- Email: [email protected]
β2GPI complex and atherosclerosis in SLE patients
Available online at www.sciencedirect.com
Autoimmunity Reviews 7 (2007) 52 – 58 www.elsevier.com/locate/autrev
OxLDL/β2GPI–anti-oxLDL/β2GPI complex and atherosclerosis in SLE patients N. Bassi a , A. Ghirardello a , L. Iaccarino a , S. Zampieri a , M.E. Rampudda a , F. Atzeni b , P. Sarzi-Puttini b , Y. Shoenfeld c , A. Doria a,⁎ a
c
Division of Rheumatology, University of Padova, Via Giustiniani 2, 35128 Padova, Italy b Rheumatology Unit, L Sacco University Hospital, Milan, Italy Department of Medicine ‘B’, Chaim Sheba Medical Center, Tel-Hashomer, Sakler Faculty of Medicine, Tel-Aviv University, Israel Received 30 May 2007; accepted 28 June 2007 Available online 24 July 2007
Abstract It has been demonstrated that atherosclerosis (ATS) is enhanced in autoimmune rheumatic diseases, such as systemic lupus erythematosus (SLE). The reason for this accelerated process is still debatable and, although traditional risk factors are more prevalent in SLE patients than in general population, they do not seem to fully explain the enhanced risk. ATS has the characteristics of an autoimmune chronic disease, involving both the innate and the adaptive immunity. Moreover, it satisfies the four criteria defining an autoimmune disease, proposed by Witebsky and Rose. It has been shown that some autoantibodies, including anti-oxLDL, anti-β2GPI, anti-HSP60/65, and more recently antioxLDL/β2GPI, play a key role in the pathogenesis of ATS. However the role of these autoantibodies in accelerated ATS in SLE patients is still controversial. In fact, some of them seem to be proatherogenic and other protective; moreover, it has been demonstrated that induced oral tolerance has a protective role against ATS. We have recently observed that the levels of oxLDL/β2GPI antigenic complexes and their antibodies were higher in patients with SLE than in healthy subjects, but we did not find a clear association between oxLDL/β2GPI complexes and IgG or IgM anti-oxLDL/β2GPI autoantibodies and subclinical ATS in SLE patients. Many other studies are required to explain the role of autoantibodies in the pathogenesis of ATS in SLE patients, because the characteristics of SLE seem to mask their effects for atherogenesis. © 2007 Elsevier B.V. All rights reserved. Keywords: Atherosclerosis; OxLDL; β2GPI; HSP60/65; OxLDL/β2GPI
Contents 1. 2. 3. 4.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Innate and adaptive immunity in atherosclerosis . . . . . . . . . . . Atherosclerosis and activation of the adaptive immunity . . . . . . . Major autoantigen–autoantibody systems involved in atherosclerosis
⁎ Corresponding author. Tel.: +39 049 8212202/8212194; fax: +39 049 8212191. E-mail address: [email protected] (A. Doria). 1568-9972/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.autrev.2007.06.003
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. 53 0 . 53 0 . 53 0 . 53 0
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58
4.1. OxLDL and anti-oxLDL . . . . . . . . . . 4.2. β2GPI and anti-β2GPI . . . . . . . . . . . 4.3. HSP60/65 and anti-HSP60/65. . . . . . . . 5. OxLDL/β2GPI complexes and anti-oxLDL/β2GPI . 6. Conclusions . . . . . . . . . . . . . . . . . . . . Take-home messages . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . .
. . . . . . .
1. Introduction SLE is a prototypic autoimmune systemic disease which can affect different organ systems, including kidney, joint, serosal tissues, skin, and central and peripheral nervous system and it is caused by genetic, immunological, hormonal and viral factors, but its etiology is not clear. Patients affected by SLE are characterized by the presence of a great variety of autoantibodies directed to different autoantigens associated with disturbed apoptosis [1]. Recently, a clear association between SLE and cardiovascular disease (CVD) has been shown [2–5]. Early autopsy and angiographic studies demonstrated a high prevalence of atherosclerotic lesions in SLE [6,7]. Subclinical atherosclerosis (ATS), represented by intima/ media thickness (IMT), was also more frequent in SLE than in healthy controls [8]. ATS is the most common cause of cardiovascular failure, myocardial infarction and death, in industrialized countries. Today it is clear that not only traditional risk factors for ATS (i.e. age, sex, cholesterol, blood pressure, cigarettes smoking), but also infectious [9], like mycobacterium infection, inflammatory and autoimmune factors [9], such as cytokines chemokines and T and B cells, are involved in its pathogenesis. Actually, ATS fulfils the four criteria proposed by Witebsky and Rose to define a condition as an autoimmune in nature [9], and there are many evidence that it can be an autoimmune disease [9]. The aim of this review is to evaluate the possible proatherogenic or protective role of some autoantigens and their autoantibodies in SLE patients.
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
53
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
0 54 0 55 0 55 0 56 0 56 0 57 0 57
the most important cell type [10]. It recognizes primitive organisms foreign to the mammalian and is mobilized very quickly, in minutes to hours, by the detection of pathogen-associated molecular patterns (PAMPs). Thus, the genome encodes the mediators of innate immunity, via a single signal transduction mechanism, the NF-kB pathway [9,10]. These signals can activate cellular component, such as macrophages, natural killer cells (NK cells) and mast cells, involving the alternative pathway of the complement and the secretion of cytokines, chemokines and cell-mediated cytotoxicity [9,10]. Their specificity is encoded in the germline. The adaptive immunity is based on the generation of antigen receptors, such as T-cell receptors (TCRs) and immunoglobulins [9]. Its induction is slow, by the recognition of unique epitopes on each pathogen/antigen. The effector mechanisms involve antibodies, cytotoxic T cells (CTL), causing the classical complement activation and antibody-dependent cell-mediated cytotoxicity, by the releasing of cytokines and chemokines. 3. Atherosclerosis and activation of the adaptive immunity Both microbial products correlated with cardiovascular disease and nonlipid mediators implicated in vascular disease can determine cytokine gene expression [11]. Atherogenic stimuli cause production of cytokines, that augment the expression of the genes for leukocyte adhesion molecules. These molecules in early atherogenesis include vascular cell adhesion molecule-1 (VCAM-1) and E- and P-selectin [11]. Also lipid components of modified lipoproteins can induce adhesion molecules [12].
