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

Role of complement activation in atherosclerosis

PURPOSE OF REVIEW

Atherosclerosis is characterized by a strong inflammatory component. One factor contributing to inflammation in the arterial intima is the complement system. Here we summarize recent progress in the field of complement research on atherogenesis.

RECENT FINDINGS

The complement system is activated in human atherosclerotic lesions and is actively regulated by the local synthesis of complement components and of complement regulatory proteins. Potential triggers of complement activation in the arterial intima include immunocomplexes, C-reactive protein, modified lipoproteins, apoptotic cells, and cholesterol crystals. Complement activation releases anaphylatoxins, and anaphylatoxin receptors have been identified in human atherosclerotic lesions. However, experiments on genetically engineered mice with severe hyperlipidemia have been unable to show a major role for complement in experimental atherogenesis.

SUMMARY

In humans there is extensive circumstantial evidence for a role of complement in atherosclerosis, which is somewhat contradictory to recent modest or negative findings in atherosclerosis-prone genetically engineered hyperlipidemic mice.

Local generation of C-reactive protein in diseased coronary artery venous bypass grafts and normal vascular tissue

BACKGROUND

Venous coronary artery bypass grafts (CABGs) are prone to accelerated atherosclerosis. In atherosclerotic diseases, serum C-reactive protein (CRP) levels have become an important diagnostic and prognostic marker. The origin of CRP in this setting remains to be elucidated.

METHODS AND RESULTS

Monoclonal anti-CRP identified CRP expression in medial and intimal alpha-actin-positive smooth muscle cells (SMCs) of diseased CABGs with type V and VI lesions and also of native saphenous veins of atherosclerotic individuals. In addition, patent coronary arteries with type IV and V but not with type I through III lesions exhibited intense SMC staining for CRP. Calcified desobliterates of occluded coronary arteries with end-stage disease did not show SMC staining for CRP and were consistently negative for CRP mRNA, as detected by means of real-time polymerase chain reaction. However, CRP mRNA was expressed in 11 of 15 diseased CABGs and also in 10 of 15 native veins. By contrast, only 3 of 18 internal mammary and 4 of 12 radial arteries with virtually no atherosclerosis were positive for CRP mRNA.

CONCLUSIONS

CRP is produced by SMCs of atherosclerotic lesions with active disease but not in end-stage plaques. The role of CRP constitutively expressed by normal vascular tissue in vein graft disease has yet to be elucidated.

Update on vascular disease in systemic lupus erythematosus

PURPOSE OF REVIEW

Young women with systemic lupus erythematosus have strikingly high rates of coronary heart disease. Current knowledge indicates that atherosclerosis is an active inflammatory and immune-mediated process. Therefore, the chronic inflammation and immune dysregulation characteristic of systemic lupus erythematosus undoubtedly contribute to the accelerated vascular disease seen in these patients. Carefully considering what is known about atherogenesis in the general population will provide clues to unraveling the complexity of why systemic lupus erythematosus and atherosclerosis are linked so frequently.

RECENT FINDINGS

Inflammation is involved in all aspects of atherogenesis from the initial endothelial "response to injury," to foam cell formation leading to the atherosclerotic lesion, to the rupture of the "vulnerable" fibrous cap, resulting in the acute coronary syndrome and potentially in death. The authors review how factors commonly seen in systemic lupus erythematosus or inherent to the underlying disease mechanism may contribute to each of the stages of atherogenesis.

SUMMARY

Our focus on the causes of vascular disease in systemic lupus erythematosus must now include nontraditional risk factors such as immune and inflammatory mediators. With the advent of noninvasive screening tools for atherosclerosis, we are better equipped to measure subclinical vascular disease and associated risk factors, including immune and inflammatory mediators. When considering strategies for preventing premature cardiovascular disease in systemic lupus erythematosus, modifying immune and inflammatory risk factors will likely become a major component of the program in addition to modifying the current traditional risk factors.

C-reactive protein correlates with macrophage accumulation in coronary arteries of hypercholesterolemic pigs

A growing body of evidence supports the hypothesis that C-reactive protein (CRP) is a marker of inflammation in coronary artery disease. The purpose of the present study was to test the hypothesis that CRP correlates with macrophage accumulation during the initial stages of coronary vascular disease. Adult male pigs were fed a normal chow (NF) or a high-fat high-cholesterol (HF) diet for 20 wk. After 20 wk, blood was collected for analyses of interleukin-6 (IL-6), CRP, and lipids. After blood collection, the pigs were euthanized and the right coronary arteries (RCA) were harvested and fixed in neutral buffered formalin. Paraffin-embedded sections of RCA were stained immunohistochemically for CRP, scavenger receptor A (SRA), and monocyte chemoattractant protein-1 (MCP-1). All cholesterol fractions were elevated in the HF vs. the NF group (P < 0.05). There was little or no positive staining for CRP, SRA, or MCP-1 in the RCA of NF pigs, but there was extensive staining in lipidladen macrophage foam cells in the HF pigs. Double staining revealed colocalization of CRP with SRA and CRP with MCP-1 in foam cells. Serum IL-6 was below the assay detection limit in all pigs. Serum CRP correlated directly with plasma total cholesterol (R = 0.727, P = 0.041) and accumulation of SRA-positive macrophages (R = 0.938, P < 0.001) in RCA of HF pigs. We conclude that serum CRP correlates with macrophage accumulation and coronary artery disease in hypercholesterolemic pigs.

Interaction of oxidative stress and inflammatory response in coronary plaque instability: important role of C-reactive protein

OBJECTIVE

C-reactive protein (CRP), a predictor of cardiovascular events, localizes in atherosclerotic arteries and exerts proinflammatory effects on vascular cells. Reactive oxygen species (ROS) have been implicated in atherogenesis and plaque instability.

