Biomarkers of atherosclerotic plaque instability and rupture

Clinical implications of the BARI 2D and COURAGE trials of coronary artery disease

The results of the Bypass Angioplasty Revascularization Investigation 2 Diabetes (BARI 2D) and Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) clinical trials raise important questions about the prevention and treatment of coronary heart disease among type 2 diabetics and nondiabetics. The BARI 2D and COURAGE trials showed that pharmacological therapy is as effective as surgery or angioplasty, because of the incidence of total mortality and cardiovascular disease events. The results are consistent with the clinical trials of lipid-lowering, antihypertensive therapy. The efficacy of lowering glycohemoglobin below 7% or benefits of specific glucose-lowering drugs is still unresolved. The BARI 2D trial focused on more advanced atherosclerotic disease. An important question is whether newly incident diabetics should be screened for subclinical atherosclerosis and treated aggressively with pharmacological therapy as in the BARI 2D trial. We are still uncertain whether raising high-density lipoprotein cholesterol will provide further benefit in reducing coronary heart disease. Better measurement of plaque morphology, determinants of hypercoagulable status, and drugs to reduce thrombosis and plaque are of high priority. Longer follow-up of the BARI 2D and COURAGE trials will provide important information about the risks of cardiovascular disease events and disability. It will be important but difficult to translate the results of the trials to community practice under the current health care system.

Peroxynitrite modifies the structure and function of the extracellular matrix proteoglycan perlecan by reaction with both the protein core and the heparan sulfate chains

The heparan sulfate (HS) proteoglycan perlecan is a major component of basement membranes, plays a key role in extracellular matrix (ECM) structure, interacts with growth factors and adhesion molecules, and regulates the adhesion, differentiation and proliferation of vascular cells. Atherosclerosis is characterized by chronic inflammation and the presence of oxidized materials within lesions, with the majority of protein damage present on ECM, rather than cell, proteins. Weakening of ECM structure plays a key role in lesion rupture, the major cause of heart attacks and strokes. In this study peroxynitrite, a putative lesion oxidant, is shown to damage perlecan structurally and functionally. Exposure of human perlecan to peroxynitrite decreases recognition by antibodies raised against both the core protein and heparan sulfate chains; dose-dependent formation of 3-nitrotyrosine was also detected. These effects were modulated by bicarbonate and reaction pH. Oxidant exposure resulted in aggregate formation, consistent with oxidative protein crosslinking. Peroxynitrite treatment modified functional properties of perlecan that are dependent on both the protein core (decreased binding of human coronary artery endothelial cells), and the HS chains (diminished fibroblast growth factor-2 (FGF-2) receptor-mediated proliferation of Baf-32 cells). The latter is consistent with a decrease in FGF-2 binding to the HS chains of modified perlecan. Immunofluorescence of advanced human atherosclerotic lesions provided evidence for the presence of perlecan and extensive formation of 3-nitrotyrosine epitopes within the intimal region; these materials showing marked co-localization. These data indicate that peroxynitrite induces major structural and functional changes to perlecan and that damage to this material occurs within human atherosclerotic lesions.

Oxidized LDL in human carotid plaques is related to symptomatic carotid disease and lesion instability

BACKGROUND

Oxidative stress is an important determinant in atherosclerosis development. Various markers of oxidative stress, such as oxidation of low-density lipoprotein (LDL), nitrosative stress, lipid peroxidation, and protein oxidation, have been implicated in the initiation and/or progression of atherosclerosis, but their association with plaque erosion and symptomatic carotid disease has not been fully defined. In addition, certain oxidative markers have been shown in various models to promote plaque remodeling through matrix metalloproteinase (MMP) activation.

OBJECTIVE

To perform a global investigation of various oxidative stress markers and assess for potential relationships with destabilization and symptomatic development in human carotid plaques.

METHODS

Thirty-six patients undergoing endarterectomy were evaluated and compared with 20 control specimens obtained at the time of autopsy. Differences between stable and unstable plaques, symptomatic and asymptomatic patients, and >or=90% and <90% stenosis were evaluated. Oxidized LDL (ox-LDL), nitrotyrosine (NT), malondialdehyde (MDA), and protein carbonyls (PCs) levels were determined in atheromatic plaques homogenates by corresponding biochemical assays. Immunohistochemical (IHC) analysis was also employed to determine the percentage and topological distribution of cells expressing NT and metalloproteinase-9 (MMP-9) in serial sections from corresponding atheromatic plaques. MMP-9 expression was further verified using Western blot analysis.

RESULTS

Ox-LDL was increased in symptomatic patients (P < .05). Also, ox-LDL and NT levels were significantly higher in unstable versus stable carotid plaques (P < .05, respectively). Furthermore, IHC serial section analysis, corroborated by statistical analysis, showed a topological and expressional correlation between NT and MMP-9 (P < .05). MDA and PCs levels, although increased in carotid plaques, did not distinguish stable from unstable carotid plaques as well as symptomatic from asymptomatic patients with various degrees of stenosis.

CONCLUSION

All types of investigated oxidative stress markers were significantly increased in human carotid plaques, but only ox-LDL levels were associated with clinical symptoms, while peroxynitrite products and MMP-9 were specifically related to plaque instability.

Past, current and future concepts in atherosclerotic biobanking

Knowledge on the pathogenesis of atherosclerotic disease mainly originates from observations made by pathologists who systemically collected vascular tissue. Biobanking of human tissues has become a professionalized joint effort, including the expertise of epidemiologists, pathologists and biologists. Mostly, biobanks are used for cross-sectional studies and the obtained specimens often represent later stages of disease. Technical improvements in high-throughput genetic and proteomic screening lead to important new insights into pathophysiological processes. Atherosclerotic disease progression is a major killer in the Western society. Pathological biobanking studies revealed insights in plaque progression and destabilization. However, atherosclerotic disease is a typical example where insights into progression of the disease may be hampered by the cross-sectional design of the biobanks. This article will focus on the accomplishments that have been made through biobanking of atherosclerotic tissues in the past and the present. In addition, future potentials of atherosclerotic plaque biobanks will be discussed.

