Apolipoprotein B (Apo B) Validity in DM

1. Apolipoprotein B (Apo B)Validity in DM Dr. Lamia M Al-Naama Biochemistry Dept Basrah Medical College

2. Dyslipidemia in patients with Diabetes • High triglyceride (TG) levels • TG-rich remnant lipoproteins (VLDL) • Altered metabolism of LDL and HDL particles • Absolute levels of LDL cholesterol are commonly not significantly increased, number of LDL particles • Predominantly small, dense LDL particles • Low levels of HDL cholesterol (may reduce reverse cholesterol transport) Adapted from Haffner SM Diabetes Care 2003; 26: S83-6 and Garvey WT et al. Diabetes 2003; 52: 453-62

3. Overall LDL cholesterol may also be elevated. High triglyceride levels manifest as high triglyceride-rich remnant lipoproteins (VLDL) and alter the metabolism of LDL and HDL particles. Because a mixed dyslipidemic profile increases the risk of developing cardiovascular disease, it is also referred to as the atherogenic lipid triad or atherogenic dyslipidemia. Atherogenic dyslipidemia contributes to an increased risk for cardiovascular disease.

4. Metabolic Basis for Atherogenic Dyslipidemia: Concordant Increase in VLDL and Small LDL and Reduction of HDL LPL LPL/HL LDL VLDL Remnants Smaller LDL TG HL Cholesterol TG CETP TG Smaller HDL Apo AI HDL Renal clearance Apo AI: apolipoprotein AI CETP: cholesteryl ester transfer protein HL: hepatic lipase LPL: lipoprotein lipase TG: triglycerides Adapted from Haffner SM Diabetes Care 2003; 26: S83-6 and Garvey WT et al. Diabetes 2003; 52: 453-62

5. LDL Size Certainly Seems to Matter “The mean concentration of LDL cholesterol in those with type 2 diabetes is not significantly different from that in those individuals who do not have diabetes.” “However, qualitative changes in LDL cholesterol may be present. Patients with diabetes tend to have a higher proportion of smaller and denser LDL particles which are more susceptible to oxidation and may therefore increase the risk of cardiovascular events.” Diabetes Care 2004;27:S68

6. Small Dense LDL and CHD: Potential Atherogenic Mechanisms • Increased susceptibility to oxidation • Increased vascular permeability • Conformational change in apo B • Decreased affinity for LDL receptor • Association with insulin resistance syndrome • Association with high TG and low HDL Austin MA et al. CurrOpinLipidol 1996;7:167-171.

7. Conventional lipid measurements • Total Cholesterol =VLDL+LDL +HDL • FriedewaldEquation: VLDL= TG/5 • Calculated LDL = TC – (HDL + TG/5) • Triglycerides • HDL-C

9. 130 mg/dL 130 mg/dL LDL Cholesterol Balance 20+ years of studies: Patients with smaller LDL size have greater CHD risk at any given level of LDL-C. Lower risk Higher risk Large LDL (Pattern A) Small LDL (Pattern B) But they also have more particles! www.myheathywiast.org

10. LDL Cholesterol Underestimates the Number of LDL Particles When Levels of Small LDL Are Increased Larger LDL (phenotype A) More cholesterol/particle Smaller LDL (phenotype B) Less cholesterol/particle Similar LDL cholesterol Apo B Cholesteryl ester • Slower plasma clearance • Greater artery uptake & retention • Faster oxidation • More particles www.myheathywiast.org

11. Particle number v/s Lipid level • Cholesterol is carried into the arterial wall within a LP particle and … • thenumber of LP particlesdetermines the likelihood of cholesterol entering and lodging within an arterial wall • Now, the lipid composition of the principal atherogenic lipoproteins differs substantially amongst individuals • because the number of particles within any lipoprotein fraction determines the likelihood of any member of that class entering and lodging within an arterial wall

12. Particle number v/s Lipid level • Thus, for the same amount of cholesterol measured in 2 individuals, their LPparticle numbermay be different • Therefore, lipid levels do not automatically match lipoprotein particlelevels • And the risk due to a lipid fraction not same as the risk due to the LP fraction • Hence, thetotal numberof atherogenic particles is a more important determinant of the risk of vascular disease than the level of any of the conventional lipids (TC, TG etc)

14. Size (nm) Density (g/ml) 25 50 19 22 1.004 1.013 1.044 1.023 Buoyant LDL DenseLDL RLP VLDL Mean Endothelial Pore Size TG-rich Lipoproteins Atherogenic Particles

15. For example the amount of cholesterol carried by an LDL particle varies greatly between individuals and can also change in response to lipid altering Rx. Apo B versus cholesterol in estimating cardiovascular risk and in guiding therapy: report of the thirty‐person/ten‐country panel Report of the thirty person/ten country panel Journal of Internal Medicine, 10 FEB 2006

16. So how does one measure the particle number ? • 1. NMR spectroscopy • 2. By measuring apoB

17. What is Apo B Apolipoprotein B (apoB) is a major structural protein for atherogenic lipoproteins including chylomicron, VLDL, intermediate-density lipoprotein, large buoyant LDL, and small dense LDL. ApoB is required to transport lipids from the liver and gut to peripheral tissues.

