- Email: [email protected]
Emerging high-density lipoprotein infusion therapies: Fulfilling the promise of epidemiology?
Journal of Clinical Lipidology (2010) 4, 399–404
NLA Symposium on High Density Lipoproteins
Emerging high-density lipoprotein infusion therapies: Fulfilling the promise of epidemiology? Jean-Claude Tardif, MD* Department of Medicine, Research Centre, Montreal Heart Institute, 5000 Belanger Street, Montreal, Quebec H1T 1C8, Canada, and Universite´ de Montre´al, Montreal, Canada KEYWORDS: ApoA-1 Milano; Atherosclerosis; HDL-cholesterol; Intravascular ultrasound
Abstract: High-density lipoprotein (HDL) plays a key role in reverse cholesterol transport but also activates nitric oxide synthase and stimulates prostacyclin release, enhances endothelial repair, inhibits cell adhesion molecule expression on vascular endothelium and monocyte recruitment into the arterial wall, and exerts antithrombotic effects. In experimental animals, infusions of HDL or apolipoprotein A-1 (apoA-1) halt the progression or induce regression of atherosclerosis, with favorable effects on plaque composition. Remarkably, a benefit is observed after a single infusion. In a pilot study, weekly infusions of ETC-216, a formulation of recombinant apoA-1 Milano, were administered at two doses for 5 weeks to patients beginning within 2 weeks of an acute coronary syndrome (ACS). Among the 47 patients completing the study, percent atheroma volume by intracoronary ultrasound was reduced in the combined active treatment groups but not in the placebo group. In a larger trial, the Effect of rHDL on Atherosclerosis–Safety and efficacy (ERASE), 183 post-ACS patients were randomized to 4 weekly infusions of placebo or one of two doses of CSL-111, which consists of apoA-1 derived from human plasma and combined with soybean phosphatidylcholine. The greater dose was discontinued because of a high incidence of hepatic enzyme elevation. Among the 136 patients with evaluable end point data, percent change in atheroma volume, the primary endpoint, improved significantly in the CSL-111 group but not in the placebo group. The secondary end points of plaque characterization indices and quantitative coronary angiographic changes both improved significantly in the CSL-111 group compared with the group receiving placebo. Taken together, this evidence suggests that infusions of HDL or apoA-1 may reduce events, particularly among patients with ACS. Ó 2010 National Lipid Association. All rights reserved.
Epidemiologic data suggests that a 1-mg/dL increment in high-density lipoprotein (HDL) will be associated with a 2% decrement in coronary heart disease risk in men and a 3% decrement in women.1 Because the epidemiologic relationship between low-density lipoprotein (LDL) and cardiovascular events turned out to be quite predictive of the benefit associated with statin-induced LDL reduction, the
* Corresponding author. E-mail address: [email protected] Submitted June 17, 2010. Accepted for publication August 18, 2010.
assumption was widespread that drugs that increased HDL would invariably be associated with significant clinical benefit. The failure of torcetrapib, a potent cholesterol ester transfer protein inhibitor that increased HDL by 72% in the Study Examining Torcetrapib/Atorvastatin and Atorvastatin Effects on Clinical CV Events in Patients With Heart Disease (ILLUMINATE) trial but also increased mortality and morbidity,2 has led to the realization that the epidemiologic promise of HDL could be illusory. Nevertheless, a large coherent body of experimental evidence supports the hypothesis that increasing HDL will reduce cardiovascular events.
