- Email: [email protected]
Inclusion of Lipoprotein Subfractions Among Efficacy Parameters
Inclusion of Lipoprotein Subfractions Among Efficacy Parameters H. Robert Superko, here is now abundant evidence that triglyceriderich lipoproteins are major contributors to atheroT sclerosis and that lowering the concentration of these particles is a significant clinical endpoint in that it is associated with arteriographic benefit.1,2 Most Phase III and IV investigations of lipoprotein-active drugs have focused on low-density lipoprotein (LDL) cholesterol. The LDL cholesterol value obtained by indirect b quantification and used as an endpoint partly includes the cholesterol in intermediate-density lipoprotein (IDL). This is particularly important to appreciate since, according to Framingham data, 80% of individuals who develop coronary artery disease have the same total plasma cholesterol as individuals who do not.3 Thus, investigations of LDL cholesterol focus on only a fraction of those dyslipidemic individuals destined to develop coronary artery disease. In the Stanford Coronary Risk Intervention Project (SCRIP), patients with coronary artery disease were recruited with no restrictions as to plasma cholesterol value and thus represent a more typical coronary artery disease population. At entry, 22% had LDL cholesterol ,130 mg/dL (3.4 mmol/L), and 46% had LDL cholesterol ,160 mg/dL (4.1 mmol/L), but 59% were classified as LDL subclass pattern B. This reflects the predominance of abnormalities of lipoprotein subclass and of triglyceride-rich lipoproteins in the coronary artery disease population that is not reflected by measures of total or LDL cholesterol.4 The presence of small, dense LDL (pattern B) is a significant predictor of coronary artery disease risk that is independent of total, LDL, and high-density lipoprotein (HDL) cholesterol, as well as triglycerides; it is present in 50% of male coronary artery disease patients.2,13 Plasma lipoprotein responses to diet and to several drugs have been shown to be significantly different in patient populations defined on the basis of the relative abundance or lack of triglyceride-rich lipoproteins. Specifically, persons with the LDL pattern B trait (excess IDL and LDL [Svedberg flotation constant, Sf 0 –7]) have been shown to have a significantly greater LDL cholesterol and apolipoprotein (apo) B response to a low-fat diet and better reduction in small LDL in response to niacin and resin than LDL pattern A subjects.5–7 In response to gemfibrozil treatment LDL cholesterol remains unchanged, but there is a significant reduction in small LDL (Sf 0 –7), balanced by a significant increase in large LDL (Sf 7–12) From the Cholesterol, Genetics, and Heart Disease Institute, Lawrence Berkeley National Laboratory, University of California, and Berkeley Heart Lab, San Mateo, California, USA. Address for reprints: Carlos A. Dujovne, MD, Kansas Foundation for Clinical Pharmacology, 10550 Quivira Road, Suite 240, Overland Park, Kansas 66215,USA.
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©1998 by Excerpta Medica, Inc. All rights reserved.
MD
in pattern B but not pattern A subjects.8 This wide variability in response to treatment remains undetected by a routine “lipid panel” (total cholesterol, LDL cholesterol, HDL cholesterol, triglyceride), and it is clinically important.
