In vivo efficacy of HDL-like nanolipid particles containing multivalent peptide mimetics of apolipoprotein A-I.

We have observed that molecular constructs based on multiple apoA-I mimetic peptides attached to a branched scaffold display promising anti-atherosclerosis functions in vitro. Building on these promising results, we now describe chronic in vivo studies to assess anti-atherosclerotic efficacy of HDL-like nanoparticles assembled from a trimeric construct, administered over 10 weeks either ip or orally to LDL receptor-null mice. When dosed ip, the trimer-based nanolipids markedly reduced plasma LDL-cholesterol levels by 40%, unlike many other apoA-I mimetic peptides, and were substantially atheroprotective. Surprisingly, these nanoparticles were also effective when administered orally at a dose of 75 mg/kg, despite the peptide construct being composed of l-amino acids and being undetectable in the plasma. The orally administered nanoparticles reduced whole aorta lesion areas by 55% and aortic sinus lesion volumes by 71%. Reductions in plasma cholesterol were due to the loss of non-HDL lipoproteins, while plasma HDL-cholesterol levels were increased. At a 10-fold lower oral dose, the nanoparticles were marginally effective in reducing atherosclerotic lesions. Intriguingly, analogous results were obtained with nanolipids of the corresponding monomeric peptide. These nanolipid formulations provide an avenue for developing orally efficacious therapeutic agents to manage atherosclerosis.

Bone marrow-derived HL mitigates bone marrow-derived CETP-mediated decreases in HDL in mice globally deficient in HL and the LDLr.

The objective of this study was to determine the combined effects of HL and cholesteryl ester transfer protein (CETP), derived exclusively from bone marrow (BM), on plasma lipids and atherosclerosis in high-fat-fed, atherosclerosis-prone mice. We transferred BM expressing these proteins into male and female double-knockout HL-deficient, LDL receptor-deficient mice (HL(-/-)LDLr(-/-)). Four BM chimeras were generated, where BM-derived cells expressed 1) HL but not CETP, 2) CETP and HL, 3) CETP but not HL, or 4) neither CETP nor HL. After high-fat feeding, plasma HDL-cholesterol (HDL-C) was decreased in mice with BM expressing CETP but not HL (17 ± 4 and 19 ± 3 mg/dl, female and male mice, respectively) compared with mice with BM expressing neither CETP nor HL (87 ± 3 and 95 ± 4 mg/dl, female and male mice, respectively, P < 0.001 for both sexes). In female mice, the presence of BM-derived HL mitigated this CETP-mediated decrease in HDL-C. BM-derived CETP decreased the cholesterol component of HDL particles and increased plasma cholesterol. BM-derived HL mitigated these effects of CETP. Atherosclerosis was not significantly different between BM chimeras. These results suggest that BM-derived HL mitigates the HDL-lowering, HDL-modulating, and cholesterol-raising effects of BM-derived CETP and warrant further studies to characterize the functional properties of these protein interactions.

The LPS2 mutation in TRIF is atheroprotective in hyperlipidemic low density lipoprotein receptor knockout mice.

Signaling through MyD88, an adaptor utilized by all TLRs except TLR3, is pro-atherogenic; however, it is unknown whether signaling through TIR-domain-containing adaptor-inducing interferon-ß (TRIF), an adaptor used only by TLRs 3 and 4, is relevant to atherosclerosis. We determined that the TRIF(Lps2) lack-of-function mutation was atheroprotective in hyperlipidemic low density lipoprotein (LDL) receptor knockout (LDLr(-/-)) mice. LDLr(-/-) mice were crossed with either TRIF(Lps2) or TLR3 knockout mice. After feeding an atherogenic diet for 10-15 wks, atherosclerotic lesions in the heart sinus and aorta were quantitated. LDLr(-/-) mice with TRIF(Lps2) were significantly protected from atherosclerosis. TRIF(Lps2) led to a reduction in cytokines secreted from peritoneal macrophages (M) in response to hyperlipidemia. Moreover, heart sinus valves from hyperlipidemic LDLr(-/-) TRIF(Lps2) mice had significantly fewer lesional M. However, LDLr(-/-) mice deficient in TLR3 showed some enhancement of disease. Collectively, these data suggest that hyperlipidemia resulting in endogenous activation of the TRIF signaling pathway from TLR4 leads to pro-atherogenic events.

Atherosclerosis induced by endogenous and exogenous toll-like receptor (TLR)1 or TLR6 agonists.