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Biologic plausibility for increasing HDL The benefits of HDL most often are related to reverse cholesterol transport, the process whereby excess cholesterol is carried from peripheral cells to the liver to be eliminated via biliary excretion or to be recycled in the entero-hepatic circulation. The ATP-binding cassette transporter protein ABCA 1 plays an important role in this process by facilitating cellular cholesterol and phospholipid release to apolipoprotein A-1 (apoA)-12containing HDL precursors.3 The maintenance of cholesterol homeostasis within cells and the details of cholesterol transport are complex because many systems interact with HDL.3 In addition to reverse cholesterol transport, HDL exhibits several other mechanisms that protect against vascular disease. HDL has been shown in several studies to activate endothelial nitric oxide (NO) synthase, which would ameliorate endothelial function.4 Patients with early atherosclerosis have improved coronary artery endothelial function with greater HDL levels,5 and intravenous infusion of HDL in hypercholesterolemic subjects rapidly increases NO bioavailability and restores impaired endothelialdependent vasodilation.6 HDL also stimulates prostacyclin release and may inhibit the vasoconstrictor effects of endothelin.4 HDL stimulates endothelial cell migration and thus endothelial repair.4,7 HDL protects endothelial cells from apoptosis in a dose-dependent fashion at physiologic HDL concentrations.8 Injured endothelium expresses cell adhesion molecules that attract monocytes that adhere to the endothelium and migrate into the subendothelial space. HDL inhibits cell adhesion molecule expression in umbilical vein endothelial cells.4,9 In apoE-deficient mice, increasing HDL concentrations by overexpression of apoA-1 inhibits cell adhesion molecule expression on vascular endothelium and monocyte recruitment into the arterial wall.10 These findings appear to pertain to humans, where low HDL levels are associated with greater levels of circulating soluble cellular adhesion molecules.11 HDL exerts important antithrombotic effects through several mechanisms. As noted previously, HDL favors NO and prostacyclin release; both inhibit platelet aggregation. Von Willebrand factor levels vary inversely with HDL levels, suggesting that HDL may inhibit production of this protein that stimulates platelet adhesion and aggregation.12 High HDL levels in humans are associated with reduced ex vivo platelet thrombus deposition.13 HDL also favorably affects the balance between the activities of tissue factor and tissue factor pathway inhibitor, by suppressing the former and enhancing the latter.4 Although HDL is anti-inflammatory under normal conditions, in chronic inflammatory states and during an acute phase response HDL acquires acute-phase reactants and undergoes structural changes.14 Whether all of the protective effects of HDL remain functional under these circumstances is uncertain.4 This may be relevant to acute coronary syndromes, where the beneficial activities of
Journal of Clinical Lipidology, Vol 4, No 5, October 2010 HDL described previously would be expected to reduce the risks of a recurrent event. Indeed, the biologic activities of HDL seem perfectly suited to making it a viable therapy in acute coronary syndromes, where residual risk remains high despite current therapies.
Preclinical studies of HDL or apoA-1 infusions Infusions of HDL or of apoA-1 in animal models of experimental atherosclerosis have yielded extremely encouraging results.15-23 Badimon et al first demonstrated that weekly infusions of HDL/very high-density lipoprotein obtained by ultracentrifugation of normal rabbit plasma slowed the progression15 and induced regression of established lesions16 in cholesterol-fed rabbits. Subsequently, homologous apoA-1 was shown to slow atherosclerosis progression in the cholesterol-fed rabbit,17 and apoA-1 Milano was reported to reduce intimal thickening and macrophage content after balloon injury or perivascular manipulation in the same animal model.18,19 In apoE-deficient mice with severe hypercholesterolemia, apoA-1 Milano infusions prevented progression of aortic atherosclerosis and reduced lipid and macrophage content of plaques.20 These favorable changes were shown in later studies to occur after just one single high dose21 and to be associated with rapid reversal of endothelial dysfunction.23 Many drugs have been shown to favorably influence atherosclerosis in experimental models; however, the changes induced by HDL or apoA-1 infusions are remarkable for several reasons. First, they occur very quickly. Second, they have been shown to occur after only one high dose. Finally, the halting of progression or regression of atherosclerosis is accompanied by favorable changes in plaque composition and in endothelial function. An important caveat is that human atherosclerosis differs structurally and develops over a much longer time frame than the atherosclerosis of experimental animals, such that similar results cannot be assumed for patients.
Clinical trials of HDL or apoA-1 infusions Small proof-of-concept studies of HDL or apoA-1 infusions were begun in the late 1990s.6,24-26 The infusions appeared to be having a favorable effect on reverse cholesterol transport24,25 and improved endothelial function in one study.6 The first clinical trial, published in 2003, was a small pilot study wherein 57 patients with ACS were randomized in a 1:2:2 ratio to placebo or to 15-mg/kg or 45-mg/kg doses of ETC-216, a formulation of recombinant apoA-1 Milano in a complex with phospholipids.27 Treatment was begun within 2 weeks of the acute event and continued at weekly intervals for 5 weeks. Intravascular ultrasound
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Figure 1 Effect of recombinant apoA-1 Milano on coronary atherosclerosis.27 For the primary end point of the trial, percent atheroma volume (right), the low dose and the combined dose groups showed a statistically significant change from baseline; however, the difference between the placebo and active treatment groups were not statistically significant. A similar pattern was seen for atheroma volume (left), except that both low- and high-dose groups were significantly smaller than at baseline.
