- Email: [email protected]
Reducing plasma cholesterol is not the end of the quest
Atherosclerosis 227 (2013) 35e36
Contents lists available at SciVerse ScienceDirect
Atherosclerosis journal homepage: www.elsevier.com/locate/atherosclerosis
Invited commentary
Reducing plasma cholesterol is not the end of the quest Mohamad Navab*, Maryam Shabihkhani, Kaveh Daniel Navab, Samra Vazirian, Maryam Haghnegahdar, Srinivasa T. Reddy Department of Medicine, David Geffen School of Medicine, University of California Los Angeles, 10833 Le Conte Ave., Los Angeles, CA 90095-1679, USA
a r t i c l e i n f o Article history: Received 18 December 2012 Accepted 19 December 2012 Available online 9 January 2013 Keywords: ApoA-I Mimetic peptide ApoE Atherosclerosis Inflammation HDL
Despite the cholesterol lowering beneficial effects of statins, nearly 70% of cardiovascular disease remains unresolved. High density lipoproteins (HDL), apolipoprotein A-I (the major protein component of HDL), and apoA-I mimetic peptides exert antiinflammatory effects but have not been shown to reduce plasma cholesterol levels. Apolipoprotein E (apoE) is a protein component of chylomicron remnants, very low density lipoprotein (VLDL), and HDL. ApoE is ubiquitously expressed and secreted by many tissues in the body including liver, brain, skin, and tissue macrophages [1]. A common well-characterized polymorphism in human apoE gene accounts for the three alleles, ε2, ε3 and ε4 that are known to confer resistance or susceptibility to many diseases including Alzheimer’s disease [2] and atherosclerosis [3]. ApoE gene encodes for a 299 amino acid protein containing two domains: a receptor-binding domain at the N-terminus and a lipid-binding region at the C-terminus, [4,5]. Amino acid residues 141e150 are involved in the interaction with low density lipoprotein receptor [6] for the receptor-mediated uptake of atherogenic apoB-containing and remnant lipoproteins in the liver. Interestingly, apoE promotes regression of atherosclerosis independent of plasma cholesterol lowering suggesting multiple antiatherogenic functions for the apoE protein [15]. ApoE exhibits a central role in protecting the artery wall [7,8]. In addition, apoE also plays central DOI of original article: http://dx.doi.org/10.1016/j.atherosclerosis.2012.10.064. * Corresponding author. E-mail address: [email protected] (M. Navab). 0021-9150/$ e see front matter Ó 2013 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.atherosclerosis.2012.12.034
roles in coagulation, macrophage function, oxidative processes, central nervous system physiology, inflammation, and cell signaling [5,9,10]. ApoE is considered to be one of the carriers of the antioxidant enzyme paraoxonase 1 (PON1) [11]. ApoE is also involved in efferocytosis and reduces endoplasmic reticulum stress [12]. The manuscript by Handattu et al. in this issue of Atherosclerosis [13] pertains to small peptides that reduce plasma cholesterol levels. One of the peptides; Ac-hE18A-NH2 contains sequences that mimic some of the properties of full-length apoE. The design for Ac-hE18ANH2 was based on the idea that the receptor-binding domain of apoE (LRKLRKRLLR) when covalently linked to an anti-inflammatory apoA-I mimetic peptide 18A [14] would yield a dual-domain peptide with both cholesterol lowering as well as anti-inflammatory properties [15]. As reported for the first dual domain peptide; Ac-hE18ANH2 [16] treatment showed marked reduction in both plasma cholesterol levels as well as atherosclerosis, when administered to apoE null mice [17]. In addition, Ac-hE18A-NH2 administration increased PON-1 activity [an anti-oxidant enzyme present in HDL [18]] and improved HDL function [19]. The second peptide is a single domain peptide named mR18L (with the sequence AcGFRRFLGSWARIYRAFVG-NH2). Oral administration of the peptide mR18L, designed by modifying a model cationic class L-peptide, has also been shown to reduce plasma cholesterol and inhibit atherosclerosis in apoE null mice [20]. The manuscript by Handattu et al. in this issue of Atherosclerosis [13] reports new and important observations on the action of the two peptides; Ac-hE18A-NH2 and mR18L. The authors have shown,
