Inflammation And Accelerated Atherosclerosis- Basic Mechanisms

Rheum Dis Clin N Am 31 (2005) 355 – 362

Inflammation and Accelerated Atherosclerosis: Basic Mechanisms Andrea Doria, MDa, Yaniv Sherer, MDb, Pier L. Meroni, MDc, Yehuda Shoenfeld, MDb,* a

Division of Rheumatology, Department of Medical and Surgical Science, University of Padua, Via Guistiniani 2, 35128 Padua, Italy b Department of Medicine B, Sackler Faculty of Medicine, Center for Autoimmune Diseases, Chaim Sheba Medical Center, Tel-Aviv University, Tel-Hashomer 52621, Israel c Allergy and Clinical Immunology Unit, Department of Internal Medicine, IRCCS Istituto Auxologico Italiano, University of Milan, Via G. Spagoletto 32, 10249 Milan, Italy

The last decade was characterized by a revolution achieved in the therapy of many of the autoimmune rheumatic diseases (AIRDs), leading to decreased morbidity and mortality. The dramatic change was caused by the more efficient use of existing therapies or the use of novel biological agents including anticytokine monoclonal antibodies, fusion molecules, and peptides having neutralizing and immunomodulatory effects. These approaches enabled reduction in the doses of corticosteroids and immunosuppressants used, drugs associated with major and severe adverse effects. With these changes, novel factors have emerged determining the prognosis of AIRD. One of those factors is the accelerated atherosclerosis (AS) recorded in almost all AIRDs (ie, systemic lupus erythematosus [SLE], rheumatoid arthritis, Sjogren’s syndrome, systemic sclerosis, and vasculitis). Another aspect unraveled during the previous decade is the autoimmune nature of AS [1–4]. Atherosclerosis is a multifactorial process that commences as early as childhood but usually clinically manifests itself later in life. Atherosclerosis increasingly is considered to be an immune-mediated process of the vascular

* Corresponding author. E-mail address: [email protected] (Y. Shoenfeld). 0889-857X/05/$ – see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.rdc.2005.01.006 rheumatic.theclinics.com

356

doria et al

system. The presence of macrophages and activated lymphocytes within atherosclerotic plaques supports the concept of AS as an immuno-mediated inflammatory disorder [5]. Inflammation can be implicated in AS by means of different mechanisms, such as secondary to autoimmunity, infectious diseases and general inflammatory state. This article summarizes knowledge of the pathogenic mechanisms in AIRD as risk factors for accelerated AS.

Immune cellular components in atherosclerosis Cells of the immune system can be found within AS plaques, suggesting that they have a role in the atherogenic process. Their migration and activation within the plaques can be secondary to various stimuli such as infectious agents. These cells probably aggravate AS, as CD4+ and CD8+ T-cell depletion reduced fatty streak formation in C57BL/6 mice [6]. In addition, following crossing of ApoE knockout mice with immunodeficient scid/scid mice, the offspring had a 73% reduction in aortic fatty streak lesions compared with the immunocompetent apoE mice. Moreover, when CD4+ T cells were transferred from the immunocompetent to the immunodeficient mice, they increased lesion area in the latter by 164% [7]. Associated findings were infiltration of the transferred T cells into the atherosclerotic lesions. It is not surprising therefore that similar to autoimmune diseases, the cellular components within atherosclerotic plaques secrete various cytokines including interleukin (IL)-1, IL-2, IL-6, IL-8, IL-12, IL-10, tumor necrosis factor alpha (TNF-a), interferon gamma (INF-g), and platelet-derived growth factor (PDGF) [4]. A cellular immune response specifically directed against heat shock proteins (HSPs), oxidized low-density lipoproteins (ox-LDL) and b2-glycoprotein-I (b2GPI) has been reported, suggesting a direct involvement of these molecules in the atherosclerotic process [1–3]. b2GPI is the main target antigen recognized by antiphospholipid antibodies (aPLs) frequently present in AIRD patients. It can be found in human atherosclerotic lesions obtained from carotid endarterectomies and expressed abundantly within the subendothelial regions and the intimal–medial border of human atherosclerotic plaques and colocalizing with CD4+ lymphocytes [8]. Upon transfer of lymphocytes obtained from b2GPI-immunized LDL receptor-deficient mice into syngeneic mice, the recipients exhibited larger fatty streaks compared with mice that received lymphocytes from control mice. T-cell depletion, however, failed to induce this effect [9]. Therefore, T cells specific for b2GPI are capable of increasing AS, suggesting that b2GPI is a target autoantigen in AS. This study demonstrates that T cells reacting with a specific autoantigen can aggravate AS. There are probably many more such cell lines reacting with specific antigens that can modulate AS, either by aggravating or decreasing its extent (pro- or antiatherogenic) [10].

