Lecithin cholesterol acyl transferase (LCAT) catalyzes the conversion of unesterified, or free cholesterol (FC), to cholesteryl ester (CE), which moves from the surface of HDL into the neutral lipid core. As this iterative process continues, nascent lipid-poor HDL is converted to a series of larger, spherical cholesterol ester enriched HDL particles that can be cleared by the liver in a process that has been termed reverse cholesterol transport (RCT). We conducted a randomized, placebo controlled, cross-over study in 5 volunteers with ASCVD, to examine the effects of an acute increase of recombinant human (rh) LCAT via intravenous administration on the in vivo metabolism of HDL apolipoprotein (APO)A1 and APOA2, and the APOB100-lipoproteins, very low density (VLDL), intermediate density (IDL), and low density (LDL) lipoproteins. As expected, rhLCAT treatment significantly increased HDL CE content. This change did not affect the fractional clearance or production rates of HDL-APOA1 and HDL-APOA2. The metabolism of APOB100-lipoproteins was likewise unaffected. Our results suggest that an acute increase in LCAT activity drives greater flux of CE through the RCT pathway without altering the clearance and production of the main HDL proteins and without affecting the metabolism of APOB100-lipoproteins. Long-term elevations of LCAT might, therefore, have beneficial effects on total body cholesterol balance and atherogenesis.
Lecithin-cholesterol acyltransferase (LCAT) mediates the esterification of free cholesterol (FC) to cholesteryl ester (CE) in HDL and, therefore, plays a critical role in reverse cholesterol transport. MEDI6012, a recombinant human LCAT (rhLCAT) increases HDL-C. Our goal was to interrogate the pathways regulating the increase in HDL-C and effects of rhLCAT on apoB metabolism. Methods: We enrolled five subjects (4 Man, mean age 67) with stable ASCVD into a Phase II, placebo controlled, double-blind, randomized cross-over study to determine the effects of two IV doses of MEDI6012, administered 48-hrs apart, versus placebo, on plasma lipids and lipoproteins. Stable isotope kinetic studies with D2-Leu, 13C-Phe, D2-Glycerol were performed to examine the metabolism of apoB100, ApoA1, ApoA2 and triglyceride. Results: As expected two doses of IV MEDI6012 increased total cholesterol and HDL-C levels significantly (Table1). We did not observe significant changes in other measured lipids or lipoproteins. The significant increase in HDL-C was 34.9±10.3 (p=0.002) and due to an increase in the amount of CE (33±8.9 p=0.001); there was no change in free cholesterol (1.9±1.9). We found no changes in levels of sterols (i.e. Lathosterol) between the two periods. Preliminary in vivo kinetic studies of HDL metabolism in 3 subjects, showed no changes in the mean fractional clearance rate (FCR) or production rate (PR) of apoA1 between placebo (0.3±0.2pool/day, 1.3±0.5 mg/kg/day) and rhLCAT treatment (0.28±0.1pools/day, 1.3±0.3). There were no changes in ApoA2 FCR and PR after rhLCAT administration. Complete data for ApoA1, ApoA2 and ApoB100 and TG kinetics will be presented. Conclusions: In subjects with ASCVD, treatment with rhLCAT increased HDL-C mainly by increasing HDL CE; there were no changes in the FCR or PR of HDL ApoA1 or ApoA2. Together, these results suggest that rhLCAT treatment is associated with increased steady-state transport of CE by HDL.
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