36
M. Navab et al. / Atherosclerosis 227 (2013) 35e36
for the first time, that oxidized lipids inhibit apoE release from hepatocytes and macrophages; that was restored by both peptides albeit to different degrees. Co-incubation of ox-lipids and Ac-hE18A-NH2 enhanced apoE release several fold higher than incubation of the peptide alone with HepG2 cells. Peptide mR18L did not possess this property. When administered chronically, both peptides reduced plasma cholesterol to a similar extent. Despite decreases in plasma cholesterol, surprisingly, peptide Ac-hE18ANH2 was more effective than mR18L in inhibiting atherosclerotic lesion progression in LDL-R null mice on Western diet; perhaps, due to its enhanced ability to release apoE. Reducing cholesterol and bypassing the LDL receptor deficiency in Watanabe Heritable Hyperlipidemic (WHHL) rabbits via the administration of apoE was demonstrated in 1989 [21]. However, native apoE is too large to insert into LDL and the cholesterol reduction was limited. The apoE mimetic peptides, on the other hand, have been shown to insert into human LDL and VLDL and mediate uptake via the HSPG receptors on the liver. In addition the ability of an apoE mimetic to release cell surface apoE, which, as described above, promotes atherosclerotic lesion regression is new and novel. Since apoE also plays important roles in several other lipidmediated disorders such as diabetes and Alzheimer’s disease, further investigations of apoE mimetics along the lines of mechanisms reported in this paper are warranted. References [1] Mahley RW, Rall Jr SC. Apolipoprotein E: far more than a lipid transport protein. Annu Rev Genomics Hum Genet 2000;1:507e37. [2] Mahley RW, Nathan BP, Pitas RE. Apolipoprotein E: structure, function, and possible roles in Alzheimer’s disease. Ann N Y Acad Sci 1996;777:139e45. [3] Davignon J, Gregg RE, Sing CF. Apolipoprotein E polymorphism and atherosclerosis. Arterio Thromb Vasc Biol 1988;8:1e21. [4] Bradley WA, Hwang SL, Karlin JB, et al. Low-density lipoprotein receptor binding determinants switch from apolipoprotein E to apolipoprotein B during conversion of hypertriglyceridemic very-low-density lipoprotein to low density lipoproteins. J Biol Chem 1984;259:14728e35. [5] Gianturco SH, Gotto Jr AM, Hwang S-LC, et al. Apolipoprotein E mediates uptake of Sf 100e400 hypertriglyceridemic very low density lipoproteins by
[6]
[7] [8]
[9]
[10]
[11] [12]
[13]
[14] [15]
[16]
[17] [18]
[19]
[20]
[21]
the low density lipoprotein receptor pathway in normal human fibroblasts. J Biol Chem 1983;258:4526e33. Zaiou M, Arnold KS, Newhouse YM, et al. Apolipoprotein E-low density lipoprotein receptor interaction: influences of basic residue and amphipathic ahelix organization in the ligand. J Lipid Res 2000;41:1087e95. Davignon J. Apolipoprotein E and atherosclerosis: beyond lipid effect. Arterio Thromb Vasc Biol 2005;25:267e9. Gaudreault N, Kumar N, Posada JM, et al. ApoE suppresses atherosclerosis by reducing lipid accumulation in circulating monocytes and the expression of inflammatory monocytes on monocytes and vascular endothelium. Athero Thromb Vasc Biol 2012;32:264e72. Swertfeger DK, Hui DY. Apolipoprotein E: a cholesterol transport protein with lipid transport-independent cell signaling properties. Front BioSci 2001;6: 526e35. Stannard AK, Riddell DR, Sacre SM, et al. Cell-derived apolipoprotein e (apoe) particles inhibit vascular cell adhesion molecule-1 (vcam-1) expression in human endothelial cells. J Biol Chem 2001;276:46011e6. Gaidukov l, Viji RI, Yacobson