inflammation

&

accelerated as: basic mechanisms

357

Immune humoral components in atherosclerosis Several autoantibodies are associated with AS and its manifestations in people. Animals provide good models for studying the effect of these autoantibodies on AS. Active immunization of LDL receptor-deficient mice with anticardiolipin antibodies (aCLs: the hallmark of antiphospholipid syndrome [APS], an autoimmune procoagulant syndrome that affects many SLE patients) resulted in development of high titers of mouse aCL and increased AS compared with controls [11]. Immunization of mice with b2GPI resulted in pronounced cellular and humoral response to b2GPI, with high titers of anti-b2GPI antibodies concomitant with larger atherosclerotic lesions that contained abundant CD4+ cells [12,13]. ox-LDL is the type of LDL that is more likely to undergo uptake by macrophages, which turn into the foam cells characterizing the atherosclerotic lesions. Anti-ox-LDL antibodies are present in patients with AS and AIRD and in healthy individuals [14]. In multivariate analyses, anti–ox-LDL autoantibodies discriminated better between patients with peripheral vascular disease and control subjects than did any of the different lipoprotein analyses. There was also a tendency for higher autoantibody levels in patients with more extensive atherosclerotic lesions [15]. The autoantibodies to ox-LDL were investigated in several AIRD groups, including patients with systemic sclerosis [16,17] systemic vasculitides [14,18], and SLE [17,18]. The antibody levels were higher in each of those patient groups than in normals. There was a correlation between the total level of immunoglobulins and the level of antibodies against ox-LDL, while no correlation was demonstrated between the levels of the total immunoglobulin and the levels of antibodies to unrelated antigens (Epstein Barr virus and purified protein derivative). This finding suggests that the increasing total immunoglobulin levels in SLE patients are selective for some specific antibodies including autoantibodies against ox-LDL [17,18]. Although in people these autoantibodies are associated with manifestations and extent of AS in most studies, immunization with ox-LDL in animal models was followed by induction of anti-ox-LDL antibodies but surprisingly with suppression rather than aggravation of early atherogenesis [19]. These results support the presence of different types of anti–ox-LDL antibodies, some of which might be protective against AS [20]. This also may be true regarding aCL, as in a recent study, those antibodies that cross-react with native and ox-LDL succeeded in decreasing rather than aggravating the extent of AS [21]. These discrepancies may be explained by the presence of several types of autoantibodies that are measured together, namely protective and pathogenic autoantibodies [20]. It is possible that upon immunization with ox-LDL, the immune system acts by producing anti–ox-LDL antibodies, which help to clear the high levels of ox-LDL, thus being protective. On the other hand, upon oxidation of LDL, other autoantibodies directed toward other parts of

358

doria et al

the ox-LDL particle are produced, and these aid in uptake of ox-LDL by macrophages, turning them into foam cells within the atherosclerotic plaque (ie, pathogenic).