Leukocyte counts, myeloperoxidase, and pregnancy-associated plasma protein a as biomarkers for cardiovascular disease: towards a multi-biomarker approach

We evaluated leukocyte counts and levels of CRP, fibrinogen, MPO, and PAPP-A in patients with stable and unstable angina pectoris, acute myocardial infarction, and healthy controls. All biomarkers were analyzed again after 6 months. Leukocyte counts and concentrations of fibrinogen, CRP, MPO, and PAPP-A were significantly increased in patients with acute myocardial infarction. Leukocyte counts and concentrations of MPO were significantly increased in patients with unstable angina pectoris compared with controls. After 6 months, leukocyte counts and MPO concentrations were still increased in patients with acute myocardial infarction when compared to controls. Discriminant analysis showed that leukocyte counts, MPO, and PAPP-A concentrations classified study group designation for acute coronary events correctly in 83% of the cases. In conclusion, combined assessment of leukocyte counts, MPO, and PAPP-A was able to correctly classify acute coronary events, suggesting that this could be a promising panel for a multibiomarker approach to assess cardiovascular risk.

Beneficial effects of melatonin in cardiovascular disease

The experimental data obtained from both human and rodent studies suggest that melatonin may have utility in the treatment of several cardiovascular conditions. In particular, melatonin's use in reducing the severity of essential hypertension should be more widely considered. In rodent studies melatonin has been shown to be highly effective in limiting abnormal cardiac physiology and the loss of critical heart tissue resulting from ischemia/reperfusion injury. Melatonin may also be useful in reducing cardiac hypertrophy in some situations and thereby limiting the frequency of heart failure. Finally, some conventional drugs currently in use have cardiotoxicity as a side-effect. Based on studies in rodents, melatonin, due to its multiple anti-oxidative actions, is highly effective in abrogating drug-mediated damage to the heart. Taken together, the findings from human and animal studies support the consideration of melatonin as a cardioprotective agent.

Pericardial fat volume correlates with inflammatory markers: the Framingham Heart Study

The objective of this study was to determine whether systemic inflammatory and oxidative stress marker concentrations correlate with pericardial and intrathoracic fat volumes. Participants of the Framingham Offspring Study (n = 1,175, 53% women, mean age 59 +/- 9 years) had pericardial and intrathoracic fat volumes assessed by multidetector computed tomography (MDCT) scans, and provided fasting blood and urine samples to measure concentrations of 14 inflammatory markers: C-reactive protein (CRP), interleukin-6, monocyte chemoattractant protein-1 (MCP-1), CD40 ligand, fibrinogen, intracellular adhesion molecule-1, lipoprotein-associated phospholipase A(2) activity and mass, myeloperoxidase, osteoprotegerin, P-selectin, tumor necrosis factor-alpha, tumor necrosis factor receptor-2, and urinary isoprostanes. Multivariable linear regression models were used to determine the association of log-transformed inflammatory marker concentrations with fat volumes, using fat volume as the dependent variable. Due to smaller sample sizes, models were rerun after adding urinary isoprostanes (n = 961) and tumor necrosis factor-alpha (n = 813) to the marker panel. Upon backward elimination, four of the biomarkers correlated positively with each fat depot: CRP (P < 0.0001 for each fat depot), interleukin-6 (P < 0.05 for each fat depot), MCP-1 (P < 0.01 for each fat depot), and urinary isoprostanes (P < 0.01 for pericardial fat; P < 0.001 for intrathoracic fat). Even after adjusting for BMI, waist circumference (WC), and abdominal visceral fat, CRP (P = 0.0001) and urinary isoprostanes (P = 0.02) demonstrated significant positive associations with intrathoracic fat, but not with pericardial fat. Multiple markers of inflammation and oxidative stress correlated with pericardial and intrathoracic fat volumes, extending the known association between regional adiposity and inflammation and oxidative stress.

Chronic arthritis aggravates vascular lesions in rabbits with atherosclerosis: a novel model of atherosclerosis associated with chronic inflammation

OBJECTIVE

To determine whether systemic inflammation induced by chronic antigen-induced arthritis (AIA) accelerates vascular lesions in rabbits with atherosclerosis.

METHODS

Two models of atherosclerosis and chronic AIA were combined. Atherosclerosis was induced by coupling a hyperlipemic diet with an endothelial lesion at the femoral arteries, while chronic AIA was induced by ovalbumin injection. Markers in sera and peripheral blood mononuclear cells (PBMCs) as well as vessels and synovial membranes from the rabbits with the double phenotype (both chronic AIA and atherosclerosis) were compared with those from rabbits with each disease alone.

RESULTS

Serum levels of interleukin-6, C-reactive protein, and prostaglandin E(2) increased in rabbits with both chronic AIA and atherosclerosis as compared with healthy animals or animals with either chronic AIA alone or atherosclerosis alone. NF-kappaB binding and CCL2 and cyclooxygenase 2 (COX-2) expression were higher in PBMCs from rabbits with both chronic AIA and atherosclerosis than in PBMCs from healthy rabbits. The intima-media thickness ratio of femoral arteries was equally increased in rabbits with atherosclerosis alone and in rabbits with both chronic AIA and atherosclerosis, but the latter group showed a higher level of macrophage infiltration. Femoral CCL2 and COX-2 expression was increased in rabbits with both chronic AIA and atherosclerosis as compared with rabbits with atherosclerosis alone. In the aortas, vascular lesions were found in 27% of rabbits with atherosclerosis alone and in 60% of rabbits with both chronic AIA and atherosclerosis. Rabbits with both chronic AIA and atherosclerosis exhibited more severe synovitis and higher synovial expression of CCL2 than did rabbits with chronic AIA alone.

CONCLUSION

The onset of chronic AIA in animals with atherosclerosis resulted in the local and systemic up-regulation of mediators of tissue inflammation and plaque instability associated with a higher incidence of aortic lesions. This model could represent a novel approach to the study of inflammation-associated atherosclerosis.

Reproducibility in serial C-reactive protein and interleukin-6 measurements in post-myocardial infarction patients: results from the AIRGENE study

BACKGROUND

Among the numerous emerging biomarkers, high-sensitivity C-reactive protein (hsCRP) and interleukin-6 (IL-6) have received widespread interest, and a large database has been accumulated on their potential role as predictors of cardiovascular risk. The concentrations of inflammatory biomarkers, however, are influenced, among other things, by physiological variation, which is the natural within-individual variation occurring over time. Implementation of hsCRP and IL-6 measurement into clinical practice requires data on the reliability of such measurements.

METHODS

We serially measured hsCRP and IL-6 concentrations in up to 6 blood samples taken at monthly intervals from 200 post-myocardial infarction patients who participated in the AIRGENE study.