S, et al. ApoE induces serum paraoxonase PON1 activity and stability similar to apoA-I. Biochemistry 2010;49:532e8. Cash JG, Kuhel DG, Basford JE, et al. Apolipoprotein E4 impairs macrophage efferocytosis and potentiates apoptosis by accelerating endoplasmic reticulum stress. J Biol Chem 2012;287:27876e27884,. Handattu SP, Nayyar G, Garber DW, et al. Two apolipoprotein E mimetic peptides with similar cholesterol reducing properties exhibit differential atheroprotective effects in LDL-R null mice. Atherosclerosis 2012;227(1):58e64. Anantharamaiah GM. Synthetic peptide analogs of apolipoproteins. Methods Enzymol 1986;128:626e47. Datta G, Chaddha M, Garber DW, et al. The receptor binding domain of apolipoprotein E, linked to a model class A amphipathic helix, enhances internalization and degradation of LDL by fibroblasts. Biochemistry 2000;39: 213e20. Nayyar G, Handattu SP, Monroe CE, et al. Two adjacent domains (141-150 and 151-160) of apoE covalently linked to a class A amphipathic helical peptide exhibit opposite atherogenic effects. Atherosclerosis 2010;213:449e57. Sharifov OF, Nayyar G, Garber DW, et al. Apolipoprotein E mimetics and cholesterol lowering properties. Am J Cardiol Drugs 2011;11:371e81. Mackness B, Durrington PN, McElduff P, et al. Low paraoxonase activity predicts coronary events in the Caerphilly Prospective Study. Circulation 2003; 107:2775e9. Gupta H, White CR, Handattu S, et al. An apo E mimetic peptide dramatically lowers plasma cholesterol and restores endothelial function in watanabe heritable hyperlipidemic rabbits. Circulation 2005;111:3112e8. Handattu SP, Datta G, Epand RM, et al. Oral administration of of L-mR18L, a single domain cationic amphipathic helical peptide, inhibits lesion formation in apoE null mice. J Lipid Res 2010;51:3491e9. Yamada N, Shimano H, Mokuno H, et al. Increased clearance of plasma cholesterol after injection of apolipoprotein E into watanabe heritable hyperlipidemic rabbits. Proc Natl Acad Sci U S A 1989;86:665e9.
Contents lists available at SciVerse ScienceDirect
Atherosclerosis journal homepage: www.elsevier.com/locate/atherosclerosis
Invited commentary
Reducing plasma cholesterol is not the end of the quest Mohamad Navab*, Maryam Shabihkhani, Kaveh Daniel Navab, Samra Vazirian, Maryam Haghnegahdar, Srinivasa T. Reddy Department of Medicine, David Geffen School of Medicine, University of California Los Angeles, 10833 Le Conte Ave., Los Angeles, CA 90095-1679, USA
a r t i c l e i n f o Article history: Received 18 December 2012 Accepted 19 December 2012 Available online 9 January 2013 Keywords: ApoA-I Mimetic peptide ApoE Atherosclerosis Inflammation HDL
Despite the cholesterol lowering beneficial effects of statins, nearly 70% of cardiovascular disease remains unresolved. High density lipoproteins (HDL), apolipoprotein A-I (the major protein component of HDL), and apoA-I mimetic peptides exert antiinflammatory effects but have not been shown to reduce plasma cholesterol levels. Apolipoprotein E (apoE) is a protein component of chylomicron remnants, very low density lipoprotein (VLDL), and HDL. ApoE is ubiquitously expressed and secreted by many tissues in the body including liver, brain, skin, and tissue macrophages [1]. A common well-characterized polymorphism in human apoE gene accounts for the three alleles, ε2, ε3 and ε4 that are known to confer resistance or susceptibility to many diseases including Alzheimer’s disease [2] and atherosclerosis [3]. ApoE gene encodes for a 299 amino acid protein containing two domains: a receptor-binding domain at the N-terminus and a lipid-binding region at the C-terminus, [4,5]. Amino acid residues 141e150 are involved in the interaction with low density lipoprotein receptor [6] for the receptor-mediated uptake of atherogenic apoB-containing and remnant lipoproteins in the liver. Interestingly, apoE promotes regression of atherosclerosis independent of plasma cholesterol lowering suggesting multiple antiatherogenic functions for the apoE protein [15]. ApoE exhibits a central role in protecting the artery wall [7,8]. In addition, apoE also plays central DOI of original article: http://dx.doi.org/10.1016/j.atherosclerosis.2012.10.064. * Corresponding author. E-mail address: [email protected] (M. Navab). 0021-9150/$ e see front matter Ó 2013 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.atherosclerosis.2012.12.034
