Kuang-Yuh Chyu

Inhibition of Atherosclerosis in ApoE-Null Mice by Immunization with ApoB-100 Peptide Sequences

Objective—LDL oxidation is believed to play an important role in the development of atherosclerosis, and oxidized LDL particles have been shown to become targets for the immune system. Immunization of animals with oxidized LDL results in reduction of atherosclerosis, suggesting an atheroprotective effect of this immune response. Methods and Results—Using a polypeptide library covering the complete sequence of apoB-100, a large number of native and malondialdehyde-modified peptide sequences in apoB-100 that are recognized by antibodies in human plasma were identified. We report here that immunization with apoB-100 peptide sequences, against which high levels of IgG and IgM antibodies are present in healthy human controls, reduce atherosclerosis in apoE-null mice by about 60%. Immunizations with these peptides were also found to increase the collagen content of subvalvular lesions. Conclusions—These studies have identified peptide sequences in apoB-100 that induce immune responses, which inhibits atherosclerosis. This suggests a way of developing an immunization therapy for coronary heart disease.

Differential Effects of Green Tea–Derived Catechin on Developing Versus Established Atherosclerosis in Apolipoprotein E–Null Mice

Background—Oxidative stress has been implicated in vascular injury and atherogenesis, and antioxidant treatment has shown favorable results in preclinical studies. Despite this, antioxidant therapy has failed to show benefit in clinical trials. Failure of antioxidants in clinical trials may be partly because such therapy is started after atherosclerosis is already well established, whereas the benefits in animal models may be results from early initiation of antioxidants while atherosclerosis is still evolving. Methods and Results—To test this hypothesis, we evaluated the effect of epigallocatechin gallate (EGCG), the main antioxidant derived from green tea, on evolving and established atherosclerotic lesions in hypercholesterolemic apolipoprotein E–null mice. Established native aortic atherosclerotic lesions and evolving atherosclerotic lesions produced by periadventitial cuff injury to carotid arteries were assessed in mice after 21 and 42 days of treatment with daily intraperitoneal injections of EGCG (10 mg/kg) or PBS. EGCG treatment resulted in an increase in the antioxidant capacity in local vascular tissue and systemic circulation and reduced vascular smooth muscle cell proliferation and redox-sensitive gene activation in vitro. EGCG reduced cuff-induced evolving atherosclerotic plaque size at 21 and 42 days by 55% and 73%, respectively, compared with PBS treatment (P <0.05). Conversely, EGCG had no effect on established lesions in the aortic sinuses or the rest of the aorta. Conclusions—Our data suggest that antioxidant EGCG differentially reduces evolving atherosclerotic lesions without influencing established atherosclerosis in the apolipoprotein E–null mice.

Identification of Immune Responses Against Aldehyde-Modified Peptide Sequences in ApoB Associated With Cardiovascular Disease

Atherosclerosis develops as a result of a chronic arterial inflammation and intimal fibrosis. The disease represents in many respects a vascular repair process activated in response to injury caused by toxic breakdown products of aggregated and oxidized lipoproteins. The initial response of the artery involves expression of adhesion molecules and recruitment of leukocytes. Degenerated lipoproteins are removed from the extracellular space by macrophages. If lipoproteins continue to accumulate, the inflammatory process becomes chronic and cytokines stimulate smooth muscle to migrate into the intima. These cells proliferate and form an atherosclerotic plaque. Plaque cell death and inflammation in response to oxidized lipids and other toxic factors may cause plaques to rupture.Objective—Atherosclerosis is associated with an immune response against oxidized LDL, which modulates the progression of the disease process. Methods and Results—Using a library of polypeptides covering the complete sequence of apoB-100, the only major protein of LDL, we have identified over 100 different human antibodies reacting against aldehyde-modified apoB-100 sequences. IgM antibody titer levels decreased with age and were associated with the intima-media thickness of the carotid artery in subjects younger than 60 years. There were also inverse associations between IgM levels and oxidized LDL in plasma. In prospective clinical studies, antibody levels against several aldehyde-modified apoB-100 sites were associated with cardiovascular disease in this age group. Whether this immune response is adaptive (protective) or maladaptive (causal) in atherosclerosis requires further investigation. Conclusions—We have characterized a large number of epitopes within the apoB-100 component of oxidized LDL that provoke an immune response in humans. These findings will make it possible to study the role of immune responses against specific sites in oxidized LDL and to determine whether these immune responses influence the risk for future cardiac events.