METHODS AND RESULTS

Expressional pattern of CRP in directional coronary atherectomy specimens from 39 patients was examined. Characteristics of histological plaque instability and higher levels of serum CRP and fibrinogen were associated with the CRP immunoreactivity. In situ hybridization revealed the presence of CRP mRNA in coronary vasculature. Furthermore, the expression of CRP mRNA and protein was detected in cultured human coronary artery smooth muscle cells (CASMCs) by reverse transcriptase-polymerase chain reaction and Western blotting. In addition, CRP was frequently colocalized with p22phox, an essential component of NADH/NADPH oxidase, which is an important source of ROS in vasculature. Moreover, the incubation of cultured CASMCs with CRP resulted in the enhanced p22phox protein expression and in the generation of intracellular ROS.

CONCLUSIONS

The expression of CRP in coronary arteries was associated with histological and clinical features of vulnerable plaque, and it had a prooxidative effect on cultured CASMCs, suggesting that it might play a crucial role in plaque instability and in the pathogenesis of acute coronary syndrome via its prooxidative effect.

C-reactive protein: a novel marker of cardiovascular risk

Patients without traditional cardiovascular risk factors continue to suffer from cardiovascular events, which has prompted a search for novel markers to better assess cardiovascular risk. Inflammatory biomarkers have surfaced as prime candidates, given the integral role of inflammation in atherosclerosis. C-reactive protein (CRP) measurements in particular have emerged as powerful predictors of cardiovascular risk in a broad spectrum of patient populations. Newer high sensitivity CRP assays now in use are standardized and reproducible, and can detect variations in CRP below the limit of standard assays. In primary prevention populations, studies have shown up to a 2-4-fold increased risk of cardiovascular events in healthy patients with elevated CRP levels. In this population, models incorporating CRP and lipid parameters appear to predict risk significantly better than lipids alone. In patients with established cardiovascular disease and in patients undergoing percutaneous coronary interventions, CRP levels may help predict short- and long-term prognosis, identifying subgroups of patients at increased risk of recurrent events. CRP levels may also prove useful in targeting therapy for primary and secondary prevention, by identifying patients who would most benefit from medications such as statins and aspirin. This review presents an overview of the data regarding CRP measurement for cardiovascular risk assessment.

Association between coronary endothelial dysfunction and local inflammation of atherosclerotic coronary arteries

We have examined a possibility whether or not severity and extent of coronary atherosclerosis may associate with degree of local inflammation in relation to endothelial dysfunction as is indicated by reduced NO formation. Blood samples were obtained from aortic root (Ao) and coronary sinus (CS) of 39 patients who underwent coronary angiography. Plasma NOx levels (nitrite + nitrate, stable NO end-products) were evaluated by HPLC-Griess system, and markers of inflammation, C-reactive protein (CRP) and serum amyloid A protein (SAA), were measured by Latex Turbidimetric Immunoassay. To evaluate the changes of these substances through coronary circulation, the percentage changes of respective markers [(CS - Ao) x 100/Ao] were calculated. The extent and severity of atherosclerosis of left coronary arteries were evaluated with Gensini Score (GS). The GS correlated with the percentage changes of NOx (r = -0.35, p < 0.05) and that of SAA (r = 0.43, p < 0.05) across coronary circulation, but not with changes in CRP. Moreover, the percentage changes of NOx correlated with that of SAA (r = -0.36, p < 0.05). These results indicated that severity and extent of coronary atherosclerosis related to degree of local inflammation which has a possible association with coronary endothelial dysfunction.

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.

Detecting vulnerable plaque using peripheral blood: inflammatory and cellular markers

The concept of the vulnerable patient has arrived. Enhanced diagnostic methods will eventually permit accurately finding and treating these patients and their disease. Clinical Cardiologists now recognize that coronary atherosclerosis is two pathophysiologically distinct syndromes: stable and unstable. Stable coronary syndromes result from fixed, severe stenoses limiting blood flow and causing secondary myocardial ischemia. The unstable acute coronary syndromes are frequently catastrophic and are pathophysiologically distinct. They result from different cell subsets causing vascular inflammatory syndromes rather than gradual lumen constriction by plaque. Though pathophysiologically distinct, they may show common pathophysiology when a ruptured plaque heals and progressively becomes a critical stenosis. For the present hs-CRP measurement is the strongest correlative factor for future clinical events due to arterial inflammation: myocardial infarction, unstable angina, stroke, and peripheral vascular disease in both diseased and apparently healthy, asymptomatic patients. The CRP plasma level also is the best risk assessment in patients with either stable or unstable angina, long term after myocardial infarction, and in patients undergoing revascularization therapies. One study showed the only independent cardiovascular risk indicators using multivariate, age adjusted and traditional risk analysis were CRP and Total/HDL cholesterol ratio. If CRP, IL-6, and ICAM-1 levels are added to lipid levels, risk assessment can be improved over lipids alone. The prevalence of high-risk subjects in the general population is low, amplifying diagnostic problems for vulnerable plaque. Since no test yet has high sensitivity or specificity, diagnostic errors are high, with many false positives and negatives. Sensitivity or specificity must be increased by developing a risk marker panel, or by simultaneously finding other markers that themselves are highly sensitive and specific for vulnerable plaque.

Association between complement factor H and proteoglycans in early human coronary atherosclerotic lesions: implications for local regulation of complement activation

OBJECTIVE

Complement activation has been suggested to play a role in atherogenesis. To study the regulation of complement activation in human coronary atherosclerotic lesions, we examined the spatial relationships between the major complement inhibitor, factor H, and the complement activation products C3d and C5b-9.

METHODS AND RESULTS

In early lesions (American Heart Association types II and III), factor H was immunohistochemically found in the superficial proteoglycan-rich layer in association with numerous macrophages and C3d, whereas C5b-9 was found deeper in the intima, where factor H was virtually absent. In vitro experiments involving surface plasmon resonance and affinity chromatography analyses demonstrated that isolated human arterial proteoglycans bind factor H, and functional complement assays showed that glycosaminoglycans inhibit the complement activation induced by modified low density lipoprotein or by a foreign surface.