CLINICAL RELEVANCE The need to document the effects of treatment on measures of triglyceride-rich lipoproteins is clinically relevant for 3 reasons: (1) the powerful association of the small-LDL trait and triglyceride-rich lipoproteins with the coronary artery disease risk; (2) the different effects of treatment in patient populations with an abundance of these particles; and (3) the association of reduction in these particles with arteriographic improvement. Triglyceride-rich lipoproteins and small LDL have been associated with coronary artery disease risk for .40 years, with supportive data dating back to the pioneering work of John Goffman and Frank Lindgren.9 More recently, the Boston Area Heart Health Projects showed that LDL pattern B was associated with a 3-fold higher coronary artery disease risk.10 Analysis of the Physician’s Health Survey blood samples confirmed a 3-fold higher coronary artery disease risk with LDL pattern B that was independent of total and HDL cholesterol and apo B, but not of nonfasting triglycerides.11 The Stanford Five City Project recently presented data indicating that LDL size is the strongest physiologic risk factor in conditional logistic regression analysis and is independent of HDL cholesterol, non-HDL cholesterol, and nonfasting triglycerides but not of the ratio total cholesterol/HDL cholesterol.12 The Quebec cardiovascular study reported that LDL particle size is an independent predictor of cardiovascular events that is independent of total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides, total cholesterol/HDL cholesterol, apo B, and body mass index.13 Thus, the small dense LDL pattern, and by association, triglyceride-rich lipoprotein particles, are predictors of coronary artery disease independent of routine laboratory measurements currently required in US Food and Drug Administration (FDA) investigations. An abundance of IDL is associated with the LDL pattern B trait. Direct measurement of IDL would be of benefit in drug evaluation since it has shown14 –16 a stronger association than LDL cholesterol with atherosclerosis risk, clinical events, and arteriographically measured disease progression. The potential to err through ignoring plasma triglyceride-rich lipoproteins is illustrated by the Helsinki investigation. The initial overall analysis revealed a 34% reduction in events, but in a second 0002-9149/98/$19.00 PII S0002-9149(98)00263-X
analysis17 of a subset of patients with moderately elevated triglycerides and a poor total cholesterol/ HDL cholesterol ratio, this figure became 75%. This subgroup comprised 10% of the total study population. A later study showed that gemfibrozil decreased small LDL and IDL significantly more in LDL pattern B subjects than in pattern A subjects.8 The combination of gemfibrozil and nicotinic acid results in changes in small LDL and IDL that are not reflected by a change in LDL cholesterol.18 Arteriographic investigations have contributed significantly to our understanding of the role of triglyceride-rich lipoproteins in atherosclerosis progression. In coronary artery disease subjects who had not been selected to have elevated LDL cholesterol and who were not treated with a lipid-lowering agent, IDL was a significant predictor of coronary artery disease progression and clinical events, whereas LDL cholesterol was not.14 In the late 1980s, a report from the Lawrence Berkeley National Laboratory15 indicated that IDL and small LDL (Sf 0 –7) were significantly lower in subjects whose arteriographic images were stable than those showing arteriographic progression.15 The Monitored Atherosclerosis Regression Study (MARS) reported in 1995 that carotid atherosclerosis progression, as assessed by intimal–media thickness, is not associated with LDL cholesterol but significantly associated with IDL.16 The MARS investigation had already shown19 that although lovastatin decreased LDL cholesterol, triglyceride-rich lipoproteins were the best predictor of progression; thus, LDL cholesterol reduction alone is not sufficient to halt progression in many patients.19 The St. Thomas’s Atherosclerosis Regression Study (STARS)20 found reduction of small, dense LDL to be the best predictor of atherosclerosis regression. Similarly, in the Stanford Coronary Risk Intervention Project (SCRIP),4 drug treatment decreased LDL cholesterol to exactly the same extent in subjects with a high proportion of small, dense LDL as in those with an abundance of large, buoyant LDL, but the former group had a significantly lower rate of arteriographic progression than the latter, whereas the Familial Atherosclerosis Treatment Study (FATS)21 found that change in LDL density during treatment was a better predictor of arteriographic outcome than change in LDL cholesterol. All these investigations indicate that without measurement of LDL-subclass distribution and/or triglyceride-rich lipoproteins, the better-than-average benefit in “good responders,” and surprisingly little benefit in “poor responders,” despite adequate changes in currently used plasma lipid endpoints, will not be understood. In my opinion, this type of analysis error hinders the development of therapies that could benefit easily definable patient subgroups, which may comprise up to 50% of the study population. The currently used measurement of a limited range of plasma lipids results in the clinical impression that “one drug fits all” and ignores the important issue of patient heterogeneity.
