Immunogenic oxidized low-density lipoprotein/beta2-glycoprotein I complexes in the diagnostic management of atherosclerosis

Impaired Autophagy Induced by oxLDL/β2GPI/anti-β2GPI Complex through PI3K/AKT/mTOR and eNOS Signaling Pathways Contributes to Endothelial Cell Dysfunction

Endothelial cell dysfunction plays a fundamental role in the pathogenesis of atherosclerosis (AS), and endothelial autophagy has protective effects on the development of AS. Our previous study had shown that oxidized low-density lipoprotein/β2-glycoprotein I/anti-β2-glycoprotein I antibody (oxLDL/β2GPI/anti-β2GPI) complex could promote the expressions of inflammatory cytokines and enhance the adhesion of leukocytes to endothelial cells. In the present study, we aimed to assess the effects of oxLDL/β2GPI/anti-β2GPI complex on endothelial autophagy and explore the associated potential mechanisms. Human umbilical vein endothelial cells (HUVECs) and mouse brain endothelial cell line (bEnd.3) were used as models of the vascular endothelial cells. Autophagy was evaluated by examining the expressions of autophagic proteins using western blotting analysis, autophagosome accumulation using transmission electron microscopy, and RFP-GFP-LC3 adenoviral transfection and autophagic flux using lysosome inhibitor chloroquine. The expressions of phospho-PI3K, phospho-AKT, phospho-mTOR, and phospho-eNOS were determined by western blotting analysis. 3-Methyladenine (3-MA) and rapamycin were used to determine the role of autophagy in oxLDL/β2GPI/anti-β2GPI complex-induced endothelial cell dysfunction. We showed that oxLDL/β2GPI/anti-β2GPI complex suppressed the autophagy, evidenced by an increase in p62 protein, a decrease in LC3-II and Beclin1, and a reduction of autophagosome generation in endothelial cells. Moreover, inhibition of autophagy was associated with PI3K/AKT/mTOR and eNOS signaling pathways. Rapamycin attenuated oxLDL/β2GPI/anti-β2GPI complex-induced endothelial inflammation, oxidative stress, and apoptosis, whereas 3-MA alone induced the endothelial injury. Our results suggested that oxLDL/β2GPI/anti-β2GPI complex inhibited endothelial autophagy via PI3K/AKT/mTOR and eNOS signaling pathways and further contributed to endothelial cell dysfunction. Collectively, our findings provided a novel mechanism for vascular endothelial injury in AS patients with an antiphospholipid syndrome (APS) background.

OxLDL/β2GPI/anti‑β2GPI Ab complex induces inflammatory activation via the TLR4/NF‑κB pathway in HUVECs

Patients with antiphospholipid syndrome have been identified to have higher incidence rates of atherosclerosis (AS) due to the elevated levels of anti-β2-glycoprotein I (β2GPI) antibody (Ab). Our previous studies revealed that the anti-β2GPI Ab formed a stable oxidized low-density lipoprotein (oxLDL)/β2GPI/anti-β2GPI Ab complex, which accelerated AS development by promoting the accumulation of lipids in macrophages and vascular smooth muscle cell. However, the effects of the complex on endothelial cells, which drive the initiation and development of AS, remain unknown. Thus, the present study aimed to determine the proinflammatory roles of the oxLDL/β2GPI/anti-β2GPI Ab complex in human umbilical vein endothelial cells (HUVECs) in an attempt to determine the underlying mechanism. Reverse transcription-quantitative PCR, enzymy-linked immunosorbent assay, western blotting and immunofluorescence staining were performed to detect the expressions of inflammation related factors and adhesion molecules. Monocyte-binding assay was used to investigate the effects of oxLDL/β2GPI/anti-β2GPI Ab complex on monocyte adhesion to endothelial cells. The results demonstrated that the oxLDL/β2GPI/anti-β2GPI Ab complex upregulated the expression of Toll-like receptor (TLR)4 and the levels of NF-κB phosphorylation in HUVECs, and subsequently enhanced the expression levels of inflammatory cytokines, including TNF-α, IL-1β and IL-6, as well as those of adhesion molecules, such as intercellular adhesion molecule 1 and vascular adhesion molecule 1. In addition, the complex facilitated the recruitment of monocytes by promoting the secretion of monocyte chemotactic protein 1 in HUVECs. Notably, the described effects of the oxLDL/β2GPI/anti-β2GPI Ab complex in HUVECs were abolished by either TLR4 or NF-κB blockade. In conclusion, these findings suggested that the oxLDL/β2GPI/anti-β2GPI Ab complex may induce a hyper-inflammatory state in endothelial cells by promoting the secretion of proinflammatory cytokines and monocyte recruitment, which was discovered to be largely dependent on the TLR4/NK-κB signaling pathway.