Smoking Increases Tissue Factor Expression in Atherosclerotic Plaques Implications for Plaque Thrombogenicity

BACKGROUND Smoking increases the risk of atherothrombotic events. To determine whether smoking influences plaque thrombogenicity, we examined the effect of cigarette smoking and aspirin use on tissue factor (TF) expression in atherosclerotic plaques. METHODS AND RESULTS A total of 23 apoE-/- mice were exposed to cigarette smoke with (n=9) or without (n=14) aspirin treatment. Eleven mice who were exposed to filtered room air served as controls. Aortic root plaques of mice exposed to smoke had higher immunoreactivity for TF (14+/-4% versus 6.4+/-3%; P=0.0005), vascular cell adhesion molecule-1 (15+/-4% versus 5+/-2%; P=0.002), and macrophages (16+/-5% versus 6+/-2%; P=0.002) compared with nonsmoking controls. Aspirin treatment attenuated smoking-induced changes in plaque composition. In human plaques obtained by carotid endarterectomy, TF immunoreactivity (8+/-5% versus 2+/-2%; P=0.0002) and activity (P=0. 03) were higher in the plaques from smokers (n=28) than those from nonsmokers (n=28). Aspirin use was associated with reduced TF expression in smokers (9+/-8% versus 3+/-4%; P=0.0017). CONCLUSIONS Our results suggest increased plaque TF expression and thrombogenicity as a novel mechanism for the increased risk of atherothrombotic events in smokers. Treatment with aspirin may reduce TF expression.

Differential Effects of Apolipoprotein A-I–Mimetic Peptide on Evolving and Established Atherosclerosis in Apolipoprotein E-Null Mice

Background—Apolipoprotein (apo) A-I and apoA-I–mimetic peptides showed promise to prevent atherosclerosis development. Using a bypassed vein graft model in apoE-null mice, we evaluated the effects of oral or intraperitoneal administration of an apoA-I–mimetic peptide on evolving atherosclerotic lesions in the vein graft and compared such effects on the established atherosclerotic lesions in aortic sinus in the same mice. Methods and Results—We used apoE-null mice in which a segment of inferior vena cava was grafted into the right carotid artery at 16 weeks of age. Native aortic atherosclerotic lesions (established atherosclerosis) and vein-graft atherosclerotic lesions (evolving atherosclerosis) were assessed 4 weeks after daily oral (0.3 mg/mL) or intraperitoneal (50 &mgr;g in 200 &mgr;L saline) administration of an apoA-I–mimetic peptide, D4F. Mice receiving saline or water without D4F served as controls. Both oral and intraperitoneal administration of D4F reduced vein-graft atherosclerotic (evolving lesions) plaque size by 43% and 42%, plaque lipid by 70% and 49%, and macrophage immunoreactivity by 63% and 62%, respectively, compared with controls. In contrast, D4F had no effect on the native aortic sinus atherosclerotic lesions (established lesions). Conclusions—Oral and intraperitoneal administration of the apoA-I–mimetic peptide D4F significantly reduced rapidly evolving atherosclerotic lesions in vein grafts but not established atherosclerotic lesions in aortic sinus. These observations suggest that the type of atherosclerotic lesions and the time of initiation during the course of lesion evolution modulate the beneficial effects of apoA-I–mimetic peptides on atherosclerosis.