RECOMMENDED MODIFICATIONS
General: A family history on blood lipids, coronary artery disease, cardiovascular disease, and diabetes mellitus should be obtained and a family pedigree constructed, because of the high prevalence of inherited traits linked to atherosclerosis. This would help to identify groups of patients in whom specific medications may be more or less effective. For patients with moderate hypertriglyceridemia, a very low fat, high carbohydrate diet should not be recommended, because of the potential confounding effect of carbohydrate-induced hypertriglyceridemia. In studies of hypertriglyceridemic subjects, the diet should be standardized with regard to fat content, simple carbohydrates, and alcohol. Subjects should be standardized for alcohol consumption, exercise, and body mass index. Changes in these variables must be recorded and entered into the statistical analysis. There should be 3 triglyceride measurements obtained after fasting (24 hours without alcohol, 16 hours without food), and 3 at the end of the study, because of triglyceride variability. There should be no excessive physical activity in the 24 hours before the measurement, and the subject should not be engaged in an active weight-loss regime. The effect of new agents on amounts of triglyceride-rich lipoproteins must be assessed, either by measurement of LDL and HDL subclass distribution by means of gradient gel electrophoresis, very low-density lipoprotein (VLDL)/IDL/LDL/HDL mass distribution in Svedberg flotation intervals, density gradient ultracentrifugation, or separation of lipoprotein subclasses according to apoprotein content. Methods for gradient gel electrophoresis currently being finalized in this laboratory will allow LDL subclasses to be cost-effectively quantified. The technique can determine peak particle diameter and percent distribution within 7 LDL and 5 HDL subclasses.22 The Fredrickson, Levy, Lees classification should be replaced by one that describes lipoprotein disorders by the metabolic defect or lipoprotein characteristics. This would allow development and testing of medications targeted to specific lipoprotein disorders. Triglyceridemia should be redefined to include normal (triglycerides ,140 mg/dL, ,1.6 mmol/L), moderate hypertriglyceridemia (,400 mg/dL, ,4.5 mmol/L), and severe hypertriglyceridemia (.400 mg/ dL, .4.5 mmol/L). The definition of “normal” triglyceride values should be discussed and consideration given to determining normal values on a physiologic basis and not by population norms, since the presence of a bimodal triglyceride distribution curve results in an overall population mean that is higher than the mean in the lower curve. Use of the phrase “mild-to-moderate hyperlipidemia” should be defined more specifically. Disorders of lipoprotein metabolism should be characterized by describing the disorder, for example, hyperapobetalipoproteinemia, atherogenic lipoprotein profile (small LDL trait), hypoalphalipoproteinemia, etc. Use of data from open extensions of multicenter trials is encouraged, but not the use of a bile-acid– binding resin to A SYMPOSIUM: CLINICAL TRIAL GUIDELINES
53F
maintain the active control group instead of switching to the test drug. Use of a resin may confound the results because of a significantly different response of LDL subclass pattern A from pattern B subjects.7 Subject selection and laboratory endpoints: Subjects should be selected on the basis of LDL subclass pattern or the relative abundance or absence of triglyceride-rich lipoproteins, since patients with identical total cholesterol and LDL cholesterol yet different LDL subclass distribution respond differently to lipidlowering medications. A classification based on lipoprotein subclass distribution or apoprotein content is needed. As a significant variation in response to diet has been linked to differences in LDL subclass and apo E isoforms, these should be measured in all clinical trials. I also suggest (1) Apo C-III: heparin-precipitated and heparin supernate ratio (C-III ratio), which has been used in a few clinical trials and is relatively inexpensive, and (2) A-I– containing lipoprotein particles: A-I only, versus A-I/A-II. This has been used in cross-sectional investigations but to my knowledge has not been used in large intervention trials. The methodology is not readily available. Efficacy: Future investigations could benefit from standardized measures of lipoprotein subclass distribution and triglyceride-rich lipoprotein particles. A new definition of efficacy needs to include these parameters, with subjects identified as LDL subclass pattern A or B. Clinical endpoints should be expanded to include noninvasive measures of atherosclerosis, for example quantitative B-mode ultrasound of the carotid artery, and invasive methods including quantitative intravascular ultrasound. Interaction of the drug under investigation with commonly used cardiovascular medications should be encouraged. A recent trial23 showed a beneficial interaction of a 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitor with calcium antagonists. Future trials may benefit from the addition of calcium antagonists, angiotensin-converting enzyme inhibitors, or a blockers to the trial design.24
Use of a placebo group in primary prevention trials of LDL cholesterol reduction in patient populations with LDL cholesterol ,160 mg/dL (,4.1 mmol/L) remains a viable option. Patient populations with LDL cholesterol higher than this require a treated placebo group. Adoption of a standard statin control would benefit researchers; lovastatin is a good candidate because of its safety record in long-term use as well as availability. Resins as placebo bring problems of compliance and potential gastrointestinal effects. It is particularly important to determine LDL subclass pattern for triglyceride-lowering compounds: niacin and gemfibrozil are known to have a significantly greater effect on lipids and LDL subclass distribution in pattern B subjects than in those with pattern A. Thus, a niacinlike compound may be better than standard statin compounds for some patients, and the agent used to treat the control group should be matched for LDL subclass activity to the agent being tested. Fasting triglyceride measurement cannot accurately distinguish LDL subclass pattern A from pattern B in the triglyceride range 70 –250 mg/dL. Drug interactions: Phase III and IV investigations should include tests of interaction with commonly used lipid-lowering drugs for altered efficacy, side effects, or toxicity. Specifically, agents intended to lower LDL cholesterol should be tested in combination with resins and statins. Agents intended to lower triglycerides and LDL cholesterol should be tested in combination with niacin, fibrates, and statins. Longer-term continuation studies: Phase IV studies provide valuable information on long-term efficacy and side effects, as well as potential problems of interaction with other therapeutic agents. These studies should be encouraged but not required for FDA approval. Concomitant use of other drugs during trial: Because of the effects of some drugs on IDL, LDL subclass, and HDL subclass distribution and other lipoprotein characteristics, efforts should be made to identify subjects taking those drugs and exclude them, at least from the early trials.
