From HDL Structure to Function - How Structural Information Can Help Address Clinical Need March 17, 2012

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Duane Stafford
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1 From HDL Structure to Function - How Structural Information Can Help Address Clinical Need March 17, 2012

2 Teaching Objectives There exists no definitive test for risk of cardiovascular disease. Age and family history remain the best indicators of cardiovascular disease risk. The ability of High Density Lipoproteins (HDL) to mobilize cholesterol from the artery wall is the best functional aspect of HDL in determining risk for cardiovascular disease.

3 Adult Patient Population 81 million people have some form of cardiovascular disease in the United States (high blood pressure, CAD, stroke and heart failure) American Heart Association 2006 Annual Report

4 Problem : There Are no Accurate Diagnostics for Coronary Artery Disease (CAD) at the Individual Level HDL-C and LDL-C are the good and bad cholesterol, respectively HDL-C is the best known independent risk factor for CAD monitored in the clinic HDL-C and LDL-C are indicative of CAD but not sufficiently correlated with CAD to serve as a diagnostic marker

5 Current HDL-C Measurements Analogous to measuring flux by taking a snapshot of the number of cars on a highway A more appropriate approach is examining the dynamic flow of cholesterol or by analogy, the rate of traffic at the on ramps and off ramps Existing HDL-C assays look at plasma concentration or particle numbers (NMR) not flux

6 Current HDL-C Measurements Female patients generally do not present as at risk by this metric until after menopause CAD is the leading cause of sudden death in women above the age of 35 Children are a growing risk group for early onset cardiovascular disease due to increased incidence of obesity and diabetes (>30% are obese - BMI > 95%) Existing HDL-C assays do not provide a clear indication of cardiovascular risk in women and children

7 Contributors to Risk of CAD Rate of Cholesterol Deposition (LDL-C) Rate of Cholesterol Clearance (HDL function) Plaque stability (not well understood)

8 HDL Cholesterol Efflux Capacity - A Critical Aspect of HDL Function The cholesterol efflux potential of plasma is diagnostic of risk for CAD Dan Rader & George Rothblat found that the ABCA1 mediated cholesterol efflux capacity of plasma is strongly associated with CAD status. Inverse correlation odds ratio of 0.75 (95% CI; p<0.002) Khera, et al., (2011) N Engl J Med 364,

9 Standard Panels Total Cholesterol LDL-C HDL-C Triglycerides Lp(a) VLDL (subfractions) LDL (particle distribution) HDL (particle distribution) Homocysteine apoe Cyp2C19 Lp-PLA2 CRP Fibrinogen NT-proBNP Hemoglobin A1c

10 The Ideal Assay of HDL Function Small Volume Convenient Sample 50 µl of Sample Plasma or Serum Highly Accurate Rapid Scaleable < 4% Deviation 1-10 Minutes per Sample Can be automated

11 Reverse Cholesterol Transport Pathway

12 Reverse Cholesterol Transport Pathway

13 Reverse Cholesterol Transport Pathway

14 Fluorescence Resonance Energy Transfer

15 FRET-based Detection of ApoA-I - Lipoprotein Exchange 5 : 1

16 ApoA-I is the most specific probe of HDL known

17 HDL Oxidation impairs apoa-i exchange

18 HDL Oxidation impairs cholesterol efflux Subjecting apoa-i to the MPO-H2O2-nitrite system impairs an early step in HDL formation, namely the interaction of apoa-i with ABCA1In patients with CAD, chlorinated HDL is present in atherosclerotic plaques. Chlorination impairs the ability of apoa-i to exit the HDL particle.

19 Electron Paramagnetic Resonance Spectroscopy (EPR) Well suited for the examination of proteins with dynamic structures Reports the structural environment (regional flexibility and solvent accessibility) and the interaction distance between spin labels.

