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Rheumatology Advance Access originally published online on March 27, 2008
Rheumatology 2008 47(5):684-689; doi:10.1093/rheumatology/ken124
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© The Author 2008. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Arteriosclerosis obliterans associated with anti-cardiolipin antibody / β2-glycoprotein I antibodies as a strong risk factor for ischaemic heart disease in patients with systemic lupus erythematosus

J. Nojima1, Y. Masuda1, Y. Iwatani2, H. Kuratsune3, Y. Watanabe4, E. Suehisa1, T. Takano1, Y. Hidaka1 and Y. Kanakura5

1Laboratory for Clinical Investigation, Osaka University Hospital, Suita, Osaka, 2Division of Biomedical Informatics, Course of Health Science, Osaka University Graduate School of Medicine, Suita, 3Department of Health Science, Faculty of Health Science for Welfare, Kansai University of Welfare Science, Kashihara, 4Department of Physiology, Osaka City University Graduate School of Medicine, Abeno-ku and 5Department of Hematology and Oncology, Osaka University Graduate School of Medicine, Suita, Osaka, Japan.

Correspondence to: J. Nojima, Laboratory for Clinical Investigation, Osaka University Hospital, 2-15 Yamadaoka, Suita, Osaka 565-0871, Japan. E-mail: nojima{at}hp-lab.med.osaka-u.ac.jp


   Abstract
Top
 Abstract
Introduction
 Materials and methods
 Results
 Discussion
 References
 
Objective. The main objective of this study was to clarify the role of aPLs in the pathogenesis of arteriosclerosis obliterans (ASO), ischaemic heart disease (IHD) and cerebral vascular disorder (CVD) in patients with SLE.

Methods. We evaluated 155 patients with SLE by using objective tests for diagnosing ASO, IHD and CVD and laboratory tests including ELISA for aCL/β2-glycoprotein I antibodies (aCL/β2-GPI) and anti-phosphatidylserine/prothrombin antibodies (anti-PS/PT).

Results. Twenty-five (16.1%) of the 155 SLE patients were diagnosed with ASO. Both aCL/β2-GPI and anti-PS/PT levels were significantly higher in SLE patients with ASO (mean ± S.E., 104.3 ± 38.8 U/ml for aCL/β2-GPI, P < 0.01; 72.6 ± 48.9 U/ml for anti-PS/PT, P < 0.05) than in SLE patients without ASO (22.8 ± 9.9 U/ml for aCL/β2-GPI; 18.3 ± 4.4 U/ml for anti-PS/PT). Multivariate logistic analysis including aCL/β2-GPI, anti-PS/PT and traditional risk factors (hypercholesterolaemia, hypertension and diabetes mellitus) confirmed that the presence of aCL/β2-GPI was the most significant risk factor for ASO in SLE patients [odds ratio (OR) 3.45; 95% CI 1.40, 8.56; P < 0.01]. Furthermore, the prevalence of ASO was associated strongly with IHD (OR 11.8; 95% CI 3.45, 40.1; P < 0.0001) but not CVD (OR 1.84; 95% CI 0.65, 5.21; P = 0.25).

Conclusions. The presence of aCL/β2-GPI contributes to the risk of development of ASO, which may represent an important mechanism for the pathogenesis of IHD in patients with SLE.

KEY WORDS: Systemic lupus erythematosus, Anti-phospholipid antibodies, Arteriosclerosis obliterans, Ischaemic heart disease, Cerebral vascular disorder


   Introduction
Top
 Abstract
 Introduction
Materials and methods
 Results
 Discussion
 References
 
The aPLs are a distinct group of auto-antibodies that occur in a variety of autoimmune diseases, particularly SLE [1, 2]. It is now generally accepted that aPLs do not bind primarily to the negatively charged phospholipid itself, but rather to complexes of the phospholipid and phospholipid-binding proteins [3–6]. The most common and best characterized aPLs are aCL/β2-glycoprotein I antibodies (aCL/β2-GPI), anti-phosphatidylserine/prothrombin antibodies (anti-PS/PT) and lupus anticoagulant (LA) activity [7, 8]. aCL/β2-GPI and anti-PS/PT are detected with solid-phase immunoassays, typically ELISAs [2, 7, 9, 10]. LA activity is the activity of aPLs that inhibit certain in vitro phospholipid-dependent coagulation reactions [11].