PHASE III AND IV STUDIES
I believe that investigations of drug efficacy and side effects would greatly benefit from standardized measurements of lipoprotein subclass distribution and/or triglyceride-rich lipoproteins. Current FDAapproved drugs have significantly different effects in subjects classified as LDL pattern A or B, and gaining knowledge of these patterns in future Phase III and IV investigations is essential if we are to determine in which patient subgroups the new agent will be most effective. The information will also help guide drug development to benefit patients with specific lipid disorders predisposing them to atherosclerosis and coronary artery disease.
Primary or secondary prevention: Both primary and secondary prevention trials are currently recommended for Phase IV investigations but not Phase II or III investigations. Populations at risk should be expanded to include diabetics, women (pre- and postmenopausal), the elderly, the obese, those with unstable angina, peripheral vascular disease, hypoalphalipoproteinemia, and LDL subclass patterns A and B. Both primary and secondary trials should include prospective cost-effectiveness analysis as part of the protocol. Standardized methods of data collection and analysis should be developed to accurately compare results. Justification for placebo controls: Placebo controls should be required on short-term clinical trials of drug efficacy. 54F THE AMERICAN JOURNAL OF CARDIOLOGYT
CONCLUSIONS
1. Superko HR. What can we learn about dense LDL and lipoprotein particles
from clinical trials? Current Opinion Lipidol 1996;7:363–368.
VOL. 81 (8A)
APRIL 23, 1998
2. Krauss RM. Heterogeneity of plasma low-density lipoproteins and atheroscle-
rosis risk. Curr Opin Lipidol 1994;5:339 –349. 3. Kannel WB, Castelli WP, Gordon T. Cholesterol in the prediction of atherosclerotic disease. New perspectives based on the Framingham study. Ann Intern Med 1979;90:85–91. 4. Miller BD, Alderman EL, Haskell WL, Fair JM, Krauss RM. Predominance of dense low-density lipoprotein particles predicts angiographic benefit or therapy in the Stanford Coronary Risk Intervention project. Circulation 1996;94:2146 – 2153. 5. Dreon DM, Fernstrom H, Miller B, Krauss RM. Low density lipoprotein subclass patterns and lipoprotein response to a reduced-fat diet in men. FASEB J 1994;8:121–126. 6. Superko HR and KOS investigators. Effect of nicotinic acid on LDL subclass patterns. (Abstr.) Circulation 1994;90:I-504. 7. Superko HR, Williams PT, Alderman EL, and Stanford Coronary Risk Intervention Project Investigators. Differential lipoprotein effects of bile acid binding resin in LDL subclass pattern A versus B. (Abstr.) Circulation 1992;86:I-144. 8. Superko HR, Krauss RM. Reduction of small, dense LDL by gemfibrozil in LDL subclass pattern B. (Abstr.) Circulation 1995;92:I-250. 9. Gofman JW, Young W, Tandy R. Ischemic heart disease, atherosclerosis and longevity. (Abstr.) Circulation 1996;34:679. 10. Austin MA, Hennekens CH, Breslow HL, Buring JE, Willett WC, Krauss RM. Low density lipoprotein subclass patterns and risk of myocardial infarction: the Boston Area Health Study. Am J Epidemiol 1987;126:739 –740. 11. Stampfer MJ, Krauss RM, Blanche PJ, Holl LG, Sacks FM, Hennekens CH. A prospective study of triglyceride level, low density lipoprotein particle diameter, and risk of myocardial infarction. JAMA 1996;276:882– 888. 12. Gardner CD, Fortmann SP, Krauss RM. Small low density lipoprotein particles are associated with the incidence of coronary artery disease in men and women. JAMA 1996;276:875– 881. 