The complement system in atherosclerosis

Activation of the alternative complement pathway modulates inflammation in thoracic aortic aneurysm/dissection

Thoracic aortic aneurysm/dissection (TAAD) is a lethal vascular disease, and several pathological factors participate in aortic medial degeneration. We previously discovered that the complement C3a-C3aR axis in smooth muscle cells promotes the development of thoracic aortic dissection (TAD) through regulation of matrix metalloproteinase 2. However, discerning the specific complement pathway that is activated and elucidating how inflammation of the aortic wall is initiated remain unknown. We ascertained that the plasma levels of C3a and C5a were significantly elevated in patients with TAD and that the levels of C3a, C4a, and C5a were higher in acute TAD than in chronic TAD. We also confirmed the activation of the complement in a TAD mouse model. Subsequently, knocking out Cfb (Cfb) or C4 in mice with TAD revealed that the alternative pathway and Cfb played a significant role in the TAD process. Activation of the alternative pathway led to generation of the anaphylatoxins C3a and C5a, and knocking out their receptors reduced the recruitment of inflammatory cells to the aortic wall. Moreover, we used serum from wild-type mice or recombinant mice Cfb as an exogenous source of Cfb to treat Cfb KO mice and observed that it exacerbated the onset and rupture of TAD. Finally, we knocked out Cfb in the FBN1C1041G/+ Marfan-syndrome mice and showed that the occurrence of TAA was reduced. In summary, the alternative complement pathway promoted the development of TAAD by recruiting infiltrating inflammatory cells. Targeting the alternative pathway may thus constitute a strategy for preventing the development of TAAD.NEW & NOTEWORTHY The alternative complement pathway promoted the development of TAAD by recruiting infiltrating inflammatory cells. Targeting the alternative pathway may thus constitute a strategy for preventing the development of TAAD.

Complement Inhibition Targeted to Injury Specific Neoepitopes Attenuates Atherogenesis in Mice

Rationale: Previous studies have indicated an important role for complement in atherosclerosis, a lipid-driven chronic inflammatory disease associated to oxidative stress in the vessel wall. However, it remains unclear how complement is activated in the process of atherogenesis. An accepted general model for complement activation in the context of ischemia reperfusion injury is that ischemia induces the exposure of neoepitopes that are recognized by natural self-reactive IgM antibodies, and that in turn activate complement. Objective: We investigated whether a similar phenomenon may be involved in the pathogenesis of atherosclerosis, and whether interfering with this activation event, together with inhibition of subsequent amplification of the cascade at the C3 activation step, can provide protection against atherogenesis. Methods and Results: We utilized C2scFv-Crry, a novel construct consisting of a single chain antibody (scFv) linked to Crry, a complement inhibitor that functions at C3 activation. The scFv moiety was derived from C2 IgM mAb that specifically recognizes phospholipid neoepitopes known to be expressed after ischemia. C2scFv-Crry targeted to the atherosclerotic plaque of Apoe -/- mice, demonstrating expression of the C2 neoepitope. C2scFv-Crry administered twice per week significantly attenuated atherosclerotic plaque in the aorta and aortic root of Apoe -/- mice fed with a high-fat diet (HFD) for either 2 or 4 months, and treatment reduced C3 deposition and membrane attack complex formation as compared to vehicle treated mice. C2scFv-Crry also inhibited the uptake of oxidized low-density-lipoprotein (oxLDL) by peritoneal macrophages, which has been shown to play a role in pathogenesis, and C2scFv-Crry-treated mice had decreased lipid content in the lesion with reduced oxLDL levels in serum compared to vehicle-treated mice. Furthermore, C2scFv-Crry reduced the deposition of endogenous total IgM in the plaque, although it did not alter serum IgM levels, further indicating a role for natural IgM in initiating complement activation. Conclusion: Neoepitope targeted complement inhibitors represent a novel therapeutic approach for atherosclerosis.

Serum Complement C1q Activity Is Associated With Obstructive Coronary Artery Disease

Background: Complement C1q plays a dual role in the atherosclerosis. Previous studies showed inconsistent results about the association of serum C1q levels and coronary artery disease (CAD). Here, we explored the associations of serum C1q activity with CAD, coronary stenosis severity, cardiovascular biomarkers, and 1-year restenosis after coronary artery revascularization.

Methods: We enrolled 956 CAD patients and 677 controls to evaluate the associations of serum complement C1q activity to the presence and severity of obstructive CAD and non-obstructive CAD. Serum C1q activity and the concentrations of laboratory markers were measured in all subjects. All the data were analyzed using SPSS22.0 software.

Results: Serum C1q activity in Obstructive CAD and Non-Obstructive CAD groups was significantly higher than the control group (195.52 ± 48.31 kU/L and 195.42 ± 51.25 kU/L vs. 183.44 ± 31.75 kU/L, P < 0.05). Greater C1q activity was significantly correlated with higher total cholesterol (TC) and triglyceride (TG) levels. C1q activity was associated with an increased Odds Ratio (OR) of CAD (OR = 1.322, 95% CI 1.168–1.496, P < 0.05) and 1-year restenosis after revascularization (the highest OR = 3.544, 95% CI 1.089–12.702, P < 0.05). Complement C1q activity was not correlated with Gensini score in the Obstructive CAD group after adjustment for confounders. C1q activity has low value in predicting the incidence of CAD.

Conclusion: Serum complement C1q activity is associated with obstructive CAD.

Increased Complement 3 With Suppression of miR-145 Induces the Synthetic Phenotype in Vascular Smooth Muscle Cells From Spontaneously Hypertensive Rats

Background

We previously reported that vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHRs) show the increased expression of complement 3 (C3) and the synthetic phenotype. We targeted the SHR C3 gene (C3 knockout [C3KO] SHRs) by the zinc finger gene editing method. In the current study, we investigated the mechanisms underlying the increased expression of C3 and the role of endogenous C3 in the synthetic phenotype of SHR VSMCs in comparison to cells from Wistar‐Kyoto (WKY) rats and C3KO SHRs.

Methods and Results

Nonmuscle myosin heavy chain staining of aortas from SHRs at 1 day after birth was stronger in comparison to WKY rats and C3KO SHRs. DNA synthesis in VSMCs from SHRs was significantly higher in comparison to WKY rats and C3KO SHRs. Immunohistochemical staining of renin and liver X receptor α in VSMCs from SHRs was stronger in comparison to WKY rats and C3KO SHRs. The expression of renin, Krüppel‐like factor 5, and liver X receptor α proteins in VSMCs from SHRs was significantly higher in comparison to WKY rats and C3KO SHRs. The expression of synthetic phenotype markers osteopontin, matrix gla, and l‐caldesmon, growth factors transforming growth factor‐β1 and platelet‐derived growth factor‐A, transcription factors Krüppel‐like factor 5 and liver X receptor α, and angiotensinogen mRNAs in VSMCs from SHRs was significantly higher in comparison to WKY rats and C3KO SHRs. The expression of miR‐145 mRNA in VSMCs from SHRs was suppressed in comparison to cells from WKY rats. miR‐145 inhibitor significantly increased the expression of C3 in VSMCs from WKY rats, but not in cells from SHRs.