Several clinical studies have established that the presence of aCL/β2-GPI, anti-PS/PT and/or LA activity is associated with clinical events such as arterial and/or venous thromboembolic complications and obstetric complications [12–14]. APS is diagnosed both by clinical findings (recurrent arterial and/or venous thrombosis and obstetric complications) and laboratory evidence of persistent aPLs [15]. Although arterial and/or venous thrombosis and recurrent fetal loss are the major manifestations in APS patients, the spectrum of clinical manifestations associated with aPLs has broadened recently [16]. The nervous system in patients with aPLs is frequently affected, with migraines, balance disorders, stroke and atypical multiple sclerosis being prominent. Other features such as thrombocytopenia, psychiatric manifestations, livedo reticularis, haemolytic anaemia and cardiac valve abnormalities are also related to the presence of aPLs. Recently, atherosclerosis, ischaemic heart disease (IHD) and cerebral vascular disorder (CVD) were described as very important clinical manifestations associated with aPLs [17].

Atherosclerosis obliterans (ASO), IHD and CVD are major causes of mortality in patients with SLE [18, 19]. In ASO, large peripheral arteries are obstructed due to atherosclerosis. ASO has been hypothesized to be the major cause of IHD and/or CVD [17]. Many studies have suggested that SLE patients have increased prevalence of accelerated atherosclerosis [17, 19, 20]. Atherosclerosis occurs due to traditional risk factors such as hypercholesterolaemia, hypertension, diabetes mellitus, adiposity and smoking [17, 19, 21–23]; however, these traditional risk factors alone do not explain the high prevalence of atherosclerosis in patients with SLE. The association between SLE and atherosclerosis may be attributed to additional risk factors related closely to inflammation and autoimmunity [24]. In particular, several autoantibodies and their respective autoantigens may be possible factors in the development and progression of the atherosclerotic process in SLE [24].

Recently, a number of studies suggested that aPLs bind to the phospholipid/plasma protein complex on endothelial cells and/or the monocyte surface and that these antibodies increase levels of tissue factor (TF) messenger RNA (mRNA) synthesis and TF expression on monocytes and vascular endothelial cells [16, 25]. The increased TF activity on these cells in response to aPLs may be a mechanism for development of atherosclerosis in SLE patients with aPLs [16, 25].

In the present study, we evaluated 155 SLE patients using objective tests for diagnosis of ASO, IHD and CVD and by using laboratory tests, including aCL/β2-GPI-ELISA and anti-PS/PT-ELISA, to investigate the role of aCL/β2-GPI and anti-PS/PT in the pathogenesis of ASO, IHD and CVD in patients with SLE.


   Materials and methods
Top
 Abstract
 Introduction
 Materials and methods
Results
 Discussion
 References
 
Patients
We studied 155 patients (144 females, 11 males; age range 8–82 yrs; mean 44.2 yrs) with SLE diagnosed according to the revised criteria of the American Rheumatism Association. These patients were evaluated with objective tests for diagnosis of ASO, IHD and CVD and laboratory tests, including aCL/β2-GPI-ELISA and anti-PS/PT-ELISA. As the first step for diagnosis of ASO, the 155 patients with SLE were evaluated by determination of the ankle brachial pressure index (ABI) and Fontaine Stages (I–IV). Twenty-five (16.1%) patients satisfied both of the following diagnostic criteria: moderate-to-severe attenuation of ABI (<0.9) and stable intermittent claudication compatible with Fontaine Stage II. We performed angiography in these 25 patients and confirmed that all 25 patients had occlusive disease of the artery that disturbed blood flow (ASO-positive group). The remaining 130 patients, who had no abnormality in the ABI test, a lower limb Doppler ultrasound and clinical symptoms of ASO, were classified as the ASO-negative group. Diagnosis of IHD and CVD was based on clinical manifestations and electrocardiography (ECG), coronary angiography (CAG), Doppler ultrasonography CT and/or MRI findings. Among all SLE patients, we confirmed that 15 (9.6%) patients had IHD (13 cases of angina pectoris and two cases of myocardial infarction) and 25 patients (16.1%) had CVD (23 cases of cerebral infarction and two cases of transient cerebral ischaemic attack). We also studied 150 control plasma samples from normal healthy volunteers. These samples had been previously taken from the staff of Osaka University Hospital (62 females, 88 males; age range 21–58 yrs; mean 40.8 yrs). None of them had any history of thrombotic complications, and there were no abnormalities found by blood testing (blood cell counts, coagulation tests, liver function tests and examinations for autoimmune activity). Blood samples were taken into vacuum tubes (5.0-ml total volume, Sekisui, Japan) containing 0.5 ml of 3.13% trisodium citrate (Na3C6H5O7·2H2O), and platelet-poor plasma was prepared by double centrifugation at 2800g for 15 min at 15°C. The plasma samples were frozen at –80°C until batch assays could be performed. Written informed consent was obtained from all study participants. This research was approved by the Institutional Review Board of Osaka University Hospital.