(IVUS) was performed at baseline and soon after treatment to measure atheroma volume in a single coronary artery with a 25% to 50% narrowing. A total of 47 patients completed the trial. The primary end-point measurement, percent atheroma volume, decreased in the combined ETC-216 dose groups by 1.06 6 3.17% compared with baseline (P 5 .02) and increased slightly in the placebo group, as shown in Figure 1. The difference between the active treatment groups and the placebo group were not statistically significant. The results of this trial, although far from definitive, engendered enormous enthusiasm for HDL or apoA-1 infusions because, in contrast to previous studies with IVUS end points, changes were demonstrated with only 5 weeks of treatment, as opposed to months or years. Such early benefit validated the results of studies in animal models, and kindled hope that infusions would be effective therapy for ACS. The small company developing ETC-216, Esperion, was purchased by Pfizer for $1.3 billion in late 2003.28 However, manufacturing difficulties complicated the development of ETC-216, and in late 2009 ETC-216 was sold to The Medicines Company for $410 million, plus royalties.29 No further clinical trials with this formulation have been reported. The second clinical trial of note, the Effect of rHDL on Atherosclerosis–Safety and efficacy (ERASE),30 used CSL-111, which consists of apoA-1 derived from human plasma and combined with soybean phosphatidylcholine. The resulting recombinant HDL resembles native HDL chemically and biologically. The ERASE Study was designed to assess the safety and efficacy of infused CSL-111 in patients with recent ACS by the use of IVUS and quantitative coronary angiographic end points. The primary efficacy parameter was the percent change in atheroma volume, and secondary end points included changes in plaque characterization indices and changes in quantitative coronary angiographic score. A total of 183 patients undergoing clinically indicated coronary arteriography at 17 Canadian centers underwent an
IVUS examination at baseline and were randomized to placebo or to 40 mg/kg or 80 mg/kg of CSL-111 infusion. Weekly infusions were given for 4 weeks. The greater dose was discontinued by the safety review committee because of a high incidence of elevated hepatic enzymes, and the 12 patients who received this dose were pooled with the 109 who received the lower dose, which was much better tolerated. IVUS examinations were repeated 2 to 3 weeks after the last treatment. An IVUS recording is illustrated in Figure 2. Evaluable end-point data were available for 136 patients. As shown in Figure 3, the primary end point of ERASE, percent change in atheroma volume, improved by 3.4% in the CSL-111 group (P , .0001 compared with baseline) and by 1.6% in the placebo group (P 5 .07 compared with baseline). The difference between he groups was not statistically significant; however, significant inter-group differences were seen for secondary end points. Arc index and inner perimeter index both improved in the CSL-111 treatment group and worsened in the placebo group (P 5 .01 for between group differences), as shown in Figure 4. These changes in plaque characterization indices suggest that CSL-111 improves plaque stability. The quantitative coronary angiographic methodology used in ERASE is illustrated in Figure 5. Changes in quantitative coronary angiographic measurements have been shown in previous trials to be predictive of future coronary events.31 Coronary score improved by 0.032 mm in the CSL-111 group compared with placebo (P 5 .03). Although this difference appears numerically small, it is an average of many lesions, most of which do not change during the course of a trial. The magnitude of this change is similar to that found in angiographic trials of statins, where treatment duration was usually 2 years instead of several weeks. CSL-111 has been supplanted by CSL 112, an improved formulation now undergoing phase 2 studies to establish that it has enhanced safety compared to its predecessor.32 In a recent randomized, placebo-controlled trial of just 28 post-ACS patients, the authors used 7 weekly infusions
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Journal of Clinical Lipidology, Vol 4, No 5, October 2010
Figure 2 Example of IVUS as used in the ERASE trial.30 The red lines (left) indicate the segment of the right coronary artery selected for analysis. The segment to be analyzed is precisely localized because it begins and ends at branch points, shown by ultrasound in the two panels on the right. The middle panel depicts the longitudinal extent of the 30-mm segment of interest.
of the patient’s own delipidated HDL with an investigational device.33 Delipidation converts aHDL to preb-like HDL, a more effective form of HDL for lipid removal from arterial plaques.33 Total atheroma volume by IVUS
decreased by 12.18 6 36.75 mm3 in the delipidated group versus an increase of 2.80 6 21.25 mm3 in the control group (P 5 .268). The reinfusion sessions were tolerated well by all patients.
Figure 3 Change in atheroma volume in the ERASE trial.30 Median percent change in atheroma volume, the primary end point (left), decreased significantly from baseline in the CSL-111 group but not in the placebo group. The intergroup difference was not statistically significant. Atheroma volume (right) showed roughly similar changes, except the improvement from baseline in the placebo group was statistically significant.
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Figure 4 Changes in plaque characterization indices in the ERASE trial.30 Both arc index (left) and inner perimeter index (right) improved in the CSL-111 group and worsened in the placebo group, with the difference between the groups being statistically significant.