13. Lamarche B, Tchernof A, Moorjani S, Cantin B, Dagenais GR, Lupien PJ, Despres JP. Small, dense low-density lipoprotein particles as a predictor of the risk of ischemic heart disease in men. Prospective results from the Quebec cardiovascular study. Circulation 1997;95:69 –75. 14. Phillips NR, Waters D, Havel RJ. Plasma lipoproteins and progression of coronary artery disease evaluated by angiography and clinical events. Circulation 1993;88:2762–2770. 15. Krauss RM, Lindgren FT, Williams PT, Kelsey SF, Brensike J, Vranizan K, Detre KM, Levy RI. Intermediate-density lipoproteins and progression of coronary artery disease in hypercholesterolaemic men. Lancet 1987;2:62– 65. 16. Hodis HN, Mack WJ, Dunn M, Liu C, Selzer RH, Krauss RM. Intermediatedensity lipoproteins and progression of carotid arterial wall intima-media thickness. Circulation 1997;95:2022–2026.
17. Manninen V, Tenkanen L, Koskinen P, Huttunen JK, Manttari M, Heinonen OP, Frick MH. Joint effects of serum triglyceride and LDL cholesterol and HDL cholesterol concentrations on coronary heart disease risk in the Helsinki Heart Study. Circulation 1992;85:37– 45. 18. Superko HR, Krauss RM. LDL subclass distribution change in familial combined hyperlipidemia patients following gemfibrozil and niacin treatment. (Abstr.) J Am Coll Cardiol 1997;29:46A. 19. Hodis HN, Mack WJ. Triglyceride-rich lipoproteins and the progression of coronary artery disease. Curr Opin Lipidol 1995;6:209 –214. 20. Watts GF, Mandalia S, Brunt JN, Slavin BM, Coltart DJ, Lewis B. Independent associations between plasma lipoprotein subfraction levels and the course of coronary artery disease in the St. Thomas’ Atherosclerosis Regression Study (STARS). Metabolism 1993;42:1461–1467. 21. Zambon A, Brown BG, Hokansen JE, Brunzell JD. Hepatic lipase change predicts coronary artery disease regression/progression in the Familial Atherosclerosis Treatment Study. (Abstr.) Circulation 1996;94;I-539. 22. Krauss RM, Blanche PJ. Detection and quantitation of LDL subfractions. Curr Opin Lipidol 1992:3:377–383. 23. Jukema JW, Zwinderman AH, van Boven AJ, Reiber JH, van der Laarse A, Lie KI, Bruschke AV. Evidence for a synergistic effect of calcium channel blockers with lipid-lowering therapy in retarding progression of coronary atherosclerosis in symptomatic patients with normal to moderately raised cholesterol levels. The REGRESS Study Group. Arterioscler Thromb Vasc Biol 1996;16: 425– 430. 24. Superko HR, Krauss RM, Haskell WL, and Stanford Coronary Risk Intervention Project Investigators. Association of lipoprotein subclass distribution with use of selective and non-selective b-blocker medications in patients with coronary heart disease. Atherosclerosis 1993;101:1– 8.
DISCUSSION
David G. Orloff, MD: This article again points out the critical issue of surrogate versus ultimate clinical endpoints. The use of lipoprotein subclass distribution patterns and levels of triglyceride-rich lipoproteins to direct choice of therapy as well as to measure effects of specific interventions must be complemented by the generation of clinical endpoint data to validate the utility of these surrogates in drug development and regulation.
A SYMPOSIUM: CLINICAL TRIAL GUIDELINES
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©1998 by Excerpta Medica, Inc. All rights reserved.
MD
in pattern B but not pattern A subjects.8 This wide variability in response to treatment remains undetected by a routine “lipid panel” (total cholesterol, LDL cholesterol, HDL cholesterol, triglyceride), and it is clinically important.
