Going beyond the routine !Is measuring apo B and Lp (a) of value ? Dr Akshay Mehta Dr B Nanavati Hospital Asian Heart Institute
Why go beyond the routine (lipid profile) ?• Acute coronary syndromes in up to one-half of patients with “normal” cholesterol levels• Approximately 34% of adults in the United States have the metabolic syndrome with characteristically high TG, low HDL- C, and LDL-C often within normal limits• 30% relative risk reduction with statin therapy -significant CHD still with LDL-C at goal ---“residual risk”Increase in MetS has caused increased FFA load on liver and down regulation of LPL due to relative Insulin inefficiency.
To go beyond the routine, we have to understand……..• A paradigm of numbers• The enigma of Lp(a)
Particle number v/s Lipid level A paradigm to understand• Cholesterol is carried into the arterial wall within a LP particle and …• the number of LP particles determines the likelihood of cholesterol entering and lodging within an arterial wall• Now, the lipid composition of the principal atherogenic lipoproteins differs substantially amongst individualsbecause the number of particles within any lipoprotein fraction determines the likelihoodof any member of that class entering and lodging within an arterial wall
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
• Thus, for the same amount of cholesterol measured in 2 individuals, their LP particle number may be different• Therefore, lipid levels do not automatically match lipoprotein particle levels.• And the risk due to a lipid fraction not same as the risk due to the LP fraction• Hence, the total number of 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)
So how does one measure the particle number ?1. NMR spectroscopy2. By measuring apoB
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
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
Lipid profile in control populationin INTREHEART by ethnicity (Men)N=14,637 South Asian Chinese European Black AfricanTC (mg/dl) 184 182 203 158HDL (mg/dl) 32 41 43 41TC/ HDL 5.71 4.47 4.71 3.85Non- HDL-C 148 139 156 114Apo B (mg/dl) 88 79 93 70Apo A1( mg/dl) 105 119 122 110Apo B/Apo A1 0.84 0.66 0.76 0.64
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 4S, LIPID, AFCAPS/TexCAPS, the Leiden Heart Study and the Thrombo Study on-treatment apo B was more predictive of the residual risk of vascular events
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.
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, specificallyniacin and fenofibrate, have not been shown to additionally reduce cardiovascular riskin recent randomized trials of high-risk patients treated with statin therapy.
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- and moderate-risk patients
• Thus, although of apparently similar significance, measurement of the number of atherogenic particles may be more biologically meaningful than the measurement of the cholesterol content in these particles because :• Cholesterol is carried into the arterial wall within a LP particle and …• the number of LP particles determines the likelihood of cholesterol entering and lodging within an arterial wall
Advantages of non HDL-C• Established cutpoints which remain valid and independent of increasingly discrepant population percentiles• No additional cost• Quick calculation of TC minus HDL-C (Freedom from LDLC,TG !)• Well-documented intervention effects• Existence within our current “cholesterol-oriented” conceptual framework• Non fasting sample
Is non HDL-C better than LDL-C ?• The Lipid Research Clinics Program Follow-Up study- Pr Prev of 4,462 non–HDL-C > LDL-C as predictor of all-cause & CVD mortality• The BARI sec prev of 1,514 – 5 yrs follow up : non HDL-C a better predictor of non fatal MI• In Hypertriglyceridemic States : a pooled post-hoc analysis of outcomes using data from Framingham Cohort Study, Framingham Offspring Study, Lipid Research Clinics Prevalence Follow-Up study, and the MRFIT — significantly higher values of non–HDL-C in diabetic patients compared with nondiabetic patients but nearly identical LDL-C levels
Even independent of TG levels :• In the SHEP 4,736 primary and secondary prevention pts non HDL-C an independent predictor of CHD regardless of TG levels• EPIC-Norfolk study non–HDL-C strongest predictor of future CHD across all other lipid-stratified levels, including patients with a TG <200 mg/dl.• The ERFC (Emerging Risk Factors Collaboration) found that TG levels were not independently associated with CHD risk once adjusted for non–HDL-C in 302,430 individuals
Hence both apoB and non–HDL-C are valuable for CVD risk prediction with benefits beyond that of LDL-C
Apo B better than non HDLC• The Health Professionals Follow-Up study (2005 Circulation)• AMORIS study 2004 (apoB/A1 ratio,Lancet 2001)• Framingham Offspring Study (J Clin Lipidol. 2007)
non HDL-C as good….• Womens Heart Study• Emerging Risk Factors Collaboration ……..or better than apo B• Postmortem examination from the PDAY (Pathological Determinants of Atherosclerosis in Youth) study• Combined analysis of TNT and IDEAL
Comparison of Apo B and Non-HDL- C for Identifying CAD Risk Based on Receiver Operating Curve Analysis Stanley S. Levinson, PhD, DABCC Am J Clin Pathol. 2007;127(3):449-455.• The ability of apo B to discriminate between disease and nondisease was compared with non-HDLC and other lipoprotein lipids in 437 men who had undergone coronary angiography• When results were evaluated by multivariate techniques and expressed as odd ratios there was significant difference b/w the 2 as risk predictors• But when analysed by receiver operating characteristic (ROC) curves, and adjusted with other RF, the difference between apo B and lipid factors proved to be insignificant.
Lipid-Related Markers andCardiovascular Disease Prediction The Emerging Risk Factors Collaboration* JAMA. 2012;307(23):2499-2506 Objective To determine whether replacing or adding information on apo B and apo A-I, lp(a), or lp-associated phospholipase A2 to Total C and HDL C improves cardiovascular disease (CVD) risk prediction.