Future directions Although none of these three trials showed a significant difference in atheroma volume or percent atheroma volume between active treatment and placebo groups, each demonstrated a degree of regression of atheroma that is impressive for the short duration of treatment. Furthermore, in the ERASE trial significant changes were observed in the plaque characterization and coronary angiographic secondary end points. These results, taken along with the results of experimental studies, strongly suggest that HDL or apoA1 infusions have a beneficial effect that should improve outcomes of patients with ACS. Other intravenous formulations of HDL or apoA-1 are in different stages of clinical development.34 Oral drugs, including cholesterol ester transfer protein inhibitors and small molecules that increase apoA-1 and HDL, are also in the pipeline. It is conceivable that within a decade,
Figure 5 Quantitative coronary angiographic technique used in the ERASE trial.30 Identical conditions are required for baseline and follow-up angiograms, with intracoronary nitroglycerin given in each artery before injection. Multiple transverse and sagittal views are filmed, and measurements are made in matched projections for all nonintervened arteries. The coronary score is calculated as the per-patient mean of the minimum lumen diameter for all lesions. This frame shows the measurement algorithm applied to a left anterior descending coronary narrowing.
therapies that increase HDL will be available that will rival statins in efficacy and safety.
References 1. Gordon DJ, Probstfield JL, Garrison RJ, et al. High-density lipoprotein cholesterol and cardiovascular disease. Four prospective American studies. Circulation. 1989;79:8–15. 2. Barter PJ, Caulfield M, Eriksson M, et al., ILLUMINATE Investigators: effects of torcetrapib in patients at high risk for coronary events. N Engl J Med. 2007;357:2109–2122. 3. Schmitz G, Grandl M. Vesicular trafficking mechanisms to mediate cellular lipid homeostasis. Arterioscler Thromb Vasc Biol. 2009;29: 1718–1722. 4. Calabresi L, Gomaraschi M, Franceschini G. Endothelial protection by high-density lipoproteins. From bench to bedside. Arterioscler Thromb Vasc Biol. 2003;23:1724–1731. 5. Zeiher AM, Schachlinger V, Hohnloser SH, Saurbier B, Just H. Coronary atherosclerotic wall thickening and vascular reactivity in humans: elevated high-density lipoprotein levels ameliorate abnormal vasoconstriction in early atherosclerosis. Circulation. 1994;89:2525–2532. 6. Spieker LE, Sudano I, Hurlimann D, et al. High-density lipoprotein restores endothelial function in hypercholesterolemic men. Circulation. 2002;105:1399–1402. 7. Murugesan G, Sa G, Fox PL. High-density lipoprotein stimulates endothelial cell movement by a mechanism distinct from basic fibroblast growth factor. Circ Res. 1994;74:1149–1156. 8. Sugano M, Tsuchida K, Makino N. High-density lipoprotein protects endothelial cells from tumor necrosis factor-alpha-induced apoptosis. Biochem Biophys Res Commun. 2000;272:872–876. 9. Barter PJ, Baker PW, Rye KA. Effect of high-density lipoprotein on the expression of adhesion molecules in endothelial cells. Curr Opin Lipidol. 2002;13:285–288. 10. Theilmeier G, De Geest B, Van Veldhoven PP, et al. HDL-associated PAF-AH reduces endothelial adhesiveness in apoE-/- mice. FASEB J. 2000;14:2032–2039. 11. Calabresi L, Gomaraschi M, Villa B, Omoboni L, Dmitrieff C, Franceschini G. Elevated soluble cellular adhesion molecules in subjects with low HDL-cholesterol. Arterioscler Thromb Vasc Biol. 2002;22:656–661. 12. Conlan MG, Folsom AR, Finch A, et al. Associations of factor VIII and von Willebrand factor with age, race, sex, and risk factors for atherosclerosis: the Atherosclerosis Risk in Communities (ARIC) Study. Thromb Haemost. 1993;70:380–385.
404 13. Naqvi TZ, Shah PK, Ivey PA, et al. Evidence that high-density lipoprotein cholesterol is an independent predictor of acute platelet-dependent thrombus formation. Am J Cardiol. 1999;84: 1011–1017. 14. Navab M, Berliner JA, Subbanagounder G, et al. HDL and the inflammatory response induced by LDL-derived oxidized phospholipids. Arterioscler Thromb Vasc Biol. 2001;21:481–488. 15. Badimon JJ, Badimon L, Galvez A, Dische R, Fuster V. High density lipoprotein plasma fraction inhibits fatty streaks in cholesterol-fed rabbits. Lab Invest. 1989;60:455–461. 16. Badimon JJ, Badimon L, Fuster V. Regression of atherosclerotic lesions by high density lipoprotein plasma fraction in the cholesterolfed rabbit. J Clin Invest. 1990;85:1234–1241. 17. Miyazaki A, Sakuma S, Morikawa W, et al. Intravenous injection of rabbit apolipoprotein A-I inhibits the progression of atherosclerosis in cholesterol-fed rabbits. Arterioscler Thromb Vasc Biol. 1995;15: 1882–1888. 18. Ameli S, Hultgardh-Nilsson A, Cercek B, et al. Recombinant apolipoprotein A-I Milano reduces intimal thickening after balloon injury in hypercholesterolemic rabbits. Circulation. 1994;90:1935–1941. 19. Soma MR, Donetti E, Parolini C, Sirtori CR, Fumagalli R, Franceschini G. Recombinant apolipoprotein A-I Milano dimer inhibits carotid intimal thickening induced by perivascular manipulation in rabbits. Circ Res. 1995;76:405–411. 20. Shah PK, Nilsson J, Kaul S, et al. Effects of recombinant apolipoprotein A-I Milano on aortic atherosclerosis in apolipoprotein E-deficient mice. Circulation. 1998;97:780–785. 21. Shah PK, Yano J, Reyes O, et al. High-dose recombinant apolipoprotein A-I Milano mobilizes tissue cholesterol and rapidly reduces plaque lipid and macrophage content in apolipoprotein E-deficient mice. Potential implications for acute plaque stabilization. Circulation. 2001;103:3047–3050. 22. Chiesa G, Monteggia E, Marchesi M, et al. Recombinant apolipoprotein A-I Milano infusion into rabbit carotid artery rapidly removes lipid from fatty streaks. Circ Res. 2002;90:974–980. 23. Kaul S, Coin B, Hedayiti A, et al. Rapid reversal of endothelial dysfunction in hypercholesterolemic apolipoprotein E-null mice by recombinant apolipoprotein A-1(Milano)-phospholipid complex. J Am Coll Cardiol. 2004;44:1311–1319.