Beta-2-glycoprotein-I IgA antibodies predict coronary plaque progression in rheumatoid arthritis

OBJECTIVES

To evaluate whether anti-Beta-2-Glycoprotein-I (anti-β2GPI) IgA antibodies associate with progression of coronary atherosclerosis and cardiovascular disease (CVD) events in rheumatoid arthritis (RA).

METHODS

One hundred-fifty patients underwent plaque evaluation (total, non-calcified, mixed and calcified) with coronary computed tomography angiography; 101 were re-imaged within 6.9±0.3 years to assess progression. The Framingham-D'Agostino score assessed cardiovascular risk. Coronary artery calcium (CAC) and segment involvement score quantified plaque burden.

RESULTS

Anti-β2GPI IgA were seen in 45 (30%) patients. Despite no link to baseline plaque burden, anti-β2GPI IgA associated with segment involvement score increase (adjusted-RR=1.64 [95%CI 1.02-2.63]), CAC change (adjusted-β=0.33 [95%CI 0.002-0.656]) and developing new extensive or obstructive plaque at follow-up (adjusted-OR=4.24 [95%CI 1.30-13.87]). Adding anti-β2GPI IgA to logistic regression models with conventional risk factors predicting plaque progression outcomes increased Area under the receiver-operator curve and improved Net Reclassification and Integrated Discrimination Improvement indices (all P<0.05). In per-segment analyses, anti-β2GPI IgA predicted mixed plaque formation (adjusted-OR=3.20 [95%CI 1.01-10.09]) and lower likelihood of transition of mixed to calcified plaque (adjusted-OR=0.19 [95%CI 0.04-0.96]). Anti-β2GPI IgA moderated the effect of C-reactive protein on CAC change such that C-reactive protein associated with CAC change (β=0.26 [95%CI 0.14-0.38]) and CVD risk (adjusted-HR=1.89 [95%CI 1.02-3.51]) only in anti-β2GPI IgA positive patients.

CONCLUSION

Anti-β2GPI IgA addition to clinical risk models improved prediction accuracy of CAC, plaque progression and transition to extensive/obstructive disease. They associated with new high-risk mixed plaques and delayed healing to calcified lesions. Anti-β2GPI IgA further modified the effect of inflammation on plaque progression and CVD events.

Soluble Vascular Biomarkers in Rheumatoid Arthritis and Ankylosing Spondylitis: Effects of 1-year Antitumor Necrosis Factor-α Therapy

OBJECTIVE

Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) have been associated with cardiovascular disease. The treatment of arthritis by tumor necrosis factor-α (TNF-α) inhibitors may decrease the serum concentrations of vascular biomarkers. We determined circulating levels of oxidized low-density lipoprotein (oxLDL)/β₂ glycoprotein I (β₂-GPI) complexes, antibodies to 60 kDa heat shock protein (anti-Hsp60), soluble urokinase plasminogen activator receptor (suPAR), and B-type natriuretic peptide (BNP) fragment in sera of RA and AS patients undergoing anti-TNF treatment.

METHODS

Fifty-three patients with RA/AS were treated with etanercept or certolizumab pegol for 1 year. Circulating oxLDL/β₂-GPI complex (AtherOx), anti-Hsp60 IgG, and BNP8-29 fragment levels were assessed by ELISA. suPAR levels were determined by suPARnostic Quick Triage test. Flow-mediated vasodilation (FMD), carotid intima-media thickness (CIMT), and arterial pulse wave velocity (PWV) were determined by ultrasound.