CONCLUSIONS

The present observations raise the possibility that proteoglycans, because of their ability to bind the major complement inhibitor factor H, may inhibit complement activation in the superficial layer of the arterial intima. In contrast, deeper in the intima, where factor H and proteoglycans are absent, complement may be activated and proceed to C5b-9. Thus, the superficial and the deep layers of the human coronary artery appear to differ in their ability to regulate complement activation.

Effect of treatment of chronic periodontitis on levels of serum markers of acute-phase inflammatory and vascular responses

AIMS

Recent epidemiological work suggests an association between periodontal disease severity and cardiovascular disease risk. This study aimed to ascertain if circulating levels of cardiovascular and systemic inflammatory markers could be modified following treatment of periodontal disease.

METHOD

Adult subjects were recruited from those awaiting periodontal treatment and randomised to either immediate (test, n=24) or delayed treatment (control, n=15). Demographic and clinical data were collected and venous blood was taken before and either 6 weeks after completion of treatment or after an equivalent 3-month control period. Periodontal examination included probing depth, loss of attachment, plaque scores and bleeding scores. Blood was analysed to determine serum and plasma fibrinogen, C-reactive protein, sialic acid, tumour necrosis factor-alpha and interleukin -6 and -1beta. Effects of treatment were assessed by paired tests and analysis of variance by treatment group with baseline covariates.

RESULTS

Treatment improved plaque and bleeding scores and reduced probing depths (p<0.002). However, there were no statistically significant changes in levels of any of the systemic markers.

CONCLUSION

Improvement in periodontal health did not influence the levels of vascular markers.

Serum C-reactive protein level is associated with abdominal aortic aneurysm size and may be produced by aneurysmal tissue

BACKGROUND

Abdominal aortic aneurysms (AAA) are characterized by extensive transmural inflammation and C-reactive protein (CRP) has emerged as an independent risk factor for the development of cardiovascular disease. Therefore, we evaluated a possible association between serum CRP and aneurysm dimension in patients with asymptomatic AAA. Furthermore, the possibility of CRP production by aneurysmal tissue has been examined.

METHODS AND RESULTS

Serum CRP was determined highly sensitive (hsCRP) and aneurysmal size was measured in 39 patients with AAA. The presence of CRP mRNA was assessed in the aneurysmal tissue of 16 patients. Mean (SD) hsCRP was 3.23 (2.96) mg/L. After log-transformation, hsCRP correlated significantly with aneurysmal size (r=0.477, P=0.002). When the patients were divided into 3 equally sized groups according to hsCRP level, aortic diameter increased from lowest to upper hsCRP-tertile (49 mm, 61 mm, and 67 mm, respectively; P<0.05 for 3rd versus 1st tertile). This association persisted after correction for risk factors. CRP mRNA was found in 25% of aneurysmal aortic tissues.

CONCLUSIONS

This is the first report showing that serum hsCRP is associated with aneurysmal size and that-in at least some patients-CRP may be produced by aneurysmal tissue. These data underscore the inflammatory nature of AAA formation, suggesting that serum hsCRP may serve as a marker of AAA disease and that CRP produced in vascular tissue might contribute to aneurysm formation.

C-reactive protein: the pawn has been promoted to queen

C-reactive protein (CRP) is one of the acute phase reactants that can increase its serum level up to 100- fold during systemic inflammation. Its clinical use was limited in the past because of its lack of specificity in differentiating infection from other inflammatory processes. With the advent of a high sensitivity assay, CRP was found to be a superb predictor in identifying apparently healthy men and women at risk for developing future cardiovascular events, such as heart attacks and strokes. CRP's predictive power is most likely due to its stability, reproducibility, and proatherogenic properties. Developing consensus to incorporate CRP determination into clinical practice guidelines will be the subject of intense debate and at the same time provide clinical research opportunities in the years to come.

C-reactive protein and other inflammatory risk markers in acute coronary syndromes

Markers of myocyte necrosis such as cardiac troponin or creatine kinase-myocardial band are invaluable tools for risk stratification among patients presenting with acute coronary syndromes (ACS). Nonetheless, many patients without any evidence of myocyte necrosis may be at high risk for recurrent ischemic events. In consideration of the important role that inflammatory processes play in determining plaque stability, recent work has focused on whether plasma markers of inflammation may help improve risk stratification. Of these markers, C-reactive protein (CRP) has been the most widely studied, and there is now robust evidence that CRP is a strong predictor of cardiovascular risk among apparently healthy individuals, patients undergoing elective revascularization procedures, and patients presenting with ACS. Moreover, even among patients with troponin-negative ACS, elevated levels of CRP are predictive of future risk. Other, more upstream markers of the inflammatory cascade, such as interleukin (IL)-6, have also been found to be predictive of recurrent vascular instability. A recent report from the second FRagmin during InStability in Coronary artery disease trial investigators suggests that elevated levels of an inflammatory marker such as IL-6 may indicate which patients may benefit most from an early invasive strategy. Other inflammatory markers currently under investigation include lipoprotein-associated phospholipase A(2), myeloperoxidase, and pregnancy-associated plasma protein A. Of all these novel markers, CRP appears to meet most of the criteria required for potential clinical application. Furthermore, the benefits of lifestyle modification and drug therapy with aspirin or statins may be most marked among those with elevated CRP levels.