Results use of any of the apolipoproteins instead of current markers gave a worse prediction use of any of them on top of current markers improved risk prediction but only very slightly (C statistic)
So should we measure apoB in routine practice ?• Findings of better performance of apo B compared with non–HDL-C are controversial-• The difference b/w the two vanish when corrected for characteristics of insulin resistance• Although residual risk is 30% on std doses of statins, it is about 45% on intensive statin therapy
Also…• Doing apo B etc would not address the residual risk of other well-established cardiovascular risk factors, such as aging, male sex, hypertension, or smoking• No superiority of treatment strategies incorporating non statin lipid-modifying agents compared with intensive statin therapy –SANDS, ACCORD, AIM-HIGH, HPS THRIVE II• Hence both apoB and non–HDL-C are valuable parameters available to physicians for CVD risk prediction and stratification, with benefits beyond that of LDL-C• But non HDL-C is a more realistic target of therapy with intensive statin therapy until it can be shown by prospective studies that there is some definitive advantage on an absolute basis for using apo B.
NHDL cholesterol and CVD risk• Non HDL-C calculation Non-HDL-C = TC-HDL-C• Non- HDL-C goal 30 mg/dL above goal for LDL-C• Significance of non-HDL-C Encompasses all known and potential atherogenic lipid particles (linearly proportional to Apo B) Has been shown to be a stronger predictor of cardiovascular death than LDL-C, especially in women
Risk category LDL-C (mg/dL) Non-HDL-CCHD and CHD Risk < 100 <130equivalent(10 year CHD death risk>20%)Multiple (>= 2) risk <130 <160factors(10 years CHD death risk<20%)0-1 risk factor < 160 <190
What about Lp(a) ?• Lp(a) is a plasma protein composed of an LDL particle linked to apo(a), which has structural homology with plasminogen.• Lp(a) may therefore contribute to both intimal cholesterol deposition and prothrombotic potential• Genetically determined Lp(a) levels are continuously and linearly related to risk of CVD independent of lifestyle, lipid levels.• Thus , both a risk factor and a risk marker esp of premature CHD.• Highly consistent levels within individuals across many years since birth thus effect of Lp(a) on CHD risk can be assessed using a single measurement
Asian Indians have Lp(a) levels intermediate between whites and blacks (less dangerous large isoforms and high HDL levels) The combination of high Lp(a) and low HDL is found in 42% of Indians
Problems with Lp(a)• Measurement of Lp(a) levels is done by a variety of methods and is not fully standardized, and is performed with several assays.• Ideally, assays should be reported as nmol/l using a WHO– approved, IFCC and Laboratory Medicine reference standard apo(a) This assay measures Lp(a) as moles of apo(a) protein using specific monoclonal antibodies, is independent of isoform size.• Lp(a) can also be measured as mg/dl representing the entire mass of Lp(a) (protein, lipid, and carbohydrate). These assays must be validated with reference standards.• Lp(a) can also be measured as Lp(a) “cholesterol” in mg/dl and assayed using quantification gradient analysis, but the published database for the predictive value of this assay is significantly smaller than the others.
Problems with Lp(a)• Reference ranges vary and depend on assay and reporting laboratories.• They also differ by population and may differ regionally worldwide• Reference ranges for individual race/ethnicities yet to be developed• Specifically targeted therapies to lower Lp(a) are not available.
Available Rx for high Lp(a) Niacin and estrogens lower Lp(a) up to 30% Aspirin Statins either have no effect or increase Lp(a) levels• Thyromimetics• Cholesterol-ester-transfer protein (CETP inhibitors)• Anti-sense oligonucleopeptides to apoB -Mipomersen• Proprotein convertase subtilisin/kexin type 9 (PCSK-9) inhibitors.• L-carnitine (2 g/day) may also reduce lipoprotein a levels• Gingko biloba may be beneficial, but has not been clinically verified• Coenzyme Q-10 and pine bark extract have been suggested as beneficial, but neither has been proven in clinical trials
When to check for Lp(a) ?• premature cardiovascular disease esp not explained by routine lipid parameters or RF• family history of premature cardiovascular disease• family history of elevated lipoprotein (a)• existing heart or vascular disease, especially with normal or only mildly elevated lipids.• recurrent cardiovascular disease despite statin treatment• familial hypercholesterolaemia, especially low HDL-C• Patients with a moderate or high risk of cardiovascular disease (2010 European Atherosclerosis Society Consensus Panel)
Lp(a) Cut points1. Desirable: < 14 mg/dL (< 35 nmol/l)2. Borderline risk: 14 - 30 mg/dL (35 - 75 nmol/l)3. High risk: 31 - 50 mg/dL (75 - 125 nmol/l)4. Very high risk: > 50 mg/dL (> 125 nmol/l)5. If the level is elevated, treatment should be initiated with a goal of bringing the level below 50 mg/dL6. most studies and meta-analyses show an increase in CVD risk starting at Lp(a) >25 mg/dl
CONCLUSIONS :1. Non HDL-C a practical and realistic target of therapy beyond LDL-C2. No need for apo-B measurement in ROUTINE practice3. Continue using intensive statin therapy4. No sound evidence yet of additional non statin therapy5. Measure Lp(a) in special situations6. Await specifically targeted Rx for Lp(a)