CLINICAL RELEVANCE The need to document the effects of treatment on measures of triglyceride-rich lipoproteins is clinically relevant for 3 reasons: (1) the powerful association of the small-LDL trait and triglyceride-rich lipoproteins with the coronary artery disease risk; (2) the different effects of treatment in patient populations with an abundance of these particles; and (3) the association of reduction in these particles with arteriographic improvement. Triglyceride-rich lipoproteins and small LDL have been associated with coronary artery disease risk for .40 years, with supportive data dating back to the pioneering work of John Goffman and Frank Lindgren.9 More recently, the Boston Area Heart Health Projects showed that LDL pattern B was associated with a 3-fold higher coronary artery disease risk.10 Analysis of the Physician’s Health Survey blood samples confirmed a 3-fold higher coronary artery disease risk with LDL pattern B that was independent of total and HDL cholesterol and apo B, but not of nonfasting triglycerides.11 The Stanford Five City Project recently presented data indicating that LDL size is the strongest physiologic risk factor in conditional logistic regression analysis and is independent of HDL cholesterol, non-HDL cholesterol, and nonfasting triglycerides but not of the ratio total cholesterol/HDL cholesterol.12 The Quebec cardiovascular study reported that LDL particle size is an independent predictor of cardiovascular events that is independent of total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides, total cholesterol/HDL cholesterol, apo B, and body mass index.13 Thus, the small dense LDL pattern, and by association, triglyceride-rich lipoprotein particles, are predictors of coronary artery disease independent of routine laboratory measurements currently required in US Food and Drug Administration (FDA) investigations. An abundance of IDL is associated with the LDL pattern B trait. Direct measurement of IDL would be of benefit in drug evaluation since it has shown14 –16 a stronger association than LDL cholesterol with atherosclerosis risk, clinical events, and arteriographically measured disease progression. The potential to err through ignoring plasma triglyceride-rich lipoproteins is illustrated by the Helsinki investigation. The initial overall analysis revealed a 34% reduction in events, but in a second 0002-9149/98/$19.00 PII S0002-9149(98)00263-X
analysis17 of a subset of patients with moderately elevated triglycerides and a poor total cholesterol/ HDL cholesterol ratio, this figure became 75%. This subgroup comprised 10% of the total study population. A later study showed that gemfibrozil decreased small LDL and IDL significantly more in LDL pattern B subjects than in pattern A subjects.8 The combination of gemfibrozil and nicotinic acid results in changes in small LDL and IDL that are not reflected by a change in LDL cholesterol.18 Arteriographic investigations have contributed significantly to our understanding of the role of triglyceride-rich lipoproteins in atherosclerosis progression. In coronary artery disease subjects who had not been selected to have elevated LDL cholesterol and who were not treated with a lipid-lowering agent, IDL was a significant predictor of coronary artery disease progression and clinical events, whereas LDL cholesterol was not.14 In the late 1980s, a report from the Lawrence Berkeley National Laboratory15 indicated that IDL and small LDL (Sf 0 –7) were significantly lower in subjects whose arteriographic images were stable than those showing arteriographic progression.15 The Monitored Atherosclerosis Regression Study (MARS) reported in 1995 that carotid atherosclerosis progression, as assessed by intimal–media thickness, is not associated with LDL cholesterol but significantly associated with IDL.16 The MARS investigation had already shown19 that although lovastatin decreased LDL cholesterol, triglyceride-rich lipoproteins were the best predictor of progression; thus, LDL cholesterol reduction alone is not sufficient to halt progression in many patients.19 The St. Thomas’s Atherosclerosis Regression Study (STARS)20 found reduction of small, dense LDL to be the best predictor of atherosclerosis regression. Similarly, in the Stanford Coronary Risk Intervention Project (SCRIP),4 drug treatment decreased LDL cholesterol to exactly the same extent in subjects with a high proportion of small, dense LDL as in those with an abundance of large, buoyant LDL, but the former group had a significantly lower rate of arteriographic progression than the latter, whereas the Familial Atherosclerosis Treatment Study (FATS)21 found that change in LDL density during treatment was a better predictor of arteriographic outcome than change in LDL cholesterol. All these investigations indicate that without measurement of LDL-subclass distribution and/or triglyceride-rich lipoproteins, the better-than-average benefit in “good responders,” and surprisingly little benefit in “poor responders,” despite adequate changes in currently used plasma lipid endpoints, will not be understood. In my opinion, this type of analysis error hinders the development of therapies that could benefit easily definable patient subgroups, which may comprise up to 50% of the study population. The currently used measurement of a limited range of plasma lipids results in the clinical impression that “one drug fits all” and ignores the important issue of patient heterogeneity.