Conclusions

These findings indicate that the increased C3 with the suppression of miR‐145 induces the synthetic phenotype through Krüppel‐like factor 5 and the activation of the renin‐angiotensin system through liver X receptor α in VSMCs from SHRs.

C-reactive protein and cardiovascular disease: From animal studies to the clinic (Review)

C-reactive protein (CRP) and cardiovascular disease (CVD) have long been important research topics. CRP is an acute phase protein, while CVD is an inflammatory condition. The association between CRP and CVD remains controversial and has been attracting increasing attention. Traditionally, the main marker of CVD is considered to be low-density lipoprotein cholesterol. However, due to its unique characteristics, CRP may represent a novel marker or a new therapeutic target for CVD. Clinical studies have demonstrated that CRP is a predictor of CVD, but whether it is directly involved in the development and progression of CVD has yet to be fully elucidated. Recent clinical studies have demonstrated that lowering plasma CRP levels may reduce the incidence of CVD. The aim of the present review was to investigate the association between CRP and CVD, particularly atherosclerosis, from laboratory animal studies to clinical research.

Overexpression of complement component C5a accelerates the development of atherosclerosis in ApoE-knockout mice

BACKGROUND

In this study, we investigated the direct effect of C5a overexpression on atherosclerosis.

METHODS AND RESULTS

A recombinant adenovirus expressing mouse C5a (Ad-C5a) was constructed and injected intravenously into ApoE-/- mice. After 12 weeks of a high-fat diet, Ad-C5a injection produced more extensive lesions than control adenovirus, and its proathrosclerotic role was significantly blocked by C5a receptor antagonist. Immunohistochemical analysis showed enhanced macrophage infiltration in atherosclerotic regions with C5a overexpression. Trans-well assay revealed C5a receptor-dependent chemotaxis of C5a to macrophages. Furthermore, Ad-C5a overexpression promoted foam cell formation and lipid deposition but reduced collagen content. In addition, with Ad-C5a overexpression, the serum levels of interleukin 6 and tumor necrosis factor α were upregulated.

CONCLUSIONS

C5a overexpression could accelerate the development of atherosclerosis in ApoE-/- mice by promoting macrophage recruitment, foam cell formation and inflammatory activation. Furthermore, its proatherogetic role is mediated by the C5a receptor.

The complement system and toll-like receptors as integrated players in the pathophysiology of atherosclerosis

Despite recent medical advances, atherosclerosis is a global burden accounting for numerous deaths and hospital admissions. Immune-mediated inflammation is a major component of the atherosclerotic process, but earlier research focus on adaptive immunity has gradually switched towards the role of innate immunity. The complement system and toll-like receptors (TLRs), and the crosstalk between them, may be of particular interest both with respect to pathogenesis and as therapeutic targets in atherosclerosis. Animal studies indicate that inhibition of C3a and C5a reduces atherosclerosis. In humans modified LDL-cholesterol activate complement and TLRs leading to downstream inflammation, and histopathological studies indicate that the innate immune system is present in atherosclerotic lesions. Moreover, clinical studies have demonstrated that both complement and TLRs are upregulated in atherosclerotic diseases, although interventional trials have this far been disappointing. However, based on recent research showing an intimate interplay between complement and TLRs we propose a model in which combined inhibition of both complement and TLRs may represent a potent anti-inflammatory therapeutic approach to reduce atherosclerosis.

Role of complement and complement regulatory proteins in the complications of diabetes

It is well established that the organ damage that complicates human diabetes is caused by prolonged hyperglycemia, but the cellular and molecular mechanisms by which high levels of glucose cause tissue damage in humans are still not fully understood. The prevalent hypothesis explaining the mechanisms that may underlie the pathogenesis of diabetes complications includes overproduction of reactive oxygen species, increased flux through the polyol pathway, overactivity of the hexosamine pathway causing intracellular formation of advanced glycation end products, and activation of protein kinase C isoforms. In addition, experimental and clinical evidence reported in past decades supports a strong link between the complement system, complement regulatory proteins, and the pathogenesis of diabetes complications. In this article, we summarize the body of evidence that supports a role for the complement system and complement regulatory proteins in the pathogenesis of diabetic vascular complications, with specific emphasis on the role of the membrane attack complex (MAC) and of CD59, an extracellular cell membrane-anchored inhibitor of MAC formation that is inactivated by nonenzymatic glycation. We discuss a pathogenic model of human diabetic complications in which a combination of CD59 inactivation by glycation and hyperglycemia-induced complement activation increases MAC deposition, activates pathways of intracellular signaling, and induces the release of proinflammatory, prothrombotic cytokines and growth factors. Combined, complement-dependent and complement-independent mechanisms induced by high glucose promote inflammation, proliferation, and thrombosis as characteristically seen in the target organs of diabetes complications.

Amide-adducts in atherosclerosis

Too many hypotheses in the etiology of atherosclerosis have been proposed. Classically, lipid insudation hypothesis by Virchow and thrombogenic hypothesis by Rokitansky are famous. However, in the recent progress in the area of atherosclerosis, the response-to-injury hypothesis by Ross (Ross R Glomset JA, N Engl J Med 295:369-377, 420-425, 1976; Ross R, Arteriosclerosis 1:293-311, 1981; Ross R, N Engl J Med 314:488-500, 1986; Ross R, Nature 362:801-809, 1993; Ross R, N Engl J Med 340:115-126, 1999) has been the leading one. In this review, however, the author focuses to the recent debate on the role of oxidative modification of atherogenic lipoproteins.

The membrane attack complex of complement drives the progression of atherosclerosis in apolipoprotein E knockout mice

Aims

To examine the roles of the membrane attack complex of complement and its sole membrane regulator, CD59, in atherosclerosis.

Methods

C6 (C6^−/−) deficient and CD59a (Cd59a^−/−) knockout mice were separately crossed onto the apolipoprotein E knockout (apoE^−/−) background. The double knockout mice were fed high-fat diet in order to study the effects of absence of C6 or CD59a on the progression of atherosclerosis.

Results

C6 deficiency significantly reduced plaque area and disease severity. CD59a had the opposite effect in that deficiency was associated with a significant increase in plaque area, correlating with increased membrane attack complex (MAC) deposition in the plaque and increased smooth muscle cell proliferation in early plaques.

Conclusions

Our results demonstrate that the MAC contributes to the development of atherosclerosis, C6 deficiency being protective and CD59a deficiency exacerbating disease.