Endothelium as an additional key player in atherosclerosis Two main pathogenic hypotheses have been suggested to explain the atherosclerotic plaque formation: the injury hypothesis and the lipid hypothesis [22]. In both cases, endothelium has been suggested to play a pivotal role in all the phases of the atherosclerotic process, given its ability to regulate vessel tone and interfere with inflammatory processes and coagulation [23]. In the early and intermediate stages, endothelial cells (ECs) activated by ox-LDL or other triggers up-regulate adhesion molecules, thereby favoring monocyte adhesion and transmigration. At the same time, EC perturbation leads to proinflammatory cytokine (chemokine) secretion, which activates monocytes and ultimately facilitates the foam cell formation [22]. When activated, ECs express class II major histocompatibility complex (MHC) molecules and might serve as nonprofessional antigen presenting cells (APCd) [24]. In this way, they might cooperate with the professional APC of the vascular-associated lymphoid tissue in mounting the adaptive immune responses to endogenous (eg, ox-LDL, HSP, or b2GPI) or exogenous (infectious antigens) molecules that have been proposed as playing a role in the early phases of the atherosclerotic process [1–3]. Endothelium activation appears also to be important in favoring fibroblast and smooth muscle cell proliferation and migration through the secretion of growth factors in the intermediate steps of plaque formation [22]. The same growth factors and the pro-inflammatory cytokines (and chemokines) themselves cooperate in macrophage activation with the consequent secretion of metalloproteases able to increase the matrix turnover and eventually lead to plaque instability [22]. The final event that produces the clinical cardiovascular manifestations is the plaque rupture and subsequent thrombus formation (atherothrombosis). Interestingly, EC are involved largely in hemostasis and, once perturbed, they display a procoagulant phenotype [23]. The up-regulation of tissue factor (TF) expression and the impairment of the fibrinolytic system in perturbed ECs have been suggested to play major roles in favoring the thrombus formation on the ruptured plaques [22]. On the other hand, in AIRD, endothelium itself is also a target for several circulating immune mediators that might induce a cell perturbation potentially able to facilitate the atherosclerotic process. Complement (C) activation by circulating immune complexes or by other mechanisms might induce endothelial damage by activated products of the C cascade or even the cell membrane insertion of the membrane attack complex (MAC). The latter phenomenon was reported to result in the release of an array

inflammation

&

accelerated as: basic mechanisms

359

of growth factors and cytokines that induces proliferation, inflammation, and thrombus formation in the vascular walls [25]. These events might cooperate in all the different steps of the atherosclerotic process. C deposition has been reported in the atherosclerotic lesions recently, raising its potential role in the plaque formation [26]. Antiendothelial cell antibodies (AECAs) reacting with yet unknown EC membrane constituents have been described in sera from different AIRD [27]. In most cases, AECAs were shown to induce a proinflammatory and a procoagulant phenotype in EC monolayers in vitro [27]. It is useful to speculate on the potential role of these autoantibodies in perturbing the endothelium, thus favoring the occurrence of the accelerated AS reported in AIRD. In accordance with such a hypothesis is the demonstration of AECA in primary AS or in patients displaying conditions at risk for AS [28–30]. Besides the pure antiendothelial antibodies, other autoantibodies have been reported to react with ECd because of their ability to recognize their own antigens planted on the EC membranes. This is the case for the anti-dsDNA antibodies that can react with DNA-histone complexes adhering on EC membranes through electric charge interactions [27,31]. The binding of anti-dsDNA antibodies to their own antigens adhered on the cell membranes has been shown to induce EC activation in vitro [27,31]. A similar effect has been described when aPL is incubated with human EC monolayers in vitro. Antiphospholipid antibodies react with plasma PL-binding proteins; among them the most important one is represented by b2GPI. b2GPI was found to be expressed on ECs obtained from different anatomical localizations in in vitro and in vivo studies. The binding of the autoantibodies to adhered b2GPI has been suggested to induce a cell signaling that ends with the expression of an endothelial proinflammatory and procoagulant phenotype. Interestingly, such an effect was reported in in vivo experimental models also, suggesting that it might be one of the actual pathogenic mechanisms for the thrombophilic state associated with the persistent presence of aPL [32]. Antiphospholipid antibodies frequently are detected in AIRD and might contribute to the plaque formation through their endothelial proinflammatory effect and to the athero-thrombosis, owing to their procoagulant ability. Moreover, most AIRDs are characterized by a chronic systemic inflammatory state with elevated plasma levels of proinflammatory cytokines and chemokines. As reported in patients with primary AS, a chronic inflammatory state is suggested to represent a risk factor for plaque formation and a condition that favors its instability and rupture [33]. Being in close contact with the blood and expressing specific cell membrane receptors, the endothelium represents one of the most available cell targets for the circulating cytokines. The final result is a further EC perturbation. In line with the endothelium perturbation mediated by several circulating immune mediators is the demonstration of an impaired endothelium-dependent vasodilation in AIRD patients [34]. Such impairment is related to the reduction in vasodilator bioavailability (mainly nitric oxide), and it has been associated with the propensity of an individual to develop atherosclerotic disease [34].