Journal of Clinical Lipidology, Vol 4, No 5, October 2010 24. Eriksson M, Carlson LA, Mietinnen TA, Angelin B. Stimulation of fecal steroid excretion after infusion of recombinant proapolipoprotein A-I: potential reverse cholesterol transport in humans. Circulation. 1999;100:594–598. 25. Nanjee MN, Cooke CJ, Garvin R, et al. Intravenous apo A-1/lecithin discs increase pre-beta HDL concentration in tissue fluid and stimulate reverse cholesterol transport in humans. J Lipid Res. 2001;42:1586–1593. 26. Kujiraoka T, Nanjee MN, Oka T, et al. Effects of intravenous apolipoprotein A-I phosphatidyl choline discs on LCAT, PLTP, and CETP in plasma and peripheral lymph in humans. Arterioscler Thromb Vasc Biol. 2003;23:1653–1659. 27. Nissen SE, Tsunoda T, Tuzcu EM, et al. Effect of recombinant ApoA1 Milano on coronary atherosclerosis in patients with acute coronary syndromes: a randomized controlled trial. JAMA. 2003;290: 2292–2300. 28. CNN.com. Pfizer to buy Esperion for $1.6 bn, December 21, 2003. Available at: http://www.cnn.com/2003/BUSINESS/12/21/us.pfizer. reut/. Accessed August 24, 2010. 29. United States Securities and Exchange Commission filing. Available at: http://www.faqs.org/sec-filings/091224/MEDICINES-CO-DE_8-K. Accessed August 24, 2010. 30. Tardif JC, Gre´goire J, L’Allier PL, et al. Effect of rHDL on Atherosclerosis-Safety and Efficacy (ERASE) Investigators: effects of reconstituted high-density lipoprotein infusions on coronary atherosclerosis: a randomized controlled trial. JAMA. 2007;297:1675–1682. 31. Waters D, Craven TE, Lespe´rance J. Prognostic significance of progression of coronary atherosclerosis. Circulation. 1993;87:1067–1075. 32. Safety, tolerability and pharmacokinetics of CSL 112 in healthy volunteers. Clinicaltrials.gov #NCT01129661. Available at: http://clini caltrials.gov/ct2/show/NCT011296611. Accessed August 24, 2010. 33. Wakesman R, Torguson R, Kent KM, et al. A first-in-man, randomized, placebo-controlled study to evaluate the safety and feasibility of autologous delipidated high-density lipoprotein plasma infusions in patients with acute coronary syndrome. J Am Coll Cardiol. 2010; 55:2727–2735. 34. Cerenis Therapeutics completes CER-001 phase 1 study. Available at: http://clinicaltrials.pharmaceutical-business-review.com/news/cerenis_ therapeutics_completes_cer001_phase_1_study_100518/. Accessed August 24, 2010.