2. Innate and adaptive immunity in atherosclerosis Both innate immunity, including phagocytic leukocytes, complement and proinflammatory cytokines, and adaptive immunity, with T cells, antibodies and immunoregulatory cytokines, are involved in the pathogenesis and progression of ATS [10]. The first immunologic defensive line is the innate immunity, of which mononuclear phagocyte lineage is
4. Major autoantigen–autoantibody systems involved in atherosclerosis The immune system plays a key role in the pathogenesis of ATS [10], by involving effectors of both the innate and the adaptive immunity as demonstrated by the observation of monocytes/macrophages transformed in lipid loaded foam cells, dendritic cells, natural killer
54
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58
Table 1 Groups of autoantibodies Strength of association
Autoantibodies
Defined
Anti-β2GPI Anti-oxLDL Anti-HSP (60/65) Anti-HDL Anti-APO A-1 Anti-ECA Anti-SAA Anti-oxLDL/β2GPI complex Anti-LPL Anti-cardiolipin Anti-phosphorylcholine Anti-SAP Anti-insulin Anti-MBL Anti-CRP
Probable
Possible
that induced oral tolerance to these antigens in mice leads to a reduction of plaque formation [15]. Various autoantibodies have been reported to associate with atherosclerosis; some other could be potentially involved but no clear data have been published yet. Therefore, on the basis of the strength of association with atherosclerosis, autoantibodies may be subdivided into 3 groups (Table 1). The autoantibodies for which the association with atherosclerosis could be considered “defined” are: anti-oxidized LDL (anti-oxLDL), anti-β2 glycoprotein I (anti-β2GPI) and anti-heat shock protein 60/65 (anti-HSP60/65). For other autoantibodies, including anti-oxLDL/β2GPI complex, the association with atherosclerosis could be considered “probable” and for others still “possible”. 4.1. OxLDL and anti-oxLDL
cells, mast cells and immunoglobulins within the plaque [9,10]. Natural antibodies exhibit a remarkably conserved repertoire that includes a broad specificity for self-antigens. The self-antigens do not cause an immune reaction, because immunological tolerance plays a key role to discriminate self from nonself-antigens. The tolerance renders mature lymphocytes in the peripheral lymphoid tissues to be non-functional or hyporesponsive to an antigen [13]. It has been demonstrated that tolerance could be induced by an oral administration of this antigen [13]. The oral tolerance is dose dependent on antigen. High-dose feeding leads to clonal deletion/ anergy [13], while low doses induce regulatory cells capable of altering cytokine production [13]. Natural antibodies can be found within atherosclerotic lesions. Natural antibodies have been postulated to contribute to the elimination of autoantigens exposed during stress, tissue damage, or even conventional cell turnover. When they bind to autoantigens, they can play a protective role, masking the antigenic determinants by a nonspecific and low-affinity binding [14]. Thus, natural antibodies could prevent autoreactive clones formation, that could interact more strongly with autoantigens, leading to foam cells formation [14]. Under certain pathological conditions that involve increased accumulation of stress-induced self-structures, antibody-mediated clearance may become increasingly relevant [14]. However, in some particular conditions such as in the case of increased oxidation due to smoke, absence of antioxidants, etc., autoantibodies to different epitopes might be generated. These autoantibodies are able to accelerate the formation of lipid loaded foam cells stimulating atherogenesis. But, it has been demonstrated
OxLDL is one of the major antigens in ATS. OxLDL is taken up by macrophages in the atherosclerotic lesions, transforming these cells into foam cells. OxLDL has proinflammatory and immunologic effects that lead to lipid dysregulation. It has also been shown to possess mitogenic and chemotactic effects on the effector-cells of the immune system [16]. In fact, antibodies against oxLDL are present in sera of normal healthy individuals. Plasma levels of native LDL are regulated by LDL receptors located on endothelial cells and monocytederived macrophages. These LDL receptors are downregulated to prevent excessive intracellular lipid accumulation. In contrast, subendothelial oxLDL is removed by intima macrophages via scavenger receptors, thus causing an excessive intracellular accumulation of oxLDL and foam cell formation [17]. Oxidative stress is one of the normal host responses to many stimuli, and may be self-limiting. However, chronic vascular inflammation from different types of pathologic injury may result in chronic oxidative stress and the generation of excessive amounts of oxLDL. OxLDL has been shown to be present in atherosclerotic lesions in animal models and humans [18]. Moreover, it
Table 2 Titers of autoantibodies in general population and in patients Autoantibodies General population Anti-oxLDL Anti-β2GPI Anti-HSP60/65 Anti-oxLDL/ β2GPI
Patients
(O.D.) 0.6 ± 0.1 1.3 ± 0.1 (mg/dl) 2 ± 8 12 ± 7.5 (U.I.) 260 ± 276 325 ± 601 (U.I.) 19.18 ± 7.68 43.57 ± 34.62
pb
References
0.05 0.0001 0.04 0.05
[20] [29] [31] [39]
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58
has been demonstrated that oxLDL levels are higher in SLE patients than in healthy controls [18] (Table 2). IgG anti-oxLDL antibodies are widely detected in patients with cardiovascular diseases (CVD) [19]. In 2004 Radulescu et al. [20] demonstrated that the titres of IgG anti-oxLDL are higher in hypertensive SLE subjects than in normal controls (Table 2). In our previous study [8], we have demonstrated that the titres of these autoantibodies are high in SLE patients and that there is a good correlation between anti-oxLDL antibody levels and maximum intima/media thickness (IMT) (Table 3). IgG antibodies seem to be pathogenic for subclinical ATS in SLE patients; while IgM anti-oxLDL antibodies found in atherosclerosis-prone ApoE−/− and LDL-R−/− mice, are thought to provide protection against proinflammatory oxidized moieties [21]. In 2006 Su et al. [22] demonstrated that high levels of IgM antibodies against oxLDL predict a favourable outcome in the development of carotid ATS in hypertensive subjects. Moreover, it has been demonstrated that immunization of LDL−/− mice with oxLDL, protect from inflammation and plaque formation [14], inhibiting the uptake of oxLDL by macrophages [23] and hyperimmunization of apo-E-deficient mice suppresses early atherogenesis [24]. The explanation could be that these antibodies are heterogeneous both in Ig subclass and in their epitope specificity and affinity [25]. It has been also demonstrated that IL-5 plays an important protective role causing the expansion of natural Ig antibodies specific for oxLDL [26]. 4.2. β2GPI and anti-β2GPI β2GPI possesses natural anticoagulant properties and is a major antigenic target of antiphospholipid antibodies. It is a highly glycosylated plasma protein with an approximate molecular weight of 50 kDa that avidly binds negatively charged surfaces and substances, such as heparin, anionic phospholipids, and apoptotic cells [27]. β2GPI contains 5 short consensus repeated domains, and its partial association with various lipoproteins results in its synonymous designation as apolipoprotein H.
Table 3 Relationship of autoantibodies with IMT in SLE patients: our previous work (Ref. [8]) Autoantibodies
Titers (U/ml)
p=
Anti-oxLDL Anti-β2GPI Anti-HSP60/65
15.3 ± 31.2 22.2 ± 29.2 32.9 ± 15.7
0.002 NS NS
55