360

doria et al

Immunomodulation of atherosclerosis Several experimental studies emphasize that immunomodulation can affect AS and thus provide hope for the development of similar therapies for people. These options recently have been summarized [35]. Among them, several approaches have been shown to be effective: treatment with antibodies against CD40 ligand [36], induction of oral tolerance to autoantigens associated with AS [37], manipulation of the cytokine network in AS (upregulating the antiatherogenic cytokines and blockade of proatherogenic cytokines), and gene therapy [35]. There is also evidence for the use of statins and intravenous immunoglobulin (IVIg) as therapeutic tools to immunomodulate the atherosclerotic process [38,39]. Statins, beyond their ability to reduce serum cholesterol levels, display clear anti-inflammatory and immunomodulatory effects by reducing monocyte adhesion to EC and endothelial secretion of cytokines and MHC class II expression [38,40]. Intravenous immunoglobulins have many immunoregulatory and antiinflammatory properties and have shown the ability to reduce plaque development in a model of murine AS [41]. Looking at mechanisms specifically relevant in AS, it has been reported that IVIgs contain anti-idiotypic activity against anti– ox-LDL antibodies [42], and they are able to reduce metaloproteinase-9 (MMP-9) activity [39]; moreover IVIgs include a subset of natural antiendothelial antibodies that, opposite to pathologic AECA, directly modulate endothelial function, reducing proinflammatory and prothrombotic properties of resting EC and inhibiting cytokine and metalloprotease secretion by EC activated with proinflammatory stimuli [43]. Finally IVIgs reduce cytokine secretion and the membrane expression of adhesion molecules on EC stimulated with TNF-a and ox-LDL, and inhibit one of the pathways of internalization of ox-LDL in EC [44].

Summary The studies described in this article support a role for immunologic–inflammatory mechanisms in the pathogenesis of atherosclerosis. This immunologic–inflammatory state is evident in many autoimmune diseases, but also in the general population lacking an overt autoimmune disease. The ability to immunomodulate atherosclerosis (currently only experimental) should lead to future research into the mechanisms and treatment of atherosclerosis, the leading cause of death in the Western world.

References [1] Shoenfeld Y. Atherosclerosis and the immune system: is atherosclerosis an autoimmune disease? Seminars in Clinical Immunology 2000;1:5 – 6.