NLA Symposium on High Density Lipoproteins
Emerging high-density lipoprotein infusion therapies: Fulfilling the promise of epidemiology? Jean-Claude Tardif, MD* Department of Medicine, Research Centre, Montreal Heart Institute, 5000 Belanger Street, Montreal, Quebec H1T 1C8, Canada, and Universite´ de Montre´al, Montreal, Canada KEYWORDS: ApoA-1 Milano; Atherosclerosis; HDL-cholesterol; Intravascular ultrasound
Abstract: High-density lipoprotein (HDL) plays a key role in reverse cholesterol transport but also activates nitric oxide synthase and stimulates prostacyclin release, enhances endothelial repair, inhibits cell adhesion molecule expression on vascular endothelium and monocyte recruitment into the arterial wall, and exerts antithrombotic effects. In experimental animals, infusions of HDL or apolipoprotein A-1 (apoA-1) halt the progression or induce regression of atherosclerosis, with favorable effects on plaque composition. Remarkably, a benefit is observed after a single infusion. In a pilot study, weekly infusions of ETC-216, a formulation of recombinant apoA-1 Milano, were administered at two doses for 5 weeks to patients beginning within 2 weeks of an acute coronary syndrome (ACS). Among the 47 patients completing the study, percent atheroma volume by intracoronary ultrasound was reduced in the combined active treatment groups but not in the placebo group. In a larger trial, the Effect of rHDL on Atherosclerosis–Safety and efficacy (ERASE), 183 post-ACS patients were randomized to 4 weekly infusions of placebo or one of two doses of CSL-111, which consists of apoA-1 derived from human plasma and combined with soybean phosphatidylcholine. The greater dose was discontinued because of a high incidence of hepatic enzyme elevation. Among the 136 patients with evaluable end point data, percent change in atheroma volume, the primary endpoint, improved significantly in the CSL-111 group but not in the placebo group. The secondary end points of plaque characterization indices and quantitative coronary angiographic changes both improved significantly in the CSL-111 group compared with the group receiving placebo. Taken together, this evidence suggests that infusions of HDL or apoA-1 may reduce events, particularly among patients with ACS. Ó 2010 National Lipid Association. All rights reserved.
Epidemiologic data suggests that a 1-mg/dL increment in high-density lipoprotein (HDL) will be associated with a 2% decrement in coronary heart disease risk in men and a 3% decrement in women.1 Because the epidemiologic relationship between low-density lipoprotein (LDL) and cardiovascular events turned out to be quite predictive of the benefit associated with statin-induced LDL reduction, the
* Corresponding author. E-mail address: [email protected] Submitted June 17, 2010. Accepted for publication August 18, 2010.
assumption was widespread that drugs that increased HDL would invariably be associated with significant clinical benefit. The failure of torcetrapib, a potent cholesterol ester transfer protein inhibitor that increased HDL by 72% in the Study Examining Torcetrapib/Atorvastatin and Atorvastatin Effects on Clinical CV Events in Patients With Heart Disease (ILLUMINATE) trial but also increased mortality and morbidity,2 has led to the realization that the epidemiologic promise of HDL could be illusory. Nevertheless, a large coherent body of experimental evidence supports the hypothesis that increasing HDL will reduce cardiovascular events.
1933-2874/$ - see front matter Ó 2010 National Lipid Association. All rights reserved. doi:10.1016/j.jacl.2010.08.018
400
Biologic plausibility for increasing HDL The benefits of HDL most often are related to reverse cholesterol transport, the process whereby excess cholesterol is carried from peripheral cells to the liver to be eliminated via biliary excretion or to be recycled in the entero-hepatic circulation. The ATP-binding cassette transporter protein ABCA 1 plays an important role in this process by facilitating cellular cholesterol and phospholipid release to apolipoprotein A-1 (apoA)-12containing HDL precursors.3 The maintenance of cholesterol homeostasis within cells and the details of cholesterol transport are complex because many systems interact with HDL.3 In addition to reverse cholesterol transport, HDL exhibits several other mechanisms that protect against vascular disease. HDL has been shown in several studies to activate endothelial nitric oxide (NO) synthase, which would ameliorate endothelial function.4 Patients with early atherosclerosis have improved coronary artery endothelial function with greater HDL levels,5 and intravenous infusion of HDL in hypercholesterolemic subjects rapidly increases NO bioavailability and restores impaired endothelialdependent vasodilation.6 HDL also stimulates prostacyclin release and may inhibit the vasoconstrictor effects of endothelin.4 HDL stimulates endothelial cell migration and thus endothelial repair.4,7 HDL protects endothelial cells from apoptosis in a dose-dependent fashion at physiologic HDL concentrations.8 Injured endothelium expresses cell adhesion molecules that attract monocytes that adhere to the endothelium and migrate into the subendothelial space. HDL inhibits cell adhesion molecule expression in umbilical vein endothelial cells.4,9 In apoE-deficient mice, increasing HDL concentrations by overexpression of apoA-1 inhibits cell adhesion molecule expression on vascular endothelium and monocyte recruitment into the arterial wall.10 These findings appear to pertain to humans, where low HDL levels are associated with greater levels of circulating soluble cellular adhesion molecules.11 HDL exerts important antithrombotic effects through several mechanisms. As noted previously, HDL favors NO and prostacyclin release; both inhibit platelet aggregation. Von Willebrand factor levels vary inversely with HDL levels, suggesting that HDL may inhibit production of this protein that stimulates platelet adhesion and aggregation.12 High HDL levels in humans are associated with reduced ex vivo platelet thrombus deposition.13 HDL also favorably affects the balance between the activities of tissue factor and tissue factor pathway inhibitor, by suppressing the former and enhancing the latter.4 Although HDL is anti-inflammatory under normal conditions, in chronic inflammatory states and during an acute phase response HDL acquires acute-phase reactants and undergoes structural changes.14 Whether all of the protective effects of HDL remain functional under these circumstances is uncertain.4 This may be relevant to acute coronary syndromes, where the beneficial activities of
Journal of Clinical Lipidology, Vol 4, No 5, October 2010 HDL described previously would be expected to reduce the risks of a recurrent event. Indeed, the biologic activities of HDL seem perfectly suited to making it a viable therapy in acute coronary syndromes, where residual risk remains high despite current therapies.
