Abstract 17107: Distribution of Anti-inflammatory Activity During Remodeling of High Density Lipoprotein: Studies With CSL112

Elevated levels of circulating inflammatory markers predict an unfavorable cardiovascular outcome in acute coronary syndrome patients. CSL112 is human apolipoprotein A-I (apoA-I), reconstituted with phosphatidylcholine to form HDL particles suitable for infusion. Addition of CSL112 to stimulated human whole blood ex vivo strongly reduces pro-inflammatory cytokine production. Infusion of CSL112 into human subjects or addition to human plasma ex vivo causes remodeling of endogenous HDL. Similar remodeling occurs upon incubation of CSL112 with purified HDL3 and results in accumulation of three HDL species: enlarged HDL (HDL2), a smaller, dense species (HDL3c), and lipid-poor apoA-I (pre-β1 HDL). Study aim was to determine the anti-inflammatory activity of remodeled HDL species. CSL112 was incubated with HDL3 and the products of particle remodeling were purified by ultracentrifugation. The inhibitory effects on pro-inflammatory cytokine production were examined using human peripheral blood mononuclear cells (PBMC) stimulated with phytohemagglutinin-M (PHA-M) in vitro. Lipid-poor apoA-I, HDL3c as well as parent CSL112 exerted powerful inhibitory effects on secretion of pro-inflammatory mediators (&gt; 89.2% + 4.0% inhibition of TNF-α, IL-1β, IL-6 and Mip-1β); HDL3 and HDL2 were much less effective (&lt; 54.1% + 3.9% inhibition). The extent of inhibition correlated positively with induction of the transcription repressor ATF3, a negative regulator of pro-inflammatory cytokine production, with lipid-poor apoA-I and HDL3c inducing higher protein levels of ATF3 in PHA-stimulated PBMC compared to control medium, HDL3 or HDL2. Anti-inflammatory activity of the remodeled species also correlated with their ability to support cellular cholesterol efflux via the ABCA1 transporter: lipid-poor apoA-I and HDL3c were potent acceptors of cholesterol; HDL2 was inactive. The ability to generate HDL species with high cholesterol efflux and anti-inflammatory activity makes CSL112 a promising candidate for removing cholesterol and reducing inflammation in atherosclerotic plaque, thus reducing the high risk of early recurrent atherothrombotic events following acute MI (AMI). A Phase IIb trial (AEGIS-I; NCT02108262) of CSL112 in AMI patients is ongoing.</jats:p

The crystal structure of the platelet activator aggretin reveals a novel (alphabeta)2 dimeric structure

Aggretin is a C-type lectin purified from Calloselasma rhodostoma snake venom. It is a potent activator of platelets, resulting in a collagen-like response by binding and clustering platelet receptor CLEC-2. We present here the crystal structure of aggretin at 1.7 A which reveals a unique tetrameric quaternary structure. The two alphabeta heterodimers are arranged through 2-fold rotational symmetry, resulting in an antiparallel side-by-side arrangement. Aggretin thus presents two ligand binding sites on one surface and can therefore cluster ligands in a manner reminiscent of convulxin and flavocetin. To examine the molecular basis of the interaction with CLEC-2, we used a molecular modeling approach of docking the aggretin alphabeta structure with the CLEC-2 N-terminal domain (CLEC-2N). This model positions the CLEC-2N structure face down in the "saddle"-shaped binding site which lies between the aggretin alpha and beta lectin-like domains. A 2-fold rotation of this complex to generate the aggretin tetramer reveals dimer contacts for CLEC-2N which bring the N- and C-termini into the proximity of each other, and a series of contacts involving two interlocking beta-strands close to the N-terminus are described. A comparison with homologous lectin-like domains from the immunoreceptor family reveals a similar but not identical dimerization mode, suggesting this structure may represent the clustered form of CLEC-2 capable of signaling across the platelet membrane

Abstract 17135: Distribution of Anti-oxidative Activity During Remodeling of High Density Lipoprotein: Studies With CSL112