RESULTS

The mean (SD) of the ln-transformed plasma concentrations (in milligrams per liter for hsCRP and nanograms per liter for IL-6) for all participants over all samples was 0.16 (1.04) for hsCRP and 0.76 (0.57) for IL-6, with no significant differences between men and women. The within-individual and analytical variance component for the ln-transformed hsCRP data was 0.37, and the between-individual variance component was 0.73. For the ln-transformed IL-6 data, these values were 0.11 and 0.22, respectively. A substantial part of the total variation in plasma hsCRP and IL-6 concentrations was explained by the between-individual variation (as a percentage of the total variance, 66.1% for the ln-transformed hsCRP data and 66.2% for the ln-transformed IL-6 data). For both markers, 2 measurements were needed to reach a sufficient reliability.

CONCLUSIONS

Our results demonstrate considerable stability and good reproducibility for serial hsCRP and IL-6 measurements. Thus, there should be no major concern about misclassification in clinical practice if at least 2 subsequent measurements are taken.

Independent and additive predictive value of total cholesterol content of erythrocyte membranes with regard to coronary artery disease clinical presentation

BACKGROUND

A new mechanism for clinical instability in coronary artery disease (CAD) has been proposed where erythrocytes could play an active role in atherosclerotic plaque growth and rupture. Clinical studies showed increased total cholesterol levels in the membrane of circulating erythrocytes (CEM) in acute coronary syndrome (ACS) patients compared to patients with chronic stable angina (CSA). We investigated the independent and incremental discriminating value of CEM along with N-terminal propeptide of BNP (NT-proBNP), high sensitivity C-reactive protein (hs CRP), myeloperoxidase (MPO) and apolipoprotein B (apoB) with regard to CAD clinical presentation.

METHODS

519 consecutive angina patients were assessed; 252 had CSA (195 men, 62 ± 9 years) and 267 had ACS (213 men, 62 ± 10 years).CEM levels and serum concentrations of NT-proBNP, hs CRP, MPO and apoB were measured upon study admission.

RESULTS

Simple logistic regression models showed that all biomarkers could distinguish ACS, nevertheless CEM with greater potency (OR 9.26 95%CI 6.31-13.59, p<0.001). Multiple logistic regression models after adjustment for all the variables that were different between the 2 groups as well as for other biomarkers showed that CEM continued to be a significant and an independent predictor of ACS (OR 22.27 95%CI 10.63-46.67, p<0.001). An increment of the C-statistic was also shown when CEM levels were incorporated in the predictive model (including traditional vascular risk factors and new well established biomarkers i.e. hs CRP, MPO, apoB and NT-proBNP).

CONCLUSIONS

The present study showed that CEM levels are associated with clinical instability in CAD patients in an independent and incremental manner.

Predictive value of C-reactive protein after drug-eluting stent implantation

During the last few decades, with the evolution of techniques and materials and the increasing experience of operators, percutaneous coronary interventions (PCI) have become an equally efficient alternative to coronary artery bypass grafts for the treatment of most coronary stenoses. Bare-metal stent implantation represented a major step forward, compared with plain old balloon angioplasty (POBA), by improving the immediate angiographic success. However, the incidence of in-stent restenosis (ISR) remained unacceptably high. Development of the drug-eluting stent (DES) significantly improved the outcome of PCI by dramatically abating the rate of ISR and reducing the incidence of target lesion revascularization. However, ISR has not been eliminated and the persistence of metal vessel scaffolding also raises concern regarding the occurrence of late or very late stent thrombosis. POBA and stent implantation have been shown to induce a local and systemic inflammatory response, whose magnitude is associated with worse clinical outcome, and they increase the risk of ISR. C-reactive protein, a marker of systemic inflammation, has been demonstrated to predict clinical and angiographic outcome after POBA or bare-metal stent implantation. However, conflicting data regarding the prognostic value of C-reactive protein following DES implantation are available. In this paper, we review the literature regarding the clinical and pathophysiological association between inflammation and prognosis after DES implantation and suggest some possible therapeutic approaches to reduce inflammatory burden with the aim to improve clinical and angiographic outcome after PCI.

Risk factors for near-term myocardial infarction in apparently healthy men and women

BACKGROUND

Limited information is available regarding risk factors for the near-term (4 years) onset of myocardial infarction (MI). We evaluated established cardiovascular risk factors and putative circulating biomarkers as predictors for MI within 4 years of measurement.

METHODS

We conducted a matched, nested case-control study (252 cases and 499 controls) drawing on 45 735 men and women participating in the Copenhagen City Heart Study and the Copenhagen General Population Study. Established risk factors and 17 putative biomarkers, including inflammation-sensitive plasma proteins (C-reactive protein, fibrinogen, alpha(l)-antitrypsin, complement 3), apolipoproteins (A1, B, E, B/A1 ratio), markers of iron overload (iron, transferrin, transferrin saturation), creatinine, alkaline phosphatase, gamma-glutamyl transpeptidase, and leukocytes (lymphocyte count, neutrophil count, neutrophil/lymphocyte ratio) were assessed.

RESULTS

Among women and men, only 13% and 50%, respectively, of those with near-term MI were classified as high risk by Framingham risk score at baseline. After adjustment for established risk factors, odds ratios for near-term MI, which compared highest to lowest quintiles, were 2.87(95% CI 1.51-5.48; P = 0.001) for alpha(l)-antitrypsin, 2.84(1.42-5.67; P = 0.003) for C-reactive protein, 1.97(1.09-3.57; P = 0.03) for creatinine, 1.99(1.09-3.65; P = 0.03) for fibrinogen, and 0.37(0.19-0.73; P = 0.004) for iron. The corresponding odds ratio for all biomarkers combined was 7.24 (3.28-16.0; P < 0.001).

CONCLUSIONS

We identified 5 biomarkers associated with increased near-term risk of MI independently of established risk factors. All putative biomarkers combined explained a 7-fold increase in the odds of near-term MI.

Identification and assessment of plasma lysozyme as a putative biomarker of atherosclerosis

OBJECTIVE

To identify a plasma biomarker of atheromatous disease.