Decreased neointimal thickening after arterial wall injury in inducible nitric oxide synthase knockout mice.

Mechanical injury in vivo results in the expression of the inducible form of nitric oxide synthase (iNOS) in vascular smooth muscle cells. However, the role of iNOS in modulating neointima formation after arterial wall injury is not clear. To determine whether the induction of iNOS gene expression promotes or attenuates the neointimal response to injury, we used a murine model of perivascular injury induced by placing a periadventitial collar around the carotid arteries in both wild-type and iNOS knockout mice (iNOS-KO mice). Periadventitial injury induced iNOS expression in the wild-type but not the iNOS-KO mice. Neointimal area and the intima/media ratio were significantly less in the iNOS-KO mice compared with the wild-type mice at 21 days. Injury-induced proliferation of medial cells and vascular cell adhesion molecule-1 expression were also attenuated in iNOS-KO mice compared with wild-type mice. The induction of iNOS and the activation of the nuclear factor-kappaB-mediated pathway were also demonstrated in an in vitro injury model. We conclude that mechanical injury in vivo and in vitro induces iNOS expression and that lack of iNOS expression attenuates neointima formation after perivascular arterial injury. Taken together, these findings suggest that iNOS expression after vascular injury may promote neointima formation.

Atheroprotective immunization with MDA-modified apo B-100 peptide sequences is associated with activation of Th2 specific antibody expression.

Objective: The objective of this study was to evaluate if immunization with MDA-modified human apo B-100 fragments is associated with a shift in the Th1/Th2 balance. Methods and Results: Apo E deficient mice were immunized with one of the peptides (P45; amino acids 688–707, P74; amino acids 1123–1142 or P240; amino acids 3613–3632) at 6, 9 and 11 weeks of age and compared to controls given carrier alone. Immunization with P45 and P74 reduced atherosclerosis in the aorta of 25-week-old mice by 48% (p=0.02) and 31% (p=0.06) and macrophage content in atherosclerotic plaques by 33% (p=0.02) and 39% (p=0.02), respectively. The levels of Th2-specific IgG1 against each peptide increased more than 50-fold in response to immunization, whereas the levels of specific IgM and Th1-associated IgG2a were only marginally affected. However, there was an increase in the plaque expression of both Th1 and Th2 cytokines as assessed by real time PCR. Immunization with P240, a non-homologous peptide used as control, induced a 10-fold increase of specific IgG1 but did not influence atherosclerosis or plaque content. Conclusions: Immunization with MDA apo B-100 fragments induce a shift from Th1 to a Th2 specific oxidized LDL antibody expression, but without a concomitant downregulation of plaque IFN-γ expression.

Monoclonal Antibody Against Vascular Cell Adhesion Molecule-1 Inhibits Neointimal Formation After Periadventitial Carotid Artery Injury in Genetically Hypercholesterolemic Mice

Vascular cell adhesion molecule (VCAM)-1 is induced in smooth muscle cells after arterial injury, in which it has been implicated in the recruitment of inflammatory cells to the site of injury. To investigate the effect of hypercholesterolemia on VCAM-1 induction after injury and the role of VCAM-1 in neointimal response to injury, we injured the carotid artery of wild-type and apolipoprotein E null (KO) mice fed normal and high cholesterol chow. We demonstrate a graded response of VCAM-1 induction as well as monocyte/macrophage infiltration by immunohistochemistry 3 days after injury that correlated with increasing circulating cholesterol levels. Three weeks after injury, KO mice fed high cholesterol chow (KO HC group) had a significantly greater neointimal formation compared with wild-type and KO mice fed normal chow (P<0.05). Inhibition of VCAM-1 function in the KO HC group by monoclonal antibody treatment significantly reduced monocyte/macrophage infiltration and neointimal formation. There was reduced alpha-actin expression in KO HC mice 7 days after injury that was partially inhibited by VCAM-1 antibody treatment. Cell migration in an in vitro injury model was partially inhibited by monoclonal VCAM-1 antibody treatment. We propose an additional role for VCAM-1 in smooth muscle cell activation and neointimal formation after injury.