Complement 3 is involved in changing the phenotype of human glomerular mesangial cells

Complement activation contributes to tissue injury in various forms of glomerulopathy and is characterized by deposition of complement components, which accelerates the progression of chronic renal damage. We recently reported that complement 3 (C3), a critical component of the complement system, is associated with the synthetic phenotype of vascular smooth muscle cells. It is possible that C3 stimulates mesangial cells to assume the synthetic phenotype to, in turn, induce glomerular injury and sclerosis. We investigated the role of C3 in the growth and phenotype of mesangial cells. Cultured human mesangial cells (HMCs) expressed C3 mRNA and protein, and levels were increased in response to IFN-gamma and TNF-alpha. HMCs also expressed C3a receptor mRNA and protein. Exogenous C3a stimulated DNA synthesis in HMCs in a dose-dependent manner. C3a decreased expression h-caldesmon mRNA, a marker of the contractile phenotype, and increased the expression of osteopontin, matrix Gla, and collagen type1 alpha1 (collagen IV) mRNAs, which are markers of the synthetic phenotype. C3a decreased expression of alpha-smooth muscle actin in HMCs. Small interfering RNA (siRNA) targeting C3 reduced the DNA synthesis and proliferation of HMCs, increased expression of h-caldesmon mRNA, and decreased expression of osteopontin, matrix Gla, and collagen IV mRNAs in HMCs. These results indicate that C3 causes HMCs to convert to the synthetic phenotype and stimulates growth of mesangial cells, suggesting that C3 may play an important role in phenotypic regulation of mesangial cells in renal diseases.

Complement 3 activates the KLF5 gene in rat vascular smooth muscle cells

We have shown that spontaneously hypertensive rat (SHR)-derived vascular smooth muscle cells (VSMCs) change to the synthetic phenotype and show increased expression of complement 3 (C3) and that C3 plays a role in the change to the synthetic phenotype. To determine the mechanisms underlying the effects of C3 on this phenotypic change, we examined the effects of C3a on transcription factors involved in VSMC phenotype and found that C3a increased the expression of Krüppel-like zinc-finger transcription factor 5 (KLF5) mRNA. C3a increased KLF5 promoter activity in a concentration-dependent manner. Deletion analysis of the promoter region of the KLF5 gene revealed that the region between nucleotides-991 and -699 contains the transcriptional regulatory element stimulated by C3a. C3a induced extracellular signal-regulated kinase (ERK) phosphorylation, and C3a-increased KLF5 promoter activity was completely inhibited by the MEK inhibitor U0126. These findings suggest that C3 increases KLF5 promoter activity and gene expression via ERK signaling.

Chlamydia pneumoniae infections augment atherosclerotic lesion formation: a role for serum amyloid P

Multiple reports have demonstrated an association between Chlamydia pneumoniae (Cpn) and cardiovascular disease. In this study we evaluated the effect of Cpn infections on early lesion progression in C57BL/6J mice. Since plaque formation in these mice does not develop past the initial stage, we thought these mice might be a better model for unravelling the effect of Cpn infection on early lesion type progression. C57BL/6J mice were fed an atherogenic diet and injected 10 times with 5 x 10(7) IFU Cpn or mock. At sacrifice, lesion number, size and type were analysed. To study the role of Cpn in inflammation, serum amyloid P (SAP) in plasma was determined as well as T-cells, macrophages and SAP in the lesions. In the aortic sinus of both groups, type 2 lesions were found. Cpn infection resulted in a 2.2-fold increase in total lesion size (Cpn: 10821+/-2429 microm(2)vs mock: 5022+/-1348 microm(2); p=0.04). No difference in lesion number was observed. Also, Cpn infection increased SAP in the lesions from 1.10(-4)+/-0.1.10(-4) SAP-positive cells/lesion area to 10.10(-4)+/-1.10(-4) SAP-positive cells/lesion area (p=0.05). The influx of T-lymphocytes and macrophages in the lesions as well as SAP plasma levels were not different between groups. Multiple Cpn infections resulted in a significant increase in total lesion size of C57BL/6J mice. Increase in total SAP-positive area in infected mice suggests a role for this acute-phase protein in lesion enlargement.

Premature atherosclerotic disease in systemic lupus erythematosus — role of inflammatory mechanisms

Mounting evidence from a growing body of epidemiologic studies demonstrates that patients with systemic lupus erythematosus (SLE) are at increased risk for the development of premature cardiovascular disease (CVD). However, awareness of accelerated atherosclerosis in young SLE patients, albeit growing, is still limited, as documented by the brief case presented. Inflammation is thought to play an important role in both the pathogenesis of SLE, as well as atherosclerotic vascular disease. Inflammatory processes that are shared by SLE and atherosclerotic disease include immune complex deposition and fixation, autoantibody binding, complement activation and CD40-CD40 ligand interaction. By examining the inflammatory mechanisms in common between SLE and atherosclerotic disease, we can come to a better understanding of the pathophysiology of the accelerated atherosclerotic process seen in patients with SLE and can gain insights into developing and instituting preventative and treatment strategies. In this article, we present a case of a young woman with SLE who presents with chest pain, followed by a review of inflammation-based pathogenic mechanisms that are shared by SLE and atherosclerotic cardiovascular disease.

Upregulation of the immune system in primary hypercholesterolaemia: effect of atorvastatin therapy

OBJECTIVES

High levels of plasma high sensitivity C-reactive protein (CRP), sensitive to therapy with statins, have been described in hypercholesterolaemia. In vitro evidence shows that CRP activates the complement system, which, in turn, leads to an increased expression of ICAM-1. Our objectives were to verify whether primary hypercholesterolaemia (PHC) is associated with an upregulation of the inflammatory/immune response, and whether this is sensitive to atorvastatin.

METHODS AND RESULTS

We examined the levels of sICAM-1, C3, C4 complement fractions in 48 patients with PHC, with (CAD group) or without (No-CAD group) coronary artery disease (CAD) in comparison with a group of 48 healthy controls. The two patient groups were studied before and after atorvastatin therapy. Both hypercholesterolaemic groups showed higher mean values of sICAM-1, C3 and C4 (P < 0.0001) when compared with the controls. The two groups of patients responded differently to atorvastatin therapy. After 3 months, the C3 levels normalized in both groups of patients (P < 0.02 compared with basal values); C4 was greatly reduced only in the CAD group (P < 0.01). After 12 months of therapy, in CAD group C3 mean levels were still significantly lower than baseline values (P < 0.01); a further decrease in the C4 values (P < 0.05 with respect to levels after 3 months of therapy) and also a substantial reduction in sICAM-1 values (P < 0.001 with respect to basal values) were observed.

CONCLUSIONS

High plasma values of C3 and C4 in PHC cluster with high values of sICAM-1, distinguish subjects with CAD and could be used to monitor the anti-inflammatory effect of statin therapy in these patients.

Up regulation of C3, C4, and soluble intercellular adhesion molecule-1 co-expresses with high sensitivity C reactive protein in familial hypoalphalipoproteinaemia: further evidence of inflammatory activation

OBJECTIVE

To test the working hypothesis that inflammation underlying precocious and severe coronary atherosclerotic disease in familial hypoalphalipoproteinaemia (FH) can be mediated by up regulation of the innate immune response.

