as repressors of MHC-II–mediated T cell activation. This effect was observed in several cell types, including primary human endothelial cells and macrophages. Interestingly, this inhibition is specific for inducible MHC-II expression and does not concern either constitutive expression of MHC-II or expression of MHC-I. In repressing induction of MHC-II and subsequent T lymphocyte activation, statins therefore behave as a novel type of immunomodulator. This unexpected effect provides a scientific rationale for suggesting the use of statins as novel immunosuppressors.41 A significant percentage of patients with a selective increase in plasma low-density lipoprotein cholesterol (type IIa hyperlipoproteinemia) exhibit increased platelet reactivity.42,43 This includes enhanced platelet responsiveness against a variety of platelet-stimulating agents ex vivo and enhanced arachidonic acid metabolism associated with increased generation of arachidonic acid metabolites (thromboxane A2, 12hydroxyeicosatetraenoic acid) and secretion of platelet-storage products. It is possible that elevated cholesterol content in the platelet membranes forms a common denominator for these responses. Agents that lower total plasma or low-density lipoprotein cholesterol in hypercholesterolemic patients by interfering with cholesterol reabsorption from the gut (eg, cholestyramine, colestipol) or reduction of hepatic verylow-density lipoprotein release (eg, fibrates) do not appear to interfere with platelet hyperreactivity and do not change platelet-derived thromboxane formation.43 There is also no correlation with the action of these agents on total plasma and low-density lipoprotein cholesterol. A different situation might exist with inhibitors of the 3-hydroxy-3-methylglutaryl coenzyme A reductase, which have been found to reduce platelet hyperreactivity and thromboxane formation.42,43 However, there is increasing evidence that patients with type II hyperlipoproteinemia have a significantly (by about 50%) reduced number of specific prostacyclin-binding sites at the platelet membrane that might be involved in the reduced inhibition of platelet function by prostacyclin.43 Normalization of the reduced responsiveness against prostacyclin has also been demonstrated for statins.42,43 Many investigators have focused on the potential antithrombotic effect of statins. Hypercholesterolemia is associated with a prothrombotic state; thus, it is not surprising that effective antilipemic agents, such as statins, may attenuate thrombogenic potential. However, clinical and experimental data suggest that statins may exert antithrombotic effects independent of

cholesterol reduction.44 Statins inhibit tissue factor expression by macrophages through isoprenoid depletion and prevent the activation of nuclear factor-␬B.45 In addition, statins also prevent the downregulation of nitric oxide synthase induced by oxidized lipoproteins.46,47 The latter may represent a mechanism by which statins not only improve endothelial function and reduce oxidative stress, but it also may represent a novel pathway for the attenuation of platelet aggregation. Finally, the antithrombotic effects of statins also include their ability to promote fibrinolysis. Statins promote tissue plasminogen activator synthesis and reduce plasminogen activator inhibitor-1, resulting in increased fibrinolytic activity. These effects are independent of cholesterol levels and are related to the inhibition of the isoprenylation of Rho proteins.48 Moreover, the important role of inflammation in the genesis of atherosclerotic lesions has been fully recognized during the past decade. Several reports have linked inflammation markers to cardiovascular risk, particularly C-reactive protein. Recent studies have suggested that statins may have anti-inflammatory properties.49 In some studies, C-reactive protein reduction in the statin group was not related to the magnitude of lipid alterations during treatment, suggesting a direct anti-inflammatory effect of statins. These actions may help to stabilize the plaque and reduce the risk of acute coronary syndromes. In vitro observations of the anti-inflammatory action of statins on vascular and nonvascular cells also suggest some direct beneficial effects beyond lipid reduction. In several experimental models, statins inhibited activation of nuclear factor-␬B, a pivotal transcription factor regulating the expression of a variety of inflammatory genes.46 Inhibition of nuclear factor-␬B activation could explain the reduced synthesis of inflammatory cytokines (eg, interleukin-6) under these in vitro conditions. Signaling molecules (eg, small guanosine triphosphate– binding proteins, such as Rac, which translocate to the cell membrane) are involved in the cellular oxidative response and couple to the phospholipid cell membrane layer by isoprenylation. Because Rac is involved in nuclear factor-␬B activation and statins inhibit Rac membrane translocation, it is possible that via this mechanism statins abolish nuclear factor-␬B activation. Moreover, the synthesis of C-reactive protein in the liver is stimulated by interleukin-6, and preliminary data indicate that statin treatment interferes with low-density lipoprotein–stimulated interleukin-6 expression in human mesangial cells.50 Beneficial immunomodulatory effects of statins were reported in 2 studies demonstrating that statin administration after cardiac transplantation reduced the incidence of acute rejection and coronary vasculopathy.51,52 Among the many possible explanations, these effects may be because of the inhibiting actions of statins on the recruitment and activation of immune-competent cells. As discussed earlier in this article, in vitro studies demonstrate that statins exert inhibitory effects on several functions in immunecompetent cells, such as inhibition of expression of

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MHC-II molecules. However, animal and human data demonstrated that statin therapy by itself does not appear to affect immune function; in fact, the coadministration of cyclosporin A is necessary to observe immunomodulatory effects.51,52 In summary, statins modulate a variety of immunologic processes. These effects may contribute, along with cholesterol lowering, to the benefits of statins.