RECOMMENDED MODIFICATIONS
General: A family history on blood lipids, coronary artery disease, cardiovascular disease, and diabetes mellitus should be obtained and a family pedigree constructed, because of the high prevalence of inherited traits linked to atherosclerosis. This would help to identify groups of patients in whom specific medications may be more or less effective. For patients with moderate hypertriglyceridemia, a very low fat, high carbohydrate diet should not be recommended, because of the potential confounding effect of carbohydrate-induced hypertriglyceridemia. In studies of hypertriglyceridemic subjects, the diet should be standardized with regard to fat content, simple carbohydrates, and alcohol. Subjects should be standardized for alcohol consumption, exercise, and body mass index. Changes in these variables must be recorded and entered into the statistical analysis. There should be 3 triglyceride measurements obtained after fasting (24 hours without alcohol, 16 hours without food), and 3 at the end of the study, because of triglyceride variability. There should be no excessive physical activity in the 24 hours before the measurement, and the subject should not be engaged in an active weight-loss regime. The effect of new agents on amounts of triglyceride-rich lipoproteins must be assessed, either by measurement of LDL and HDL subclass distribution by means of gradient gel electrophoresis, very low-density lipoprotein (VLDL)/IDL/LDL/HDL mass distribution in Svedberg flotation intervals, density gradient ultracentrifugation, or separation of lipoprotein subclasses according to apoprotein content. Methods for gradient gel electrophoresis currently being finalized in this laboratory will allow LDL subclasses to be cost-effectively quantified. The technique can determine peak particle diameter and percent distribution within 7 LDL and 5 HDL subclasses.22 The Fredrickson, Levy, Lees classification should be replaced by one that describes lipoprotein disorders by the metabolic defect or lipoprotein characteristics. This would allow development and testing of medications targeted to specific lipoprotein disorders. Triglyceridemia should be redefined to include normal (triglycerides ,140 mg/dL, ,1.6 mmol/L), moderate hypertriglyceridemia (,400 mg/dL, ,4.5 mmol/L), and severe hypertriglyceridemia (.400 mg/ dL, .4.5 mmol/L). The definition of “normal” triglyceride values should be discussed and consideration given to determining normal values on a physiologic basis and not by population norms, since the presence of a bimodal triglyceride distribution curve results in an overall population mean that is higher than the mean in the lower curve. Use of the phrase “mild-to-moderate hyperlipidemia” should be defined more specifically. Disorders of lipoprotein metabolism should be characterized by describing the disorder, for example, hyperapobetalipoproteinemia, atherogenic lipoprotein profile (small LDL trait), hypoalphalipoproteinemia, etc. Use of data from open extensions of multicenter trials is encouraged, but not the use of a bile-acid– binding resin to A SYMPOSIUM: CLINICAL TRIAL GUIDELINES
53F
maintain the active control group instead of switching to the test drug. Use of a resin may confound the results because of a significantly different response of LDL subclass pattern A from pattern B subjects.7 Subject selection and laboratory endpoints: Subjects should be selected on the basis of LDL subclass pattern or the relative abundance or absence of triglyceride-rich lipoproteins, since patients with identical total cholesterol and LDL cholesterol yet different LDL subclass distribution respond differently to lipidlowering medications. A classification based on lipoprotein subclass distribution or apoprotein content is needed. As a significant variation in response to diet has been linked to differences in LDL subclass and apo E isoforms, these should be measured in all clinical trials. I also suggest (1) Apo C-III: heparin-precipitated and heparin supernate ratio (C-III ratio), which has been used in a few clinical trials and is relatively inexpensive, and (2) A-I– containing lipoprotein particles: A-I only, versus A-I/A-II. This has been used in cross-sectional investigations but to my knowledge has not been used in large intervention trials. The methodology is not readily available. Efficacy: Future investigations could benefit from standardized measures of lipoprotein subclass distribution and triglyceride-rich lipoprotein particles. A new definition of efficacy needs to include these parameters, with subjects identified as LDL subclass pattern A or B. Clinical endpoints should be expanded to include noninvasive measures of atherosclerosis, for example quantitative B-mode ultrasound of the carotid artery, and invasive methods including quantitative intravascular ultrasound. Interaction of the drug under investigation with commonly used cardiovascular medications should be encouraged. A recent trial23 showed a beneficial interaction of a 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitor with calcium antagonists. Future trials may benefit from the addition of calcium antagonists, angiotensin-converting enzyme inhibitors, or a blockers to the trial design.24