We have previously shown that reconstituted HDL has the ability to inactivate phospholipid hydroperoxides (PLOOH) in oxidized LDL by virtue of redox-active Met residues present in apolipoprotein A-I (apoA-I), with the level of activity being proportional to the amount of apoA-I protein added. CSL112 is human apoA-I, reconstituted with phosphatidylcholine to form HDL particles suitable for infusion. Infusing CSL112 into human subjects or adding it to human plasma ex vivo, causes remodeling of endogenous HDL. Similar remodeling occurs upon incubation of CSL112 with purified HDL3 and results in accumulation of three HDL species: enlarged HDL (HDL2), a smaller, dense species (HDL3c-like), and lipid-poor apoA-I (pre-β1 HDL). Here we examine the distribution of anti-oxidant activity upon remodeling of native plasma HDL induced by CSL112. We incubated CSL112 with human plasma HDL3, isolated the three populations of remodeled HDL particles by density gradient ultracentrifugation and compared (on a total protein basis) their ability to inactivate PLOOH derived from oxidized LDL as well as their apoA-I content of unoxidized and oxidized Met residues. Both parent CSL112 and HDL3 displayed anti-oxidative activity, inactivating 22±4 and 47±9% of PLOOH, respectively (n=4). Upon remodeling, this activity was mainly found in enlarged HDL2 and smaller HDL3c-like species (PLOOH inactivation, 46±3 and 47±9%, respectively) and was low (23±17%) in lipid-poor apoA-I. In parallel, apoA-I Met residues were oxidized in HDL; oxidation was several fold lower in the lipid-poor apoA-I (12±3%) compared to larger species (62±1% and 69±2% in HDL2 and HDL3c-like particles), consistent with a limited accessibility of apoA-I Met to PLOOH molecules in the lipid-poor particles. These studies further confirm the unequal distribution of HDL function among HDL subclasses and emphasize the important role of HDL remodeling in the production and maintenance of HDL functionality. The antioxidant properties of CSL112 add to its potential as a promising therapy for reducing the high risk of early recurrent atherothrombotic events following acute MI (AMI). A Phase IIb trial (AEGIS-I; NCT02108262) of CSL112 in AMI patients is ongoing.</jats:p

The Crystal Structure of the Platelet Activator Aggretin Reveals a Novel (αβ)₂ Dimeric Structure

Aggretin is a C-type lectin purified from Calloselasma rhodostoma snake venom. It is a potent activator of platelets, resulting in a collagen-like response by binding and clustering platelet receptor CLEC-2. We present here the crystal structure of aggretin at 1.7 Å which reveals a unique tetrameric quaternary structure. The two αβ heterodimers are arranged through 2-fold rotational symmetry, resulting in an antiparallel side-by-side arrangement. Aggretin thus presents two ligand binding sites on one surface and can therefore cluster ligands in a manner reminiscent of convulxin and flavocetin. To examine the molecular basis of the interaction with CLEC-2, we used a molecular modeling approach of docking the aggretin αβ structure with the CLEC-2 N-terminal domain (CLEC-2N). This model positions the CLEC-2N structure face down in the “saddle”-shaped binding site which lies between the aggretin α and β lectin-like domains. A 2-fold rotation of this complex to generate the aggretin tetramer reveals dimer contacts for CLEC-2N which bring the N- and C-termini into the proximity of each other, and a series of contacts involving two interlocking β-strands close to the N-terminus are described. A comparison with homologous lectin-like domains from the immunoreceptor family reveals a similar but not identical dimerization mode, suggesting this structure may represent the clustered form of CLEC-2 capable of signaling across the platelet membrane

Apo AI Nanoparticles Delivered Post Myocardial Infarction Moderate Inflammation

Rationale: Decades of research have examined immune-modulatory strategies to protect the heart after an acute myocardial infarction and prevent progression to heart failure but have failed to translate to clinical benefit. Objective: To determine anti-inflammatory actions of n-apo AI (Apo AI nanoparticles) that contribute to cardiac tissue recovery after myocardial infarction. Methods and Results: Using a preclinical mouse model of myocardial infarction, we demonstrate that a single intravenous bolus of n-apo AI (CSL111, 80 mg/kg) delivered immediately after reperfusion reduced the systemic and cardiac inflammatory response. N-apo AI treatment lowered the number of circulating leukocytes by 30±7% and their recruitment into the ischemic heart by 25±10% (all P &lt;5.0×10 −2 ). This was associated with a reduction in plasma levels of the clinical biomarker of cardiac injury, cardiac troponin-I, by 52±17% ( P =1.01×10 −2 ). N-apo AI reduced the cardiac expression of chemokines that attract neutrophils and monocytes by 60% to 80% and lowered surface expression of integrin CD11b on monocytes by 20±5% (all P &lt;5.0×10 −2 ). Fluorescently labeled n-apo AI entered the infarct and peri-infarct regions and colocalized with cardiomyocytes undergoing apoptosis and with leukocytes. We further demonstrate that n-apo AI binds to neutrophils and monocytes, with preferential binding to the proinflammatory monocyte subtype and partially via SR-BI (scavenger receptor BI). In patients with type 2 diabetes, we also observed that intravenous infusion of the same n-apo AI (CSL111, 80 mg/kg) similarly reduced the level of circulating leukocytes by 12±5% (all P &lt;5.0×10 −2 ). Conclusions: A single intravenous bolus of n-apo AI delivered immediately post–myocardial infarction reduced the systemic and cardiac inflammatory response through direct actions on both the ischemic myocardium and leukocytes. These data highlight the anti-inflammatory effects of n-apo AI and provide preclinical support for investigation of its use for management of acute coronary syndromes in the setting of primary percutaneous coronary interventions. </jats:sec