20 EPR Spin Coupling - A High Resolution Atomic Ruler > 20Å < 20Å

21 EPR Spectral Line Shape is Indicative of Secondary Structure Free Label Beta Sheet CONFIDENTIAL Random Coil Alpha Helix

22 Scanning EPR N C CONFIDENTIAL

23 Spin Label Solvent Accessibility Identifies Secondary Structure Alpha Helix Beta Sheet Accessibility (π) Accessibility (π) Residue # Residue # CONFIDENTIAL

24 Interpretation of Solvent Accessibility CONFIDENTIAL

25 Interpretation of Solvent Accessibility

26 Utilize difference between lipid-free and lipid-bound apoa-i to measure HDL dynamics CONFIDENTIAL J. Lagerstedt et al., JBC, 2011

27 Key Transition Site for Assessment of HDL Function CONFIDENTIAL

28 Human EPR Measurements Patient ID Statin Treatment (y/n) Diagnosed as Diabetic (y/n) LDL (mg/dl) HDL (mg/dl) TG (mg/dl) BMI N1 N N N2 N N D1 Y Y M1 N N CONFIDENTIAL

29 Human EPR Measurements Patient N1 Patient M1 Patient N2 Patient D1 1.5 Min Lipid-Free CONFIDENTIAL

30 Human EPR Measurements Patient N1 Patient M1 Patient N2 Patient D1 1.5 Min 4 Min Lipid-Free CONFIDENTIAL

31 Human EPR Measurements Patient N1 Patient M1 Patient N2 Patient D1 1.5 Min 4 Min 6 Min Lipid-Free CONFIDENTIAL

32 Human EPR Measurements Patient N1 Patient M1 Patient N2 Patient D1 1.5 Min 4 Min 6 Min 8 Min Lipid-Free CONFIDENTIAL

33 Human EPR Measurements Patient N1 Patient M1 Patient N2 Patient D1 1.5 Min 4 Min 6 Min 8 Min 10 Min Lipid-Free CONFIDENTIAL

34 The EPR Assay of HDL Function Patient ID Statin Treatment (y/n) Diagnosed as Diabetic (y/n) LDL (mg/dl) HDL (mg/dl) TG (mg/dl) BMI N2 N N CONFIDENTIAL

35 EPR Measurements of HDL Function

36 Representative Sample Set

37 Summary There exists no definitive test for risk of cardiovascular disease Existing tests are complex and evaluate multiple variables that can yield contradictory results The measure of HDL cholesterol efflux function in plasma can yield insightful information on cardiovascular risk and diabetic status

38 Future Objectives Identify limitations of the assay (sample size, material storage, etc) Expand cohort analysis to include broader spectrum of patients Assess the predictive value of the assay in the context of CAD, diabetes and Alzheimer s disease Test future medications and the utility of the assay as a companion diagnostic

Acknowledgments Oda Lab Giorgio Cavigiolio, PhD Jing Zhao, PhD

Burgess, MS Andrea Agcaolli Mandy Baker Sajiv Chandradas Nicole

Geier Leah Goodman Yumin He Daiva Pleskyte Shanna Tucker Accent

39 Acknowledgments Oda Lab Giorgio Cavigiolio, PhD Jing Zhao, PhD Ioanna Pagani, PhD Bodo Paradi, PhD Braydon L. Burgess, MS Andrea Agcaolli Mandy Baker Sajiv Chandradas Nicole DeValle Ethan G. Geier Leah Goodman Yumin He Daiva Pleskyte Shanna Tucker Accent Assays Shawn Hayes, PhD UCLA Jake Lusis, PhD Margarete Mehrabian, PhD Univ. of British Columbia Cheryl Wellington, PhD Sophie Stukas UC Davis John C. Voss, PhD Jens Lagerstedt, PhD Madhu S. Budamagunta, PhD Univ. of Washington Jay Heinecke, MD Baohai Shao, PhD Jack Oram, PhD

40 Conclusions ApoA-I binding rates to HDL correlate with plasma s efflux capacity, a potent diagnostic of CAD We are developing a powerful assay that can identify individuals with reduced cholesterol efflux capacity, even for individuals whose lipid panels appear normal

Walter B. Bayubay CLS (ASCP), AMT, MA Ed, CPI

Walter B. Bayubay CLS (ASCP), AMT, MA Ed, CPI Biochemical Analysis (Lipid Panel) Analyte Total Cholesterol Reference Range Patient A < 200 241 LDL-C /= 40 38 Triglycerides