Plasma Lipoprotein Metabolism in Familial Lecithin: Cholesterol Acyltransferase Deficiency

Liver-specific overexpression of scavenger receptor BI decreases levels of very low density lipoprotein ApoB, low density lipoprotein ApoB, and high density lipoprotein in transgenic mice

Scavenger receptor BI (SR-BI) is known to mediate the selective uptake of high density lipoprotein (HDL) cholesteryl ester (CE) in liver and steroidogenic tissues. To evaluate the role of SR-BI in plasma lipoprotein metabolism, we have generated transgenic mice with liver-specific overexpression of murine SR-BI. On a chow diet SR-BI transgenic (SR-BI Tg) mice have decreased HDL-CE, apoA-I, and apoA-II levels; plasma triglycerides, low density lipoprotein (LDL) cholesterol, and very low density lipoprotein (VLDL) and LDL apoB were also decreased, compared with control mice. Turnover studies using non-degradable CE and protein labels showed markedly increased total and selective uptake of HDL-CE in the liver and increased HDL protein catabolism in both liver and kidney. To evaluate the changes in apoB further, mice were challenged with high fat, high cholesterol diets. In SR-BI Tg mice plasma apoB levels were only 3-15% of control levels, and the dietary increase in VLDL and LDL apoB was virtually abolished. These studies show that steady state overexpression of hepatic SR-BI reduces HDL levels and increases reverse cholesterol transport. They also indicate that SR-BI can play a role in the metabolism of apoB-containing lipoproteins. The dual effects of increased reverse cholesterol transport and lowering of apoB-containing lipoproteins that result from hepatic SR-BI overexpression could have anti-atherogenic consequences.

A 31P nuclear magnetic resonance investigation of acyl group transfer from phosphatidylcholine to yield lysophosphatidylcholine in human plasma

31P nuclear magnetic resonance (NMR) spectroscopy was used to measure the rate of acyl transfer from phosphatidylcholine (lecithin, PC) in whole plasma and in high density lipoprotein (HDL). Spectral deconvolution was used to resolve overlapping resonances in the 31P NMR spectra of the phospholipids. Mean values of the acyl group transfer rates from PC in plasma and HDL were 36 mumol L-1h-1 and 19 mumol L-1h-1, respectively. The reciprocal nature of the decrease in the spectral peak intensities of PC, compared to the increase in the intensities of the lysolecithin (lysoPC) peaks, suggested a substrate/product relationship consistent with the action of lecithin:cholesterol acyltransferase (LCAT), the enzyme responsible for the esterification of free cholesterol in plasma. LCAT involvement was confirmed by measuring the cholesterol esterification rate based on the 13C NMR spectra obtained on lipid extracts from plasma that had been incubated at 37 degrees C. Within experimental error, the rate of lysoPC formation in plasma was shown to be equal to that of cholesteryl ester formation.

Lecithin-cholesterol acyltransferase: inhibition by local anesthetics in plasma from man and experimental animals in vitro

Lecithin-cholesterol acyltransferase (LCAT, EC 2.3.1.43) was assayed in vitro in plasma from normal man, rat, rabbit and dog by following the formation of 14C-cholesteryl esters subsequent to labeling the plasma with 14C-cholesterol in vitro. In all species examined, various local anesthetics were found to inhibit LCAT when studied over the concentration range of 1 to 5 mM. The order of inhibition was dibucaine>benzocaine>tetracaine>lidocaine>procaine. Since LCAT activity represents the combined effect of a deacylation step and an esterification step, inhibition of LCAT by local anesthetics could theoretically involve either or both steps.

Characterization of high density lipoproteins in human cholestasis

High density lipoproteins (HDL) of plasma from patients with long-standing cholestasis were studied by several methods including crossed immunoelectrophoresis, gel filtration, and zonal ultracentrifugation. The crossed immunoelectrophoretic pattern against anti-HDL was characterized by the presence of several immunoprecipitates, in striking contrast to the pattern formed by normal HDL. One of these precipitates corresponded to a lipoprotein species dominated by apoprotein A-II (apo A-II). Zonal ultracentrifugation of cholestatic plasma showed a decrease of HDL and a disappearance of the normal delineation of HDL2 and HDL3. In addition a new component designated HDL1-C was observed. Consistent results were found at studies of the molecular size distribution of cholestatic HDL by gel filtration on Sephadex G-200. The lipid and apoprotein composition of isolated cholestatic HDL fractions differed considerably from normal. Most notable were the high proportions of phospholipids and free cholesterol and the occurrence of the apoprotein E (arginine-rich protein) in remarkably high amounts especially in the abnormal HDL1-C.

Studies on human serum high-density lipoproteins. V. Isolation and characterization of a cholesterol ester-rich lipoprotein after in vitro incubation

Purified high-density lipoprotein (HDL), obtained by preparative ultracentrifugation at density 1.063-1.19 g/ml in the cold, were subfractionated by hydroxyl apatite column chromatography. Two of the obtained subfractions (subfractions II and III) turned turbid after incubation at 37 degrees C for 12 h. The turbid material was recovered in the supernatant of D 1.006 g/ml after centriguation at 30,000 g for 2 h. The lipoprotein fraction causing the turbidity was composed of 94% cholesterol ester and 2% apolipoprotein (by weight). On polyacrylamide gel electrophoresis the apolipoprotein moiety appeared as one polypeptide with the electrophoretic mobility of polypeptide A-I, revealed a blocked NH2-terminal amino acid, and had a total amino acid composition that differed from that of A-I and of the arginine-rich polypeptide.

Lipoprotein and lecithin: cholesterol acyltransferase changes in galactosamine-induced rat liver injury

Abnormal lipoproteins and drcreased lecithin: cholesterol acyltransferase activity are found in rat plasma following intraperitoneal injection of D-galactosamine. The changes observed, including absence of alpha-lipoprotein and the presence of lipoproteins rich in phospholipid and unesterified cholesterol but deficient in cholesteryl esters, are remarkably similar to changes found in human pathologic states of lecithin: cholesterol acyltransferase deficiency. When examined by electron microscopy, all of the major lipoprotein classes isolated by ultracentrifugation showed morphological abnormalities including the formation of rouleaus consisting of disk-shaped particles.