inflammation

&

accelerated as: basic mechanisms

361

[2] Shoenfeld Y, Sherer Y, Haratz D. Atherosclerosis as an infectious, inflammatory and autoimmune disease. Trends Immunol 2001;22:293 – 5. [3] Sherer Y, Shoenfeld Y. Atherosclerosis: is atherosclerosis a cellular or humoral mediated autoimmune disease? Ann Rheum Dis 2002;61:97 – 9. [4] George J, Harats D, Shoenfeld Y. Inflammatory and immune aspects of atherosclerosis. Isr Med Assoc J 1999;1:112 – 6. [5] Ross R. Atherosclerosis — an inflammatory condition. N Engl J Med 1999;340:115 – 26. [6] Emeson EE, Shen ML, Bell CG, et al. Inhibition of atherosclerosis in CD4 T-cell-depleted and nude (nu/nu) C57BL/6 hyperlipidemic mice. Am J Pathol 1996;149:675 – 85. [7] Zhou X, Nicoletti A, Elhage R, et al. Transfer of CD4 + T cells aggravates atherosclerosis in immunodeficient apolipoprotein E knockout mice. Circulation 2000;102:2919 – 22. [8] George J, Harats D, Gilburd B, et al. Immunolocalization of b2-glycoprotein I (apolipoprotein H) to human atherosclerotic plaques: potential implications for lesion progression. Circulation 1999; 99:2227 – 30. [9] George J, Harats D, Gilburd B, et al. Adoptive transfer of beta-2-glycoprotein-I-reactive lymphocytes enhances early atherosclerosis in LDL receptor-deficient mice. Circulation 2000;102: 1822 – 7. [10] George J, Afek A, Gilburd B, et al. Cellular and humoral immune responses to heat shock protein both involved in promoting fatty-streak formation in LDL-deficient mice. J Am Coll Cardiol 2001;38:900 – 5. [11] George J, Afek A, Gilburd B, et al. Atherosclerosis in LDL-receptor knockout mice is accelerated by immunization with anticardiolipin antibodies. Lupus 1997;6:723 – 9. [12] Afek A, George J, Shoenfeld Y, et al. Enhancement of atherosclerosis in beta-2-glycoprotein I-immunized apolipoprotein E-deficient mice. Pathobiology 1999;67:19 – 25. [13] George J, Afek A, Gilburd B, et al. Induction of early atherosclerosis in LDL-receptor-deficient mice immunized with beta2-glycoprotein I. Circulation 1998;98:1108 – 15. [14] Wu R, Lefvert AK. Autoantibodies against oxidized low density lipoproteins (oxLDL): characterization of antibody isotope, subclass, affinity and effect on the macrophage uptake of oxLDL. Clin Exp Immunol 1995;102:174 – 80. [15] Bergmark C, Wu R, de Faire U, et al. Patients with early onset of peripheral vascular disease have high levels of autoantibodies against oxidized low-density lipoproteins. Arterioscler Thromb Vasc Biol 1995;15:441 – 5. [16] Wu R, Shoenfeld Y, Matucci M, et al. Nontraditional factors vary in patients with autoimmune diseases. Clin Invest Med, in press. [17] Wu R, Svenungsson E, Gunnarsson I, et al. Antibodies against lysophosphatidylcholine and oxidized LDL in-patients with SLE. Lupus 1999;8:142 – 50. [18] Wu R, Svenungsson E, Gunnarsson I, et al. Antibodies to adult human endothelial cells crossreact with oxidized LDL and b2-glycoprotein I in SLE. Clin Exp Immunol 1999;115:561 – 6. [19] George J, Afek A, Gilburd B, et al. Hyperimmunization of apo-E mice with homologous malondialdehyde low-density lipoprotein suppresses early atherogenesis. Atherosclerosis 1998; 138:147 – 52. [20] Wu R, Dearing L, Matsuura E, et al. Are anti-oxLDL antibodies pathogenic or protective? Circulation 2004;110:2252 – 8. [21] Nicolo D, Goldman BI, Monestier M. Reduction of atherosclerosis in low-density lipoprotein receptor-deficient mice by passive administration of antiphospholipid antibody. Arthritis Rheum 2003;48:2974 – 8. [22] Lusis AJ. Atherosclerosis. Nature 2000;407:233 – 41. [23] Cines DB, Pollak ES, Buck CA, et al. Endothelial cells in physiology and in the pathophysiology of vascular disorders. Blood 1998;91:3527 – 61. [24] Rothermel AL, Wang Y, Schechner J, et al. Endothelial cells present antigens in vivo. BMC Immunol 2005;16:5 – 24. [25] Acosta J, Qin X, Halperin J. Complement and complement regulatory proteins as potential molecular targets for vascular diseases. Curr Pharm Des 2004;10:203 – 11.