Detection of aCL/β2-GPI
Concentrations of aCL/β2-GPI were measured with an aCL/β2-GPI ELISA Kit (Yamasa Shoyus Co., Ltd, Japan). The cardiolipin-coated wells were washed three times with 250 µl of PBS (pH 7.4) containing 0.05% Tween-20 (PBS–Tween). The wells were then incubated with 50 µl of purified human β2-GPI (30 µg/ml) (β2-GP I+ wells) or with 50 µl of PBS containing 0.5% BSA (0.5% BSA–PBS) (β2-GP I– wells) for 30 min at room temperature. After incubation, 50 µl of plasma sample (diluted 101 times with 0.5% BSA–PBS) was added to both β2-GP I+ wells and β2-GP I– wells. To exclude the effect of β2-GPI present in plasma, we diluted plasma samples 101 times with PBS. Measurement of aCL/β2-GPI was not influenced by the β2-GPI in plasma because the final concentration of β2-GPI was <1 µg/ml. A 50 µl volume of calibration standard sera was added to β2-GP I+ wells. Following a 60-min incubation at room temperature, the wells were washed three times with PBS–Tween and then incubated with 100 µl of peroxidase-labelled anti-human IgG for 30 min at room temperature. Wells were then washed three times with PBS–Tween and 100 µl of 0.3 mM tetramethylbenzidine solution containing 0.003% of H2O2 was added to each well. After a 30-min incubation at room temperature, the reaction was terminated by addition of 100 µl of 2N H2SO4, and the absorbance was measured at 450 nm. The absorbance levels for each sample in the β2-GP I+ and β2-GP I– wells were compared for the evaluation of β2-GPI dependency of antibody binding. In this experiment, all samples in β2-GP I+ wells showed higher levels of absorbance than those in β2-GP I– wells. The levels of aCL/β2-GPI were derived from the calibration curve from β2-GP I+ wells.

Detection of anti-PS/PT
Concentrations of anti-PS/PT were measured with an anti-PS/PT IgG ELISA Kit (Cosmic Corporation, Japan). This kit detects PS-dependent anti-PT antibodies (aPS/PT) in human plasma. The PS-coated wells were washed three times with 300 µl of PBS containing 0.5% BSA, 5 mM CaCl2 and 0.05% Tween-20 (Wash buffer). The wells were then incubated with 50 µl of purified human PT (30 µg/ml, PT+ wells) or with 50 µl of 0.5% BSA–PBS (PT– wells) for 60 min at room temperature. PT was added to wells coated with PS to refine the PS–PT complex. After washing, 100 µl of plasma sample (diluted 101 times with 0.5% BSA–PBS containing 5 mM CaCl2) was added to both PT+ and PT– wells. Calibration standard sera (100 µl) were added to PT+ wells and incubated for 60 min at room temperature. The second incubation allows any anti-PS/PT present to bind to the immobilized PS–PT complex. After washing, 100 µl of peroxidase-labelled anti-human IgG was added to both PT+ and PT– wells and incubated for 60 min at room temperature. A third incubation allows the enzyme label to bind to anti-PS/PT that has attached to the wells. A 100 µl of 0.3 mM tetramethylbenzidine solution containing 0.003% of H2O2 was added to each well after washing and then incubated for 30 min at room temperature. The reaction was stopped by addition of stop solution, and absorbance of the resulting yellow colour product was measured spectrophotometrically at 450 nm. Levels of anti-PS/PT were calculated from the calibration curve obtained with PT+ wells.