METHODS AND RESULTS

52 patients with FH were compared with 52 healthy controls with regard to immune system markers such as C reactive protein (CRP), soluble intercellular adhesion molecule-1 (sICAM-1), C3c, and C4. Patients differed from controls in their significantly lower concentrations of high density lipoprotein cholesterol (30.2 (4.0) v 50.5 (13.6) mg/dl, p < 0.0001) and apolipoprotein A I (113.2 (19.9) v 148.7 (25.1) mg/dl, p < 0.0001) and their higher triglyceride (139.3 (63.2) v 81.4 (41.7) mg/dl, p < 0.0001) and CRP plasma concentrations (median 0.33 mg/dl, range 0.02-4.66 mg/dl v median 0.07 mg/dl, range 0.02-0.85 mg/dl, p < 0.0001), but not in their total cholesterol and low density lipoprotein cholesterol concentrations. Concentrations of protein complement were higher in patients (C3: 150.8 (42.3) v 101.9 (17.4) mg/dl, p < 0.0001; C4: 35.5 (13.6) v 22.8 (6.4) mg/dl, p < 0.0001) and sICAM-1 concentrations were more than double those found in the controls (335.1 (107.5) v 159.5 (78.2) mg/dl, p < 0.0001).

CONCLUSIONS

Increased concentrations of sICAM-1, C3c, and C4 co-express with high concentrations of CRP in FH. The lack of signs and symptoms of inflammation in these patients may suggest that the immune response is up regulated as part of the pro-inflammatory mechanisms that are activated in this atherogenic condition.

Autoimmune and inflammatory mechanisms in atherosclerosis

The present review focuses on the concept that cellular and humoral immunity to the phylogenetically highly conserved antigen heat shock protein 60 (HSP60) is the initiating mechanism in the earliest stages of atherosclerosis. Subjecting arterial endothelial cells to classical atherosclerosis risk factors leads to the expression of HSP60 that then may serve as a target for pre-existent cross-reactive antimicrobial HSP60 immunity or bona fide autoimmune reactions induced by biochemically altered autologous HSP60. Endothelial cells can also bind microbial or autologous HSP60 via Toll-like receptors, providing another possibility for targetting adaptive or innate immunological effector mechanisms.

Complement 3 is involved in the synthetic phenotype and exaggerated growth of vascular smooth muscle cells from spontaneously hypertensive rats

Vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) show the synthetic phenotype and exaggerated growth in comparison with VSMCs from normotensive Wistar-Kyoto (WKY) rats. We investigated genes associated with the synthetic phenotype and exaggerated growth of VSMCs from SHR by microarray. Expression of 1300 transcripts was evaluated by microarray with total mRNA extracted from mid-layer aortic smooth muscle of 3-week-old SHR/Izumo and WKY/Izumo rats. mRNAs encoding sodium-dependent neurotransmitter transporter, epidermal growth factor precursor, EEF2, leptin receptor long-isoform b, clathrin assembly protein short form, and preprocomplement 3 (pre-pro-C3) were expressed only in aortic smooth muscle from SHR by microarray and by reverse-transcription polymerase chain reaction analysis. Pre-pro-C3 mRNA was detected only in cultured VSMCs from SHR. Exogenous C3 changed VSMCs to the synthetic phenotype. Antisense oligodeoxynucleotides (ODN) to C3 reduced the higher level of DNA synthesis in VSMCs from SHR. Antisense ODN to C3 increased expression of SM22alpha mRNA and decreased expression of osteopontin and matrix Gla mRNAs. It also decreased expression of growth factor mRNAs in VSMCs from SHR. In conclusion, we have shown that C3, independent of other complement molecules, has direct effects on the phenotype of VSMCs and stimulates growth of these cells. C3 is produced only by VSMCs from SHR. Therefore, C3 may be the gene underlying the synthetic phenotype and exaggerated growth of VSMCs from SHR. C3 may be a new target for the treatment of hypertension.

Lack of complement factor C3, but not factor B, increases hyperlipidemia and atherosclerosis in apolipoprotein E-/- low-density lipoprotein receptor-/- mice

OBJECTIVE

To investigate the effect of complement deficiency on atherogenesis and lipidemia, we used mice deficient in the third complement component (C3-/-) or factor B (FB-/-).

METHODS AND RESULTS

Complement-deficient mice were crossed with mice deficient in both apolipoprotein E and the low-density lipoprotein receptor (Apoe-/- LDLR-/-). The percent lesion area in the aorta at 16 weeks, determined by en face analysis, was 84% higher in C3-/- mice than in controls (11.8%+/-0.4% versus 6.4%+/-0.8%, mean+/-SEM, P<0.00005). The C3-/- mice also had 58% higher serum triglyceride levels (P<0.05) and a more proatherogenic lipoprotein profile, with significantly more low-density lipoprotein cholesterol and very-low-density lipoprotein triglycerides than control mice. The C3-/- mice weighed 13% less (P<0.01) and had a lower body fat content (3.5%+/-1.0% versus 13.1%+/-3.0%, P<0.01). There were no differences between FB-/- mice and controls.

CONCLUSIONS

Complement activation by the classical or lectin pathway exerts atheroprotective effects, possibly through the regulation of lipid metabolism.

The terminal complement complex inhibits apoptosis in vascular smooth muscle cells by activating an autocrine IGF-1 loop

Two counteracting processes determine accumulation of human vascular smooth muscle cells (SMCs) in atherosclerotic lesions: cell proliferation and apoptosis. SMCs synthesize insulin-like growth factor-1 (IGF-1), which potently inhibits apoptosis. The terminal complement complex C5b-9 interacts with SMCs in early human atherogenesis. In this study, we investigated whether C5b-9 may activate the IGF-1 system in SMCs, resulting in the inhibition of SMC apoptosis. C5b-9 generation on SMCs in vitro markedly reduced CD95-mediated apoptosis as assessed by flowcytometric analysis of annexin V binding and in caspase 3 assays. C5b-9 induced both significant IGF-1 release and up-regulation of IGF-1 binding sites in SMCs. Immunoneutralization of IGF-1 with a monoclonal IGF-1 antibody abolished the antiapoptotic effects of C5b-9. We conclude that C5b-9 inhibits apoptosis in SMCs by inducing an autocrine IGF-1 loop. This mechanism may contribute to the accumulation of SMCs in early human atherosclerotic lesions.

Deficiency of the mouse complement regulatory protein mCd59b results in spontaneous hemolytic anemia with platelet activation and progressive male infertility

Basal complement activity presents a potential danger for "self" cells that are tightly protected by complement regulators including CD59. Mice express two Cd59 genes (mCd59a and mCd59b); mCd59b has approximately a 6-fold higher specific activity than mCd59a. Consistently, mCd59b knockout mice present a strong phenotype characterized by hemolytic anemia with increased reticulocytes, anisopoikilocytosis, echinocytosis, schistocytosis, free hemoglobin in plasma, hemoglobinuria with hemosiderinuria, and platelet activation. Remarkably, mCd59b(-/-) males express a progressive loss of fertility associated with immobile dysmorphic and fewer sperm cells after 5 months of age. This work indicates that mCd59b is a key complement regulator in mice and that CD59 is critical in protecting self cells; it also provides a novel model to study complement regulation in human diseases.

