In vitro factors affecting the concentration of gamma-LpE (γ-LpE) in human plasma

• Main Authors: Larbi Krimbou, Michel Tremblay, Hélène Jacques, Jean Davignon, Jeffrey S. Cohn
• Format: Article
• Language: English
• Published: Elsevier 1998-04-01
• Series: Journal of Lipid Research
• Subjects: HDL; cholesterol efflux; apoE
• Online Access: http://www.sciencedirect.com/science/article/pii/S0022227520325724

Gamma-LpE (γ-LpE), a sphingomyelin-rich lipoprotein that contains apolipoprotein (apo) E as its only protein component, has been proposed to play a role in cellular cholesterol efflux by acting, like pre-β1-LpA-I, as an initial acceptor of cell-derived cholesterol. In order to further characterize the presence of γ-LpE in human plasma, we have separated γ-LpE by two-dimensional non-denaturing polyacrylamide-gradient gel electrophoresis and detected its presence by immunoblotting with 125I-labeled polyclonal anti-apoE antibody. Five species of γ-LpE were routinely detected in human plasma, ranging in mean particle diameter from 9.5 to 16.5 nm. The largest proportion of γ-migrating apoE was associated with γ2-LpE having a diameter of 13.0 nm. Neither the amount of γ-LpE apoE (representing less than 1–2% of total plasma apoE) nor the number of γ-LpE subfractions was different in serum vs. plasma, or was affected by the presence of agents able to inhibit protein dimerization. γ-LpE subfractions were present in the plasma of patients having different apoE phenotypes (i.e., apoE 2/2, 3/3, or 4/4). Incubation of plasma at 37°C (90 min) caused a significant decrease in plasma γ-LpE (>80%) that was not dependent on LCAT or CETP activity. Storage (at –70°C) of hypertriglyceridemic but not normolipidemic plasma resulted in an increase in γ-LpE. Freezing of postprandial plasma samples, containing increased amounts of triglyceride-rich lipoproteins (TRL) enriched in apoE, also caused an increase in γ-LpE. Incubation of VLDL (d < 1.006 g/ml) with lipase resulted in the production of γ-migrating apoE. These results demonstrate that: 1) different γ-LpE subfractions exist in human plasma; 2) the amount of apoE associated with γ-LpE subfractions is dependent on in vitro conditions of plasma storage; and 3) TRL can act as a source of γ-LpE apoE in vitro.—Krimbou, L., M. Tremblay, H. Jacques, J. Davignon, and J. S. Cohn. In vitro factors affecting the concentration of gamma-LpE (γ-LpE) in human plasma. J. Lipid Res. 1998. 39: 861–872.