This protein possesses several properties that may bear relevance to progression of human atherosclerotic plaque [28]: It binds platelets and apoptotic cells; it inhibits intrinsic blood coagulation pathways and ADPdependent platelet aggregation; it has a role in the activation of endothelial cells induced by aPL; and it may assist in mediating clearance of senescent cells and foreign particles from circulation [27]. In 1999 Jacob George et al. [27] demonstrated that β2GPI is abundantly present in human atherosclerotic plaques from carotid arteries. Although randomly expressed in the different layers of the plaque, it was found to be most prominent in subendothelial regions and in the intimal–medial border of the lesions. β2GPI colocalized with CD4-positive lymphocytes. It was also shown that anti-β2GPI antibodies could be a marker for arterial thrombosis in SLE [27]. These antibodies have been shown in vitro to activate cultured endothelial cells, leading to enhanced monocyte adherence [28]. Moreover the induction of these antibodies in transgenic mice was associated with accelerated ATS [28]. In 2002 Delgado Alves et al. [29] demonstrated that both IgG and IgM levels are higher in SLE patients compared with healthy subjects (Table 2). In our study [8], the titres of anti-β2GPI were high in SLE patients, with no relationship to IMT was found (Table 3). In 2004 George et al. [13] demonstrated that induced oral tolerance to β2GPI suppresses the early atherosclerosis in LDL-receptor deficient mice, an animal model for SLE. So β2GPI and anti-β2GPI antibodies seem to be proatherogenic, but their pathogenic effect for ATS can be secondary in SLE patients. 4.3. HSP60/65 and anti-HSP60/65 HSPs are a group of evolutionarily conserved proteins, which show high sequence homology between different species, from bacteria to humans, and are involved in maintaining various cellular proteins in their correctly folded functional forms [30]. But these proteins can become autoantigens, leading to autoantigens production. Circulating anti-HSP antibodies may be induced and maintained by different mechanisms [31]: infection with microbes containing homologous HSP proteins; the protein itself could become immunogenic because of structural alteration or post-translational modification; other foreign or self-antigens could interact with HSP to form immunogenic complexes; soluble HSP might not be recognized as a self-protein. In 2000 Xu et al. [31] showed that levels of serum soluble HSP60 were significantly elevated in subjects
56
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58
with prevalent/incident carotid atherosclerosis and that these levels were correlated with common carotid artery intima/media thickness. High levels of circulating antiHSP autoantibodies have been associated with increasing severity of ATS in patients [31]. Moreover HSPs and their autoantibodies have been shown to elicit production of proinflammatory cytokines. These autoimmune reactions to HSPs expressed in the vascular tissue can contribute to both initiation and perpetuation of ATS. Many independent [22,33] groups subsequently confirmed that anti-HSP60 antibodies were also elevated in patients with atherosclerotic plaque and seropositive individuals not only showed a higher prevalence of coronary artery disease but also their disease severity was correlated with antibody titres. In 1993 Xu et al. [30] demonstrated that serum antibodies against HSP65 were significantly higher in subjects with carotid ATS than in those without lesions (Table 2). A subsequent study from the same group [32] demonstrated that levels of anti-HSP65 antibodies remain elevated in subjects with progressive carotid ATS. And other evidence derived from in vivo studies by immunization of mice with HSP65 mice, confirming its role in the development of fatty streaks and early ATS [34]. But Harats et al. [15] demonstrated that oral tolerization to HSP65 in LDL−/− mice determined a reduction in fatty streaks and a suppression of plaque formation, by the involvement of clonal anergy/deletion. Moreover, in our study [8] also anti-HSP60/65 were high in SLE patients with no association to carotid abnormalities was found (Table 3). It has been demonstrated that HSP proteins and their antibodies play a key role in pathogenesis ATS, but probably their effect is masked in SLE patients. 5. OxLDL/β2GPI complexes and anti-oxLDL/ β2GPI Lipid peroxidation resulting in oxLDL production is a common occurrence in patients with systemic autoimmune diseases as well as in chronic inflammatory (non-autoimmune) disorders and certain systemic infections. OxLDL, but not native LDL, bind to β2GPI to form oxLDL/β2GPI complexes [35]. In 2001 Liu et al. [36] reported that 7-ketocholesteryl-9-carboxinonanoate, so-called oxLig-1, is the major ligand of oxLDL for β2GPI; in 2002 the same group [37] demonstrated that ω-carboxilated 7-ketocholesteryl esters are critical for β2GPI binding. The first step in the formation of oxidized LDL/β2GPI is an electrostatic interaction between ω-carboxyl functions and lysine residues of β2GPI
leading to an intermediate reversible complex. This interaction later progresses to a much more stable bond such as Schiff base formation [35]. Circulating oxLDL/β2GPI complexes level is increased in SLE patients than in healthy controls [38]. However, these complexes do not seem to be associated with SLE disease activity. It can be hypothesized that the formation of these complexes might be related to chronic inflammation of the vasculature and oxidative stress that occurs in autoimmune patients. The physiologic relevance of oxLDL/β2GPI complexes and their IgG antibodies has been demonstrated in vitro by enhanced macrophage uptake of IgG immune complexes with oxLDL/β2GPI [35]. IgG anti-oxLDL/β2GPI antibody levels are significantly higher in SLE patients compared to healthy controls [38,39] (Table 2). Moreover, the level of these antibodies is significantly higher in SLE patients with APS than in SLE patients without APS [35]. IgG antioxLDL/β2GPI antibodies seem to be a distinct subset of antiphospholipid antibodies that coexist with other antiphospholipid antibodies. Thus, they appear to be a serological marker for atherothrombotic risk in autoimmune patients and seem to be highly specific for APS and, probably are proatherogenic. We recently [39] found a significant correlation between IgG anti-oxLDL/β2GPI and IgG anti-β2GPI. Moreover, IgG anti-oxLDL/β2GPI antibody levels were associated with positive IgG anticardiolipin antibody and lupus anticoagulant; IgM anti-oxLDL/β2GPI levels were correlated with IgM anticardiolipin antibody. Regarding SLE features, only an association between increased levels of oxLDL/β2GPI and renal involvement was found [39], according to the oxidative stress of patients with renal diseases. Unfortunately, we did not find any relationship between oxLDL/β2GPI or antiIgG or IgM anti-oxLDL/β2GPI complex and subclinical ATS in SLE patients. It has been suggested that while IgG antibodies are proatherogenic, IgM antibodies are protective, but the role of these autoantibodies in atherogenesis is still controversial [22,25]. 6. Conclusions Today, ATS is considered in part to be a chronic autoimmune disease, because it involves the components of both innate and adaptive immunity [8]. It is enhanced in many autoimmune diseases, such as SLE, for traditional and nontraditional risk factors, such as age, blood pressure and cigarette smoking. SLE is a prototypic autoimmune disease, involving many organ
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58
systems; but its characteristics can mask the pathogenic role of some of the autoantibodies in the development of ATS. In fact, there are many evidence that risk factors like hypercholesterolemia, hypertension, age and smoking cigarettes play a major role in the progression of the atherogenic process, but the opinions about the autoantibodies are discordant, because they can play only a secondary role in the pathogenesis of ATS. It has been demonstrated the presence of higher titres of antioxLDL, anti-β2GPI, anti-HSP60/65 and anti-oxLDL/ β2GPI complex in SLE patients than in healthy controls and they are present in the plaque; but sometimes no relationship is found between the titres of these antibodies and the IMT [8]. Instead, in other autoimmune diseases, like RA, there is a relationship between some traditional risk factors, such as hypertension and hypercholesterolemia, and the titres of some autoantibodies, like anticardiolipin antibodies [40]. Moreover the titres of these autoantibodies correlate with IMT in RA patients [40]. In some cases it has been demonstrated that IgM autoantibodies can have a protective role for atherogenesis and can reduce the formation of plaque, because they block the interaction of autoreactive clones with the autoantigen, reducing foam cells formation [22]. Moreover, some investigators demonstrated the efficacy of induced oral tolerance with the autoantigens to reduce the plaque, causing an anergy/depletion of reactive clones by a precedent oral administration of the antigen [14,15,23]. Many other studies are required to explain the role of the autoantibodies in the pathogenesis of ATS, in particular to demonstrate their role in SLE patients. Moreover, it is important to clarify the possible protective role of IgM autoantibodies [14] and the efficacy of induced oral tolerance, as probable solution to high reactivity of autoreactive clones, to reduce the foam cells formation. Take-home messages • Atherosclerosis (ATS) is considered a chronic autoimmune disease in which autoantibodies like anti-oxLDL, anti-β2GPI, anti-HSP60/65, and more recently anti-oxLDL/β2GPI complex play a pathogenetic role. • ATS is enhanced in systemic lupus erythematosus (SLE) as well as other autoimmune rheumatic diseases; however the role of proatherogenic autoantibodies in SLE patients is still controversial. • Circulating levels of oxLDL/β2GPI complex and respective antibodies are higher in SLE patients than