18. What is Apo B In general, one molecule of apoB is present on each lipoprotein particle; The total apo B level represents the total number of atherogenic particles and reflects the atherogenic potential of the whole lipoprotein fraction .

19. Why apo B ? • each VLDL, IDL, LDL, and Lp(a) lipoprotein particle contains one molecule of apo B100 • Each chylomicron and chylomicron remnant particle contains one molecule of apo B48. • Clinical assays of apoB measure both apo B100 and apo B48. • Hence total plasma apo B = (apo B100 +apo B48) represents the total atherogenic particle number

20. Atherogenic Particles Apolipoprotein B MEASUREMENTS: VLDL VLDLR Small,denseLDL IDL LDL TG-rich lipoproteins From Lipids Online: http://www.lipidsonline.org/

21. Atherogenic Particles Apolipoprotein B MEASUREMENTS: Non-HDL-C VLDL VLDLR Small,denseLDL IDL LDL TG-rich lipoproteins From Lipids Online: http://www.lipidsonline.org/

22. Is apo B better than LDL-C ? • Insulin resistance and type 2 diabetes mellitus, MetS, CKD • Familial combined hyperlipidaemia, (associated with premature coronary artery disease) • The Quebec Cardiovascular Study, the AMORIS study, the Thrombo Study , the Thrombo Metabolic Syndrome Study, the Northwick Park Heart Study, the Nurses’ Health Study and patients with type 2 diabetes in the Health Professionals’ Follow-up Study • INTERHEART Study – 52 countries, 30,000 people – value of apo B/A1 ratio (accounted for over 50% of CV events) • Hence apo B has entered ESC guidelines for risk estimation and target of Rx

23. What happens on statin Rx ? • LDL cholesterol reduced more than apo B • Thus apo B on statin therapy will be relatively higher than LDL cholesterol • Thus on treatment apo B should be a more reliable index of the residual risk • In Studies : AFCAPS/TexCAPS, the Leiden Heart Study and the Thrombo Study on-treatment … • apo B was more predictive of the residual risk of vascular events

24. Thus, advantages of measuring apo B: • apo B-guided statin therapy should be substantially more effective than Rx guided by LDL cholesterol • Enables focus on one rather than several variables • Non fasting sample • Measurement standardized by IFCC/WHO • Indirect measurement of LDL-C requires fasting sample and direct measurement of LDL-C not standardized.

25. But problems with apo B testing • Test costs ($79.15 v/s $59.20 for an entire conventional lipid panel) • Significant lag time in test result reporting   • Poor goal attainment rates on standard therapies, including high-dose statins, with limited evidence for other available interventions and therapeutic effects. • Discrepant cut off values……. • Drug therapies known to alter advanced lipoprotein analysis parameters, specifically niacin and fenofibrate, have not been shown to additionally reduce cardiovascular risk in recent randomized trials of high-risk patients treated with statin therapy. 

26. Discrepant apo B cutoffs • The American Diabetes Association (ADA)/American College of Cardiology (ACC) position statement recommends an apoB goal of <80 mg/dl in highest-risk patients and <90 mg/dl in high-risk patients. • In contrast, the American Association of Clinical Chemistry (AACC) recommends an apoB goal of <80 mg/dl in high-risk patients and <100mg/dl in moderate risk people. • The Canadian Cardiovascular Society is in disagreement with the ADA/ACC and the AACC, as they recommend an apoB <80 mg/dl as the primary therapeutic target in high-& moderate-risk patients

27. Can non HDL-C be a surrogate for apo B ?

28. Several large prospective studies have demonstrated that the apo B level is a better predictor of cardiovascular risk than any other lipid measurements . • In the AMORIS study, apoB was found to be superior to LDL cholesterol as a marker to assess cardiovascular risk, particularly in patients with normal or low LDL cholesterol levels . • Data from numerous clinical trials with statins have also reported that residual risk is more strongly associated with the apoB level rather than LDL or non-HDL cholesterol levels . • In the THROMBO study in patients who had recovered from myocardial infarction, higher apoB levels were independently associated with an increased risk of recurrent events, whereas conventional lipid measurements were not .

29. Conclusion ApoB measurements is better indicator of atherogenic risk than LDL-C. New guidelines should be advocated by Expert Panels Like the NCEP or ATP (Adult Treatment Panel) to implement ApoB measurements A unified cut-off values for Apo B

30. THANK YOU!!