RENIN–ANGIOTENSIN SYSTEM AND IMMUNE MODULATION Activation of the renin–angiotensin system may exert numerous fatal effects on the cardiovascular system (ie, in atherosclerosis and arterial hypertension).53–55 Traditionally, the renin–angiotensin system has been described as an endocrine system in which renin of renal origin acts on angiotensinogen (an acute phase protein) of hepatic origin to produce angiotensin I in the plasma, which in turn is converted by pulmonary endothelial ACE to angiotensin II.56 Angiotensin II is considered to be the main mediator of the physiologic actions of the renin–angiotensin system. More recently, the importance of local tissue renin–angiotensin system57; of other angiotensin peptides in addition to angiotensin II, such as angiotensin III, IV, and angiotensin-(1-7)58; and of the interaction with other systems, such as the endogenous kallikrein– kininogen– kinin system,57,59 have been established. It has also recognized that although most actions of angiotensin II are exerted through angiotensin II type 1 receptors,60 other specific cell surface receptors, including angiotensin II type 2,61 angiotensin II type 4,62 and angiotensin-(1-7),58 are involved in the actions of angiotensin peptides. The effects of angiotensin II include the following: (1) vasoconstriction; (2) vascular smooth muscle cell migration, proliferation, and hypertrophy; (3) increased extracellular matrix formation; (4) release of thromboxane A2; and (5) enhanced matrix metalloproteinase production. More recent findings show (1) effects on plasminogen activator inhibitor–1 synthesis62; (2) activation of nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate oxidases63,64; and (3) release of mediators of inflammation, such as interleukin-6.65 Clinical consequences of these effects include an increase in blood pressure, myocardial and vascular hypertrophy and remodeling, and potential plaque growth and rupture. However, the question remains: do ACE inhibitors elicit direct antiinflammatory and immunomodulatory effects? Traditionally, ACE inhibitors elicit their effects by inhibiting conversion of angiotensin I to angiotensin II. In addition, ACE inhibitors decrease the breakdown of bradykinin. Bradykinin acts on endothelial cells, leading to the release of nitric oxide, PGs (eg, prostacyclin), and endothelium-derived hyperpolarizing factor; bradykinin causes vasodilation, enhanced endogenous fibrinolysis, and improved endothelial function.59 Thus, an improved microcirculation and regional perfusion may blunt the local accumulation and action of proinflammatory mediators, such as chemokines and cytokines. On the other hand, recent in 16H THE AMERICAN JOURNAL OF CARDIOLOGY姞

vitro studies indicate that angiotensin II may directly enhance synthesis and release of proinflammatory cytokines, especially interleukin-6.65 The latter can be blunted in vitro by ACE inhibition.66 Because interleukin-6 mediates B-cell maturation, complement activation, and cytokine release,66 ACE inhibitors may elicit their immunomodulatory potencies via the suppression of proinflammatory cytokines. Moreover, in vitro analysis revealed that ACE is expressed at the shoulder region of atherosclerotic plaques in areas of clustered macrophages close to interleukin-6.66,67 Because ACE activity is enhanced in human unstable plaques compared with stable atherosclerotic lesions68 –70 and interleukin-6 induces metalloprotease activation,71 blockade of angiotensin II formation by ACE inhibition may have plaque-stabilizing as well as anti-inflammatory and immunomodulatory effects. Given the proinflammatory pathophysiology of atherosclerosis53,54 and the potential anti-inflammatory potency of ACE inhibition, ACE inhibitors would be expected to reduce the risk of acute coronary events. Large-scale clinical trials reported that administration of ACE inhibitors after myocardial infarction or in patients with documented coronary artery disease reduced not only the cumulative incidence of heart failure but also the incidence of cardiovascular events, such as stroke, unstable angina, or myocardial infarction.72–76 The Heart Outcomes and Prevention Evaluation (HOPE) study77 convincingly demonstrated that chronic ACE inhibition abolished cardiovascular events (eg, unstable angina, myocardial infarction, or stroke) in patients with severe atherosclerosis. The underlying mechanisms were, at least in part, caused by a direct interaction of components of the renin– angiotensin system with inflammatory cytokines, such as interleukin-6.66 Importantly, interleukin-6 serum levels were shown to be elevated in patients with unstable angina and have been implicated in the prognosis of patients with acute coronary events.78 Although such a relation has not been reported for other cytokines (eg, tumor necrosis factor-␣ or interleukin-1␤), the pathophysiologic role for interleukin-6 and its negative regulator interleukin-10 may be of particular pathophysiologic and therapeutic interest. We have demonstrated that ACE inhibitors not only reduce proinflammatory mediators but also enhance the concentration of antiinflammatory cytokines, such as interleukin-10,79 suggesting a direct anti-inflammatory potency of ACE inhibitors in patients as previously found in several animal models of atherosclerosis.80 – 82 Together, these observations are consistent with the notion that ACE inhibitors elicit anti-inflammatory and immunomodulatory effects that may contribute to plaque passivation and regression of atherosclerosis.

CONCLUSION Cardiovascular events may be prevented by the established cardiovascular pharmacotherapy consisting of aspirin, statins, and ACE inhibitors. Anti-inflammatory and immunomodulatory potencies, including cytokine or chemokine suppression, modula-

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