57
in healthy subjects, but a clear association between oxLDL/β2GPI complex and IgG or IgM anti-oxLDL/ β2GPI antibodies and subclinical ATS in SLE was not demonstrated. References [1] Sherer Y, Gorstein A, Fritzler MJ, Shoenfeld Y. Autoantibodies explosion in systemic lupus erythematosus: more than 100 different antibodies found in SLE patients. Semin Arthritis Rheum 2004;34:501–37. [2] Shoenfeld Y, Gerli R, Doria A, Matsuura E, Cerinic MM, Ronda N, et al. Accelerated atherosclerosis in autoimmune rheumatic diseases. Circulation 2005;112:3337–47. [3] Doria A, Sarzi-Puttini P, Shoenfeld Y. 2nd conference on heart, rheumatism and autoimmunity, Pescara, Italy, May 19–20, vol. 5. Autoimmun Rev; 2006. p. 55–63. [4] Sarzi-Puttini P, Atzeni F, Doria A, Iaccarino L, Turiel M. Tumor necrosis factor-alpha, biologic agents and cardiovascular risk. Lupus 2005;14:780–4. [5] Doria A, Iaccarino L, Sarzi-Puttini P, Atzeni F, Turiel M, Petri M. Cardiac involvement in systemic lupus erythematosus. Lupus 2005;14:683–6. [6] Zampieri S, Iaccarino L, Ghirardello A, Taricone E, Arienti S, Sarzi-Puttini P, et al. Systemic lupus erythematosus, atherosclerosis, and autoantibodies. Ann NY Acad Sci 2005;1051:351–61. [7] Turiel M, Peretti R, Sarzi-Puttini P, Atzeni F, Doria A. Cardiac imaging techniques in systemic autoimmune diseases. Lupus 2005;14:727–31. [8] Doria A, Shoenfeld Y, Wu R, Gambari PF, Puato M, Ghirardello A, et al. Risk factors for subclinical atherosclerosis in a prospective cohort of patients with systemic lupus erythematosus. Ann Rheum Dis 2003;62:1071–7. [9] Gordon PA, George J, Khamashta M, Harats D, Hughes G, Shoenfeld Y. Atherosclerosis and autoimmunity. Lupus 2001;10: 249–52. [10] Doria A, Sherer Y, Meroni PL, Shoenfeld Y. Inflammation and accelerated atherosclerosis: basic mechanisms. Rheum Dis Clin North Am 2005;31:355–62. [11] Cybulsky MI, Iiyama K, Li H, Zhu S, Chen M, Iiyama M, et al. A major role for VCAM-1, but not ICAM-1, in early atherosclerosis. J Clin Invest 2001;107:1255–62. [12] Shih PT, Elices MJ, Fang ZT, Ugarova TP, Strahl D, Territo MC, et al. Minimally modified low-density lipoprotein induces monocyte adhesion to endothelial connecting segment-1 by activating β1 integrin. J Clin Invest 1999;103:613–25. [13] George J, Yacov N, Breitbart E, Bangio L, Shaish A, Gilburd B, et al. Suppression of early atherosclerosis in LDL-receptor deficient mice by oral tolerance with β2-glycoprotein I. Cardiovasc Res 2004;62:603–9. [14] Toubi E, Shoenfeld Y. Predictive and protective autoimmunity in cardiovascular diseases: is vaccination therapy a reality? Lupus 2005;14:665–9. [15] Harats D, Yacov N, Gilburd B, Shoenfeld Y, George J. Oral tolerance with heat shock protein 65 attenuates Mycobacterium tuberculosis-induced and high-fat-diet-driven atherosclerotic lesions. J Am Coll Cardiol 2002;40:1333–8. [16] Lopez LR, Salazar-Paramo MM, Palafox-Sanchez C, Hurley BL, Matsuura E, Garcia-De La Torre I. Oxidized low-density lipoprotein and beta2-glycoprotein I in patients with systemic lupus
58
[17] [18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58 erythematosus and increased carotid intima–media thickness: implication in autoimmune-mediated atherosclerosis. Lupus 2006;15:80–6. Davi G, Falco A. Oxidant stress, inflammation and atherogenesis. Lupus 2005;14:760–4. George J, Afek A, Gilburd B, Harats D, Shoenfeld Y. Autoimmunity in atherosclerosis: lessons from experimental models. Lupus 2000;9:223–7. Sherer Y, Tenenbaum A, Blank M, Shemesh J, Harats D, Fisman EZ, et al. Autoantibodies to oxidized low-density lipoprotein in coronary artery disease. Am J Hypertens 2001;14:149–54. Radulescu L, Stancu C, Antohe F. Antibodies against human oxidized low-density lipoprotein (LDL) as markers for human plasma modified lipoproteins. Med Sci Monit 2004;10:207–14. Matsuura E, Kobayashi K, Tabuchi M, Lopez LR. Oxidative modification of low-density lipoprotein and immune regulation of atherosclerosis. Prog Lipid Res 2006;45:466–86. Su J, Georgiades A, Wu R, Thulin T, de Faire U, Frostegård J. Antibodies of IgM subclass to phosphorylcholine and oxidized LDL are protective factors for atherosclerosis in patients with hypertension. Atherosclerosis 2006;188:160–6. Shaw PX, Hörkkö S, Tsimikas S, Chang MK, Palinski W, Silverman GJ, et al. Human-derived anti-oxidized LDL autoantibody blocks uptake of oxidized LDL by macrophages and localizes to atherosclerotic lesions in vivo. Arterioscler Thromb Vasc Biol 2001;21:1333–9. George J, Afek A, Gilburd B, Levkovitz H, Shaish A, Goldberg I, et al. Hyperimmunization of apo-E-deficient mice with homologous malondialdehyde low-density lipoprotein suppresses early atherogenesis. Atherosclerosis 1998;138:147–52. Shoenfeld Y, Wu R, Dearing LD, Matsuura E. Are anti-oxidized lowdensity lipoprotein antibodies pathogenic or protective? Circulation 2004;110:2552–8. Binder CJ, Hartvgsen K, Chang MK, Miller M, Broide D, Palinski W, et al. IL-5 links adaptive and natural immunity specific for epitopes of oxLDL and protects from atherosclerosis. J Clin Invest 2004;114:427–37. George J, Harats D, Gilburd B, Afek A, Levy Y, Schneiderman J, et al. Immunolocalization of β2-glycoprotein I (apolipoprotein H) to human atherosclerotic plaques potential implication for lesion progression. Circulation 1999;99:2227–30. Afek A, George J, Shoenfeld Y, Gilburd B, Levy Y, Shaish A, et al. Enhancement of atherosclerosis in beta-2 glycoprotein I-immunized apolipoprotein E-deficient mice. Pathobiology 1999;67: 19–25. Delgado Alves J, Ames PRJ, Donohue S, Stanyer L, NouroozZadeh J, Ravirajan C, et al. Antibodies to high-density lipoprotein
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
and β2-glicoprotein I are inversely correlated with paraoxonase activity in systemic lupus erythematosus and primary antiphospholipid syndrome. Arthritis Rheum 2002;46:2686–94. Xu Q, Willeit J, Marosi M, Kleindienst R, Oberhollenzer F, Kiechl S, et al. Association of serum antibodies to heat-shock protein 65 with carotid atherosclerosis. Lancet 1993;341:255–9. Xu Q, Schett G, Perschinka H, Mayr M, Egger G, Oberhollenzer F, et al. Serum soluble heat shock protein 60 is elevated in subjects with atherosclerosis in a general population. Circulation 2000;102:14–20. Xu Q, Kiechl S, Mayr M, Metzler B, Egger G, Oberhollenzer F, et al. Association of serum antibodies to heat-shock protein 65 with carotid atherosclerosis: clinical significance determined in a follow-up study. Circulation 1999;100:1169–74. Mandal K, Foteinos G, Jahangiri M, Xu Q. Role of antiheat shock protein 60 autoantibodies in atherosclerosis. Lupus 2005;14: 742–6. Afek A, George J, Gilburd B, Rauova L, Goldberg I, Kopolovic J, et al. Immunization of low-density lipoprotein receptor deficient (LDL-RD) mice with heat shock protein 65 (HSP-65) promotes early atherosclerosis. J Autoimmun 2000;14:115–21. Kobayashi K, Kishi M, Atsumi T, Bertolaccini ML, Makino H, Sakairi N, et al. Circulating oxidized LDL forms complexes with β2-glycoprotein I: implication as an atherogenic autoantigen. J Lipid Res 2003;44:716–26. Kobayashi K, Matsuura E, Liu QP, Furukawa J, Kaihara K, Inagaki J, et al. A specific ligand for β2-glycoprotein I mediates autoantibody-dependent uptake of oxidized low density lipoprotein by macrophages. J Lipid Res 2001;42:697–709. Liu Q, Kobayashi K, Furukawa J, Inagaki J, Sakairi N, Iwado A, et al. ω-Carboxil variants of 7-ketocholesteryl esters are ligands for β2-glycoprotein I mediates autoantibody-dependent uptake of oxidized LDL by macrophages. J Lipid Res 2002;43:1486–95. Matsuura E, Kobayashi K, Inoue K, Lopez LR, Shoenfeld Y. Oxidized LDL/β2-glycoprotein I complexes: new aspects in atherosclerosis. Lupus 2005;14:736–41. Bassi N, Ghirardello A, Iaccarino L, Zampieri S, Rampudda ME, Atzeni F, et al. 5th international congress on autoimmunity, Sorrento, Italy, November 29–December 3, vol. 12. Autoimmun Rev; 2006. p. 19–20. Sherer Y, Gerli R, Gilburd B, Bartoloni Bocci E, Vaudo G, Mannarino E, et al. Thickened carotid artery intima–media in rheumatoid arthritis is associated with elevated anticardiolipin antibodies. Lupus 2007;16:259–64.
Hormone replacement therapy in systemic lupus erythematosus. Hormone replacement therapy (HRT) has been reported as associated with increased risk for cardiovascular diseases. Fernandez et al. (J Clin Rheumatol 2007;13:261-265) studied the occurrence of vascular arterial and venous thrombotic events in postmenopausal women with systemic lupus erythematosus. HRT use was not associated with the occurrence of vascular arterial events in these patients. The authors concluded that HRT use in women with SLE should be individualized, and its use may be safe if antiphospholipid antibodies are not present or vascular arterial events have not previously occurred.
