Plasma Myeloperoxidase as a Biomarker for Risk Stratification in Stable Coronary Artery Disease

2. Introduction • Atherosclerotic coronary artery disease (CAD) Medical management common in stable CAD • COURAGE trial showed equivalent outcomes when managed either with aggressive medical management versus revascularization. • Risk stratification for aggressive management • Biomarker identification of high-risk individuals • JUPITER trial showed early statin therapy in patients with increased high-sensitivity C-reactive protein (hsCRP) leads to improved outcomes.

3. Introduction (con’t) • Myeloperoxidase (MPO) Potential marker of plaque vulnerability • Hemoprotein enzyme stored within neutrophils, monocytes, and certain tissue macrophages. • Released during leukocyte activation. • Produces hypochlorous acid as part of the innate host defense. • Enriched in atherosclerotic plaque and culprit lesions. • Prognostic value seen in setting of acute coronary syndrome. • Study Objective • To examine the potential for plasma MPO concentrations to identify who may be at heightened long-term risk among stable CAD patients in the setting of aggressive medical therapy.

4. Questions • What is an appropriate patient population to test the clinical utility of a biomarker for risk stratification? • How do you test a specific biomarker in the setting of existing clinical practice strategies of clinical and biochemical risk stratification?

5. Materials and Methods • Study Population Cleveland Clinic GeneBank study • Prospective cohort from 2001-6. • Stable individuals undergoing either cardiac catheterization or coronary computed tomography angiography for evaluation. • Current study included 2,460 consecutive individuals without evidence of myocardial infarction (cardiac troponin I <0.03 g/L) with significant CAD (50% stenosis at any coronary artery). • Excluded patients with revascularization within 30 days before or after procedure. • Endpoint: Major Adverse Cardiovascular Event (MACE) • Death, non-fatal myocardial infarction, non-fatal cerebrovascular accident over ensuing 3 years.

6. Materials and Methods (con’t) • Plasma MPO Assay Abbott Architect ci8200 • Analyzed venous blood samples collected in EDTA tubes stored at -80F • Chemiluminescent automated immunoassay using MPO-specific monoclonal antibodies in a 2-step sandwich format • Dynamic range of 0–10,000 pmol/L • Limit of detection <20.0 pmol/L • Functional sensitivity of < 50.0 pmol/L • Total CV 20%

7. Materials and Methods (con’t) • Statistical Analysis • Between group comparison with student t-test or Wilcoxon rank-sum test for continuous variables, χ2 test for categorical variables. • Cochran-Armitage test for trend analyses across quartiles • ROC curve analyses and 5-fold cross validation to determine optimal MPO cut-off. • Kaplan-Meier survival analysis with log-rank test according to MPO and MPO/hsCRP cut-off values. • Cox proportional hazard regression analysis with covariates including traditional risk factors, hsCRP, and creatinine clearance. • Pencina method for reclassification analysis, using ratio of 6:3:1 categorization due to non-parametric distribution of MPO. • Performed using R 2.8.0, p<0.05 as statistical significance.

8. Questions • What are the statistical analyses that can provide the best bedside clinical relevance for a clinical test? • What are the strengths and limitations of a single cut-off value for a clinical test for the purpose of risk stratification? • What are the strengths and limitations of novel statistical analyses for biomarkers?

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14. Results (con’t) Correlation Analyses • Weak correlation between MPO and hsCRP (r = 0.186; p<0.0001) Novel Statistical Analyses • Area under ROC curve (AUC) was 67% • Integrated discrimination improvement (IDI) of 10% (p<0.001) • Event-specific net reclassification (NRI) of 6% (p=0.022)

15. Discussion Conclusions • Plasma MPO concentration provide independent prognostic value for the prediction of long-term incident major adverse cardiovascular events in a stable, medically managed patient population with coronary artery disease. • In individuals with increased hsCRP concentrations, we observed lower risk of incident MACEs when concomitant MPO concentrations were lower versus when MPO concentrations were higher.

16. Discussion (con’t) Take-Home Messages: • Different biomarkers may provide distinctive insights into underlying pathophysiology. • Identification of intermediate risk patients may provide useful clinical insights into individual disease states. • Clinical significance of a specific biomarker requires appropriate clinical interpretation of patient populations being studied, with the support of rigorous statistical justification. • Standard statistical analyses techniques provide quantification of incremental risk, but are difficult to apply in clinical setting.