Elevated Troponin I Level on Admission Is Associated With Adverse Outcome of Primary Angioplasty in Acute Myocardial Infarction

BackgroundIn patients with acute myocardial infarction (AMI) undergoing thrombolytic therapy, an elevated troponin level on admission is associated with a lower reperfusion rate and a complicated clinical course. Whether an elevated troponin level on admission similarly predicts an adverse outcome in patients undergoing primary angioplasty is currently unknown and was investigated in the present study. Methods and ResultsCardiac troponin I (cTnI) was determined on admission in 110 consecutive patients with AMI associated with ST-segment elevation or left bundle branch block who underwent primary angioplasty. Fifty-four patients (49%) had an elevated cTnI (≥0.4 ng/mL) on admission. In patients with elevated cTnI, primary angioplasty was less likely to achieve TIMI 3 flow (as classified by the Thrombolysis in Myocardial Infarction trial) in univariate (76% versus 96%, P =0.03) or in multivariate (odds ratio 0.1, 95% CI 0.02 to 0.54) analysis. Patients with elevated cTnI were more likely to develop congestive heart failure (23% versus 9%, P <0.05) and death, heart failure, or shock (30% versus 9%, P =0.006). Elevated cTnI remained a significant predictor of the composite end point after controlling for other clinical data that were available early in the course, including time to presentation and angiographic results (relative risk 5.2, 95% CI 1.03 to 26.3). During a follow-up of 426±50 days, elevated admission cTnI was a predictor of cardiac mortality (11% versus 0%, P =0.012), adverse cardiac events (cardiac mortality or nonfatal reinfarction; 19% versus 5.4%, P =0.04), and adverse cardiac events plus target vessel revascularization (32% versus 14%, P =0.054). ConclusionsIn patients with ST-segment elevation AMI, an elevated cTnI on admission is associated with an increased risk of primary angioplasty failure and a more complicated clinical course.

Intramural Delivery of Recombinant Apolipoprotein A-IMilano/Phospholipid Complex (ETC-216) Inhibits In-Stent Stenosis in Porcine Coronary Arteries

Background—We have previously demonstrated vasculoprotective effects after repeated intravenous administration of recombinant apolipoprotein A-IMilano (apoA-Im)/phospholipid complex. In this study, we sought to determine the effects of local recombinant apoA-Im/1-palmitoyl,2-oleoyl phosphatidylcholine complex (ETC-216) delivered intramurally via the Infiltrator catheter on luminal narrowing in a porcine coronary artery stent overstretch injury model. Methods and Results—In twelve domestic swine (≈25 kg), two arteries each were infiltrated with 0.4 mL ETC-216 (14 mg/mL) or vehicle control immediately before deployment of GFX stents (stent:artery ratio=1.3:1). Animals were euthanized at day 28, and evaluation by QCA revealed a significant improvement in mean lumen loss index with ETC-216 treatment (21±22% versus 43±13% lumen loss;P =0.01). Histomorphometric analysis showed that ETC-216 treatment significantly reduced the intimal area (6.7±1.5 versus 5.2±1.4 mm2, −22%;P =0.02) and the stenosis index (0.76±0.15 versus 0.59±0.15;P =0.01), and increased the lumen area (2.1±1.4 versus 3.7±1.8 mm2, +76%;P =0.02). Regression analysis showed significant differences in lumen area (P =0.004), neointimal area (P =0.003), stenosis index (P =0.001), and neointimal thickness (P =0.003) adjusted for injury score in favor of ETC-216. Conclusions—A single intramural administration of ETC-216 significantly inhibited injury-induced luminal narrowing in the porcine stent overstretch model through reduction of intimal hyperplasia. These data show that local intracoronary delivery of ETC-216 may be useful to prevent restenosis after coronary stenting.