Detection of LA activity
LA activity was detected with both the diluted Russell Viper Venom Time (dRVVT; Gradipore Ltd, Sydney, Australia) and STACLOT LA (Diagnostica Stago) tests. The dRVVT and STACLOT LA tests were performed with commercially available screening and confirmatory tests.

Statistical analysis
The non-parametric Mann–Whitney test and the Kruskal–Wallis test were used to compare levels of aCL/β2-GPI and anti-PS/PT between ASO patients, non-ASO patients and control subjects. As an approximation of the relative risk, the odds ratio (OR) and 95% CI were calculated for several putative risk factors with multivariate logistic regression analysis with the statistical program Stat Flex (version 4.2, Artech, Inc., Osaka, Japan). An OR was considered to be statistically significant when the lower limit of the 95% CI was >1.0. In the multivariate logistic regression analysis, P < 0.05 was considered statistically significant.


   Results
Top
 Abstract
 Introduction
 Materials and methods
 Results
Discussion
 References
 
Relation between LA activity and aCL/β2-GPI and/or anti-PS/PT
We studied levels of aCL/β2-GPI and anti-PS/PT in 150 normal healthy control subjects. The levels, detected by ELISA, were log transformed with the Stat Flex program to approximate normality before statistical analysis was performed. The mean + 3 S.D. in the 150 normal controls were chosen as the cut-off point for each antibody level. Cut-off values for aCL/β2-GPI and anti-PS/PT were 3.5 and 10.2 U/ml, respectively. For the SLE patients, the result was regarded as positive when the absorbance exceeded each cut-off value. The aCL/β2-GPI and anti-PS/PT were detected in 61 (39.4%) and 42 (27.1%) of the 155 SLE patients, respectively. Thirty-four patients had both aCL/β2-GPI and anti-PS/PT, 27 had aCL/β2-GPI alone and 8 had anti-PS/PT alone.

It was recently reported that the presence of LA activity is the strongest risk factor for thromboembolic events in patients with SLE [12]. However, LA activity is heterogeneous with respect to the specificities and functional capacities of the antibodies, which recognize different antigens, including complexes of phospholipid/plasma proteins such as CL/β2-GPI and PS/PT [2, 26, 27]. More recently, some studies showed anti-PS/PT and aCL/β2-GPI to be independently responsible for LA activity [7, 8]. Therefore, we examined the relation between LA activity and aCL/β2-GPI and/or anti-PS/PT in our 155 SLE patients. LA activity was present in 56 (36.1%) of the 155 SLE patients. Forty-four (72.1%) of 61 aCL/β2-GPI-positive cases had LA activity and 37 (88.1%) of 42 anti-PS/PT-positive cases had LA activity. Multivariate logistic regression analysis revealed that the prevalence of LA activity correlated strongly with the presence of aCL/β2-GPI and anti-PS/PT (OR 9.2 and 19.4, respectively; 95% CI 3.52, 23.8 and 6.18, 60.9, respectively; P < 0.001 and P < 0.001, respectively).

Relation between the presence of aCL/β2-GPI and/or anti-PS/PT and the prevalence of ASO
We evaluated 155 patients with SLE using objective tests for diagnosis of ASO. Twenty-five patients were assigned to the ASO-positive group. The remaining 130 patients with SLE, who showed no abnormalities on the objective tests for diagnosis of ASO, were considered ASO-negative (ASO-negative group). Levels of aCL/β2-GPI and anti-PS/PT were compared between the ASO-positive group and ASO-negative group. As shown in Fig. 1, levels of both aCL/β2-GPI and anti-PS/PT were significantly higher in the ASO-positive group (aCL/β2-GPI, mean ± S.E., 104.3 ± 38.8 U/ml, P < 0.001; anti-PS/PT, 72.6 ± 48.9 U/ml, P < 0.05) than in the ASO-negative group (aCL/β2-GPI, 22.8 ± 9.9 U/ml; anti-PS/PT, 18.3 ± 4.4 U/ml).