roles in coagulation, macrophage function, oxidative processes, central nervous system physiology, inflammation, and cell signaling [5,9,10]. ApoE is considered to be one of the carriers of the antioxidant enzyme paraoxonase 1 (PON1) [11]. ApoE is also involved in efferocytosis and reduces endoplasmic reticulum stress [12]. The manuscript by Handattu et al. in this issue of Atherosclerosis [13] pertains to small peptides that reduce plasma cholesterol levels. One of the peptides; Ac-hE18A-NH2 contains sequences that mimic some of the properties of full-length apoE. The design for Ac-hE18ANH2 was based on the idea that the receptor-binding domain of apoE (LRKLRKRLLR) when covalently linked to an anti-inflammatory apoA-I mimetic peptide 18A [14] would yield a dual-domain peptide with both cholesterol lowering as well as anti-inflammatory properties [15]. As reported for the first dual domain peptide; Ac-hE18ANH2 [16] treatment showed marked reduction in both plasma cholesterol levels as well as atherosclerosis, when administered to apoE null mice [17]. In addition, Ac-hE18A-NH2 administration increased PON-1 activity [an anti-oxidant enzyme present in HDL [18]] and improved HDL function [19]. The second peptide is a single domain peptide named mR18L (with the sequence AcGFRRFLGSWARIYRAFVG-NH2). Oral administration of the peptide mR18L, designed by modifying a model cationic class L-peptide, has also been shown to reduce plasma cholesterol and inhibit atherosclerosis in apoE null mice [20]. The manuscript by Handattu et al. in this issue of Atherosclerosis [13] reports new and important observations on the action of the two peptides; Ac-hE18A-NH2 and mR18L. The authors have shown,
36
M. Navab et al. / Atherosclerosis 227 (2013) 35e36
for the first time, that oxidized lipids inhibit apoE release from hepatocytes and macrophages; that was restored by both peptides albeit to different degrees. Co-incubation of ox-lipids and Ac-hE18A-NH2 enhanced apoE release several fold higher than incubation of the peptide alone with HepG2 cells. Peptide mR18L did not possess this property. When administered chronically, both peptides reduced plasma cholesterol to a similar extent. Despite decreases in plasma cholesterol, surprisingly, peptide Ac-hE18ANH2 was more effective than mR18L in inhibiting atherosclerotic lesion progression in LDL-R null mice on Western diet; perhaps, due to its enhanced ability to release apoE. Reducing cholesterol and bypassing the LDL receptor deficiency in Watanabe Heritable Hyperlipidemic (WHHL) rabbits via the administration of apoE was demonstrated in 1989 [21]. However, native apoE is too large to insert into LDL and the cholesterol reduction was limited. The apoE mimetic peptides, on the other hand, have been shown to insert into human LDL and VLDL and mediate uptake via the HSPG receptors on the liver. In addition the ability of an apoE mimetic to release cell surface apoE, which, as described above, promotes atherosclerotic lesion regression is new and novel. Since apoE also plays important roles in several other lipidmediated disorders such as diabetes and Alzheimer’s disease, further investigations of apoE mimetics along the lines of mechanisms reported in this paper are warranted. References [1] Mahley RW, Rall Jr SC. Apolipoprotein E: far more than a lipid transport protein. Annu Rev Genomics