Preclinical studies of HDL or apoA-1 infusions Infusions of HDL or of apoA-1 in animal models of experimental atherosclerosis have yielded extremely encouraging results.15-23 Badimon et al first demonstrated that weekly infusions of HDL/very high-density lipoprotein obtained by ultracentrifugation of normal rabbit plasma slowed the progression15 and induced regression of established lesions16 in cholesterol-fed rabbits. Subsequently, homologous apoA-1 was shown to slow atherosclerosis progression in the cholesterol-fed rabbit,17 and apoA-1 Milano was reported to reduce intimal thickening and macrophage content after balloon injury or perivascular manipulation in the same animal model.18,19 In apoE-deficient mice with severe hypercholesterolemia, apoA-1 Milano infusions prevented progression of aortic atherosclerosis and reduced lipid and macrophage content of plaques.20 These favorable changes were shown in later studies to occur after just one single high dose21 and to be associated with rapid reversal of endothelial dysfunction.23 Many drugs have been shown to favorably influence atherosclerosis in experimental models; however, the changes induced by HDL or apoA-1 infusions are remarkable for several reasons. First, they occur very quickly. Second, they have been shown to occur after only one high dose. Finally, the halting of progression or regression of atherosclerosis is accompanied by favorable changes in plaque composition and in endothelial function. An important caveat is that human atherosclerosis differs structurally and develops over a much longer time frame than the atherosclerosis of experimental animals, such that similar results cannot be assumed for patients.
Clinical trials of HDL or apoA-1 infusions Small proof-of-concept studies of HDL or apoA-1 infusions were begun in the late 1990s.6,24-26 The infusions appeared to be having a favorable effect on reverse cholesterol transport24,25 and improved endothelial function in one study.6 The first clinical trial, published in 2003, was a small pilot study wherein 57 patients with ACS were randomized in a 1:2:2 ratio to placebo or to 15-mg/kg or 45-mg/kg doses of ETC-216, a formulation of recombinant apoA-1 Milano in a complex with phospholipids.27 Treatment was begun within 2 weeks of the acute event and continued at weekly intervals for 5 weeks. Intravascular ultrasound
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Figure 1 Effect of recombinant apoA-1 Milano on coronary atherosclerosis.27 For the primary end point of the trial, percent atheroma volume (right), the low dose and the combined dose groups showed a statistically significant change from baseline; however, the difference between the placebo and active treatment groups were not statistically significant. A similar pattern was seen for atheroma volume (left), except that both low- and high-dose groups were significantly smaller than at baseline.