METHODS AND RESULTS

Surface-enhanced laser desorption ionization-time-of-flight mass spectrometry was used to identify possible plasma protein biomarkers of atheromatous disease in patients presenting with chronic stable angina pectoris by comparing those with 3-vessel disease with those without any evidence of coronary artery disease. The level of a 14.7-kDa protein was elevated; this protein was isolated and identified as a lysozyme. Arterial plasma lysozyme levels, measured by immunoassay, confirmed this observation in separate cohorts of patients. The application of arterial plasma lysozyme levels to 197 patients with varying degrees of coronary artery disease, using a cutoff value of 1.5 microg/mL, was able to distinguish patients with 1 or more occluded coronary arteries, with 86% sensitivity and 93% specificity. Of 20 patients with carotid atheroma, 19 had increased arterial plasma levels. In contrast, C-reactive protein levels showed no association with disease severity. Venous lysozyme levels in patients with carotid atheroma were shown to decrease after intensive atorvastatin treatment.

CONCLUSION

Raised plasma lysozyme levels may be a useful biomarker of atherosclerotic cardiovascular disease and response to therapy. Additional studies to investigate this are warranted.

Hepatitis C virus coinfection and the risk of cardiovascular disease among HIV-infected patients

BACKGROUND

Among HIV-infected patients, hepatitis C virus (HCV) coinfection is associated with lower cholesterol levels, but it remains unclear how it affects cardiovascular outcomes.

METHODS

We performed logistic regression to evaluate acute myocardial infarction (AMI) and cerebrovascular disease (CVD) events by HCV status among HIV-infected US veterans in the highly active antiretroviral therapy (HAART) era (1996-2004). We then performed survival analyses to evaluate incident AMI and CVD, exploring antiretroviral therapy (ART) as a time-dependent variable.

RESULTS

A total of 19 424 HIV-infected patients [31.6% of whom were HCV-coinfected (HIV/HCV)] contributed 76 376 patient-years of follow-up. HCV coinfection was associated with lower rates of hypercholesterolaemia (18.0% in HIV/HCV vs. 30.7% in HIV-only patients; P<0.001), but higher rates of hypertension (43.8%vs. 35.6%; P<0.0001), type 2 diabetes mellitus (16.2%vs. 11.1%; P<0.0001) and smoking (36.7%vs. 24.7%; P=0.009). Rates of AMI and CVD were significantly higher among HIV/HCV than HIV-only patients: 4.19 vs. 3.36 events/1000 patient-years, respectively (P<0.001), for AMI; and 12.47 vs. 11.12 events/1000 patient-years, respectively (P<0.001), for CVD. When analyses were controlled for diabetes mellitus, hypertension, age and duration of ART, hazard ratios (HRs) among those with HIV/HCV (vs. HIV only) were 1.25 [95% confidence interval (CI) 0.98-1.61; P=0.072] for AMI and 1.20 (CI 1.04-1.38; P=0.013) for CVD. Hypertension (HR 2.05; P<0.001), greater age (HR 1.79; P<0.001) and longer duration (cumulative years) of antiretroviral use (HR 1.12; P=0.0411) were also associated with increased risk of AMI in the adjusted model.

CONCLUSIONS

In the HAART era, HCV coinfection was associated with a significantly increased risk of CVD and a trend towards an increased risk of AMI among HIV-infected patients.

Survival as a function of HbA(1c) in people with type 2 diabetes: a retrospective cohort study

BACKGROUND

Results of intervention studies in patients with type 2 diabetes have led to concerns about the safety of aiming for normal blood glucose concentrations. We assessed survival as a function of HbA(1c) in people with type 2 diabetes.

METHODS

Two cohorts of patients aged 50 years and older with type 2 diabetes were generated from the UK General Practice Research Database from November 1986 to November 2008. We identified 27 965 patients whose treatment had been intensified from oral monotherapy to combination therapy with oral blood-glucose lowering agents, and 20 005 who had changed to regimens that included insulin. Those with diabetes secondary to other causes were excluded. All-cause mortality was the primary outcome. Age, sex, smoking status, cholesterol, cardiovascular risk, and general morbidity were identified as important confounding factors, and Cox survival models were adjusted for these factors accordingly.

FINDINGS

For combined cohorts, compared with the glycated haemoglobin (HbA(1c)) decile with the lowest hazard (median HbA(1c) 7.5%, IQR 7.5-7.6%), the adjusted hazard ratio (HR) of all-cause mortality in the lowest HbA(1c) decile (6.4%, 6.1-6.6) was 1.52 (95% CI 1.32-1.76), and in the highest HbA(1c) decile (median 10.5%, IQR 10.1-11.2%) was 1.79 (95% CI 1.56-2.06). Results showed a general U-shaped association, with the lowest HR at an HbA(1c) of about 7.5%. HR for all-cause mortality in people given insulin-based regimens (2834 deaths) versus those given combination oral agents (2035) was 1.49 (95% CI 1.39-1.59).

INTERPRETATION

Low and high mean HbA(1c) values were associated with increased all-cause mortality and cardiac events. If confirmed, diabetes guidelines might need revision to include a minimum HbA(1c) value.

FUNDING

Eli Lilly and Company.

Abacavir-based therapy does not affect biological mechanisms associated with cardiovascular dysfunction

OBJECTIVE

To assess the effects of initiating abacavir-containing therapy on plasma lipids and cardiovascular biomarkers.

DESIGN

Sub-study of the BICOMBO study in which participants were randomized to switch their nucleoside backbone to either abacavir/lamivudine or tenofovir/emtricitabine.

METHODS

We assessed 48-week changes in fasting lipids and several biomarkers including serum high-sensitivity C-reactive protein (hsCRP), monocyte chemoattractant protein-1 (MCP-1), osteoprotegerin, interleukin (IL)-6, IL-10, tumor necrosis factor alpha (TNF-alpha), intercellular adhesion molecule-1 (ICAM-1), vascular adhesion molecule-1 (VCAM-1), selectin E and P, adiponectin, insulin, and D-dimer in otherwise healthy, virologically suppressed HIV-infected patients randomly switched to abacavir/lamivudine or tenofovir/emtricitabine with no history of cardiovascular disease, no prior abacavir or tenofovir use, and no virological failure or AIDS during follow-up.