Atherosclerosis is a chronic inflammatory vascular disease. Toll-like receptors (TLRs) are major initiators of inflammation. TLR2 promotes atherosclerosis in LDL receptor (LDLr)-deficient mice fed a high-fat diet (HFD). TLR2 forms heterodimers with TLR1 or TLR6 to enable inflammatory responses in the presence of distinct ligands. Here we asked whether TLR1 and/or TLR6 are required. We studied atherosclerotic disease using either TLR1- or TLR6-deficient mice. Deficiency of TLR1 or TLR6 did not diminish HFD-driven disease. When HFD-fed LDLr-deficient mice were challenged with Pam3 or MALP2, specific exogenous ligands of TLR2/1 or TLR2/6, respectively, atherosclerotic lesions developed with remarkable intensity in the abdominal segment of the descending aorta. In contrast to atherosclerosis induced by the endogenous agonists, these lesions were diminished by deficiency of either TLR1 or TLR6. The endogenous ligand(s) that arise from consumption of a HFD and promote disease via TLR2 are unknown. Either TLR1 or TLR6 are redundant for this endogenous ligand detection, or they are both irrelevant to endogenous ligand detection. However, the exogenous ligands Pam3 and MALP2 promote severe abdominal atherosclerosis in the descending aorta that is dependent on TLR1 and TLR6, respectively.

Reduced cholesterol and triglycerides in mice with a mutation in Mia2, a liver protein that localizes to ER exit sites.

Through forward genetic screening in the mouse, a recessive mutation (couch potato, cpto) has been discovered that dramatically reduces plasma cholesterol levels across all lipoprotein classes. The cpto mutation altered a highly conserved residue in the Src homology domain 3 (SH3) domain of the Mia2 protein. Full-length hepatic Mia2 structurally and functionally resembled the related Mia3 protein. Mia2 localized to endoplasmic reticulum (ER) exit sites, suggesting a role in guiding proteins from the ER to the Golgi. Similarly to the Mia3 protein, Mia2's cytosolic C terminus interacted directly with COPII proteins Sec23 and Sec24, whereas its lumenal SH3 domain may facilitate interactions with secretory cargo. Fractionation of plasma revealed that Mia2(cpto/cpto) mice had lower circulating VLDL, LDL, HDL, and triglycerides. Mia2 is thus a novel, hepatic, ER-to-Golgi trafficking protein that regulates cholesterol metabolism.

Nonenzymatic glycation impairs the antiinflammatory properties of apolipoprotein A-I.

OBJECTIVE: The goal of this study was to investigate the effects of nonenzymatic glycation on the antiinflammatory properties of apolipoprotein (apo) A-I. METHODS AND RESULTS: Rabbits were infused with saline, lipid-free apoA-I from normal subjects (apoA-I(N)), lipid-free apoA-I nonenzymatically glycated by incubation with methylglyoxal (apoA-I(Glyc in vitro)), nonenzymatically glycated lipid-free apoA-I from subjects with diabetes (apoA-I(Glyc in vivo)), discoidal reconstituted high-density lipoproteins (rHDL) containing phosphatidylcholine and apoA-I(N), (A-I(N))rHDL, or apoA-I(Glyc in vitro), (A-I(Glyc in vitro))rHDL. At 24 hours postinfusion, acute vascular inflammation was induced by inserting a nonocclusive, periarterial carotid collar. The animals were euthanized 24 hours after the insertion of the collar. The collars caused intima/media neutrophil infiltration and increased endothelial expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). ApoA-I(N) infusion decreased neutrophil infiltration and VCAM-1 and ICAM-1 expression by 89%, 90%, and 66%, respectively. The apoA-I(Glyc in vitro) infusion decreased neutrophil infiltration by 53% but did not reduce VCAM-1 or ICAM-1 expression. ApoA-I(Glyc in vivo) did not inhibit neutrophil infiltration or adhesion molecule expression. (A-I(Glyc in vitro))rHDL also inhibited vascular inflammation less effectively than (A-I(N))rHDL. The reduced antiinflammatory properties of nonenzymatically glycated apoA-I were attributed to a reduced ability to inhibit nuclear factor-kappaB activation and reactive oxygen species formation. CONCLUSIONS: Nonenzymatic glycation impairs the antiinflammatory properties of apoA-I.

Macrophage PLTP is atheroprotective in LDLr-deficient mice with systemic PLTP deficiency.