Complement components, but not complement inhibitors, are upregulated in atherosclerotic plaques

Complement activation occurs in atherosclerotic plaques. The capacity of arterial tissue to inhibit this activation through generation of the complement regulators C1 inhibitor, decay accelerating factor, membrane cofactor protein (CD46), C4 binding protein (C4BP), and protectin (CD59) was evaluated in pairs of aortic atherosclerotic plaques and nearby normal artery from 11 human postmortem specimens. All 22 samples produced mRNAs for each of these proteins. The ratios of plaque versus normal artery pairs was not significantly different from unity for any of these inhibitors. However, in plaques, the mRNAs for C1r and C1s, the substrates for the C1 inhibitor, were increased 2.35- and 4.96-fold, respectively, compared with normal artery; mRNA for C4, the target for C4BP, was elevated l.34-fold; and mRNAs for C7 and C8, the targets for CD59, were elevated 2.61- and 3.25-fold, respectively. By Western blotting and immunohistochemistry, fraction Bb of factor B, a marker of alternative pathway activation, was barely detectable in plaque and normal arterial tissue. These data indicate that it is primarily the classical, not the alternative pathway, that is activated in plaques and that key inhibitors are not upregulated to defend against this activation.

Generation of C-reactive protein and complement components in atherosclerotic plaques

C-reactive protein (CRP) and complement are hypothesized to be major mediators of inflammation in atherosclerotic plaques. We used the reverse transcriptase-polymerase chain reaction technique to detect the mRNAs for CRP and the classical complement components C1 to C9 in both normal arterial and plaque tissue, establishing that they can be endogenously generated by arteries. When the CRP mRNA levels of plaque tissue, normal artery, and liver were compared in the same cases, plaque levels were 10.2-fold higher than normal artery and 7.2-fold higher than liver. By Western blotting, we showed that the protein levels of CRP and complement proteins were also up-regulated in plaque tissue and that there was full activation of the classical complement pathway. By in situ hybridization, we detected intense signals for CRP and C4 mRNAs in smooth muscle-like cells and macrophages in the thickened intima of plaques. By immunohistochemistry we showed co-localization of CRP and the membrane attack complex of complement. We also detected up-regulation in plaque tissue of the mRNAs for the macrophage markers CD11b and HLA-DR, as well as their protein products. We showed by immunohistochemistry macrophage infiltration of plaque tissue. Because CRP is a complement activator, and activated complement attacks cells in plaque tissue, these data provide evidence of a self-sustaining autotoxic mechanism operating within the plaques as a precursor to thrombotic events.

Structure-apoptotic potency evaluations of novel sterols using human leukemic cells

Three oxidized analogs of cholesterol have been characterized for their ability to cause apoptotic cell death in CEM-C7-14 human leukemic cells. In addition to testing 15-ketocholestenol (K15), 15-ketocholestenol hydroxyethyl ether (CK15), and 7-ketocholesterol hydroxyethyl ether (CK7), an oxysterol of known apoptotic response, 25-hydroxycholesterol (25OHC), served as a standard for comparison. Growth studies based on dye exclusion by viable cells while using a sublethal concentration of oxysterols ranked their potency for cell kill as 25OHC > K15 > CK15 > CK7. Both the TUNEL assay (terminal deoxynucleotidyl transferase-mediated dUTP-X nick end labeling), which quantifies the amount of DNA nicks caused by a toxic agent, and the MTT assay, which measures cell metabolism and thus reflects cell viability, substantiated the same rank order. An ELISA assay for evaluating release of DNA fragments into the cytosol after treatment gave a similar potency order. The oncogene c-myc mRNA was suppressed by all three oxysterols, with 25OHC and K15 being the most potent suppressors. Hoechst and Annexin V staining documented that these oxysterols kill cells by an apoptotic pathway as evidenced by condensation of nuclear chromatin and plasma membrane inversion, respectively. From these in vitro studies, we believe that 25OHC, K15, and possibly CK15 have the potential to be chemotherapeutic agents.

mRNA expression of complement components and regulators in rat arterial smooth muscle cells

The presence of C5b-9 complexes, some complement regulators, and abundant cytokines in atherosclerotic lesions has been reported. However, it is unclear whether these complement-associated proteins are produced by vascular smooth muscle cells (SMCs) and how they are influenced by the cytokines. In the present study, we demonstrated, by the reverse transcription-polymerase chain reaction method, the mRNA expression of complement components (C3, C4, and C5) and membrane regulators (decay-accelerating factor, membrane cofactor protein, Crry, and CD59) in cultured SMCs derived from the rat carotid artery. The expression of C9 mRNA was also induced upon stimulation by interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha) and/or lipopolysaccharide (LPS). Northern blot analysis showed that the mRNA expression of C3, C4, DAF and Crry was up-regulated, but that of CD59 was down-regulated by IFN-gamma, TNF-alpha and/or LPS alone or by synergy. The increase of C3 mRNA by TNF-alpha or LPS and that of C4 mRNA by IFN-gamma was induced in a dose-dependent manner. The results indicate that the arterial SMCs of rat have the ability to produce complement components and regulators, which is affected by cytokines and/or LPS. Since atherosclerosis is characterized by the intimal proliferation of SMCs, the complement system including its regulators may be involved in the pathogenesis of the disease.

C-reactive protein as a cardiovascular risk factor: more than an epiphenomenon?

BACKGROUND

Circulating levels of C-reactive protein (CRP) may constitute an independent risk factor for cardiovascular disease. How CRP as a risk factor is involved in cardiovascular disease is still unclear.

METHODS AND RESULTS

By reviewing available studies, we discuss explanations for the associations between CRP and cardiovascular disease. CRP levels within the upper quartile/quintile of the normal range constitute an increased risk for cardiovascular events, both in apparently healthy persons and in persons with preexisting angina pectoris. High CRP responses after acute myocardial infarction indicate an unfavorable outcome, even after correction for other risk factors. This link between CRP and cardiovascular disease has been considered to reflect the response of the body to the inflammatory reactions in the atherosclerotic (coronary) vessels and adjacent myocardium. However, because CRP localizes in infarcted myocardium (with colocalization of activated complement), we hypothesize that CRP may directly interact with atherosclerotic vessels or ischemic myocardium by activation of the complement system, thereby promoting inflammation and thrombosis.

CONCLUSIONS

CRP constitutes an independent cardiovascular risk factor. Unraveling the molecular background of this association may provide new directions for prevention of cardiovascular events.

Prevention of neointimal formation by a serine protease inhibitor, FUT-175, after carotid balloon injury in rats

BACKGROUND AND PURPOSE

In vivo and vitro studies revealed the activation of thrombin and the complement system in vascular lesion formation during the process of atherosclerosis, along with pathological proliferation of smooth muscle cells. We examined the effect of the synthetic serine protease inhibitor FUT-175 (developed as a potent inhibitor of thrombin and the complement system) on vascular lesions using balloon dilatation-induced neointimal formation in the carotid artery of rats.