Figure 1
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  		FIG. 1. Levels of aCL/β2-GPI and anti-PS/PT in 155 SLE patients with or without ASO.

 
The aCL/β2-GPI and anti-PS/PT were significantly present more in ASO-positive patients (aCL/β2-GPI, 16/25 cases, 64.0%, P < 0.01; anti-PS/PT, 10/25 cases, 40.0%, P < 0.05) than in ASO-negative patients (45/130 cases, 34.6%; 32/130 cases, 24.6%; respectively). The results of logistic regression analysis of risk factors for ASO are shown in Table 1. In this analysis, all values were analysed as positive or negative irrespective of the concentrations of antibodies. The logistic regression analysis of risk factors for ASO revealed that the presence of aCL/β2-GPI was a strong risk factor for ASO (OR 3.36; 95% CI 1.37, 8.20, P < 0.01). However, the presence of anti-PS/PT was not reliable as a risk factor for ASO in patients with SLE.


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  		TABLE 1. Association between the presence of each aPL and the prevalence of ASO

 
Comparison between aCL/β2-GPI and traditional risk factors
Because traditional risk factors, including hyperlipaemia, hypertension and diabetes, are reported to contribute to the prevalence of ASO [17, 21], we examined the presence of these traditional risk factors in 155 SLE patients with or without ASO. Hyperlipaemia was diagnosed as LDL cholesterol levels of >140 mg/dl or as triglyceride levels of >150 mg/dl. Hypertension was defined by a systolic blood pressure of >140 mmHg and diastolic blood pressure of >90 mmHg. Diagnosis of diabetes mellitus was made according to the criteria of the Japanese Diabetes Society. Hyperlipaemia, hypertension and diabetes mellitus were detected in 44 (28.4%), 41 (26.5%) and 19 (12.3%) of the 155 SLE patients, respectively.

The results of multivariate logistic analysis, including aCL/β2-GPI and traditional risk factors (hyperlipaemia, hypertension and diabetes mellitus), are shown in Table 2. Hyperlipaemia, hypertension and diabetes mellitus were not reliable risk factors for ASO in patients with SLE (OR 1.09, 0.93 and 0.51, respectively; 95% CI 0.41, 2.92; 0.34, 2.56; and 0.11, 2.44, respectively; P = 0.86, P = 0.89, P = 0.40, respectively), and the presence of aCL/β2-GPI was the most significant risk factor for ASO in SLE patients (OR 3.45; 95% CI 1.40, 8.56; P < 0.01).


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  		TABLE 2. Multivariate logistic regression analysis of risk factors for ASO

 
Relation between the presence of ASO and the prevalence of IHD and/or CVD
It has been suggested that atherosclerosis may contribute to development of IHD and CVD [17, 24]. Therefore, we examined the relation between the presence of ASO and the prevalence of IHD and/or CVD in our 155 SLE patients. The prevalence of IHD was significantly higher in SLE patients with ASO (9/25 cases, 36.0%, P < 0.0001, Table 3) than in those without ASO (6/130 cases, 4.6%). In contrast, there was no statistically significant difference in the prevalence of CVD between SLE patients with ASO (6/25 cases, 24.0%) and those without ASO (19/130 cases, 14.6%). Multivariate logistic analysis revealed that the prevalence of ASO was strongly associated with IHD (OR 11.8; 95% CI 3.45, 40.1; P < 0.0001) but not CVD (OR 1.84; 95% CI 0.65, 5.21; P = 0.25; Table 3).