Involvement of C-reactive protein obtained by directional coronary atherectomy in plaque instability and developing restenosis in patients with stable or unstable angina pectoris

We investigated whether positive immunohistochemical staining of C-reactive protein (CRP) in initial culprit lesions is related to coronary plaque instability and whether it could affect the outcome of directional coronary atherectomy (DCA). The plasma level of CRP is a reliable marker of the risk of coronary events and restenosis after percutaneous coronary intervention. However, the influence of tissue CRP in atheromatous plaque on plaque vulnerability and restenosis remains unknown. Samples of DCA obtained from 12 patients with stable angina pectoris and 15 patients with unstable angina pectoris were immunohistochemically stained with a monoclonal antibody against CRP. We performed follow-up coronary angiography on 22 of 27 patients to evaluate the presence of restenosis after DCA. Immunoreactivity to CRP was localized to macrophages, smooth muscle cells, and necrotic areas. The ratio of CRP positive cells to total cells was significantly higher in DCA samples from patients with unstable (17.9 +/- 2.0%) than with stable angina (11.0 +/- 2.5%) (p <0.05). Follow-up coronary angiography showed that 12 of 22 patients developed restenosis after DCA. The ratio was also significantly higher in DCA specimens from patients with restenosis (19.3 +/- 2.8%) compared with those without restenosis (11.0 +/- 2.0%) (p <0.05). In addition, the ratio significantly correlated with late luminal loss (r = 0.428, p <0.05) and loss index (r = 0.636, p = 0.0011) after DCA. Immunoreactivity to CRP in coronary atheromatous plaque increases in culprit lesions of unstable angina, and it affects restenosis after DCA. These findings suggest that CRP in atheromatous plaque plays an important role in the pathogenesis of unstable angina and restenosis after coronary intervention.

Selective COX-2 inhibition improves endothelial function in coronary artery disease

BACKGROUND

There is an ongoing debate as to whether the gastrointestinal safety of COX-2 inhibition compared with nonsteroidal antiinflammatory drugs (NSAIDs) may come at the cost of increased cardiovascular events. In view of the large number of patients at cardiovascular risk requiring chronic analgesic therapy with COX-2 inhibitors for arthritic and other inflammatory conditions, the effects of selective COX-2 inhibition on clinically useful surrogates for cardiovascular disease, particularly endothelial function, need to be determined.

METHODS AND RESULTS

Fourteen male patients (mean age, 66+/-3 years) with severe coronary artery disease (average of 2.6 vessels with stenosis >75%) undergoing stable background therapy with aspirin and statins were included. The patients received celecoxib (200 mg BID) or placebo for a duration of 2 weeks in a double-blind, placebo-controlled, crossover fashion. After each treatment period, flow-mediated dilation of the brachial artery, high-sensitivity C-reactive protein, oxidized LDL, and prostaglandins were measured. Celecoxib significantly improved endothelium-dependent vasodilation compared with placebo (3.3+/-0.4% versus 2.0+/-0.5%, P=0.026), whereas endothelium-independent vasodilation, as assessed by nitroglycerin, remained unchanged (9.0+/-1.6% versus 9.5+/-1.3%, P=0.75). High-sensitivity C-reactive protein was significantly lower after celecoxib (1.3+/-0.4 mg/L) than after placebo (1.8+/-0.5 mg/L, P=0.019), as was oxidized LDL (43.6+/-2.4 versus 47.6+/-2.6 U/L, P=0.028), whereas prostaglandins did not change.

CONCLUSIONS

This is the first study to demonstrate that selective COX-2 inhibition improves endothelium-dependent vasodilation and reduces low-grade chronic inflammation and oxidative stress in coronary artery disease. Thus, selective COX-2 inhibition holds the potential to beneficially impact outcome in patients with cardiovascular disease.

Role of inflammation in cardiovascular disease: how to use C-reactive protein in clinical practice

Acute coronary syndromes, stroke, and sudden death are common complications of a disrupted atherosclerotic plaque. Unstable plaque is a result of multiple factors but is commonly characterized by an infiltrate of inflammatory cells. Medical research strongly supports a role for inflammation in the pathogenesis, progression, and disruption of atherosclerotic plaque. Medical science also has improved our understanding of the complex interactions between our environment and our immune, coagulation, and cardiovascular systems. Clinical studies have demonstrated systemic markers of inflammation to be strong predictors of clinical events, and specific treatments of atherosclerosis and its risk factors have been associated with reductions in inflammatory markers. The authors review the current understanding of the role of inflammation in the pathogenesis of atherosclerosis, the common inflammatory markers, and potential anti-inflammatory therapy. Among several potential circulating markers of vascular inflammation, high sensitivity C-reactive protein is best validated and standardized as a marker for cardiovascular risk assessment. Nevertheless, there remain many uncertainties in utilizing C-reactive protein in clinical practice. Here, the authors describe the central role of C-reactive protein in atherosclerosis, review the studies demonstrating predictive value of C-reactive protein, describe the factors requiring consideration when utilizing C-reactive protein, discuss clinical scenarios in which measurement of C-reactive protein may be helpful, and suggest ways to interpret and treat elevated C-reactive protein levels. Finally, the authors summarize future expectations for assessing and modulating the vascular inflammation to inhibit initiation and progression of the atherosclerotic process.

Local neuroinflammation and the progression of Alzheimer's disease

Postmortem immunohistochemical studies have revealed a state of chronic inflammation limited to lesioned areas of brain in Alzheimer's disease. Some key actors in this inflammation are activated microglia (brain macrophages), proteins of the classical complement cascade, the pentraxins, cytokines, and chemokines. The inflammation does not involve the adaptive immune system or peripheral organs, but is rather due to the phylogenetically much older innate immune system, which appears to operate in most tissues of the body. Chronic inflammation can damage host tissue and the brain may be particularly vulnerable because of the postmitotic nature of neurons. Many of the inflammatory mediators have been shown to be locally produced and selectively elevated in affected regions of Alzheimer's brain. Moreover, studies of tissue in such degenerative processes as atherosclerosis and infarcted heart suggest a similar local innate immune reaction may be important in such conditions. Much epidemiological and limited clinical evidence suggests that nonsteroidal anti-inflammatory drugs may impede the onset and slow the progression of Alzheimer's disease. But these drugs strike at the periphery of the inflammatory reaction. Much better results might be obtained if drugs were found that could inhibit the activation of microglia or the complement system in brain, and combinations of drugs aimed at different inflammatory targets might be much more effective than single agents.