METHODS

Sprague-Dawley (SD) rats underwent balloon dilatation injury of the left carotid artery to induce neointimal formation. Three groups of these rats (n=8, each) were treated with daily intraperitoneal injections of 1 of the following doses of FUT-175: 0.5, 1.0, or 2.0 mg/d in 1 mL of saline for 7 consecutive days. The control group (n=8) was similarly treated with 1 mL of saline for 7 days. The injections were started immediately after balloon injury. Two weeks after the injury, the left carotid arteries were perfusion-fixed, and the areas of the neointimal and medial layer were analyzed under a microscope.

RESULTS

A morphometric analysis revealed that there were significant differences in the intima-media ratio between the 4 groups treated with vehicle (saline) or a low, medium, or high dose of FUT-175 (1.45+/-0.11, 1.08+/-0.06, 0.71+/-0.04, or 0.32+/-0.04, respectively). This suppression was achieved in a dose-dependent manner by the administration of FUT-175 after balloon injury. In the histological study, it was demonstrated that FUT-175 suppresses the production of platelet-derived growth factor (PDGF)-BB in the neointima and the medial smooth muscle cell layer.

CONCLUSIONS

After balloon injury activated proteases that were inhibited by FUT-175 were demonstrated to have an essential role in the development of the pathological thickening of the arterial wall.

Complement C6 deficiency protects against diet-induced atherosclerosis in rabbits

Low-density lipoprotein (LDL) can be transformed to an atherogenic moiety by nonoxidative, enzymatic degradation. Enzymatically degraded LDL induces macrophage foam cell formation, provokes release of cytokines, and also activates complement. To determine whether complement activation may contribute to atherogenesis, 6 pairs of homozygous C6-deficient rabbits and their non-C6-deficient heterozygous siblings were fed a cholesterol-rich diet for 14 weeks. Cholesterol levels and plasma lipoprotein profiles of the animals in the C6-competent and C6-deficient groups did not significantly differ, and the high density lipoprotein and LDL cholesterol ratios at the end of the experiment were 0.07+/-0.01 and 0.08+/-0.01 (SEM), respectively. However, differences in atherosclerotic plaque formation were discernible macroscopically, with extensive aortic lesions being visible in all C6-competent animals and absent in all C6-deficient animals. Aortas were sectioned from thorax to abdomen, and 10 sections were stained from each aorta. Quantification of atherosclerotic lesions and lumen stenosis with the use of computer-based morphometry documented a dramatic protective effect of C6 deficiency on the development of diet-induced atherosclerosis. We conclude that the terminal complement sequence is centrally involved in atherosclerotic lesion progression.

Reviparin-sodium prevents complement-mediated myocardial injury in the isolated rabbit heart

The cytoprotective action of reviparin-sodium (LU-47311: Clivarin), a low-molecular-weight heparin, was examined in an ex vivo model of complement-mediated myocardial injury. The effective concentration of reviparin was determined by using an in vitro rabbit erythrocyte-lysis assay using 4% normal human plasma. Reviparin (0.01-2.73 mg/ml) reduced erythrocyte lysis in a concentration-dependent manner. Subsequently, 0.91 mg/ml of reviparin was evaluated in an ex vivo rabbit isolated-heart model of human complement-mediated injury. Hearts perfused in the presence of 0.91 mg/ml of reviparin (n = 10) demonstrated significant preservation of ventricular function compared with vehicle-treated hearts (n = 10), as evidenced by coronary artery perfusion pressure, left ventricular developed pressure, and left ventricular end-diastolic pressure. A reduction in myocyte creatine kinase release was observed in reviparin-treated hearts compared with controls. Myocardial injury in vehicle-treated hearts was associated with an increased assembly of the membrane-attack complex, as determined by immunohistochemical localization of C5b-9 neoantigen. Reviparin decreased fluid-phase Bb formation detected in the lymphatic drainage of plasma-perfused hearts. The results of this study demonstrate that reviparin inhibits complement-mediated myocardial injury as assessed in an ex vivo experimental model of complement activation.

Immunohistochemical colocalization of the terminal complex of human complement and smooth muscle cell alpha-actin in early atherosclerotic lesions

There is substantial evidence that activated components of the complement cascade are present in atherosclerotic lesions, and it was suggested some years ago that smooth muscle cells may be an important target of complement attack by the terminal components of the cascade, C5b-9, also called the membrane attack complex. Recent in vitro studies have shown that assembly of membrane attack complex on smooth muscle cells leads to the release of monocyte chemotactic protein-1, and, if this were to occur in vivo, then it could be responsible for the recruitment of monocytes into the lesion. In this study we have investigated the localization of C5b-9 in early atherosclerotic lesions of human coronary arteries, collected from autopsies, by immunohistochemical staining, C5b-9 was found to colocalize widely with smooth muscle cell alpha-actin, but not with intact macrophages, thus supporting the hypothesis that interaction of complement with smooth muscle cells may indeed be important in atherogenesis.

Processes in atherogenesis: complement activation

The complement system consists of a complex group of plasma proteins, which, on activation, lead to a cascade of interactions culminating in the production of a variety of pro-inflammatory molecules. The system also contains cellular receptors for complement fragments produced during activation and regulatory molecules. It is part of the innate immune system representing humoral defence, but in certain circumstances may itself contribute to disease. In the formation of atherosclerotic lesions, there are two outstanding cellular phenomena, monocyte recruitment, with subsequent development of lipid-filled foam cells and smooth muscle cell activation. Subendothelial deposition of low density lipoprotein appears to be an important stimulus in these events and substantial evidence suggests that complement activation may be a link between lipoprotein deposition and subsequent lesion development.

Development of the lipid-rich core in human atherosclerosis

In recent years the role of the atherosclerotic core in promoting plaque rupture has become well recognized. A new insight into core development is its origination early in atherogenesis, before formation of the fibrous plaque. The early core is associated with accumulation of vesicular lipid rich in free cholesterol. Later in core development, lipid deposits become more diverse. The weight of evidence points toward a direct extracellular process, probably lipoprotein aggregation and fusion, as the chief pathway of cholesteryl ester accumulation, although foam cell death may also contribute cholesteryl ester. The mechanism or mechanisms of formation of vesicular, cholesterol-rich deposits are unknown. Since the increase in free cholesterol is likely to have deleterious effects on cells bordering the core, the further elucidation of cellular and biochemical pathways leading to and responding to free cholesterol accumulation is of great importance. Complement activation and cellular stress responses are prominent in the vicinity of core lipids, but their pathogenetic roles remain to be established. Since the core appears so early in atherogenesis, these as well as other, yet to be determined cellular responses to core lipids, oxidized and unoxidized, could have a considerable effect on overall lesion development. Much remains to be learned about macrophage and smooth muscle responses, calcification, capillarization, and matrix protein alterations in the evolution of the core and surrounding arterial intima.