Systemic phospholipid transfer protein (PLTP) is a recognized risk factor for coronary heart disease. In apolipoprotein E-deficient mice, systemic PLTP deficiency is atheroprotective, whereas PLTP overexpression is proatherogenic. As expected, we also observed significantly smaller lesions (P < 0.0001) in hypercholesterolemic double mutant low density lipoprotein receptor-deficient (LDLr(-/-)) PLTP-deficient (PLTP(-/-)) mice compared with LDLr(-/-) mice expressing systemic PLTP. To assess the specific contribution of only macrophage-derived PLTP to atherosclerosis progression, bone marrow transplantation was performed in LDLr(-/-) mice that also lacked systemic PLTP. Groups of double mutant PLTP(-/-)LDLr(-/-) mice were irradiated with 1,000 rad and injected with bone marrow (BM) cells collected from either PLTP(-/-) or wild-type mice. When fed a high-fat diet, BM cell expression of PLTP decreased plasma cholesterol of PLTP(-/-)LDLr(-/-) mice from 878 +/- 220 to 617 +/- 183 mg/dl and increased HDL cholesterol levels from 54 +/- 11 to 117 +/- 19 mg/dl. This decreased total plasma cholesterol and increased HDL cholesterol contributed to the significantly smaller atherosclerotic lesions in both aortas and heart sinus valves observed in these mice. Thus, unlike total systemic PLTP, locally produced macrophage-derived PLTP beneficially alters lipoprotein metabolism and reduces lesion progression in hyperlipidemic mice.

Atheroprotective potential of macrophage-derived phospholipid transfer protein in low-density lipoprotein receptor-deficient mice is overcome by apolipoprotein AI overexpression.

OBJECTIVE: Using bone marrow transplantation, we assessed the impact of macrophage-derived phospholipid transfer protein (PLTP) on lesion development in hypercholesterolemic mice that expressed either normal levels of mouse apolipoprotein AI (apoAI) or elevated levels of only human apoAI. METHODS AND RESULTS: Bone marrow transplantations were performed in low-density lipoprotein receptor-deficient mice (LDLr-/-) that expressed either normal levels of mouse apoAI (msapoAI) or high levels of only human apoAI (msapoAI-/-, LDLr-/-, huapoAITg). Mice were lethally irradiated, reconstituted with either PLTP-expressing or PLTP-deficient bone marrow cells, and fed a high-fat diet over 16 weeks. Macrophage PLTP deficiency increased atherosclerosis in LDLr-/- mice with minimal changes in total plasma cholesterol levels. In contrast, the extent of atherosclerosis in msapoAI-/-, LDLr-/-, huapoAITg mice was not significantly different between groups that had received PLTP-/- or PLTP+/+ bone marrow. In vitro studies indicated that PLTP deficiency led to a significant decrease in alpha-tocopherol content and increased oxidative stress in bone marrow cells. CONCLUSIONS: Our observations suggest an atheroprotective role of macrophage-derived PLTP in mice with normal apoAI plasma levels. The atheroprotective properties of macrophage-derived PLTP were not observable in the presence of elevated plasma concentrations of apoAI.

Participation of macrophages in atherosclerotic lesion morphology in LDLr-/- mice.

Lystbeige (beige) mice crossed with LDL receptor-deficient (LDLr-/-) mice had a distinct atherosclerotic lesion morphology that was not observed in LDLr-/- mice. This morphology is often associated with a stable plaque phenotype. We hypothesized that macrophage expression of the beige mutation accounted for this distinct morphology. Cultured bone marrow-derived macrophages from LDLr-/- and beige,LDLr-/- mice were compared for their ability to accumulate cholesterol, efflux cholesterol, migrate in response to chemotactic stimuli through Matrigel-coated membranes, and express matrix metalloproteinase 9 (MMP9). No differences in cholesterol metabolism were identified. Beige,LDLr-/- macrophage invasion in vitro appeared to be less than LDLr-/- macrophage invasion but did not achieve significance. Nevertheless, tumor necrosis factor-alpha-induced MMP9 expression, secretion, and enzymatic activity of beige,LDLr-/- macrophages were all significantly decreased compared with those of LDLr-/- macrophages (P < 0.05). For in vivo analyses of macrophage function, bone marrow transplantation (BMT) studies were performed. LDLr-/- mice and beige,LDLr-/- mice were irradiated and reconstituted with wild-type or beige bone marrow from mice expressing green fluorescent protein (GFP). Identification of GFP cells provided for direct identification of donor-derived cells within lesions. Only expression of the beige mutation in the BMT recipients altered the macrophage location and collagen content of the lesions. These results suggested that impaired macrophage function by itself did not account for the stable lesion morphology of beige,LDLr-/- double-mutant mice.