Use of a placebo group in primary prevention trials of LDL cholesterol reduction in patient populations with LDL cholesterol ,160 mg/dL (,4.1 mmol/L) remains a viable option. Patient populations with LDL cholesterol higher than this require a treated placebo group. Adoption of a standard statin control would benefit researchers; lovastatin is a good candidate because of its safety record in long-term use as well as availability. Resins as placebo bring problems of compliance and potential gastrointestinal effects. It is particularly important to determine LDL subclass pattern for triglyceride-lowering compounds: niacin and gemfibrozil are known to have a significantly greater effect on lipids and LDL subclass distribution in pattern B subjects than in those with pattern A. Thus, a niacinlike compound may be better than standard statin compounds for some patients, and the agent used to treat the control group should be matched for LDL subclass activity to the agent being tested. Fasting triglyceride measurement cannot accurately distinguish LDL subclass pattern A from pattern B in the triglyceride range 70 –250 mg/dL. Drug interactions: Phase III and IV investigations should include tests of interaction with commonly used lipid-lowering drugs for altered efficacy, side effects, or toxicity. Specifically, agents intended to lower LDL cholesterol should be tested in combination with resins and statins. Agents intended to lower triglycerides and LDL cholesterol should be tested in combination with niacin, fibrates, and statins. Longer-term continuation studies: Phase IV studies provide valuable information on long-term efficacy and side effects, as well as potential problems of interaction with other therapeutic agents. These studies should be encouraged but not required for FDA approval. Concomitant use of other drugs during trial: Because of the effects of some drugs on IDL, LDL subclass, and HDL subclass distribution and other lipoprotein characteristics, efforts should be made to identify subjects taking those drugs and exclude them, at least from the early trials.
PHASE III AND IV STUDIES
I believe that investigations of drug efficacy and side effects would greatly benefit from standardized measurements of lipoprotein subclass distribution and/or triglyceride-rich lipoproteins. Current FDAapproved drugs have significantly different effects in subjects classified as LDL pattern A or B, and gaining knowledge of these patterns in future Phase III and IV investigations is essential if we are to determine in which patient subgroups the new agent will be most effective. The information will also help guide drug development to benefit patients with specific lipid disorders predisposing them to atherosclerosis and coronary artery disease.
Primary or secondary prevention: Both primary and secondary prevention trials are currently recommended for Phase IV investigations but not Phase II or III investigations. Populations at risk should be expanded to include diabetics, women (pre- and postmenopausal), the elderly, the obese, those with unstable angina, peripheral vascular disease, hypoalphalipoproteinemia, and LDL subclass patterns A and B. Both primary and secondary trials should include prospective cost-effectiveness analysis as part of the protocol. Standardized methods of data collection and analysis should be developed to accurately compare results. Justification for placebo controls: Placebo controls should be required on short-term clinical trials of drug efficacy. 54F THE AMERICAN JOURNAL OF CARDIOLOGYT
CONCLUSIONS
1. Superko HR. What can we learn about dense LDL and lipoprotein particles
from clinical trials? Current Opinion Lipidol 1996;7:363–368.
VOL. 81 (8A)
APRIL 23, 1998
2. Krauss RM. Heterogeneity of plasma low-density lipoproteins and atheroscle-
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DISCUSSION
David G. Orloff, MD: This article again points out the critical issue of surrogate versus ultimate clinical endpoints. The use of lipoprotein subclass distribution patterns and levels of triglyceride-rich lipoproteins to direct choice of therapy as well as to measure effects of specific interventions must be complemented by the generation of clinical endpoint data to validate the utility of these surrogates in drug development and regulation.
A SYMPOSIUM: CLINICAL TRIAL GUIDELINES
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