Abstract 128: Recombinant Lecithin Cholesterol Acyltransferase Generates Mature High Density Lipoprotein with Increased Capacity to Efflux Cholesterol via ABCG1 in Cynomolgus Monkeys

Introduction: Lecithin cholesterol acyltransferase (LCAT) esterifies free cholesterol to cholesteryl esters on the HDL particle and is considered a key component of reverse cholesterol transport. We have developed a recombinant human LCAT fusion protein with high LCAT activity and characterized the effects of this molecule on lipoprotein metabolism and cholesterol efflux in cynomolgus monkeys. Methods: Cynomolgus monkeys received a single injection of rhLCAT at 0, 0.5, 1, or 5 mpk. Blood samples were drawn for analysis at pre-dose and up to 5 days after administration. HDL-C and apoAI were measured using standard clinical analyzers, apoE was measured by ELISA, and rhLCAT was measured by MSD immunoassay. ApoAI containing HDL subfractions were determined by two-dimensional non-denaturing gradient gel electrophoresis as described in the literature. Cholesterol efflux was measured ex vivo from ABCA1, ABCG1, or SRB1 transfected BHK cells, or J774 mouse macrophages using apoB depleted serum. Results: After administration, serum rhLCAT concentrations increased dose proportionately. HDL-C increased rapidly, beginning within the first 6 hours after dosing, and was dose dependent with maximum increases of 87% observed in the 1 and 5 mpk dose groups. ApoAI concentrations increased by as much as 15% and 21% in the 0.5 and 1 mpk groups, respectively, but decreased in the 5 mpk group by as much as 23%. The ratio of HDL-C to apoAI increased dose dependently indicating the formation of HDL particles containing increasingly more cholesterol. 2D gels confirmed the formation of large, primarily α-1, HDL particles. ApoE on HDL particles increased dose dependently with large increases observed following the 1 mpk (169%) and 5 mpk (910%) doses. Changes in the HDL particle were accompanied by changes in the ability of HDL to efflux cholesterol from cells. ABCG1 mediated efflux increased by as much as 21% and 24% in the 1 and 5 mpk dose groups, respectively. Conversely, efflux via ABCA1, SRB1, and from J774 cells was reduced dose dependently. Conclusions: The administration of rhLCAT in cynos resulted in the formation of large HDL particles that were enriched in cholesterol and ApoE. These larger particles showed increased capacity to efflux cholesterol via the ABCG1 transporter.