Autoimmunity Reviews 7 (2007) 52 – 58 www.elsevier.com/locate/autrev
OxLDL/β2GPI–anti-oxLDL/β2GPI complex and atherosclerosis in SLE patients N. Bassi a , A. Ghirardello a , L. Iaccarino a , S. Zampieri a , M.E. Rampudda a , F. Atzeni b , P. Sarzi-Puttini b , Y. Shoenfeld c , A. Doria a,⁎ a
c
Division of Rheumatology, University of Padova, Via Giustiniani 2, 35128 Padova, Italy b Rheumatology Unit, L Sacco University Hospital, Milan, Italy Department of Medicine ‘B’, Chaim Sheba Medical Center, Tel-Hashomer, Sakler Faculty of Medicine, Tel-Aviv University, Israel Received 30 May 2007; accepted 28 June 2007 Available online 24 July 2007
Abstract It has been demonstrated that atherosclerosis (ATS) is enhanced in autoimmune rheumatic diseases, such as systemic lupus erythematosus (SLE). The reason for this accelerated process is still debatable and, although traditional risk factors are more prevalent in SLE patients than in general population, they do not seem to fully explain the enhanced risk. ATS has the characteristics of an autoimmune chronic disease, involving both the innate and the adaptive immunity. Moreover, it satisfies the four criteria defining an autoimmune disease, proposed by Witebsky and Rose. It has been shown that some autoantibodies, including anti-oxLDL, anti-β2GPI, anti-HSP60/65, and more recently antioxLDL/β2GPI, play a key role in the pathogenesis of ATS. However the role of these autoantibodies in accelerated ATS in SLE patients is still controversial. In fact, some of them seem to be proatherogenic and other protective; moreover, it has been demonstrated that induced oral tolerance has a protective role against ATS. We have recently observed that the levels of oxLDL/β2GPI antigenic complexes and their antibodies were higher in patients with SLE than in healthy subjects, but we did not find a clear association between oxLDL/β2GPI complexes and IgG or IgM anti-oxLDL/β2GPI autoantibodies and subclinical ATS in SLE patients. Many other studies are required to explain the role of autoantibodies in the pathogenesis of ATS in SLE patients, because the characteristics of SLE seem to mask their effects for atherogenesis. © 2007 Elsevier B.V. All rights reserved. Keywords: Atherosclerosis; OxLDL; β2GPI; HSP60/65; OxLDL/β2GPI
Contents 1. 2. 3. 4.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Innate and adaptive immunity in atherosclerosis . . . . . . . . . . . Atherosclerosis and activation of the adaptive immunity . . . . . . . Major autoantigen–autoantibody systems involved in atherosclerosis
⁎ Corresponding author. Tel.: +39 049 8212202/8212194; fax: +39 049 8212191. E-mail address: [email protected] (A. Doria). 1568-9972/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.autrev.2007.06.003
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. 53 0 . 53 0 . 53 0 . 53 0
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58
4.1. OxLDL and anti-oxLDL . . . . . . . . . . 4.2. β2GPI and anti-β2GPI . . . . . . . . . . . 4.3. HSP60/65 and anti-HSP60/65. . . . . . . . 5. OxLDL/β2GPI complexes and anti-oxLDL/β2GPI . 6. Conclusions . . . . . . . . . . . . . . . . . . . . Take-home messages . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . .
. . . . . . .
1. Introduction SLE is a prototypic autoimmune systemic disease which can affect different organ systems, including kidney, joint, serosal tissues, skin, and central and peripheral nervous system and it is caused by genetic, immunological, hormonal and viral factors, but its etiology is not clear. Patients affected by SLE are characterized by the presence of a great variety of autoantibodies directed to different autoantigens associated with disturbed apoptosis [1]. Recently, a clear association between SLE and cardiovascular disease (CVD) has been shown [2–5]. Early autopsy and angiographic studies demonstrated a high prevalence of atherosclerotic lesions in SLE [6,7]. Subclinical atherosclerosis (ATS), represented by intima/ media thickness (IMT), was also more frequent in SLE than in healthy controls [8]. ATS is the most common cause of cardiovascular failure, myocardial infarction and death, in industrialized countries. Today it is clear that not only traditional risk factors for ATS (i.e. age, sex, cholesterol, blood pressure, cigarettes smoking), but also infectious [9], like mycobacterium infection, inflammatory and autoimmune factors [9], such as cytokines chemokines and T and B cells, are involved in its pathogenesis. Actually, ATS fulfils the four criteria proposed by Witebsky and Rose to define a condition as an autoimmune in nature [9], and there are many evidence that it can be an autoimmune disease [9]. The aim of this review is to evaluate the possible proatherogenic or protective role of some autoantigens and their autoantibodies in SLE patients.
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
53
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
. . . . . . .
0 54 0 55 0 55 0 56 0 56 0 57 0 57
the most important cell type [10]. It recognizes primitive organisms foreign to the mammalian and is mobilized very quickly, in minutes to hours, by the detection of pathogen-associated molecular patterns (PAMPs). Thus, the genome encodes the mediators of innate immunity, via a single signal transduction mechanism, the NF-kB pathway [9,10]. These signals can activate cellular component, such as macrophages, natural killer cells (NK cells) and mast cells, involving the alternative pathway of the complement and the secretion of cytokines, chemokines and cell-mediated cytotoxicity [9,10]. Their specificity is encoded in the germline. The adaptive immunity is based on the generation of antigen receptors, such as T-cell receptors (TCRs) and immunoglobulins [9]. Its induction is slow, by the recognition of unique epitopes on each pathogen/antigen. The effector mechanisms involve antibodies, cytotoxic T cells (CTL), causing the classical complement activation and antibody-dependent cell-mediated cytotoxicity, by the releasing of cytokines and chemokines. 3. Atherosclerosis and activation of the adaptive immunity Both microbial products correlated with cardiovascular disease and nonlipid mediators implicated in vascular disease can determine cytokine gene expression [11]. Atherogenic stimuli cause production of cytokines, that augment the expression of the genes for leukocyte adhesion molecules. These molecules in early atherogenesis include vascular cell adhesion molecule-1 (VCAM-1) and E- and P-selectin [11]. Also lipid components of modified lipoproteins can induce adhesion molecules [12].