The possible role of complement activation in Alzheimer disease

Molecular pathological studies of Alzheimer disease (AD) brain have revealed the presence of a spectrum of inflammatory mediators. Epidemiological studies have indicated that the use of anti-inflammatory agents, especially non-steroidal anti-inflammatory drugs (NSAIDs), results in a substantially reduced risk of contracting the disease. It is possible that well targeted anti-inflammatory agents will also be useful in treating established AD. Inhibitors of cyclooxygenase-2 have been unsuccessful in this regard, and traditional NSAIDs have produced mixed results. The complement system, which is strongly activated in AD brain, is an attractive target for therapeutic intervention, particularly through inhibition of the autodestructive action of the membrane attack complex. The complement system works in conjunction with activated microglia, which express high levels of complement receptors. Overactive microglia secrete many toxic materials. Inhibition of microglial activation is another potential therapeutic target.

Statin-induced expression of decay-accelerating factor protects vascular endothelium against complement-mediated injury

Complement-mediated vascular injury is important in the pathophysiology of atherosclerosis and myocardial infarction. Because recent evidence shows that statins have beneficial effects on endothelial cell (EC) function independent of lipid lowering, we explored the hypothesis that statins modulate vascular EC resistance to complement through the upregulation of complement-inhibitory proteins. Human umbilical vein and aortic ECs were treated with atorvastatin or simvastatin, and decay-accelerating factor (DAF), membrane cofactor protein, and CD59 expression was measured by flow cytometry. A dose-dependent increase in DAF expression of up to 4-fold was seen 24 to 48 hours after treatment. Statin-induced upregulation of DAF required increased steady-state mRNA and de novo protein synthesis. L-Mevalonate and geranylgeranyl pyrophosphate reversed the effect, confirming the role of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibition and suggesting that constitutive DAF expression is negatively regulated by geranylgeranylation. Neither farnesyl pyrophosphate nor squalene inhibited statin-induced DAF expression, suggesting that the effect is independent of cholesterol lowering. Statin-induced DAF upregulation was mediated by the activation of protein kinase Calpha and inhibition of RhoA and was independent of phosphatidylinositol-3 kinase and NO activity. The increased DAF expression was functionally effective, resulting in significant reduction of C3 deposition and complement-mediated lysis of antibody-coated ECs. These observations provide evidence for a novel cytoprotective action of statins on vascular endothelium that is independent of the effect on lipids and results in enhanced protection against complement-mediated injury. Modulation of complement regulatory protein expression may contribute to the early beneficial effects of statins in reducing the morbidity and mortality associated with atherosclerosis.

Membrane attack complex contributes to destruction of vascular integrity in acute lung allograft rejection

The lung is known to be particularly susceptible to complement-mediated injury. Both C5a and the membrane attack complex (MAC), which is formed by the terminal components of complement (C5b-C9), can cause acute pulmonary distress in nontransplanted lungs. We used C6-deficient rats to investigate whether MAC causes injury to lung allografts. PVG.R8 lungs were transplanted orthotopically to MHC class I-incompatible PVG.1U recipients. Allografts from C6-sufficient (C6(+)) donors to C6(+) recipients were rejected with an intense vascular infiltration and diffuse alveolar hemorrhage 7 days after transplantation (n = 5). Ab and complement (C3d) deposition was accompanied by extensive vascular endothelial injury and intravascular release of von Willebrand factor. In contrast, lung allografts from C6-deficient (C6(-)) donors to C6(-) recipients survived 13-17 days (n = 5). In the absence of C6, perivascular mononuclear infiltrates of ED1(+) macrophages and CD8(+) T lymphocytes were present 7 days after transplantation, but vascular endothelial cells were quiescent, with minimal von Willebrand factor release and no evidence of alveolar hemorrhage or edema. Lung allografts were performed from C6(-) donors to C6(+) recipients (n = 5) and from C6(+) donors to C6(-) recipients (n = 5) to separate the effects of systemic and local C6 production. Lungs transplanted from C6(+) donors to C6(-) recipients had increased alveolar macrophages and capillary injury. C6 production by lung allografts was demonstrated at the mRNA and protein levels. These results demonstrate that MAC causes vascular injury in lung allografts and that the location of injury is dependent on the source of C6.

Inflammatory bio-markers and cardiovascular risk prediction

Inflammatory processes are now recognized to play a central role in the pathogenesis of atherosclerosis and its complications. Plasma levels of several markers of inflammation have been found to be associated with future cardiovascular risk in a variety of clinical settings. These markers include cell adhesion molecules, cytokines, pro-atherogenic enzymes and C-reactive protein (CRP). Initially thought of as an inactive downstream marker of the inflammatory cascade, emerging evidence suggests that CRP may be directly involved in atherogenesis, and that arterial plaque can produce CRP, independent of traditional hepatic pathways. In addition to being a strong predictor of future cardiovascular risk amongst patients presenting with acute coronary syndromes, numerous studies have found that baseline levels of CRP are associated with risk of future myocardial infarction, stroke, peripheral vascular disease and cardiovascular death amongst apparently healthy populations. The combination of measurement of a marker of inflammation with lipid testing may improve upon risk stratification based on lipid testing alone, and intensification of programmes for exercise, weight loss, and smoking cessation is recommended for those with elevated CRP levels. Further trials are needed to confirm the potential benefits of statins amongst individuals with elevated CRP levels.