RESULTS

Eighty (46 abacavir/lamivudine and 34 tenofovir/emtricitabine) patients were included. Baseline characteristics were similar between groups and between patients in the sub-study vs. those not. There were no significant differences in baseline lipids and markers between groups. Although total (6.5 vs. -6.7%, P < 0.0001) and low-density lipoprotein (LDL) (8.6 vs. -9.1%, P = 0.004) cholesterol increased significantly in the abacavir/lamivudine group relative to the tenofovir/emtricitabine group, we found no significant changes in the biomarkers: CRP (-3.9 vs. 0.0%), MCP-1 (5.9 vs. 4.0%), osteoprotegerin (5.1 vs. -2.8%), IL-6 (0.0 vs. 0.0%), IL-10 (0.0 vs. 0.0%), TNF-alpha (0.0 vs. 0.0%), ICAM-1 (6.6 vs. 5.2%), VCAM-1 (0.02 vs. -0.01%), selectin E (-0.4 vs. 7.8%), selectin P (4.6 vs. 12.6%), insulin (-2.5 vs. 8.8%), adiponectin (-2.2 vs. 15.4%), and D-dimer (0.0 vs. 0.0%) (P > or = 0.12 for all comparisons).

CONCLUSION

Abacavir/lamivudine increased total and LDL cholesterol compared with tenofovir/emtricitabine, but it did not cause inflammation, endothelial dysfunction, insulin resistance, or hypercoagulability in virologically suppressed HIV-infected patients.

The use of contrast enhanced ultrasound in carotid arterial disease

Traditionally, stroke risk stratification has centred on the degree of internal carotid artery stenosis, and the presence of focal neurological symptoms. However, degree of stenosis alone is a relatively poor predictor of future stroke in asymptomatic patients; the Asymptomatic Carotid Surgery Trial highlighting the need to identify a subgroup of asymptomatics that may benefit from intervention. Attempting to define this subgroup has inspired imaging research to identify, in vivo, high-risk plaques. In addition to pre-operative risk stratification of carotid stenosis, contrast enhanced ultrasound (CEUS) may be employed in monitoring response to plaque-stabilising therapies. Unlike most contrast agents used for computed tomography and magnetic resonance imaging, microbubbles used in CEUS remain within the vascular space and can hence be used to study the vasculature. In addition to improving current carotid structural scans, CEUS has potential to add extra information on plaque characteristics. Furthermore, by targeting microbubbles to specific ligands expressed on vascular endothelium, CEUS may have the ability to probe plaque biology. This review describes the current carotid ultrasound examination and the need to improve it, rationale for imaging neovascularisation, use of CEUS to image neovascularisation, microbubbles in improving the structural imaging of plaque, potential problems with CEUS, and future directions.

Progression and observational frequency of atheromatous plaques in autopsied coronary arteries

Background and Objectives

Virtual histology-intravascular ultrasound (VH-IVUS) studies on early-stage fibroatheroma, the probable precursor lesion of progression to thin-cap fibroatheroma (TCFA), have only rarely been done in man. We investigated the progression and observational frequency of fibroatheromas, and compared plaque components between early-stage and advance-staged fibroatheromas in the general population.

Subjects and Methods

We assessed coronary fibroatheromas using VH-IVUS and histopathologic analysis of 109 coronary lesions from 40 autopsied cases that were not due to sudden cardiac death (NSCD cases). Fibroatheromas were grouped into early fibroatheroma, late fibroatheroma, thick-cap fibroatheroma (TkCFA), and thin-cap fibroatheroma.

Results

Mean patient age was 45±11 years old and 71% were males. Of 109 lesions, 27% were early fibroatheromas, 53% late fibroatheromas, 9% TkCFA, and 11% TCFA. VH-IVUS showed that there was relatively less fibrotic and fibrofatty plaque and more dense calcium deposits as fibroatheromas progressed. Furthermore, the relative amounts of fibrotic and fibrofatty plaque decreased (r=0.773, p<0.001 and r=0.538, p<0.001, respectively) as the necrotic core increased, while the relative area of dense calcium increased (r=0.665, p<0.001) as the size of the necrotic core increased.

Conclusion

Of NSCD cases in Korea, 27% were early fibroatheromas, 53% were late fibroatheromas, 9% were TkCFA, and 11% were TCFA. Advance-staged fibroatheromas show more necrotic core volume and more dense calcium than small, early-stage fibroatheromas.

[C-reactive protein and carotid intima-media thickness in atherothrombotic ischemic stroke]

BACKGROUND AND OBJECTIVE

We aimed to investigate the relation between values of C-reactive protein (CRP) and carotid artery intima-media thickness (IMT) in patients with atherothrombotic ischemic stroke.

PATIENTS AND METHOD

One hundred and thirty five patients within 48h after index ischemic stroke were included. CRP levels were obtained at this time and a carotid ultrasonography was performed. Neurological and functional disability were evaluated, and all patients underwent a cardiovascular risk stratification. Patients were divided in three groups according to the tertiles of they IMT distribution. We adjusted for the possible confounding effect using a multivariate logistic model.

RESULTS

Forty three in-patients were classified into group 1 (IMT between 0.7 and 1.1 millimetres), 43 into group 2 (IMT between 1.2 and 1.5 millimetres) and 49 into group 3 (IMT higher of 1.6 millimetres). We found a significant elevation of CRP levels at different groups (p<0.0008), with medians by group of 0.3, 0.4 and 1.5mg/dl respectively. Likewise, we found significant differences by group in functional disability (p<0.03) and in vascular risk stratification (p<0.02).

CONCLUSIONS

CRP is a marker of increased IMT in patients with atherothrombotic ischemic stroke. A cutoff point of 1.5mg/dl for CRP provided a greater IMT and a worse outcome in functional disability as cardiovascular risk. Therefore, this group requires a more intensive treatment in secondary prevention.

Usefulness of elevations in serum choline and free F2)-isoprostane to predict 30-day cardiovascular outcomes in patients with acute coronary syndrome

Our objectives were to evaluate the prognostic value of several biomarkers in patients with acute coronary syndrome (ACS) through an evaluation of the 30-day clinical outcomes. Multiple biomarkers have emerged as potentially useful in risk stratification of ACS. Specifically, markers of vascular inflammation and oxidative stress might be helpful in the determination of clinical outcomes. We evaluated patients presenting with chest pain. ACS was defined by symptoms of cardiac ischemia plus electrocardiographic changes or positive troponin I. Levels of serum troponin I, high sensitivity C-reactive protein, serum choline, and free F(2)-isoprostane were obtained. Patients were followed up for 30 days (n = 108) with determination of nonfatal myocardial infarction, congestive heart failure, need for revascularization, and death. Of the 108 patients, 26 had a cardiac event. Free F(2)-isoprostane and choline levels (but not high-sensitivity C-reactive protein levels) predicted 30-day cardiac events. To determine the value of choline and F(2)-isoprostane levels in predicting 30-day cardiac events, receiver operating curves were generated. The optimal cutoff point of these markers was a serum F(2)-isoprostane level of 124.5 pg/ml (r = 0.82) and a serum choline level of 30.5 mumol/L (r = 0.76). F(2)-isoprostane and choline had a positive predictive value of 57% and 44% and a negative predictive value of 90% and 89%, respectively. In conclusion, serum choline and free F(2)-isoprostane are predictors of cardiac events in ACS. A model that includes an array of biomarkers, including troponin, choline, and free F(2)-isoprostane, might be useful in predicting patients at greater risk of future events in ACS.