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  		TABLE 3. Association between the ASO and IHD and/or CVD

 
Relation between the prevalence of IHD and the presence of ASO, aCL/β2-GPI and/or anti-PS/PT
SLE patients were divided into the following four groups according to their complications (ASO and/or IHD): Group A, ASO-positive patients who had IHD (n = 9); Group B, ASO-positive patients who had no IHD (n = 16); Group C, ASO-negative patients who had IHD (n = 6); and Group D, ASO-negative patients who had no IHD (n = 124). Levels of aCL/β2-GPI and anti-PS/PT were compared among these four groups. As shown in Fig. 2, the aCL/β2-GPI level was significantly higher in Group A (mean ± S.E., 135.7 ± 67.9, P < 0.001) and Group B (86.7 ± 48.2, P < 0.05) than in Group D (23.8 ± 10.3), but no statistical difference was observed between Group A and Group B. Furthermore, the aCL/β2-GPI level in Group A was significantly higher than that in Group C (135.7 ± 67.9 vs 2.3 ± 0.8, P < 0.01). There was no statistical difference in the aCL/β2-GPI level between Group C and Group B.


Figure 2
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  		FIG. 2. Comparison of aCL/β2-GPI levels and anti-PS/PT levels among SLE patient groups. Group A, ASO-positive patients who had IHD (n = 9); Group B, ASO-positive patients who had no IHD (n = 16); Group C, ASO-negative patients who had IHD (n = 6); and Group D, ASO-negative patients who had no IHD (n = 124). NS: not significant.

 
The anti-PS/PT level was significantly higher in Group A (160.3 ± 134.6, P < 0.05) than in Group D (16.7 ± 4.3). However, there were no statistical differences in the levels of anti-PS/PT between Groups B (23.2 ± 9.9), C (52.1 ± 31.9) and D (16.7 ± 4.3).


   Discussion
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
References
 
IHD such as angina pectoris and myocardial infarction are major causes of morbidity and mortality in patients with SLE [17]. However, the precise mechanism that underlies IHD in these patients remains unclear. In the present study, we showed that the presence of aCL/β2-GPI contributes to the risk of development of ASO, which may represent an important mechanism for the pathogenesis of IHD in patients with SLE.

Atherosclerosis is a pathological process that affects arterial walls [24]. Atherosclerosis is a chronic inflammatory response to the deposition of lipoproteins (cholesterol and triglycerides) in the walls of arteries [24]. In addition to the chronic inflammatory response, many components of the immune system, including monocytes and macrophages, T cells, autoantibodies and their respective autoantigens and cytokines secreted by cells within atherosclerotic plaques, are thought to be involved in the pathological processes that underlie development of atherosclerosis [24, 28].

It was previously reported that aPLs promote atherosclerosis by attracting monocytes to endothelial cells and/or promoting influx of oxidized low-density lipoprotein into macrophages [29]. Moreover, many studies have suggested that aPLs cause persistently high expression of TF on monocytes and vascular endothelial cells and that increased TF activity on these cells in response to aPLs may be involved in the pathogenesis of atherosclerosis in SLE patients [25, 30–36]. Furthermore, recent experimental evidence suggested that aPLs induce expression of TF gene and protein by monocytes and vascular endothelial cells by simultaneously and independently activating phosphorylation of p38 mitogen-activated protein kinase (MAP kinase), nuclear translocation and activation of NF-{kappa}B/Rel proteins, and phosphorylation of MEK-1/ERK proteins [16, 33, 34]. Activation of p38 MAPK increases activities of pro-inflammatory cytokines, such as TNF-{alpha} and IL-1β, and this may also contribute to the development of atherosclerosis in SLE patients with aPLs [24].

In the present study, we examined levels of aCL/β2-GPI and anti-PS/PT by using specific ELISAs in addition to LA activity detected by phospholipid-dependent coagulation assays in 155 SLE patients with or without ASO. The presence of LA activity is reported to be a strong risk factor for thromboembolic events in patients with SLE [12], and we confirmed that the presence of LA activity also contributed to the development of ASO in SLE patients (OR 2.67; 95% CI 1.12, 6.37). However, LA activity detected with a phospholipid-dependent coagulation assay can be heterogeneous, and some studies showed that expression of LA activity is dependent on the ability of aCL/β2-GPI and anti-PS/PT [7, 8]. Therefore, we investigated the role of aCL/β2-GPI and anti-PS/PT in the pathogenesis of ASO. It is important to note that antibodies detected by the anti-PS/PT ELISA differ from those detected by the aCL/β2-GPI ELISA and that anti-PS/PT and aCL/β2-GPI are independently responsible for LA activity. Although levels of both aCL/β2-GPI and anti-PS/PT were significantly higher in SLE patients with ASO than in SLE patients without ASO, logistic regression analysis of risk factors for ASO revealed that the presence of aCL/β2-GPI but not anti-PS/PT is a strong risk factor for ASO.