C-reactive protein: history and revival

C-reactive protein (CRP) is the prototype acute-phase protein, which can increase up to 1000-fold after the onset of a stimulus. Aside from its disputed role as a marker of infection and/or inflammation in daily clinical practice, the protein has a wide variety of biological properties and functions. Due to its opsonizing abilities and its capability to activate human complement, CRP plays an important role in the innate host defense against different microorganisms, such as bacteria and fungi. The same opsonophagocyting properties can lead to clearance of host cell material, including nuclear constituents. Inflammation is one of the cornerstones in the etiology and pathogenesis of atherosclerosis, which led to worldwide attention being focused on CRP and its role in the process of atherosclerosis. This role may have a dual character. First, CRP levels reflect the 'burden' of inflammation within atherosclerotic lesions, thus reflecting the grade of vulnerability and instability of the plaques. For this reason, an increased level of the protein may be a prelude to rupture of the plaque and, thus, to occlusive arterial disease. Secondly, CRP may play an active role in the atherosclerotic process. CRP plays a role in the expression of different adhesion molecules on endothelial cells and the protein is able to activate human complement within the plaque. Furthermore, the recent discovery of local production of CRP and complement proteins within the plaque suggests an active role for the protein in the inflammatory cascade. Whatever the role for CRP in the atherosclerotic process, it has been proven that an elevated CRP level, with a cut-off point of approximately 3 mg/l, is associated with an increased risk of occlusive arterial disease, especially acute coronary syndromes.

Inflammatory processes in amyotrophic lateral sclerosis

Neuroinflammation is a characteristic of pathologically affected tissue in several neurodegenerative disorders. These changes can be observed in the brainstem and spinal cord of amyotrophic lateral sclerosis (ALS) cases and in mouse models of the disease. They include an accumulation of large numbers of activated microglia and astrocytes, as well as small numbers of T cells, mostly adhering to postcapillary venules. Accompanying biochemical alterations include the appearance of numerous molecules characteristic of free-radical attack, the occurrence of proteins associated with activation of the complement cascade, and a sharp upregulation of the enzyme cyclooxygenase 2 (COX-2). Anti-inflammatory agents may have a role to play in treating ALS. COX-2 is a particularly attractive target because of its marked increase in ALS spinal cord.

Regulation of the vasculature: clues from lupus

Blood vessel homeostasis involves a complex interplay between inflammatory signals, hormones, and other mediators. Recent research suggests that although atherosclerosis is primarily a problem of impaired lipid regulation, the very processes of cholesterol and triglyceride metabolism are intrinsically tied to inflammatory and hormonal regulatory signals. Similarities between inflammatory and endocrine disturbances in systemic lupus and the predicted consequences for vascular regulation help explain the high incidence of premature atherosclerosis in lupus. Atherosclerosis in systemic lupus, then, may be a consequence of imbalances in what are intrinsic homeostatic mechanisms, rather than a result of externally superimposed pathologic changes.

Macrophage uptake of low-density lipoprotein bound to aggregated C-reactive protein: possible mechanism of foam-cell formation in atherosclerotic lesions

Foam cells found in atherosclerotic lesions are believed to derive from macrophages that take up aggregated low-density lipoprotein (LDL) particles bound to the extracellular matrix of arterial walls. C-reactive protein (CRP) is an acute-phase protein found in atherosclerotic lesions, which when immobilized on a solid phase, can bind and cluster LDL particles in a calcium-dependent manner. In the present study, we examined whether CRP-bound aggregated LDL could be taken up by macrophages in culture. CRP molecules were aggregated in the presence of calcium and immobilized on the surface of polystyrene microtitre wells. Human LDL added to the wells bound to and aggregated on the immobilized CRP, also in a calcium-dependent manner. On incubation with macrophages, the immobilized CRP-bound LDL aggregates were readily taken up by the cells, as demonstrated by immunofluorescence microscopy, by the cellular accumulation of cholesterol and by the overexpression of adipophilin. Immunofluorescence microscopy and flow-cytometry analysis established that the uptake of the LDL-CRP complex was not mediated by the CRP receptor CD32. These observations with immobilized CRP and LDL, approximating the conditions that exist in the extracellular matrix of the arterial wall, thus suggest that CRP may contribute to the formation of foam cells in atherosclerotic lesions by causing the aggregation of LDL molecules that are then taken up by macrophages through a CD32-independent pathway.

Innate immunity, local inflammation, and degenerative disease

The brain lesions associated with Alzheimer's disease (AD), which are referred to as neurofibrillary tangles and senile plaques, are characterized by the presence of a broad spectrum of inflammatory mediators. Surprisingly, these mediators, which include complement proteins, inflammatory cytokines, prostaglandins, and acute phase reactants such as C-reactive protein and amyloid P, are produced by resident brain cells, including neurons. Although secondary to the fundamental pathology caused by the presence of tangles and plaques, there is strong evidence that inflammation exacerbates the neuronal loss. In particular, AD lesions show evidence of self-attack by the complement system--a part of the immune system that normally functions to rid the body of invading pathogens. However, the lesions are devoid of significant T cell infiltration, a hallmark of an inflammatory immune response, and antibodies. We define this phenomenon as autotoxicity to distinguish it from classical autoimmunity, in which the body raises antibodies to normal endogenous macromolecules. Locally produced inflammatory mediators have also been identified in atherosclerotic plaques, along with evidence of complement self-attack. As was previously shown for heart attacks, epidemiological evidence indicates that extended use of nonsteroidal anti-inflammatory drugs (NSAIDs) results in a reduced risk of AD. NSAIDs inhibit the production of prostaglandin inflammatory mediators, but powerful new therapeutic agents might be developed by targeting more critical inflammatory mechanisms, especially the complement system.

Expression of COX-1 and COX-2 mRNAs in atherosclerotic plaques

Inflammation is a characteristic of atherosclerotic plaques. Prostaglandins are inflammatory mediators whose production is controlled by cyclooxygenase (COX). There are two isoforms: COX-1 and COX-2. COX-1 is relatively stable while COX-2 is induced in inflammatory states. In order to evaluate their possible contribution to atherosclerotic plaque inflammation, we measured their relative levels in postmortem plaque and adjacent normal arterial tissue. Eleven pairs of atherosclerotic plaque and adjacent normal arterial tissue were obtained from postmortem specimens. Total RNA was extracted and relative levels of COX-1 and COX-2 determined by the technique of RT-PCR. COX-2 levels were 4.8-fold higher in plaque tissue than in normal artery. COX-1 levels were only 1.1-fold higher. There was no relationship between sex, age, postmortem delay or cause of death and COX-2 or COX-1 levels. COX-2 levels are sharply upregulated in atherosclerotic plaques, indicating that it may be a significant contributor to plaque inflammation. Accordingly, COX-2 inhibitors may reduce the degree of inflammation and protect against future cardiovascular events.