Enhanced proatherogenic inflammation after recombinant human TSH administration in patients monitored for thyroid cancer remnant

OBJECTIVE

To evaluate the effect of recombinant human TSH (rhTSH) on biomarkers of vascular endothelial cell and platelet activation in patients monitored for thyroid carcinoma remnant.

METHODS

Circulating levels of soluble(s) intercellular adhesion molecule (sICAM)-1 and sE-selectin, as indices of vascular endothelial cell activation, of sP-selectin and sCD40 ligand (sCD40L), as indices of platelet activation, and of 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)), as an index of lipid peroxidation, were evaluated in 20 patients (16 females, 48.0 +/- 13.6 years) at baseline and after intramuscular rhTSH injection (0.9 mg/day on two consecutive days).

RESULTS

At baseline, serum TSH values were below normal whereas free T3 and free T4 were within the normal range. After rhTSH injection, serum TSH increased significantly but free T3 and free T4 remained unchanged. Concomitantly, plasma sICAM-1 concentrations increased significantly (from 155.9 +/- 39.1 to 183.6 +/- 38.1 ng/ml, P < 0.03), as did those of sE-selectin (from 74.8 +/- 15.4 to 91.4 +/- 12.2 ng/ml, P < 0.0006), sP-selectin (from 56.4 +/- 13.7 to 72.2 +/- 14.9 ng/ml, P < 0.002), sCD40L (from 2.1 +/- 0.9 to 2.8 +/- 1.1 ng/ml, P < 0.03) and total 8-iso-PGF(2alpha)(from 238.5 +/- 47.0 to 307.8 +/- 41.2 pg/l, P < 0.0001). Changes in circulating levels of sCD40L were directly correlated with changes in levels of plasma total 8-iso-PGF(2alpha) (r = 0.523, P < 0.02) and sP-selectin (r = 0.480, P < 0.03).

CONCLUSIONS

Supraphysiological concentrations of rhTSH might exert proatherogenic effects by promoting activation of vascular endothelial cells and platelets probably through enhanced oxidative stress.

Atherosclerotic progression attenuates the expression of Nogo-B in autopsied coronary artery: pathology and virtual histology intravascular ultrasound analysis

The relation of Nogo-B to atherosclerotic plaque progression is not well understood. Thus, the purpose of this study was to assess the expression of Nogo-B in fibroatheromas (FA) of different stages, classified using virtual histology intravascular ultrasound (VH-IVUS) analysis in 19 autopsied cases of non-sudden cardiac death. VH-IVUS imaging analysis was performed 30 mm from the ostium of each coronary artery. VH-IVUS revealed 11 early FAs (34.5+/-8.3 yr), 12 late FAs (42.6+/-16.6 yr), 8 thick-cap FAs (TkCFAs) (46.4+/-11.1 yr), and 6 thin-cap FAs (TCFAs) (51.8+/-6.8 yr). TkCFAs and TCFAs were defined as advanced FA. FA progression advanced with age (P=0.04). VH-IVUS analysis of small, early FAs showed smaller necrotic cores and relatively less calcium compared to more advanced FAs with large necrotic cores (P<0.001). Histopathology and immunohistochemical stains demonstrated that early or late FAs had smaller necrotic cores, less empty space of decalcification, and greater Nogo-B expression compared to advanced FAs (vs. early FA, P=0.013; vs. late FA, P=0.008, respectively). These findings suggest that FA progression is inversely associated with Nogo-B expression. Local reduction of Nogo-B may contribute to plaque formation and/or instability.

Dissociation of Pentameric to Monomeric C-Reactive Protein on Activated Platelets Localizes Inflammation to Atherosclerotic Plaques

C-reactive protein (CRP) is a predictor of cardiovascular risk. It circulates as a pentamer (pentameric CRP) in plasma. The in vivo existence of monomeric (m)CRP has been postulated, but its function and source are not clear. We show that mCRP is deposited in human aortic and carotid atherosclerotic plaques but not in healthy vessels. pCRP is found neither in healthy nor in diseased vessels. As source of mCRP, we identify a mechanism of dissociation of pCRP to mCRP. We report that activated platelets, which play a central role in cardiovascular events, mediate this dissociation via lysophosphatidylcholine, which is present on activated but not resting platelets. Furthermore, the dissociation of pCRP to mCRP can also be mediated by apoptotic monocytic THP-1 and Jurkat T cells. The functional consequence is the unmasking of proinflammatory effects of CRP as demonstrated in experimental settings that are pathophysiologically relevant for atherogenesis: compared to pCRP, mCRP induces enhanced monocyte chemotaxis; monocyte activation, as determined by conformational change of integrin Mac-1; generation of reactive oxygen species; and monocyte adhesion under static and physiological flow conditions. In conclusion, we demonstrate mCRP generation via pCRP dissociation on activated platelets and H 2 O 2 -treated apoptotic THP-1 and Jurkat T cells, thereby identifying a mechanism of localized unmasking of the proinflammatory properties of CRP. This novel mechanism provides a potential link between the established cardiovascular risk marker, circulating pCRP, and localized platelet-mediated inflammatory and proatherogenic effects.