RESULTS

One-year anti-TNF treatment significantly decreased oxLDL/β₂-GPI levels, as well as suPAR levels in patients with critically high suPAR levels at baseline. In RA, BNP levels were higher in seropositive vs seronegative patients. Serum levels of these vascular biomarkers variably correlated with lipids, anticitrullinated protein antibodies, rheumatoid factor, and C-reactive protein. CIMT positively correlated with BNP, and PWV with suPAR and anti-Hsp60, whereas FMD inversely associated with anti-Hsp60. In repeated measures ANOVA analysis, disease activity supported the effects of anti-TNF treatment on 12-month changes in oxLDL/β₂-GPI. CIMT supported the effects of therapy on changes in anti-Hsp60 and suPAR.

CONCLUSION

These biomarkers may be involved in the pathogenesis of atherosclerosis underlying RA/AS. TNF inhibition variably affects the serum levels of oxLDL/β₂-GPI, suPAR, and BNP.

Physiology and pathophysiology of oxLDL uptake by vascular wall cells in atherosclerosis

Atherosclerosis is a progressive disease in which endothelial cell dysfunction, macrophage foam cell formation, and smooth muscle cell migration and proliferation, lead to the loss of vascular homeostasis. Oxidized low-density lipoprotein (oxLDL) may play a pre-eminent function in atherosclerotic lesion formation, even if their role is still debated. Several types of scavenger receptors (SRs) such as SR-AI/II, SRBI, CD36, lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), toll-like receptors (TLRs) and others can promote the internalization of oxLDL. They are expressed on the surface of vascular wall cells (endothelial cells, macrophages and smooth muscle cells) and they mediate the cellular effects of oxLDL. The key influence of both oxLDL and SRs on the atherogenic process has been established in atherosclerosis-prone animals, in which antioxidant treatment and/or silencing of SRs has been shown to reduce atherogenesis. Despite some discrepancies, the indication from cohort studies that there is an association between oxLDL and cardiovascular (CV) events seems to point toward a role for oxLDL in atherosclerotic plaque progress and disruption. Finally, randomized clinical trials using antioxidants have demonstrated benefits only in high-risk patients, suggesting that additional proofs are still needed to better define the involvement of each type of modified LDL in the development of atherosclerosis.

Accelerated vascular disease in systemic lupus erythematosus: role of macrophage

Atherosclerosis is a chronic inflammatory condition that is considered a major cause of death worldwide. Striking phenomena of atherosclerosis associated with systemic lupus erythematosus (SLE) is its high incidence in young patients. Macrophages are heterogeneous cells that differentiate from hematopoietic progenitors and reside in different tissues to preserve tissue integrity. Macrophages scavenge modified lipids and play a major role in the development of atherosclerosis. When activated, macrophages secret inflammatory cytokines. This activation triggers apoptosis of cells in the vicinity of macrophages. As such, macrophages play a significant role in tissue remodeling including atherosclerotic plaque formation and rupture. In spite of studies carried on identifying the role of macrophages in atherosclerosis, this role has not been studied thoroughly in SLE-associated atherosclerosis. In this review, we address factors released by macrophages as well as extrinsic factors that may control macrophage behavior and their effect on accelerated development of atherosclerosis in SLE.

Macrophage Heterogeneity and Plasticity: Impact of Macrophage Biomarkers on Atherosclerosis

Cardiovascular disease (CVD) is a global epidemic, currently representing the worldwide leading cause of morbidity and mortality. Atherosclerosis is the fundamental pathophysiologic component of CVD, where the immune system plays an essential role. Monocytes and macrophages are key mediators in this aspect: due to their heterogeneity and plasticity, these cells may act as either pro- or anti-inflammatory mediators. Indeed, monocytes may develop heterogeneous functional phenotypes depending on the predominating pro- or anti-inflammatory microenvironment within the lesion, resulting in classic, intermediate, and non-classic monocytes, each with strikingly differing features. Similarly, macrophages may also adopt heterogeneous profiles being mainly M1 and M2, the former showing a proinflammatory profile while the latter demonstrates anti-inflammatory traits; they are further subdivided in several subtypes with more specialized functions. Furthermore, macrophages may display plasticity by dynamically shifting between phenotypes in response to specific signals. Each of these distinct cell profiles is associated with diverse biomarkers which may be exploited for therapeutic intervention, including IL-10, IL-13, PPAR-γ, LXR, NLRP3 inflammasomes, and microRNAs. Direct modulation of the molecular pathways concerning these potential macrophage-related targets represents a promising field for new therapeutic alternatives in atherosclerosis and CVD.