The role of inflammation and infection in the pathogenesis and evolution of coronary artery disease

Inflammation plays a major role in the initiation and progression of coronary artery disease (CAD) and the precipitation of acute coronary events. However, the inflammatory triggers are poorly understood. Noninfectious stimuli undoubtedly play a role. Recently, chronic infection has been proposed as another inflammatory trigger. Histologically, unstable atherosclerotic plaque contains activated macrophages and T lymphocytes, adhesion molecules, chemokines and cytokines, matrix-degrading enzymes, and prothrombotic factors. Circulating inflammatory markers such as C-reactive protein, fibrinogen, and interleukins are increased in high-risk cohorts and predict future risk. Experimental models and human studies have supported a role of infection in the promotion of atherosclerosis. Although the independent predictive value of seropositivity to individual agents has varied, total pathogen burden, the sum of seropositivities to many bacterial and viral vectors, has been more consistent. Whether antibiotics or vaccines will be useful in CAD prevention remains to be shown. Meanwhile, therapies with proven vascular anti-inflammatory effects (eg, diet, exercise, smoking cessation, aspirin, statins) should be optimized.

Effects of C-reactive protein and pentosan polysulphate on human complement activation

Complement (C) activation is believed to play an adverse role in several chronic degenerative disease processes, including atherosclerosis, myocardial infarction and Alzheimer's disease. We developed several in vitro quantitative assays to evaluate processes which activate C in human serum, and to assess candidates which might block that activation. Binding of C-reactive protein (CRP) to immobilized cell surfaces was used as a tissue-based method of activation, while immunoglobulin G in solution was used as a surrogate antibody method. Activation was assessed by deposition of C fragments on fixed cell surfaces, or by capture of C5b-9 from solution. We observed that several cell lines, including SH-SY5Y, U-937, THP-1 and ECV304, bound CRP and activated C following attachment of cells to a plastic surface by means of air drying. Treatment of human neuroblastoma SH-SY5Y cells with the reactive oxygen intermediates generated by xanthine (Xa) - xanthine oxidase (XaOx) prior to air drying or by hydrogen peroxide solutions after air drying, enhanced C activation, possibly through oxidation of the cell lipid membrane. Several C inhibitors were tested for their effectiveness in blocking these systems. Pentosan polysulphate (PPS), an orally active agent, blocked C activation in the same concentration range of 1-1000 microg/ml as heparin, dextran sulphate, compstatin and fucoidan. PPS may have practical application as a C inhibitor.

Influence of C3 deficiency on atherosclerosis

BACKGROUND

The influence of complement activation on atherosclerosis is not well understood. The purpose of this study was to examine the effects of C3 deficiency on the extent and phenotype of atherosclerosis.

METHODS AND RESULTS

Aortic atherosclerosis was analyzed in low-density lipoprotein receptor (ldlr)/C3-deficient mice (ldlr(-/-)C3(-/-)) and ldlr(-/-)C3(+/-) littermate control mice after 15 weeks on a 1.25% (wt/wt) cholesterol diet. Serum lipoprotein profiles and immunoglobulin levels were not significantly different between the 2 experimental groups. The lipid-positive en face lesional area in thoracic and abdominal aorta was greater in C3-deficient mice than in control mice (3.9% versus 2.1%, median, P=0.0076). Similarly, the lipid-positive area in aortic arch sections was greater in C3-deficient mice than in controls (0.04 mm2 versus 0.02 mm2, median, P=0.0089). Analysis of aortic arch sections showed greater lesional macrophage content in C3-deficient versus control mice (8.24+/-1.36% versus 5.9+/-1.63% intimal area, mean+/-SEM, P=0.003), less smooth muscle cell content in C3-deficient versus control mice (0.06+/-0.05% versus 0.92+/-0.32% intimal area, mean+/-SEM, P<0.0001), and less collagen content in C3-deficient versus control mice (0.52+/-1.26% versus 11+/-10.43% intimal area, mean+/-SEM, P=0.008).

CONCLUSIONS

The maturation of atherosclerotic lesions beyond the foam cell stage is strongly dependent on an intact complement system.

Elevated C-reactive protein values and atherosclerosis in sudden coronary death: association with different pathologies

BACKGROUND

Elevations in serum C-reactive protein measured by high-sensitivity assay (hs-CRP) have been associated with unstable coronary syndromes. There have been no autopsy studies correlating hs-CRP to fatal coronary artery disease.

METHODS AND RESULTS

Postmortem sera from 302 autopsies of men and women without inflammatory conditions other than atherosclerosis were assayed for hs-CRP. There were 73 sudden deaths attributable to atherothrombi, 71 sudden coronary deaths with stable plaque, and 158 control cases (unnatural sudden deaths and noncardiac natural deaths without conditions known to elevate CRP). Atherothrombi were classified as plaque ruptures (n=55) and plaque erosion (n=18); plaque burden was estimated in each heart. Total cholesterol, high-density lipoprotein cholesterol, diabetes, smoking history, and body mass index were also determined. Immunohistochemical stains for CRP and numbers of thin cap atheromas per heart were quantitated in coronary deaths with hs-CRP in the highest and lowest quintiles. The median hs-CRP was 3.2 microg/mL in acute rupture, 2.9 microg/mL in plaque erosion, 2.5 microg/mL in stable plaque, and 1.4 microg/mL in controls. Mean log hs-CRP was higher in rupture (P<0.0001), erosion (P=0.005), and stable plaque (P=0.0003) versus controls. By multivariate analysis, atherothrombi (P=0.02), stable plaque (P=0.003), and plaque burden (P=0.03) were associated with log hs-CRP independent of age, sex, smoking, and body mass index. Mean staining intensity for CRP of macrophages and lipid core in plaques was significantly greater in cases with high hs-CRP than those with low CRP (P=0.0001), as were mean numbers of thin cap atheromas (P<0.0001).