2. Innate and adaptive immunity in atherosclerosis Both innate immunity, including phagocytic leukocytes, complement and proinflammatory cytokines, and adaptive immunity, with T cells, antibodies and immunoregulatory cytokines, are involved in the pathogenesis and progression of ATS [10]. The first immunologic defensive line is the innate immunity, of which mononuclear phagocyte lineage is
4. Major autoantigen–autoantibody systems involved in atherosclerosis The immune system plays a key role in the pathogenesis of ATS [10], by involving effectors of both the innate and the adaptive immunity as demonstrated by the observation of monocytes/macrophages transformed in lipid loaded foam cells, dendritic cells, natural killer
54
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58
Table 1 Groups of autoantibodies Strength of association
Autoantibodies
Defined
Anti-β2GPI Anti-oxLDL Anti-HSP (60/65) Anti-HDL Anti-APO A-1 Anti-ECA Anti-SAA Anti-oxLDL/β2GPI complex Anti-LPL Anti-cardiolipin Anti-phosphorylcholine Anti-SAP Anti-insulin Anti-MBL Anti-CRP
Probable
Possible
that induced oral tolerance to these antigens in mice leads to a reduction of plaque formation [15]. Various autoantibodies have been reported to associate with atherosclerosis; some other could be potentially involved but no clear data have been published yet. Therefore, on the basis of the strength of association with atherosclerosis, autoantibodies may be subdivided into 3 groups (Table 1). The autoantibodies for which the association with atherosclerosis could be considered “defined” are: anti-oxidized LDL (anti-oxLDL), anti-β2 glycoprotein I (anti-β2GPI) and anti-heat shock protein 60/65 (anti-HSP60/65). For other autoantibodies, including anti-oxLDL/β2GPI complex, the association with atherosclerosis could be considered “probable” and for others still “possible”. 4.1. OxLDL and anti-oxLDL
cells, mast cells and immunoglobulins within the plaque [9,10]. Natural antibodies exhibit a remarkably conserved repertoire that includes a broad specificity for self-antigens. The self-antigens do not cause an immune reaction, because immunological tolerance plays a key role to discriminate self from nonself-antigens. The tolerance renders mature lymphocytes in the peripheral lymphoid tissues to be non-functional or hyporesponsive to an antigen [13]. It has been demonstrated that tolerance could be induced by an oral administration of this antigen [13]. The oral tolerance is dose dependent on antigen. High-dose feeding leads to clonal deletion/ anergy [13], while low doses induce regulatory cells capable of altering cytokine production [13]. Natural antibodies can be found within atherosclerotic lesions. Natural antibodies have been postulated to contribute to the elimination of autoantigens exposed during stress, tissue damage, or even conventional cell turnover. When they bind to autoantigens, they can play a protective role, masking the antigenic determinants by a nonspecific and low-affinity binding [14]. Thus, natural antibodies could prevent autoreactive clones formation, that could interact more strongly with autoantigens, leading to foam cells formation [14]. Under certain pathological conditions that involve increased accumulation of stress-induced self-structures, antibody-mediated clearance may become increasingly relevant [14]. However, in some particular conditions such as in the case of increased oxidation due to smoke, absence of antioxidants, etc., autoantibodies to different epitopes might be generated. These autoantibodies are able to accelerate the formation of lipid loaded foam cells stimulating atherogenesis. But, it has been demonstrated
OxLDL is one of the major antigens in ATS. OxLDL is taken up by macrophages in the atherosclerotic lesions, transforming these cells into foam cells. OxLDL has proinflammatory and immunologic effects that lead to lipid dysregulation. It has also been shown to possess mitogenic and chemotactic effects on the effector-cells of the immune system [16]. In fact, antibodies against oxLDL are present in sera of normal healthy individuals. Plasma levels of native LDL are regulated by LDL receptors located on endothelial cells and monocytederived macrophages. These LDL receptors are downregulated to prevent excessive intracellular lipid accumulation. In contrast, subendothelial oxLDL is removed by intima macrophages via scavenger receptors, thus causing an excessive intracellular accumulation of oxLDL and foam cell formation [17]. Oxidative stress is one of the normal host responses to many stimuli, and may be self-limiting. However, chronic vascular inflammation from different types of pathologic injury may result in chronic oxidative stress and the generation of excessive amounts of oxLDL. OxLDL has been shown to be present in atherosclerotic lesions in animal models and humans [18]. Moreover, it
Table 2 Titers of autoantibodies in general population and in patients Autoantibodies General population Anti-oxLDL Anti-β2GPI Anti-HSP60/65 Anti-oxLDL/ β2GPI
Patients
(O.D.) 0.6 ± 0.1 1.3 ± 0.1 (mg/dl) 2 ± 8 12 ± 7.5 (U.I.) 260 ± 276 325 ± 601 (U.I.) 19.18 ± 7.68 43.57 ± 34.62
pb
References
0.05 0.0001 0.04 0.05
[20] [29] [31] [39]
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58
has been demonstrated that oxLDL levels are higher in SLE patients than in healthy controls [18] (Table 2). IgG anti-oxLDL antibodies are widely detected in patients with cardiovascular diseases (CVD) [19]. In 2004 Radulescu et al. [20] demonstrated that the titres of IgG anti-oxLDL are higher in hypertensive SLE subjects than in normal controls (Table 2). In our previous study [8], we have demonstrated that the titres of these autoantibodies are high in SLE patients and that there is a good correlation between anti-oxLDL antibody levels and maximum intima/media thickness (IMT) (Table 3). IgG antibodies seem to be pathogenic for subclinical ATS in SLE patients; while IgM anti-oxLDL antibodies found in atherosclerosis-prone ApoE−/− and LDL-R−/− mice, are thought to provide protection against proinflammatory oxidized moieties [21]. In 2006 Su et al. [22] demonstrated that high levels of IgM antibodies against oxLDL predict a favourable outcome in the development of carotid ATS in hypertensive subjects. Moreover, it has been demonstrated that immunization of LDL−/− mice with oxLDL, protect from inflammation and plaque formation [14], inhibiting the uptake of oxLDL by macrophages [23] and hyperimmunization of apo-E-deficient mice suppresses early atherogenesis [24]. The explanation could be that these antibodies are heterogeneous both in Ig subclass and in their epitope specificity and affinity [25]. It has been also demonstrated that IL-5 plays an important protective role causing the expansion of natural Ig antibodies specific for oxLDL [26]. 4.2. β2GPI and anti-β2GPI β2GPI possesses natural anticoagulant properties and is a major antigenic target of antiphospholipid antibodies. It is a highly glycosylated plasma protein with an approximate molecular weight of 50 kDa that avidly binds negatively charged surfaces and substances, such as heparin, anionic phospholipids, and apoptotic cells [27]. β2GPI contains 5 short consensus repeated domains, and its partial association with various lipoproteins results in its synonymous designation as apolipoprotein H.
Table 3 Relationship of autoantibodies with IMT in SLE patients: our previous work (Ref. [8]) Autoantibodies
Titers (U/ml)
p=
Anti-oxLDL Anti-β2GPI Anti-HSP60/65
15.3 ± 31.2 22.2 ± 29.2 32.9 ± 15.7
0.002 NS NS
55