Inhibition of Tumor Necrosis Factor-α–Induced Interleukin-6 Expression by Telmisartan Through Cross-Talk of Peroxisome Proliferator-Activated Receptor-γ With Nuclear Factor κB and CCAAT/Enhancer-Binding Protein-β

Telmisartan, an angiotensin II type 1 receptor antagonist, was reported to be a partial agonist of peroxisome proliferator-activated receptor-γ. Although peroxisome proliferator-activated receptor-γ activators have been shown to have an anti-inflammatory effect, such as inhibition of cytokine production, it has not been determined whether telmisartan has such effects. We examined whether telmisartan inhibits expression of interleukin-6 (IL-6), a proinflammatory cytokine, in vascular smooth muscle cells. Telmisartan, but not valsartan, attenuated IL-6 mRNA expression induced by tumor necrosis factor-α (TNF-α). Telmisartan decreased TNF-α–induced IL-6 mRNA and protein expression in a dose-dependent manner. Because suppression of IL-6 mRNA expression was prevented by pretreatment with GW9662, a specific peroxisome proliferator-activated receptor-γ antagonist, peroxisome proliferator-activated receptor-γ may be involved in the process. Telmisartan suppressed IL-6 gene promoter activity induced by TNF-α. Deletion analysis suggested that the DNA segment between −150 bp and −27 bp of the IL-6 gene promoter that contains nuclear factor κB and CCAAT/enhancer-binding protein-β sites was responsible for telmisartan suppression. Telmisartan attenuated TNF-α–induced nuclear factor κB– and CCAAT/enhancer-binding protein-β–dependent gene transcription and DNA binding. Telmisartan also attenuated serum IL-6 level in TNF-α–infused mice and IL-6 production from rat aorta stimulated with TNF-α ex vivo. These data suggest that telmisartan may attenuate inflammatory process induced by TNF-α in addition to the blockade of angiotensin II type 1 receptor. Because both TNF-α and angiotensin II play important roles in atherogenesis through enhancement of vascular inflammation, telmisartan may be beneficial for treatment of not only hypertension but also vascular inflammatory change.

Effect of Bosentan on Plasma Markers of Endothelial Cell Activity in Patients with Secondary Pulmonary Hypertension Related to Connective Tissue Diseases

Objective.

To evaluate plasma markers of endothelial cell activity in patients with pulmonary arterial hypertension (PAH) induced by connective tissue diseases (CTD) before and after 3-month administration of bosentan.

Methods.

We quantified E, L and P-selectin (sE-S, sL-S, sP-S), thrombomodulin (TM), monocyte-chemotactic protein 1 (MCP-1), human soluble CD40 ligand (sCD40L), and nitric oxide (NO) in 18 patients and 18 controls. We evaluated right ventricular systolic pressure (RVSP) and the 6-minute walk test (6-MWT).

Results.

All plasma markers but sL-S and TM at Time 0 were significantly higher in patients compared with controls. After 3 months of therapy, decreased levels were noted in NO (Time 0 24.05 ± 6.01 mmol/l, Time 1 13.92 ± 3.40 mmol/l; p < 0.001) and sCD40L (Time 0 1685.33 ± 866 pg/ml, Time 1 1055.11 ± 630.6 pg/ml; p = 0.017). In contrast, sP-S was significantly increased (Time 0 88.36 ± 47.76 ng/ml, Time 1 147.21 ± 94.43 ng/ml; p = 0.021). All patients remained stable in WHO class III, and in 9 patients we noted an improvement in 6-MWT. A correlation was found between Δ of RVSP and 6-MWT (r2= 0.5355, p < 0.001) as well as between Δ-sP-S and both Δ-6-MWT and Δ-RVSP. An increase sP-S level was found in 89% of nonresponder patients, whereas 55% of responders showed a stable or reduced sP-S level (p = 0.016 responder vs nonresponder).

Conclusion.

Treatment with bosentan for 3 months induced a beneficial effect by restoring endothelial function through a decrease in the markers of endothelial cell activity, leading to stabilization or improvement of severe PAH.

Update on integrated biomarkers for assessment of long-term risk of cardiovascular complications in initially healthy subjects and patients with manifest atherosclerosis

Risk stratification for cardiovascular diseases (CVD) remains suboptimal even after the introduction of global risk assessment by various scores. This has prompted the search for additional biomarkers which might help to improve risk stratification. Basically, there are blood biomarkers representing various pathophysiological pathways of atherosclerosis, and markers of subclinical disease. Since inflammatory processes accompany all stages of atherosclerosis, measurement of plasma/serum concentrations of circulating inflammatory biomarkers have received great attention. Such biomarkers can be measured systemically by sensitive assays, and elevated concentrations in the circulation have been shown to be associated with future CVD events. Thus, they might add to the predictive value of the atherogenic lipoprotein phenotype to further improve CVD risk assessment. In addition, several non-invasive imaging techniques are available for which also a predictive value for CVD could be established. However, for most of these biomarkers the clinical utility has not yet been firmly established. This review attempts to give an update on the potential use of biomarkers for risk stratification in initially healthy subjects and patients with manifest, chronic atherosclerosis, particularly focusing on the integrated value of the combination of these markers.

Immune and inflammatory responses to stroke: good or bad?

Inflammatory and immune responses play important roles following ischaemic stroke. Inflammatory responses contribute to damage and also contribute to repair. Injury to tissue triggers an immune response. This is initiated through activation of the innate immune system. In stroke there is microglial activation. This is followed by an influx of lymphocytes and macrophages into the brain, triggered by production of pro-inflammatory cytokines. This inflammatory response contributes to further tissue injury. There is also a systemic immune response to stroke, and there is a degree of immunosuppression that may contribute to the stroke patient's risk of infection. This immunosuppressive response may also be protective, with regulatory lymphocytes producing cytokines and growth factors that are neuroprotective. The specific targets of the immune response after stroke are not known, and the details of the immune and inflammatory responses are only partly understood. The role of inflammation and immune responses after stroke is twofold. The immune system may contribute to damage after stroke, but may also contribute to repair processes. The possibility that some of the immune response after stroke may be neuroprotective is exciting and suggests that deliberate enhancement of these responses may be a therapeutic option.

The association of elevated reactive oxygen species levels from neutrophils with low-grade inflammation in the elderly

Background

Reactive oxygen species (ROS), including free radicals, oxygen ions, and peroxides, are implicated in cell damage. The objective of this study was to investigate whether the spontaneous production of ROS from neutrophils changes with age and is associated with the conventional inflammatory markers.