Apolipoprotein A-II inhibits high density lipoprotein remodeling and lipid-poor apolipoprotein A-I formation.

The high density lipoproteins (HDL) in human plasma are classified on the basis of apolipoprotein composition into those containing apolipoprotein (apo) A-I but not apoA-II, (A-I)HDL, and those containing both apoA-I and apoA-II, (A-I/A-II)HDL. Cholesteryl ester transfer protein (CETP) transfers core lipids between HDL and other lipoproteins. It also remodels (A-I)HDL into large and small particles in a process that generates lipid-poor, pre-beta-migrating apoA-I. Lipid-poor apoA-I is the initial acceptor of cellular cholesterol and phospholipids in reverse cholesterol transport. The aim of this study is to determine whether lipid-poor apoA-I is also formed when (A-I/A-II)rHDL are remodeled by CETP. Spherical reconstituted HDL that were identical in size had comparable lipid/apolipoprotein ratios and either contained apoA-I only, (A-I)rHDL, or (A-I/A-II)rHDL were incubated for 0-24 h with CETP and Intralipid(R). At 6 h, the apoA-I content of the (A-I)rHDL had decreased by 25% and there was a concomitant formation of lipid-poor apoA-I. By 24 h, all of the (A-I)rHDL were remodeled into large and small particles. CETP remodeled approximately 32% (A-I/A-II)rHDL into small but not large particles. Lipid-poor apoA-I did not dissociate from the (A-I/A-II)rHDL. The reasons for these differences were investigated. The binding of monoclonal antibodies to three epitopes in the C-terminal domain of apoA-I was decreased in (A-I/A-II)rHDL compared with (A-I)rHDL. When the (A-I/A-II)rHDL were incubated with Gdn-HCl at pH 8.0, the apoA-I unfolded by 15% compared with 100% for the apoA-I in (A-I)rHDL. When these incubations were repeated at pH 4.0 and 2.0, the apoA-I in the (A-I)rHDL and the (A-I/A-II)rHDL unfolded completely. These results are consistent with salt bridges between apoA-II and the C-terminal domain of apoA-I, enhancing the stability of apoA-I in (A-I/A-II)rHDL and possibly contributing to the reduced remodeling and absence of lipid poor apoA-I in the (A-I/A-II)rHDL incubations.

Evidence that phospholipids play a key role in pre-beta apoA-I formation and high-density lipoprotein remodeling.

The initial plasma acceptor of unesterified cholesterol and phospholipids from peripheral cells has been identified as pre-beta migrating, lipid-free, or lipid-poor apolipoprotein (apo) A-I (pre-beta apoA-I). Pre-beta apoA-I is formed when plasma factors, such as cholesteryl ester transfer protein (CETP), remodel high-density lipoproteins (HDL). The aim of this study is to determine how phospholipids influence pre-beta apoA-I formation during the CETP-mediated remodeling of HDL. Reconstituted HDL (rHDL) containing either 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC), 1-palmitoyl-2-linoleoyl phosphatidylcholine (PLPC), 1-palmitoyl-2-arachidonyl phosphatidylcholine (PAPC), or 1-palmitoyl-2-docosahexanoyl phosphatidylcholine (PDPC) as the only phospholipid were prepared. The rHDL were comparable in size and core lipid/protein molar ratio and contained only cholesteryl esters in their core and apoA-I as the sole apolipoprotein. The (POPC)rHDL, (PLPC)rHDL, (PAPC)rHDL, and (PDPC)rHDL were respectively incubated for 0-24 h with CETP and microemulsions containing triolein and either POPC, PLPC, PAPC, or PDPC. The rate at which the rHDL were depleted of core lipids and remodeled to small particles varied widely with (POPC)rHDL < (PLPC)rHDL < (PDPC)rHDL approximately (PAPC)rHDL. Pre-beta apoA-I was not formed in the (POPC)rHDL incubations. Pre-beta apoA-I was apparent by 24 h in the (PLPC)rHDL incubations and by 12 h in the (PAPC)rHDL and (PDPC)rHDL incubations. The enhanced formation of pre-beta apoA-I in the (PAPC)rHDL and (PDPC)rHDL incubations reflected the increased core lipid depletion of the particles combined with the destabilization and progressive exclusion of apoA-I from the particle surface. In conclusion, these results show that phospholipids play a key role in the CETP-mediated remodeling of rHDL and pre-beta apoA-I formation.