This protein possesses several properties that may bear relevance to progression of human atherosclerotic plaque [28]: It binds platelets and apoptotic cells; it inhibits intrinsic blood coagulation pathways and ADPdependent platelet aggregation; it has a role in the activation of endothelial cells induced by aPL; and it may assist in mediating clearance of senescent cells and foreign particles from circulation [27]. In 1999 Jacob George et al. [27] demonstrated that β2GPI is abundantly present in human atherosclerotic plaques from carotid arteries. Although randomly expressed in the different layers of the plaque, it was found to be most prominent in subendothelial regions and in the intimal–medial border of the lesions. β2GPI colocalized with CD4-positive lymphocytes. It was also shown that anti-β2GPI antibodies could be a marker for arterial thrombosis in SLE [27]. These antibodies have been shown in vitro to activate cultured endothelial cells, leading to enhanced monocyte adherence [28]. Moreover the induction of these antibodies in transgenic mice was associated with accelerated ATS [28]. In 2002 Delgado Alves et al. [29] demonstrated that both IgG and IgM levels are higher in SLE patients compared with healthy subjects (Table 2). In our study [8], the titres of anti-β2GPI were high in SLE patients, with no relationship to IMT was found (Table 3). In 2004 George et al. [13] demonstrated that induced oral tolerance to β2GPI suppresses the early atherosclerosis in LDL-receptor deficient mice, an animal model for SLE. So β2GPI and anti-β2GPI antibodies seem to be proatherogenic, but their pathogenic effect for ATS can be secondary in SLE patients. 4.3. HSP60/65 and anti-HSP60/65 HSPs are a group of evolutionarily conserved proteins, which show high sequence homology between different species, from bacteria to humans, and are involved in maintaining various cellular proteins in their correctly folded functional forms [30]. But these proteins can become autoantigens, leading to autoantigens production. Circulating anti-HSP antibodies may be induced and maintained by different mechanisms [31]: infection with microbes containing homologous HSP proteins; the protein itself could become immunogenic because of structural alteration or post-translational modification; other foreign or self-antigens could interact with HSP to form immunogenic complexes; soluble HSP might not be recognized as a self-protein. In 2000 Xu et al. [31] showed that levels of serum soluble HSP60 were significantly elevated in subjects
56
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58
with prevalent/incident carotid atherosclerosis and that these levels were correlated with common carotid artery intima/media thickness. High levels of circulating antiHSP autoantibodies have been associated with increasing severity of ATS in patients [31]. Moreover HSPs and their autoantibodies have been shown to elicit production of proinflammatory cytokines. These autoimmune reactions to HSPs expressed in the vascular tissue can contribute to both initiation and perpetuation of ATS. Many independent [22,33] groups subsequently confirmed that anti-HSP60 antibodies were also elevated in patients with atherosclerotic plaque and seropositive individuals not only showed a higher prevalence of coronary artery disease but also their disease severity was correlated with antibody titres. In 1993 Xu et al. [30] demonstrated that serum antibodies against HSP65 were significantly higher in subjects with carotid ATS than in those without lesions (Table 2). A subsequent study from the same group [32] demonstrated that levels of anti-HSP65 antibodies remain elevated in subjects with progressive carotid ATS. And other evidence derived from in vivo studies by immunization of mice with HSP65 mice, confirming its role in the development of fatty streaks and early ATS [34]. But Harats et al. [15] demonstrated that oral tolerization to HSP65 in LDL−/− mice determined a reduction in fatty streaks and a suppression of plaque formation, by the involvement of clonal anergy/deletion. Moreover, in our study [8] also anti-HSP60/65 were high in SLE patients with no association to carotid abnormalities was found (Table 3). It has been demonstrated that HSP proteins and their antibodies play a key role in pathogenesis ATS, but probably their effect is masked in SLE patients. 5. OxLDL/β2GPI complexes and anti-oxLDL/ β2GPI Lipid peroxidation resulting in oxLDL production is a common occurrence in patients with systemic autoimmune diseases as well as in chronic inflammatory (non-autoimmune) disorders and certain systemic infections. OxLDL, but not native LDL, bind to β2GPI to form oxLDL/β2GPI complexes [35]. In 2001 Liu et al. [36] reported that 7-ketocholesteryl-9-carboxinonanoate, so-called oxLig-1, is the major ligand of oxLDL for β2GPI; in 2002 the same group [37] demonstrated that ω-carboxilated 7-ketocholesteryl esters are critical for β2GPI binding. The first step in the formation of oxidized LDL/β2GPI is an electrostatic interaction between ω-carboxyl functions and lysine residues of β2GPI
leading to an intermediate reversible complex. This interaction later progresses to a much more stable bond such as Schiff base formation [35]. Circulating oxLDL/β2GPI complexes level is increased in SLE patients than in healthy controls [38]. However, these complexes do not seem to be associated with SLE disease activity. It can be hypothesized that the formation of these complexes might be related to chronic inflammation of the vasculature and oxidative stress that occurs in autoimmune patients. The physiologic relevance of oxLDL/β2GPI complexes and their IgG antibodies has been demonstrated in vitro by enhanced macrophage uptake of IgG immune complexes with oxLDL/β2GPI [35]. IgG anti-oxLDL/β2GPI antibody levels are significantly higher in SLE patients compared to healthy controls [38,39] (Table 2). Moreover, the level of these antibodies is significantly higher in SLE patients with APS than in SLE patients without APS [35]. IgG antioxLDL/β2GPI antibodies seem to be a distinct subset of antiphospholipid antibodies that coexist with other antiphospholipid antibodies. Thus, they appear to be a serological marker for atherothrombotic risk in autoimmune patients and seem to be highly specific for APS and, probably are proatherogenic. We recently [39] found a significant correlation between IgG anti-oxLDL/β2GPI and IgG anti-β2GPI. Moreover, IgG anti-oxLDL/β2GPI antibody levels were associated with positive IgG anticardiolipin antibody and lupus anticoagulant; IgM anti-oxLDL/β2GPI levels were correlated with IgM anticardiolipin antibody. Regarding SLE features, only an association between increased levels of oxLDL/β2GPI and renal involvement was found [39], according to the oxidative stress of patients with renal diseases. Unfortunately, we did not find any relationship between oxLDL/β2GPI or antiIgG or IgM anti-oxLDL/β2GPI complex and subclinical ATS in SLE patients. It has been suggested that while IgG antibodies are proatherogenic, IgM antibodies are protective, but the role of these autoantibodies in atherogenesis is still controversial [22,25]. 6. Conclusions Today, ATS is considered in part to be a chronic autoimmune disease, because it involves the components of both innate and adaptive immunity [8]. It is enhanced in many autoimmune diseases, such as SLE, for traditional and nontraditional risk factors, such as age, blood pressure and cigarette smoking. SLE is a prototypic autoimmune disease, involving many organ
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58
systems; but its characteristics can mask the pathogenic role of some of the autoantibodies in the development of ATS. In fact, there are many evidence that risk factors like hypercholesterolemia, hypertension, age and smoking cigarettes play a major role in the progression of the atherogenic process, but the opinions about the autoantibodies are discordant, because they can play only a secondary role in the pathogenesis of ATS. It has been demonstrated the presence of higher titres of antioxLDL, anti-β2GPI, anti-HSP60/65 and anti-oxLDL/ β2GPI complex in SLE patients than in healthy controls and they are present in the plaque; but sometimes no relationship is found between the titres of these antibodies and the IMT [8]. Instead, in other autoimmune diseases, like RA, there is a relationship between some traditional risk factors, such as hypertension and hypercholesterolemia, and the titres of some autoantibodies, like anticardiolipin antibodies [40]. Moreover the titres of these autoantibodies correlate with IMT in RA patients [40]. In some cases it has been demonstrated that IgM autoantibodies can have a protective role for atherogenesis and can reduce the formation of plaque, because they block the interaction of autoreactive clones with the autoantigen, reducing foam cells formation [22]. Moreover, some investigators demonstrated the efficacy of induced oral tolerance with the autoantigens to reduce the plaque, causing an anergy/depletion of reactive clones by a precedent oral administration of the antigen [14,15,23]. Many other studies are required to explain the role of the autoantibodies in the pathogenesis of ATS, in particular to demonstrate their role in SLE patients. Moreover, it is important to clarify the possible protective role of IgM autoantibodies [14] and the efficacy of induced oral tolerance, as probable solution to high reactivity of autoreactive clones, to reduce the foam cells formation. Take-home messages • Atherosclerosis (ATS) is considered a chronic autoimmune disease in which autoantibodies like anti-oxLDL, anti-β2GPI, anti-HSP60/65, and more recently anti-oxLDL/β2GPI complex play a pathogenetic role. • ATS is enhanced in systemic lupus erythematosus (SLE) as well as other autoimmune rheumatic diseases; however the role of proatherogenic autoantibodies in SLE patients is still controversial. • Circulating levels of oxLDL/β2GPI complex and respective antibodies are higher in SLE patients than
57