Hum Genet 2000;1:507e37. [2] Mahley RW, Nathan BP, Pitas RE. Apolipoprotein E: structure, function, and possible roles in Alzheimer’s disease. Ann N Y Acad Sci 1996;777:139e45. [3] Davignon J, Gregg RE, Sing CF. Apolipoprotein E polymorphism and atherosclerosis. Arterio Thromb Vasc Biol 1988;8:1e21. [4] Bradley WA, Hwang SL, Karlin JB, et al. Low-density lipoprotein receptor binding determinants switch from apolipoprotein E to apolipoprotein B during conversion of hypertriglyceridemic very-low-density lipoprotein to low density lipoproteins. J Biol Chem 1984;259:14728e35. [5] Gianturco SH, Gotto Jr AM, Hwang S-LC, et al. Apolipoprotein E mediates uptake of Sf 100e400 hypertriglyceridemic very low density lipoproteins by
[6]
[7] [8]
[9]
[10]
[11] [12]
[13]
[14] [15]
[16]
[17] [18]
[19]
[20]
[21]
the low density lipoprotein receptor pathway in normal human fibroblasts. J Biol Chem 1983;258:4526e33. Zaiou M, Arnold KS, Newhouse YM, et al. Apolipoprotein E-low density lipoprotein receptor interaction: influences of basic residue and amphipathic ahelix organization in the ligand. J Lipid Res 2000;41:1087e95. Davignon J. Apolipoprotein E and atherosclerosis: beyond lipid effect. Arterio Thromb Vasc Biol 2005;25:267e9. Gaudreault N, Kumar N, Posada JM, et al. ApoE suppresses atherosclerosis by reducing lipid accumulation in circulating monocytes and the expression of inflammatory monocytes on monocytes and vascular endothelium. Athero Thromb Vasc Biol 2012;32:264e72. Swertfeger DK, Hui DY. Apolipoprotein E: a cholesterol transport protein with lipid transport-independent cell signaling properties. Front BioSci 2001;6: 526e35. Stannard AK, Riddell DR, Sacre SM, et al. Cell-derived apolipoprotein e (apoe) particles inhibit vascular cell adhesion molecule-1 (vcam-1) expression in human endothelial cells. J Biol Chem 2001;276:46011e6. Gaidukov l, Viji RI, Yacobson S, et al. ApoE induces serum paraoxonase PON1 activity and stability similar to apoA-I. Biochemistry 2010;49:532e8. Cash JG, Kuhel DG, Basford JE, et al. Apolipoprotein E4 impairs macrophage efferocytosis and potentiates apoptosis by accelerating endoplasmic reticulum stress. J Biol Chem 2012;287:27876e27884,. Handattu SP, Nayyar G, Garber DW, et al. Two apolipoprotein E mimetic peptides with similar cholesterol reducing properties exhibit differential atheroprotective effects in LDL-R null mice. Atherosclerosis 2012;227(1):58e64. Anantharamaiah GM. Synthetic peptide analogs of apolipoproteins. Methods Enzymol 1986;128:626e47. Datta G, Chaddha M, Garber DW, et al. The receptor binding domain of apolipoprotein E, linked to a model class A amphipathic helix, enhances internalization and degradation of LDL by fibroblasts. Biochemistry 2000;39: 213e20. Nayyar G, Handattu SP, Monroe CE, et al. Two adjacent domains (141-150 and 151-160) of apoE covalently linked to a class A amphipathic helical peptide exhibit opposite atherogenic effects. Atherosclerosis 2010;213:449e57. Sharifov OF, Nayyar G, Garber DW, et al. Apolipoprotein E mimetics and cholesterol lowering properties. Am J Cardiol Drugs 2011;11:371e81. Mackness B, Durrington PN, McElduff P, et al. Low paraoxonase activity predicts coronary events in the Caerphilly Prospective Study. Circulation 2003; 107:2775e9. Gupta H, White CR, Handattu S, et al. An apo E mimetic peptide dramatically lowers plasma cholesterol and restores endothelial function in watanabe heritable hyperlipidemic rabbits. Circulation 2005;111:3112e8. Handattu SP, Datta G, Epand RM, et al. Oral administration of of L-mR18L, a single domain cationic amphipathic helical peptide, inhibits lesion formation in apoE null mice. J Lipid Res 2010;51:3491e9. Yamada N, Shimano H, Mokuno H, et al. Increased clearance of plasma cholesterol after injection of apolipoprotein E into watanabe heritable hyperlipidemic rabbits. Proc Natl Acad Sci U S A 1989;86:665e9.