Traditional risk factors such as hyperlipaemia, hypertension and diabetes contribute to the prevalence of ASO [17, 19, 21–23]. Therefore, we examined the frequencies of these traditional risk factors in 155 SLE patients with or without ASO. Multivariate logistic analysis including aCL/β2-GPI and traditional risk factors (hyperlipaemia, hypertension and diabetes mellitus) confirmed that the presence of aCL/β2-GPI is the most significant risk factor for ASO in SLE patients. These results suggest that ASO in SLE patients may be mediated by the pro-inflammatory and pro-coagulant activities of aCL/β2-GPI and that the presence of aCL/β2-GPI promotes development and progression of ASO in patients with SLE.

Although the risk of IHD and/or CVD was reported to be increased in patients with SLE [17, 24], it is still not clear how aPL-associated ASO is related to this risk. Therefore, we examined the relation between the presence of ASO and the prevalence of IHC and/or CVD. Multivariate logistic analysis revealed that the presence of ASO is strongly associated with the prevalence of IHD in SLE patients. SLE patients with ASO had an 11.8 (OR) increased risk of IHD compared with that of SLE patients without ASO. Furthermore, we divided 155 SLE patients into four groups as described in the ‘Materials and methods’ section, and compared the levels of aCL/β2-GPI among these four groups. It is important to note that the aCL/β2-GPI level was significantly higher in SLE patients who had both ASO and IHD than in SLE patients who had IHD but not ASO. These results suggest that ASO caused by aCL/β2-GPI contributes to the risk of development of IHD in patients with SLE.

In contrast, the presence of ASO does not appear to be an important risk factor for the prevalence of CVD as indicated by the multivariate logistic regression analysis. In the present study, we confirmed that the prevalence of IHD was higher in the ASO group (36.0%, 9/25 patients) than in the non-ASO group (4.6%, 6/130 patients), whereas there was no statistically significant difference in the prevalence of CVD between the ASO group (24.0%, 6/25 patients) and the non-ASO group (14.6%, 19/130 patients). These results suggest that although the prevalence of IHD is strongly associated with the presence of ASO, the prevalence of CVD in SLE patients may be associated not only with ASO but also with other factors. With respect to the pathogenesis of CVD in SLE patients, platelet activation induced by aPLs is thought to be a possible mechanism of aPL-associated CVD [35, 37, 38]. Our previous studies indicated that SLE patients with both aCL/β2-GPI and anti-PS/PT have a high prevalence of cerebral infarction and that aCL/β2-GPI and anti-PS/PT promote platelet activation that may contribute to the pathogenesis of cerebral infarction in patients with SLE [39]. Because platelets in SLE patients are thought to be frequently activated by aPLs, infection, inflammation and endothelial cell damage, the high prevalence of CVD in SLE patients may be due not only to atherosclerosis but also to other factors such as platelet activation and endothelial cell damage.

In conclusion, in addition to the traditional risk factors for cardiovascular disease, the presence of ASO caused by aCL/β2-GPI is an important risk factor for development and progression of IHD in patients with SLE.

Formula

Disclosure statement: The authors have declared no conflicts of interest.


   References
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 

  1. Nojima J, Kuratsune H, Suehisa E, et al. Association between the prevalence of antibodies to beta(2)-glycoprotein I, prothrombin, protein C, protein S, and annexin V in patients with systemic lupus erythematosus and thrombotic and thrombocytopenic complications. Clin Chem (2001) 47:1008–15.[Abstract/Free Full Text]
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Submitted 12 December 2007; revised version accepted 22 February 2008.
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