Reduced beta2-glycoprotein I protects macrophages from ox-LDL-induced foam cell formation and cell apoptosis

Background

Reduced beta2-glycoprotein I (beta2-GPI) is a free thiol-containing form of beta2-GPI that displays a powerful effect in protecting endothelial cells from oxidative stress-induced cell death. The present study aims to investigate the effect of beta2-GPI or reduced beta2-GPI on ox-LDL-induced foam cell formation and on cell apoptosis and to determine the possible mechanisms.

Methods

The RAW264.7 macrophage cell line was selected as the experimental material. Oil red O staining and cholesterol measurement were used to detect cholesterol accumulation qualitatively and quantitatively, respectively. Flow cytometry was used to detect cell apoptosis. Real-time quantitative PCR was used to detect the mRNA expression of the main proteins that are associated with the transport of cholesterol, such as CD36, SRB1, ABCA1 and ABCG1. Western blot analysis was used to detect the protein expression of certain apoptosis-related proteins, such as caspase-9, caspase-3, p38 MAPK/p-p38 MAPK and JNK/p-JNK.

Results

Beta2-GPI or reduced beta2-GPI decreased ox-LDL-induced cholesterol accumulation (96.45 ± 8.51 μg/mg protein vs. 114.35 ± 10.38 μg/mg protein, p < 0.05;74.44 ± 5.27 μg/mg protein vs. 114.35 ± 10.38 μg/mg protein, p < 0.01) and cell apoptosis (30.00 ± 5.10% vs. 38.70 ± 7.76%, p < 0.05; 20.66 ± 2.50% vs. 38.70 ± 7.76%, p < 0.01), and there are significant differences between beta2-GPI and reduced beta2-GPI (p < 0.05). Reduced beta2-GPI decreased the ox-LDL-induced expression of CD36 mRNA and ABCA1 mRNA (p < 0.05), as well as CD36, cleaved caspase-9, cleaved caspase-3, p-p38 MAPK and p-JNK proteins (p < 0.05 or p < 0.01). Beta2-GPI did not significantly decrease the expression of ABCA1 mRNA and the p-p38 MAPK protein.

Conclusions

Both beta2-GPI and reduced beta2-GPI inhibit ox-LDL-induced foam cell formation and cell apoptosis, and the latter exhibits a stronger inhibition effect. Both of these glycoproteins reduce the lipid intake of macrophages by downregulating CD36 as well as protein expression. Reduced beta2-GPI inhibits cell apoptosis by reducing the ox-LDL-induced phosphorylation of p38 MAPK and JNK, and the amount of cleaved caspase-3 and caspase-9. Beta2-GPI does not inhibit the ox-LDL-induced phosphorylation of p38 MAPK.

C-reactive protein/oxidised low-density lipoprotein/β2-glycoprotein I complex promotes atherosclerosis in diabetic BALB/c mice via p38mitogen-activated protein kinase signal pathway

Background

The aim of this study was to investigate the effect of C-reactive protein/oxidised low-density lipoprotein/β2-glycoprotein I (CRP/oxLDL/β2GPI) complex on atherosclerosis (AS) in diabetic BALB/c mice.

Methods

BALB/c mice were fed high-fat and normal diet. Eight weeks later, the mice fed with high-fat diet were injected with streptozotocin (STZ) to induce diabetes. The diabetic mice were respectively injected twice monthly with 20 μg oxLDL, 20 μg β2GPI, 40 μg oxLDL/β2GPI complex, 44 μg CRP/oxLDL/β2GPI complex, and PBS. Aortas were stained with Sudan IV to investigate lipid plaque formation. The infiltration condition of smooth muscle cells (SMCs), macrophages, and T cells in the aortas were determined by immunohistochemistry (IH). The mRNA expressions of receptors associated with lipid metabolism were quantified by real-time PCR. The phosphorylation of p38 mitogen-activated protein kinase (p38MAPK) and MKK3/6 in aorta tissues were assessed by Western blot. The expression of inflammation cytokines was evaluated by protein chip.