Autoantibodies against heat shock protein 60 mediate endothelial cytotoxicity

Stress or heat shock proteins (hsp) are a family of approximately two dozen proteins with a high degree of amino acid sequence homology between different species, ranging from prokaryotes to humans, and are representative of a generalized response to environmental and metabolic stressors. Our previous studies showed increased expression of human hsp60 on endothelial cells of arterial intima with atherosclerotic lesions, and elevated levels of serum antibodies (Ab) against hsp65/60 in subjects with carotid atherosclerosis. To investigate the possible involvement of anti-hsp65/60 Ab in endothelial injury, specific hsp-Ab were isolated from human high titer sera by affinity chromatography and probed on heat-shock human umbilical vein endothelial cells. Purified human anti-hsp65/60 Ab reacted specifically with mycobacterial hsp65, human hsp60, and a 60-kD protein band of heat-shocked endothelial cells. High levels of hsp60 mRNA expression in endothelial cells were found between 4 and 12 h after 30 min treatment at 42 degrees C. In immunofluorescence tests, positive staining of heat-stressed endothelial cells was observed not only in the cytoplasm but also on the cell surface. Furthermore, only heat-stressed, but not untreated, Cr-labeled endothelial cells were lysed by anti-hsp65/60 Ab in the presence of complement (complement-mediated cytotoxicity) or peripheral blood mononuclear cells (antibody-dependent cellular cytotoxicity). Control Abs, including human anti-hsp65/60 low titer antiserum, human Ig fraction deprived of hsp65/60 Ab, and mAbs to Factor VIII, alpha-actin, hsp70, and CD3 showed no cytotoxic effect. In conclusion, human serum anti-hsp65 antibodies act as autoantibodies reacting with hsp60 on stressed endothelial cells and are able to mediate endothelial cytotoxicity. Thus, a humoral immune reaction to hsp60 may play an important role in the pathogenesis of atherosclerosis.

Association of serum C3 levels with the risk of myocardial infarction

PURPOSE

Serum complement and IgA levels have been found to be retrospectively associated with the presence of diffuse atherosclerosis. This study was performed to assess whether serum immunoglobulins and complement components are predictive of future ischemic events.

PATIENTS AND METHODS

The baseline values of IgG, IgA, IgM, C3, and C4 were measured in the sera from a cohort of 860 inhabitants of the town of Brisighella, Italy. They were 444 men and 416 women, mean age 53.9 years (SD 12.4, range 23 to 84), who had not had any ischemic events (myocardial infarction [MI], angina pectoris, stroke, transient ischemic attack, or intermittent claudication) at the time of blood sampling in 1984. Their baseline values for the main recognized risk factors for atherosclerosis were known at baseline and for 4 years of follow-up. Multiple logistic regression analysis was performed for associations between ischemic events and immunologic variables (including serum IgG, IgA, IgM, C3, and C4) and risk factors for atherosclerosis (including age, sex, diastolic blood pressure, cigarette consumption, Quetelet index, total cholesterol, HDL cholesterol, triglycerides and blood glucose).

RESULTS

During follow-up, 57 subjects experienced ischemic events, including 28 cases of coronary heart disease (17 MI and 11 angina pectoris). Of the immunologic variables studied, only serum C3 was found to be independently associated with ischemic events (P < 0.005 for any ischemic events, coronary heart disease, and MI). The population was divided into thirds according to C3 values. The cumulative incidence of MI was 7.1/1,000 in the low third, 10.6/1,000 in the middle third and 40.8/1,000 in the high third (risk ratio for high versus middle plus low = 4.2 after adjustment for age and sex; 95% CI 1.5 to 11.7). A separate analysis for the sexes showed that serum C3 was a particularly powerful predictor of MI in men. Men whose C3 levels were in the top third had a 72.6/1,000 incidence of MI while the incidence in the rest of the male population was 6.2/1,000 (risk ratio 10.7 after adjustment for age; 95% CI 2.3 to 49.0). When similar analyses were performed for angina pectoris, stroke, and intermittent claudication, no significant increase in risk was found to be associated with serum C3.

CONCLUSION

C3 levels measured in sera from male subjects without previous ischemic events are independently associated with the risk of MI.

Physiology and pathophysiology of complement: progress and trends

The complement system comprises a family of at least 20 plasma and membrane proteins that interact in a tightly regulated cascade system to destroy invading bacteria and prevent the deposition of immune complexes in the tissues. This brief review addresses the basic mechanisms of complement activation and control and describes the active fragments produced during complement activation. The biological importance of the complement system is amply illustrated in patients with complement deficiencies, who are susceptible to bacterial infections and immune complex diseases. The involvement of complement in other immunological diseases is an expanding area of clinical research, supported by the development of new assays for the identification of complement activation. This area is discussed here with particular reference to neurological diseases. A promising new prospect involves the use of complement inhibitory molecules in therapy of complement-mediated disease and this exciting area is also discussed. Novel physiological roles of complement also are being revealed and new evidence that complement and complement receptors play an important role in reproduction is summarized. It is hoped that this brief overview will convey some of the enthusiasm currently pervading research in this underappreciated area of immunology.

Elevated complement activities of sera from patients with high density lipoprotein deficiency (Tangier disease): the presence of normal level of clusterin and the possible implication in the atherosclerosis

Clusterin (apolipoprotein J, SP-40,40), as well as apolipoprotein A-I (apo A-I) and apolipoprotein A-II (apo A-II), are apolipoprotein components of high density lipoprotein (HDL), but not of low density lipoprotein. In spite of the deficiencies of apo A-I, apo A-II and HDL in the sera of patients with Tangier disease, clusterin was found in them at normal level. While clusterin was present as the component of HDL with apo A-I in sera of normal donors, it was present as a protein which did not form a complex in sera of Tangier patients. SC5b-9 made from the sera of Tangier patients contained normal amounts of clusterin and was deficient in apo A-I, indicating that clusterin could be incorporated into the SC5b-9 complex without apo A-I. The complement activities of the sera of the patients were higher than those of normal donors. These results may be explained by the deficiencies of apo A-I, apo A-II and HDL in the patients, because they were suggested to be the inhibitors of the reactive haemolysis of complement. The elevated complement activities of the patients might be related to the severe atherosclerotic lesions in Tangier disease.

