Action of lecithin-cholesterol acyltransferase on low-density lipoproteins in native pig plasma

Abstract

The action of lecithin-cholesterol acyltransferase (LCAT, EC 2.3.1.43) on the different pig lipoprotein classes was investigated with emphasis on low-density lipoproteins (LDL). It was demonstrated previously that LDL can serve as substrate for LCAT, probably because they contain sufficient amounts of apoA-I and other non-apoB proteins, known as LCAT activators. Upon a 24-h incubation of pig plasma in vitro in the presence of active LCAT, both pig LDL subclasses, LDL-1 and LDL-2, fused together, forming one fraction, as revealed by analytical ultracentrifugation. This fusion was time dependent, becoming visible after 3 h and complete after 18 h of incubation. Concomitantly, free cholesterol and phospholipids decreased and cholesteryl esters increased. When isolated LDL-1 and LDL-2 were incubated with purified pig LCAT for 24 h, LDL-1 floated toward higher densities and LDL-2 toward lower densities, although this effect was not as pronounced as in incubations of whole serum. In further experiments, pig serum was incubated for various periods of time in the presence and absence of the LCAT inhibitor sodium iodoacetate. The individual lipoproteins then were separated by density gradient ultracentrifugation or by specific immunoprecipitation and chemically analyzed. Both methods revealed that in the absence of active LCAT there was a transfer of free cholesterol from LDL to high-density lipoproteins (HDL) and a small transfer of cholesteryl esters in the opposite direction. In the presence of LCAT the loss of free cholesterol started immediately in all three lipoprotein classes, was most prominent in LDL, and was proportional to the newly synthesized cholesteryl esters incorporated in each fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of cholesteryl ester transfer protein activity by monoclonal antibody. Effects on cholesteryl ester formation and neutral lipid mass transfer in human plasma.

“…A recent study using pig plasma, which lacks neutral lipid the presence transfer activity, has suggested that LDL is the major substrate vity (from Fig. for LCAT (38). The conclusion that the majority of newly mple.…”

The role of lecithin: cholesterol acyltransferase for lipoprotein (a) assembly. Structural integrity of low density lipoproteins is a prerequisite for Lp(a) formation in human plasma.

“…Each plasma or incubation mixture was centrifuged in duplicate. One of the duplicate tubes contained Coomassie brilliant blue as protein dye (36) to facilitate documentation and identification of lipoprotein fractions. Lipoproteins in the second tube were not stained and were used for further experiments and analyses.…”

Metabolic origins and clinical significance of LDL heterogeneity

“…In a spontaneously hypercholesterolemic strain of pigs, two metabolically distinct LDL subclasses have been characterized: the larger, more buoyant species appears to accumulate as a results of both increased production and reduced receptor clearance resulting from an apoB mutation (57). This subclass does not appear to arise either from catabolism of plasma VLDL, or from enlargement of smaller LDL (58), although an LCAT-induced increase in buoyancy of the denser LDL species in pigs has been reported (59).…”