in healthy subjects, but a clear association between oxLDL/β2GPI complex and IgG or IgM anti-oxLDL/ β2GPI antibodies and subclinical ATS in SLE was not demonstrated. References [1] Sherer Y, Gorstein A, Fritzler MJ, Shoenfeld Y. Autoantibodies explosion in systemic lupus erythematosus: more than 100 different antibodies found in SLE patients. Semin Arthritis Rheum 2004;34:501–37. [2] Shoenfeld Y, Gerli R, Doria A, Matsuura E, Cerinic MM, Ronda N, et al. Accelerated atherosclerosis in autoimmune rheumatic diseases. Circulation 2005;112:3337–47. [3] Doria A, Sarzi-Puttini P, Shoenfeld Y. 2nd conference on heart, rheumatism and autoimmunity, Pescara, Italy, May 19–20, vol. 5. Autoimmun Rev; 2006. p. 55–63. [4] Sarzi-Puttini P, Atzeni F, Doria A, Iaccarino L, Turiel M. Tumor necrosis factor-alpha, biologic agents and cardiovascular risk. Lupus 2005;14:780–4. [5] Doria A, Iaccarino L, Sarzi-Puttini P, Atzeni F, Turiel M, Petri M. Cardiac involvement in systemic lupus erythematosus. Lupus 2005;14:683–6. [6] Zampieri S, Iaccarino L, Ghirardello A, Taricone E, Arienti S, Sarzi-Puttini P, et al. Systemic lupus erythematosus, atherosclerosis, and autoantibodies. Ann NY Acad Sci 2005;1051:351–61. [7] Turiel M, Peretti R, Sarzi-Puttini P, Atzeni F, Doria A. Cardiac imaging techniques in systemic autoimmune diseases. Lupus 2005;14:727–31. [8] Doria A, Shoenfeld Y, Wu R, Gambari PF, Puato M, Ghirardello A, et al. Risk factors for subclinical atherosclerosis in a prospective cohort of patients with systemic lupus erythematosus. Ann Rheum Dis 2003;62:1071–7. [9] Gordon PA, George J, Khamashta M, Harats D, Hughes G, Shoenfeld Y. Atherosclerosis and autoimmunity. Lupus 2001;10: 249–52. [10] Doria A, Sherer Y, Meroni PL, Shoenfeld Y. Inflammation and accelerated atherosclerosis: basic mechanisms. Rheum Dis Clin North Am 2005;31:355–62. [11] Cybulsky MI, Iiyama K, Li H, Zhu S, Chen M, Iiyama M, et al. A major role for VCAM-1, but not ICAM-1, in early atherosclerosis. J Clin Invest 2001;107:1255–62. [12] Shih PT, Elices MJ, Fang ZT, Ugarova TP, Strahl D, Territo MC, et al. Minimally modified low-density lipoprotein induces monocyte adhesion to endothelial connecting segment-1 by activating β1 integrin. J Clin Invest 1999;103:613–25. [13] George J, Yacov N, Breitbart E, Bangio L, Shaish A, Gilburd B, et al. Suppression of early atherosclerosis in LDL-receptor deficient mice by oral tolerance with β2-glycoprotein I. Cardiovasc Res 2004;62:603–9. [14] Toubi E, Shoenfeld Y. Predictive and protective autoimmunity in cardiovascular diseases: is vaccination therapy a reality? Lupus 2005;14:665–9. [15] Harats D, Yacov N, Gilburd B, Shoenfeld Y, George J. Oral tolerance with heat shock protein 65 attenuates Mycobacterium tuberculosis-induced and high-fat-diet-driven atherosclerotic lesions. J Am Coll Cardiol 2002;40:1333–8. [16] Lopez LR, Salazar-Paramo MM, Palafox-Sanchez C, Hurley BL, Matsuura E, Garcia-De La Torre I. Oxidized low-density lipoprotein and beta2-glycoprotein I in patients with systemic lupus
58
[17] [18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
N. Bassi et al. / Autoimmunity Reviews 7 (2007) 52–58 erythematosus and increased carotid intima–media thickness: implication in autoimmune-mediated atherosclerosis. Lupus 2006;15:80–6. Davi G, Falco A. Oxidant stress, inflammation and atherogenesis. Lupus 2005;14:760–4. George J, Afek A, Gilburd B, Harats D, Shoenfeld Y. Autoimmunity in atherosclerosis: lessons from experimental models. Lupus 2000;9:223–7. Sherer Y, Tenenbaum A, Blank M, Shemesh J, Harats D, Fisman EZ, et al. Autoantibodies to oxidized low-density lipoprotein in coronary artery disease. Am J Hypertens 2001;14:149–54. Radulescu L, Stancu C, Antohe F. Antibodies against human oxidized low-density lipoprotein (LDL) as markers for human plasma modified lipoproteins. Med Sci Monit 2004;10:207–14. Matsuura E, Kobayashi K, Tabuchi M, Lopez LR. Oxidative modification of low-density lipoprotein and immune regulation of atherosclerosis. Prog Lipid Res 2006;45:466–86. Su J, Georgiades A, Wu R, Thulin T, de Faire U, Frostegård J. Antibodies of IgM subclass to phosphorylcholine and oxidized LDL are protective factors for atherosclerosis in patients with hypertension. Atherosclerosis 2006;188:160–6. Shaw PX, Hörkkö S, Tsimikas S, Chang MK, Palinski W, Silverman GJ, et al. Human-derived anti-oxidized LDL autoantibody blocks uptake of oxidized LDL by macrophages and localizes to atherosclerotic lesions in vivo. Arterioscler Thromb Vasc Biol 2001;21:1333–9. George J, Afek A, Gilburd B, Levkovitz H, Shaish A, Goldberg I, et al. Hyperimmunization of apo-E-deficient mice with homologous malondialdehyde low-density lipoprotein suppresses early atherogenesis. Atherosclerosis 1998;138:147–52. Shoenfeld Y, Wu R, Dearing LD, Matsuura E. Are anti-oxidized lowdensity lipoprotein antibodies pathogenic or protective? Circulation 2004;110:2552–8. Binder CJ, Hartvgsen K, Chang MK, Miller M, Broide D, Palinski W, et al. IL-5 links adaptive and natural immunity specific for epitopes of oxLDL and protects from atherosclerosis. J Clin Invest 2004;114:427–37. George J, Harats D, Gilburd B, Afek A, Levy Y, Schneiderman J, et al. Immunolocalization of β2-glycoprotein I (apolipoprotein H) to human atherosclerotic plaques potential implication for lesion progression. Circulation 1999;99:2227–30. Afek A, George J, Shoenfeld Y, Gilburd B, Levy Y, Shaish A, et al. Enhancement of atherosclerosis in beta-2 glycoprotein I-immunized apolipoprotein E-deficient mice. Pathobiology 1999;67: 19–25. Delgado Alves J, Ames PRJ, Donohue S, Stanyer L, NouroozZadeh J, Ravirajan C, et al. Antibodies to high-density lipoprotein
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
and β2-glicoprotein I are inversely correlated with paraoxonase activity in systemic lupus erythematosus and primary antiphospholipid syndrome. Arthritis Rheum 2002;46:2686–94. Xu Q, Willeit J, Marosi M, Kleindienst R, Oberhollenzer F, Kiechl S, et al. Association of serum antibodies to heat-shock protein 65 with carotid atherosclerosis. Lancet 1993;341:255–9. Xu Q, Schett G, Perschinka H, Mayr M, Egger G, Oberhollenzer F, et al. Serum soluble heat shock protein 60 is elevated in subjects with atherosclerosis in a general population. Circulation 2000;102:14–20. Xu Q, Kiechl S, Mayr M, Metzler B, Egger G, Oberhollenzer F, et al. Association of serum antibodies to heat-shock protein 65 with carotid atherosclerosis: clinical significance determined in a follow-up study. Circulation 1999;100:1169–74. Mandal K, Foteinos G, Jahangiri M, Xu Q. Role of antiheat shock protein 60 autoantibodies in atherosclerosis. Lupus 2005;14: 742–6. Afek A, George J, Gilburd B, Rauova L, Goldberg I, Kopolovic J, et al. Immunization of low-density lipoprotein receptor deficient (LDL-RD) mice with heat shock protein 65 (HSP-65) promotes early atherosclerosis. J Autoimmun 2000;14:115–21. Kobayashi K, Kishi M, Atsumi T, Bertolaccini ML, Makino H, Sakairi N, et al. Circulating oxidized LDL forms complexes with β2-glycoprotein I: implication as an atherogenic autoantigen. J Lipid Res 2003;44:716–26. Kobayashi K, Matsuura E, Liu QP, Furukawa J, Kaihara K, Inagaki J, et al. A specific ligand for β2-glycoprotein I mediates autoantibody-dependent uptake of oxidized low density lipoprotein by macrophages. J Lipid Res 2001;42:697–709. Liu Q, Kobayashi K, Furukawa J, Inagaki J, Sakairi N, Iwado A, et al. ω-Carboxil variants of 7-ketocholesteryl esters are ligands for β2-glycoprotein I mediates autoantibody-dependent uptake of oxidized LDL by macrophages. J Lipid Res 2002;43:1486–95. Matsuura E, Kobayashi K, Inoue K, Lopez LR, Shoenfeld Y. Oxidized LDL/β2-glycoprotein I complexes: new aspects in atherosclerosis. Lupus 2005;14:736–41. Bassi N, Ghirardello A, Iaccarino L, Zampieri S, Rampudda ME, Atzeni F, et al. 5th international congress on autoimmunity, Sorrento, Italy, November 29–December 3, vol. 12. Autoimmun Rev; 2006. p. 19–20. Sherer Y, Gerli R, Gilburd B, Bartoloni Bocci E, Vaudo G, Mannarino E, et al. Thickened carotid artery intima–media in rheumatoid arthritis is associated with elevated anticardiolipin antibodies. Lupus 2007;16:259–64.
Hormone replacement therapy in systemic lupus erythematosus. Hormone replacement therapy (HRT) has been reported as associated with increased risk for cardiovascular diseases. Fernandez et al. (J Clin Rheumatol 2007;13:261-265) studied the occurrence of vascular arterial and venous thrombotic events in postmenopausal women with systemic lupus erythematosus. HRT use was not associated with the occurrence of vascular arterial events in these patients. The authors concluded that HRT use in women with SLE should be individualized, and its use may be safe if antiphospholipid antibodies are not present or vascular arterial events have not previously occurred.