362

doria et al

[26] Niculescu F, Rus H. The complement activation in atherosclerosis. Immunol Res 2004;30: 73 – 80. [27] Meroni PL, Raschi E, Testoni C, et al. Functional heterogeneity of pathogenic anti-endothelial antibodies. In: Shoenfeld Y, Harats D, Wick G, editors. Atherosclerosis and autoimmunity. Amsterdam7 Elsevier; 2001. p. 211 – 20. [28] George J, Meroni PL, Gilburd B, et al. Antiendothelial cell antibodies in patients with coronary atherosclerosis. Immunol Lett 2000;73:23 – 7. [29] Farsi A, Domeneghetti MP, Brunelli T, et al. Activation of the immune system and coronary artery disease: the role of antiendothelial cell antibodies. Atherosclerosis 2001;154:429 – 36. [30] Faulk WP, Rose M, Meroni PL, et al. Antibodies to human endothelial cells identify myocardial damage and predicts development of coronary artery disease in patients with transplanted hearts. Hum Immunol 1999;60:826 – 32. [31] Lai KN, Leung JC, Lai KB, et al. Upregulation of adhesion molecules on endothelial cells by anti-DNA autoantibodies in systemic lupus erythematosus. Clin Immunol Immunopathol 1996;81:229 – 38. [32] Meroni PL, Raschi E, Testoni C, et al. Endothelial cell activation by antiphospholipid antibodies. Clin Immunol 2004;112:169 – 74. [33] Libby P, Ridker P, Maseri A. Inflammation and atherosclerosis. Circulation 2002;105:1135 – 43. [34] Bonetti PO, Lilach OL, Lerman A. Endothelial dysfunction. A marker of atherosclerotic risk. Arterioscler Thromb Vasc Biol 2003;23:168 – 75. [35] Sherer Y, Shoenfeld Y. Immunomodulation for treatment and prevention of atherosclerosis. Autoimmun Rev 2002;1:21 – 7. [36] Toubi E, Shoenfeld Y. The role of DC40–CD154 interactions in autoimmunity and the benefit of disrupting this pathway. Autoimmunity 2004;37:457 – 64. [37] Harats D, Yacov N, Gilburd B, et al. Oral tolerance with heat shock protein 65 attenuates Mycobacterium tuberculosis-induced and high-fat-diet-driven atherosclerotic lesions. J Am Coll Cardiol 2002;7:1333 – 8. [38] Shovman O, Levy Y, Gilburd B, et al. Anti-inflammatory and immunomodulatory properties of statins. Immunol Res 2002;25:271 – 85. [39] Shapiro S, Shoenfeld Y, Gilburd B, et al. Intravenous gamma globulin inhibits the production of matrix metalloproteinase-9 in macrophages. Cancer 2002;95:2032 – 7. [40] Meroni PL, Luzzana C, Ventura D. Anti-inflammatory and immunomodulating properties of statins. An additional tool for the therapeutic approach of systemic autoimmune diseases? Clin Rev Allergy Immunol 2002;23:263 – 77. [41] Nicoletti A, Kaveri S, Caligiuri G, et al. Immunoglobulin treatment reduces atherosclerosis in apo E knockout mice. J Clin Invest 1998;102:910 – 8. [42] Wu R, Shoenfeld Y, Sherer Y, et al. Anti-idiotypes to oxidized LDL antibodies in intravenous immunoglobulin preparations—possible immunomodulation of atherosclerosis. Autoimmunity 2003;36:91 – 7. [43] Ronda N, Leonardi S, Orlandini G, et al. Natural antiendothelial cell antibodies (AECA). J Autoimmun 1999;13:121 – 7. [44] Ronda N, Bernini F, Giacosa R, et al. Normal human IgG prevents endothelial cell activation induced by TNFa and oxidized low-density lipoprotein atherogenic stimuli. Clin Exp Immunol 2003;133:219 – 26.