Hypoxia causes an abnormal contractile response in the atherosclerotic rabbit aorta. Implication of reduced nitric oxide and cGMP production

Both atherosclerotic lesions and hypoxia alter the contractile properties of the arterial wall and, in particular, may interfere with the relaxation mechanisms dependent or not on the endothelium. The present study was designed to test the effect of severe hypoxia on the contractile behavior of the atherosclerotic rabbit aorta. Segments of aortas obtained from control, cholesterol-fed, or Watanabe hereditary hyperlipidemic rabbits were mounted in organ chambers for isometric tension recording. A change of the bath PO2 from "normoxic" conditions (95% O2-5% CO2) to "hypoxic" conditions (95% N2-5% CO2) caused relaxation in the precontracted control aortas (by approximately 85%) but a transient contraction (approximately 20% of the maximal contraction obtained with 30 mM KCl) followed by a relaxation in the precontracted atherosclerotic aortas. Both types of responses were observed in aortas contracted with aggregating platelets, 5-hydroxytryptamine (5-HT), norepinephrine, endothelin, and prostaglandin F2 alpha. The hypoxic contractions in atherosclerosis were not dependent on the presence of an intact endothelium. They could not be antagonized by blockers of alpha-adrenoceptors, 5-HT2 receptors, histamine receptors, thromboxane receptors, and muscarinic cholinoreceptors. Inhibitors of cyclooxygenase, lipoxygenase, Na+, K(+)-ATPase, and free radical scavengers or an activator of endothelium-derived relaxing factor did not significantly affect the hypoxic contraction; the absence of effect of some inhibitors of protein synthesis seems to rule out the involvement of endothelin, angiotensin II, and bradykinin. The hypoxic contraction was not influenced by omission of Ca2+ from the medium or by inhibition of Ca2+ influx but was prevented by blockade of intracellular Ca2+. The inhibitor of nitric oxide synthase (nitro-L-arginine, 100 microM) and the guanylyl cyclase inhibitor (methylene blue, 10 microM) both enhanced the initial contractile responses to 5-HT to a similar extent as hypoxia and completely prevented the hypoxic contraction in the atherosclerotic tissues. The cyclic nucleotide analogues 8-bromo-cGMP and dibutyryl cAMP also inhibited the hypoxic contraction in the atherosclerotic aorta. The cGMP levels were markedly decreased and the cAMP levels were moderately decreased in the aortas of the cholesterol-fed rabbits as compared with the control aortas. Hypoxia further decreased cGMP but not the cAMP levels in atherosclerotic aortas with and without endothelium. Our data thus demonstrate the occurrence of an unusual vasoconstrictor response in atherosclerotic arteries; this constrictor response depends on the availability of intracellular Ca2+ and seems to be due to the further inhibition of an already impaired cGMP production.(ABSTRACT TRUNCATED AT 400 WORDS)

Association of serum antibodies to heat-shock protein 65 with carotid atherosclerosis

Arteriosclerotic lesions can be induced in normocholesterolaemic rabbits by immunisation with heat-shock protein (hsp) 65, a stress protein expressed in high concentrations in human atherosclerotic lesions. If an immune reaction to hsp65 also plays a part in human atherogenesis, it should be possible to detect anti-hsp65 antibodies in patients with atherosclerotic lesions. To study the possible relation between immune reaction to hsp65 and atherosclerosis, 867 normal inhabitants of South Tyrol, aged 40-79 years, were selected randomly for determination of serum antibodies against hsp65, simultaneous sonographic assessment of carotid atherosclerotic lesions, and evaluation of established risk factors--ie, blood cholesterol, hypertension, smoking, diabetes mellitus, and obesity. Autoantibodies to nuclear antigens, thyroid antigens, and rheumatoid factors were also measured. Serum anti-hsp65 antibodies were significantly (p < 0.05) increased in subjects aged 60-79 years with carotid atherosclerosis compared with those without lesions, and increased antibody concentration was independent of age, sex, and other established risk factors. On the other hand, the incidence and titres of autoantibodies did not correlate with carotid atherosclerotic lesions. Our data provide the first evidence of a strong correlation between anti-hsp65 antibodies and carotid atherosclerosis, suggesting that hsp65 might be involved in the pathogenesis of atherosclerosis.

Induction of arteriosclerosis in normocholesterolemic rabbits by immunization with heat shock protein 65

Previous studies have established the presence of high numbers of activated T lymphocytes and "aberrant" expression of major histocompatibility complex class II antigens by endothelial and smooth muscle cells in human atherosclerotic lesions, implicating the involvement of a local cellular immune response. The identity of the antigen(s) eliciting this immune response, the extent of their effect, and the atherogenic stage at which they occur remain to be determined. In the present studies, 120 normocholesterolemic New Zealand White rabbits were immunized one or more times with various antigens, with or without adjuvants. The antigens and adjuvants included human or rabbit atherosclerotic lesion proteins, ovalbumin, Freund's complete and/or incomplete adjuvants, recombinant mycobacterial heat shock protein 65 (hsp65), and two hsp-free adjuvants, Ribi complete adjuvant and lipopeptide. In addition, some groups received a high-cholesterol diet. Sixteen weeks after the first immunization the animals were killed, and arteriosclerotic lesions in the intima of the aortic arch were found to have developed only in those animals immunized with antigenic preparations containing hsp, either in the form of whole mycobacteria or as purified recombinant hsp65, although their serum cholesterol levels were normal. No arteriosclerotic changes exceeding those of controls were found in the other groups, irrespective of the antigen used. Immunohistopathologic examination revealed that the lesions contained 20% T cells, 10-30% macrophages, and 10-40% smooth muscle cells. Analysis of the peripheral blood T-lymphocyte proliferative responses revealed that the occurrence of lesions was positively correlated with the presence of hsp65-reactive T cells, suggesting that hsp65 is involved in the induction of arteriosclerotic lesions. Furthermore, combined immunization with hsp-containing material and a cholesterol-rich diet provoked development of significantly more severe atherosclerosis and the appearance of characteristic foam cells. We conclude that an (auto)immune response to hsp may initiate the development of atherosclerosis and that a high blood cholesterol level is only one albeit a very important risk factor.

The apolipoprotein(a) moiety of lipoprotein(a) interacts with the complement activation fragment iC3b but does not functionally affect C3 activation or degradation

A previous study has shown that complement component C3 binds to recombinant apolipoprotein(a) (r-apo(a)). In the present report we have investigated the interactions between lipoprotein(a) (Lp(a)), r-apo(a) and C3 in relation to complement activation and degradation. Neither Lp(a) nor r-apo(a) affected complement activation as indicated by sheep and rabbit red blood cell hemolytic assays, and by assessment of the amount of C3a generated in zymosan-activated human serum in the presence or absence of Lp(a). Crossed immunoelectrophoretic analyses indicated that Lp(a) retarded the migration of iC3b in complement-activated serum but had no effects on C3, C3b, C3c or C3dg. Recombinant apo(a) exhibited the same properties as intact Lp(a) indicating that it is the apo(a) portion of Lp(a) that mediates this effect and not the lipid moiety. Low density lipoprotein had no effect on the migration of C3 cleavage fragments. Treatment of Lp(a) or apo(a) with neuraminidase abolished their capacity to alter iC3b migration. SDS-PAGE immunoblotting analysis of C3 activation fragments generated in the presence of Lp(a) demonstrated the usual physiologic C3 cleavage fragments. Rocket intermediate gel immunoelectrophoresis of complement-activated serum demonstrated that Lp(a) did not hinder or accelerate the generation of C3c and C3dg breakdown fragments of iC3b. The results indicate that the apo(a) moiety of Lp(a) alters the migration of iC3b in an electric field but does not affect complement activation or degradation of activated C3. The sialic acid residues on apo(a) are necessary for the apo(a)-iC3b interaction.