(IVUS) was performed at baseline and soon after treatment to measure atheroma volume in a single coronary artery with a 25% to 50% narrowing. A total of 47 patients completed the trial. The primary end-point measurement, percent atheroma volume, decreased in the combined ETC-216 dose groups by 1.06 6 3.17% compared with baseline (P 5 .02) and increased slightly in the placebo group, as shown in Figure 1. The difference between the active treatment groups and the placebo group were not statistically significant. The results of this trial, although far from definitive, engendered enormous enthusiasm for HDL or apoA-1 infusions because, in contrast to previous studies with IVUS end points, changes were demonstrated with only 5 weeks of treatment, as opposed to months or years. Such early benefit validated the results of studies in animal models, and kindled hope that infusions would be effective therapy for ACS. The small company developing ETC-216, Esperion, was purchased by Pfizer for $1.3 billion in late 2003.28 However, manufacturing difficulties complicated the development of ETC-216, and in late 2009 ETC-216 was sold to The Medicines Company for $410 million, plus royalties.29 No further clinical trials with this formulation have been reported. The second clinical trial of note, the Effect of rHDL on Atherosclerosis–Safety and efficacy (ERASE),30 used CSL-111, which consists of apoA-1 derived from human plasma and combined with soybean phosphatidylcholine. The resulting recombinant HDL resembles native HDL chemically and biologically. The ERASE Study was designed to assess the safety and efficacy of infused CSL-111 in patients with recent ACS by the use of IVUS and quantitative coronary angiographic end points. The primary efficacy parameter was the percent change in atheroma volume, and secondary end points included changes in plaque characterization indices and changes in quantitative coronary angiographic score. A total of 183 patients undergoing clinically indicated coronary arteriography at 17 Canadian centers underwent an
IVUS examination at baseline and were randomized to placebo or to 40 mg/kg or 80 mg/kg of CSL-111 infusion. Weekly infusions were given for 4 weeks. The greater dose was discontinued by the safety review committee because of a high incidence of elevated hepatic enzymes, and the 12 patients who received this dose were pooled with the 109 who received the lower dose, which was much better tolerated. IVUS examinations were repeated 2 to 3 weeks after the last treatment. An IVUS recording is illustrated in Figure 2. Evaluable end-point data were available for 136 patients. As shown in Figure 3, the primary end point of ERASE, percent change in atheroma volume, improved by 3.4% in the CSL-111 group (P , .0001 compared with baseline) and by 1.6% in the placebo group (P 5 .07 compared with baseline). The difference between he groups was not statistically significant; however, significant inter-group differences were seen for secondary end points. Arc index and inner perimeter index both improved in the CSL-111 treatment group and worsened in the placebo group (P 5 .01 for between group differences), as shown in Figure 4. These changes in plaque characterization indices suggest that CSL-111 improves plaque stability. The quantitative coronary angiographic methodology used in ERASE is illustrated in Figure 5. Changes in quantitative coronary angiographic measurements have been shown in previous trials to be predictive of future coronary events.31 Coronary score improved by 0.032 mm in the CSL-111 group compared with placebo (P 5 .03). Although this difference appears numerically small, it is an average of many lesions, most of which do not change during the course of a trial. The magnitude of this change is similar to that found in angiographic trials of statins, where treatment duration was usually 2 years instead of several weeks. CSL-111 has been supplanted by CSL 112, an improved formulation now undergoing phase 2 studies to establish that it has enhanced safety compared to its predecessor.32 In a recent randomized, placebo-controlled trial of just 28 post-ACS patients, the authors used 7 weekly infusions
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Figure 2 Example of IVUS as used in the ERASE trial.30 The red lines (left) indicate the segment of the right coronary artery selected for analysis. The segment to be analyzed is precisely localized because it begins and ends at branch points, shown by ultrasound in the two panels on the right. The middle panel depicts the longitudinal extent of the 30-mm segment of interest.
of the patient’s own delipidated HDL with an investigational device.33 Delipidation converts aHDL to preb-like HDL, a more effective form of HDL for lipid removal from arterial plaques.33 Total atheroma volume by IVUS
decreased by 12.18 6 36.75 mm3 in the delipidated group versus an increase of 2.80 6 21.25 mm3 in the control group (P 5 .268). The reinfusion sessions were tolerated well by all patients.
Figure 3 Change in atheroma volume in the ERASE trial.30 Median percent change in atheroma volume, the primary end point (left), decreased significantly from baseline in the CSL-111 group but not in the placebo group. The intergroup difference was not statistically significant. Atheroma volume (right) showed roughly similar changes, except the improvement from baseline in the placebo group was statistically significant.
Tardif
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Figure 4 Changes in plaque characterization indices in the ERASE trial.30 Both arc index (left) and inner perimeter index (right) improved in the CSL-111 group and worsened in the placebo group, with the difference between the groups being statistically significant.
Future directions Although none of these three trials showed a significant difference in atheroma volume or percent atheroma volume between active treatment and placebo groups, each demonstrated a degree of regression of atheroma that is impressive for the short duration of treatment. Furthermore, in the ERASE trial significant changes were observed in the plaque characterization and coronary angiographic secondary end points. These results, taken along with the results of experimental studies, strongly suggest that HDL or apoA1 infusions have a beneficial effect that should improve outcomes of patients with ACS. Other intravenous formulations of HDL or apoA-1 are in different stages of clinical development.34 Oral drugs, including cholesterol ester transfer protein inhibitors and small molecules that increase apoA-1 and HDL, are also in the pipeline. It is conceivable that within a decade,
Figure 5 Quantitative coronary angiographic technique used in the ERASE trial.30 Identical conditions are required for baseline and follow-up angiograms, with intracoronary nitroglycerin given in each artery before injection. Multiple transverse and sagittal views are filmed, and measurements are made in matched projections for all nonintervened arteries. The coronary score is calculated as the per-patient mean of the minimum lumen diameter for all lesions. This frame shows the measurement algorithm applied to a left anterior descending coronary narrowing.
therapies that increase HDL will be available that will rival statins in efficacy and safety.
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