Results

The lipid plaques were more extensive, the lumen area was obviously narrower, the ratio of intima and media thickness were increased, and the normal internal elastic lamia structure and endothelial cell disappeared (P < 0.05) in the oxLDL and CRP/oxLDL/β2GPI groups (P < 0.05). CRP/oxLDL/β2GPI complex dramatically promoted infiltration of SMCs, macrophages, and T cells, improved the mRNA expression of ABCA1 and ABCG1, but reduced the mRNA expression of SR-BI and CD36 and increased the phosphorylation of p38MAPK and MKK3/6 (all P < 0.05). The highest expression levels of IL-1, IL-9, PF-4, bFGF, and IGF-II were detected in the CRP/oxLDL/β2GPI group (P < 0.05).

Conclusions

CRP/oxLDL/β2GPI complex aggravated AS in diabetic BALB/c mice by increasing lipid uptake, the mechanism of which may be mediated by the p38MAPK signal pathway.

The biology of reactive intermediates in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune syndrome marked by autoantibody production. Innate immunity is essential to transform humoral autoimmunity into the clinical lupus phenotype. Nitric oxide (NO) is a membrane- permeable signaling molecule involved in a broad array of biologic processes through its ability to modify proteins, lipids, and DNA and alter their function and immunogenicity. The literature regarding mechanisms through which NO regulates inflammation and cell survival is filled with contradictory findings. However, the effects of NO on cellular processes depend on its concentration and its interaction with reactive oxygen. Understanding this interaction will be essential to determine mechanisms through which reactive intermediates induce cellular autoimmunity and contribute to a sustained innate immune response and organ damage in SLE.

Effect of hormone replacement therapy on total serum anti-oxidant potential and oxidized LDL/β2-glycoprotein I complexes in postmenopausal women

Oxidative stress and consequent oxidized lipoprotein production is thought to play a central role in both the initiation and progression of atherosclerosis. Oxidized low-density lipoprotein (oxLDL)/β2-glycoprotein I (β2GPI) complexes are etiologically important in the development of atherosclerosis. The aim of the present study was to investigate whether long-term treatment with conventional hormone replacement therapy (HRT) in postmenopausal women could affect total serum antioxidant capacity (TAC) and serum levels of oxLDL/β2GPI complexes. A total of 60 normolipidemic postmenopausal women treated with oral estrogen together with progestin therapy for 3 months were selected. TAC and serum levels of oxLDL/β2GPI complexes were measured at the beginning and end of the HRT. HRT led to a significant increase in TAC (15%, P=0.02) and a minor but statistically nonsignificant decrease of oxLDL/β2GPI complexes (3%, P=0.30) when compared with the baseline control levels. There was also no significant association between TAC and oxLDL/β2GPI complexes changes related to HRT. This study indicates that, HRT in postmenopausal women leads to an increase in TAC without an equivalent change in serum levels of oxLDL/β2GPI complexes. It is concluded that beneficial effects of HRT could be explained, at least in part, by improving antioxidant status, but may not be directly associated with a change in oxidized lipoprotein production.

Clinical significance of the humoral immune response to modified LDL

Human low density lipoprotein (LDL) undergoes oxidation and glycation in vivo. By themselves, oxidized LDL (oxLDL) and AGE-LDL have proinflammatory properties and are considered atherogenic. But the atherogenicity of these lipoproteins are significantly increased as a consequence of the formation of immune complexes (IC) involving specific autoantibodies. OxLDL and AGE antibodies have been shown to be predominantly of the IgG1 and IgG3 isotypes. OxLDL antibodies are able to activate the complement system by the classical pathway and to induce FcR-mediated phagocytosis. In vitro and ex vivo studies performed with modified LDL-IC have proven their pro-inflammatory and atherogenic properties. Clinical studies have demonstrated that the levels of circulating modified LDL-IC correlate with parameters indicative of cardiovascular and renal disease in diabetic patients and other patient populations. The possibility that spontaneously formed or induced modified LDL antibodies (particularly IgM oxLDL antibodies) may have a protective effect has been suggested, but the data is unclear and needs to be further investigated.