CONCLUSIONS

hs-CRP is significantly elevated in patients dying suddenly with severe coronary artery disease, both with and without acute coronary thrombosis, and correlates with immunohistochemical staining intensity and numbers of thin cap atheroma.

Statin attenuates increase in C-reactive protein during estrogen replacement therapy in postmenopausal women

BACKGROUND

HMG-CoA reductase inhibitor (statin) therapy reduces cardiovascular risk, mechanisms of which may include diminished arterial inflammation, as suggested by reduction in levels of C-reactive protein (CRP). Because oral estrogens increase CRP in postmenopausal women, with potential inflammatory and thrombotic consequences that could compromise any benefit to cardiovascular risk, we determined whether the coadministration of a statin might modify the estrogenic effect on CRP.

METHODS AND RESULTS

In a double-blind, 3-period crossover study, 28 postmenopausal women (average LDL cholesterol 163+/-36 mg/dL) were randomly assigned to daily conjugated equine estrogens (CEEs) 0.625 mg, simvastatin 10 mg, or their combination for 6 weeks, with each treatment period separated by 6 weeks. CEEs increased median CRP levels from 0.27 to 0.46 mg/dL, simvastatin decreased CRP from 0.29 to 0.28 mg/dL, and the therapies combined increased CRP from 0.28 to 0.36 mg/dL (all P< or =0.02 versus respective baseline values). Post hoc testing showed that the 29% increase in CRP on the combination of CEEs with simvastatin was significantly less than the 70% increase in CRP on CEEs alone (P<0.05). The effect of combination therapy on CRP levels did not correlate with baseline CRP or with baseline or treatment-induced changes in levels of interleukin-6, lipoproteins, or flow-mediated dilation of the brachial artery as a measure of nitric oxide bioactivity.

CONCLUSIONS

The combination of statin with estrogen may attenuate the potential harmful effects of estrogen therapy in postmenopausal women and maximize any benefit to cardiovascular risk.

bFGF and VEGF synergistically enhance endothelial cytoprotection via decay-accelerating factor induction

The complement-regulatory protein decay-accelerating factor (DAF) can be upregulated on endothelial cells (EC) by protein kinase C (PKC)-dependent and -independent pathways. We hypothesized that basic fibroblast growth factor (bFGF) might induce EC DAF expression, providing a cytoprotective mechanism for angiogenic neovessels against complement-mediated injury. Incubation of umbilical vein, aortic, and dermal EC with bFGF or vascular endothelial growth factor (VEGF) significantly increased DAF expression. Growth factor-induced EC proliferation was inhibited by PKC antagonists. In contrast, although PKC antagonists inhibited VEGF-induced DAF expression, bFGF-induced DAF was unaffected. Investigation of mitogen-activated kinase (MAPK) pathways also revealed differences, with bFGF-induced DAF dependent on p44/42 and p38 MAPK and VEGF requiring activation of p38 MAPK alone. Upregulation of DAF by bFGF was functionally relevant, reducing C3 deposition on EC after complement activation by 60% and resulting in marked reduction in complement-mediated EC lysis. bFGF and VEGF were synergistic in terms of DAF expression, resulting in enhanced cytoprotection. These observations reveal parallel PKC-dependent and -independent pathways regulating complement activation during angiogenesis. Further elucidation of these pathways may provide important insights into innate cytoprotective mechanisms in endothelium.

Do AV fistulas contribute to cardiac mortality in hemodialysis patients?

Potential fistula-related problems which may impact on patient survival include high fistula flow with hyperkinetic circulation and cardiac failure, low fistula flow with the risks of underdialysis and fistula thrombosis, vascular access infection with local or systemic manifestations, and possibly induction and maintenance of a microinflammatory state (at least for synthetic grafts). All these complications are much more common with prosthetic grafts than with native arteriovenous (AV) fistulas. Fistula flow should be monitored (e.g., by duplex sonography) to guarantee adequate flow and permit preemptive intervention to avoid fistula thrombosis.

Novel clinical markers of vascular wall inflammation

Inflammatory processes play a pivotal role in the pathogenesis of atherosclerosis and mediate many of the stages of atheroma development from initial leukocyte recruitment to eventual rupture of the unstable atherosclerotic plaque. Elevated plasma levels of several markers of the inflammatory cascade have been shown to predict future risk of plaque rupture. These markers include P-selectin, interleukin-6, tumor necrosis factor-alpha, soluble intercellular adhesion molecule-1, and C-reactive protein (CRP). Produced in the liver in response to interleukin-6, CRP has emerged as the most powerful inflammatory marker of future cardiovascular risk. Initially considered an innocent bystander in the atherosclerotic process, recent evidence suggests that CRP may have direct proinflammatory effects. Numerous large-scale, prospective studies have found that elevated baseline levels of CRP are a strong independent predictor of future vascular risk. Furthermore, aspirin and statin therapy appear to be particularly effective among individuals with high CRP levels. The addition of CRP screening to traditional lipid testing has the potential to identify individuals at high risk for future cardiovascular events who may benefit from targeted preventive interventions.

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.

Inflammation dampened by gelatinase A cleavage of monocyte chemoattractant protein-3

Tissue degradation by the matrix metalloproteinase gelatinase A is pivotal to inflammation and metastases. Recognizing the catalytic importance of substrate-binding exosites outside the catalytic domain, we screened for extracellular substrates using the gelatinase A hemopexin domain as bait in the yeast two-hybrid system. Monocyte chemoattractant protein-3 (MCP-3) was identified as a physiological substrate of gelatinase A. Cleaved MCP-3 binds to CC-chemokine receptors-1, -2, and -3, but no longer induces calcium fluxes or promotes chemotaxis, and instead acts as a general chemokine antagonist that dampens inflammation. This suggests that matrix metalloproteinases are both effectors and regulators of the inflammatory response.