Results

Thirty-seven elderly subjects (median age, 87, range 70–95 years) and 22 young subjects (median age, 26, range 21–37 years) participated in this study. Circulating levels of C-reactive protein, serum amyloid A, tumor necrosis factor-α, interleukin (IL)-1, IL-6, IL-8, monocyte chemotactic protein-1, and heat shock protein (HSP)70 were measured with enzyme-linked immunosorbent assays. The N-formyl-methionyl-leucyl-phenylalanine and lipopolysaccharide-stimulated ROS of neutrophils were quantified by flow cytometry. Both spontaneous ROS production and circulating levels of inflammatory markers were higher in the elderly group than in the younger group. In addition, spontaneous ROS production by neutrophils was negatively associated with HSP70 in plasma. We could not find the association between spontaneous ROS production by neutrophils and the other inflammatory markers including cytokines.

Conclusion

The results suggest that spontaneous ROS production from neutrophils may increase with age and represent the different aspect of age-associated immune dysregulation.

Noninvasive diagnosis of ruptured peripheral atherosclerotic lesions and myocardial infarction by antibody profiling

Novel biomarkers, such as circulating (auto)antibody signatures, may improve early detection and treatment of ruptured atherosclerotic lesions and accompanying cardiovascular events, such as myocardial infarction. Using a phage-display library derived from cDNAs preferentially expressed in ruptured peripheral human atherosclerotic plaques, we performed serological antigen selection to isolate displayed cDNA products specifically interacting with antibodies in sera from patients with proven ruptured peripheral atherosclerotic lesions. Two cDNA products were subsequently evaluated on a validation series of patients with peripheral atherosclerotic lesions, healthy controls, and patients with coronary artery disease at different stages. Our biomarker set was able to discriminate between patients with peripheral ruptured lesions and patients with peripheral stable plaques with 100% specificity and 76% sensitivity. Furthermore, 93% of patients with an acute myocardial infarction (AMI) tested positive for our biomarkers, whereas all patients with stable angina pectoris tested negative. Moreover, 90% of AMI patients who initially tested negative for troponin T, for which a positive result is known to indicate myocardial infarction, tested positive for our biomarkers upon hospital admission. In conclusion, antibody profiling constitutes a promising approach for noninvasive diagnosis of atherosclerotic lesions, because a positive serum response against a set of 2 cDNA products showed a strong association with the presence of ruptured peripheral atherosclerotic lesions and myocardial infarction.

New and emerging risk factors for CVD

Morphological and immunocytochemical studies have elucidated the complex processes involved in atherogenesis. The notion of plaque instability has emerged from this work and underscored the importance of inflammation in determining clinical complications associated with atherosclerosis, such as acute coronary syndrome. Cells of the immune system have been detected within atherosclerotic lesions and auto-antibodies directed against modified LDL and heat-shock proteins have been identified in the blood of individuals with atherosclerosis. The use of risk 'engines', e.g. the Framingham coronary risk score, has facilitated the identification of individuals at high risk, but the constituent classical risk factors used in these algorithms do not adequately differentiate individuals at moderate risk. As age is a major component of the equations used in these algorithms they are not particularly useful in young adults, and their applicability to non-Caucasian populations has been questioned. Biomarkers of early disease and plaque instability have therefore both been sought. Although some of these markers have been shown individually to be associated with a significant hazard ratio, no substantial improvement in discrimination has been demonstrated when they are incorporated into a risk 'engine'. The latter has generally been assessed by receiver operator characteristic curve analysis, although this approach has been criticised. Other modalities, including imaging and functional assessments of vascular function, are now being developed for clinical use.

Markers of inflammation in patients with symptomatic and asymptomatic carotid artery stenosis: a case-control study

OBJECTIVES

There is evidence that inflammation plays a role in the pathogenesis of atherosclerosis. We compared levels of inflammatory markers between patients undergoing carotid endarterectomy (CEA) and controls, and between patients with symptomatic and asymptomatic internal carotid artery (ICA) stenosis.

MATERIALS AND METHODS

A total of 180 patients with ICA stenosis were compared with 180 age-matched and sex-matched controls. The biomarkers evaluated were high-sensitivity C-reactive protein (hs-CRP), soluble intercellular adhesion molecule 1, soluble vascular cell adhesion molecule 1 (sVCAM-1), and interleukin-6 (IL-6).

RESULTS

The levels of hs-CRP, sVCAM-1, and IL-6 in the CEA group were significantly higher than in the control group (1.87 mg/mL vs 1.44 mg/mL, P = .011; 1408 ng/dL vs 672 ng/dL, P < .001; 11.9 pg/mL vs 6.3 pg/mL, P < .001). Multivariate linear regression analysis, adjusted for all clinical and physiologic parameters, showed a significant association between ICA stenosis and hs-CRP, sVCAM-1, and IL-6 concentrations. Analysis of symptomatic (n = 101) and asymptomatic (n = 79) ICA stenosis did not detect a difference in levels of these markers.

CONCLUSIONS

Our study suggests that inflammatory markers could serve as markers for ICA atherosclerosis but are not useful to identify carotid plaque at risk for symptomatic conversion.

Does high C-reactive protein concentration increase atherosclerosis? The Whitehall II Study

BACKGROUND

C-reactive protein (CRP), a marker of systemic inflammation, is associated with risk of coronary events and sub-clinical measures of atherosclerosis. Evidence in support of this link being causal would include an association robust to adjustments for confounders (multivariable standard regression analysis) and the association of CRP gene polymorphisms with atherosclerosis (Mendelian randomization analysis).

METHODOLOGY/PRINCIPAL FINDINGS

We genotyped 3 tag single nucleotide polymorphisms (SNPs) [+1444T>C (rs1130864); +2303G>A (rs1205) and +4899T>G (rs 3093077)] in the CRP gene and assessed CRP and carotid intima-media thickness (CIMT), a structural marker of atherosclerosis, in 4941 men and women aged 50-74 (mean 61) years (the Whitehall II Study). The 4 major haplotypes from the SNPs were consistently associated with CRP level, but not with other risk factors that might confound the association between CRP and CIMT. CRP, assessed both at mean age 49 and at mean age 61, was associated both with CIMT in age and sex adjusted standard regression analyses and with potential confounding factors. However, the association of CRP with CIMT attenuated to the null with adjustment for confounding factors in both prospective and cross-sectional analyses. When examined using genetic variants as the instrument for serum CRP, there was no inferred association between CRP and CIMT.

CONCLUSIONS/SIGNIFICANCE

Both multivariable standard regression analysis and Mendelian randomization analysis suggest that the association of CRP with carotid atheroma indexed by CIMT may not be causal.