Selective isolation of human plasma low-density lipoprotein particles containing apolipoproteins B and E by use of a monoclonal antibody to apolipoprotein B

ApoB (apolipoprotein B)-containing lipoprotein particles, such as chylomicrons, very-low-density and low-density lipoprotein particles, transport triacylglycerol and cholesteryl esters in the bloodstream. A palmitoylation site was previously mapped to Cys-1085 in a functional truncated apoB variant (apoB-29) and abolished by mutagenesis. This Cys-1085Ser mutation resulted in secretion of smaller and denser lipoprotein particles containing 80% less cholesteryl ester and triacylglycerol than wild-type controls. We show that palmitoylation of apoB-29 occurs in the ER (endoplasmic reticulum), stimulates the ER–Golgi transport rate of apoB-29 almost 2-fold, doubles the secretion efficiency of wild-type apoB-29 in comparison with (Cys-1085Ser)apoB-29 and reduces significantly the association of wild-type apoB-29 with calnexin in comparison with (Cys-1085Ser)apoB-29. While non-palmitoylated apoB-29 co-localized extensively with constitutively secreted transferrin, wild-type apoB-29 did so only partially and was enriched in ER extensions. Our results suggest that palmitoylation of apoB regulates the biogenesis of nascent apoB-containing lipoprotein particles by concentrating apoB in a specialized ER compartment and by stimulating dissociation from constituents of the ER quality-control machinery. This reduced interaction would lead to a faster ER–Golgi transit time and a higher secretion efficiency of wild-type apoB-29. Palmitoylation could regulate the amount of apoB available for secretion of neutral lipids.

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Apparent loss of apolipoprotein B immunoreactivity of isolated low density lipoprotein during storage: Consequences for the quantification of apolipoprotein B in human plasma

Clinica Chimica Acta ◽

10.1016/0009-8981(81)90178-9 ◽

1981 ◽

Vol 116 (1) ◽

pp. 131-135 ◽

Cited By ~ 11

Author(s):

Louis Havekes

Keyword(s):

Human Plasma ◽

Apolipoprotein B ◽

Low Density Lipoprotein ◽

Density Lipoprotein ◽

Low Density ◽

Apparent Loss

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Regulation of plasma LDL: the apoB paradigm

Clinical Science ◽

10.1042/cs20090402 ◽

2009 ◽

Vol 118 (5) ◽

pp. 333-339 ◽

Cited By ~ 28

Author(s):

Allan D. Sniderman ◽

Jacqueline De Graaf ◽

Patrick Couture ◽

Ken Williams ◽

Robert S. Kiss ◽

...

Keyword(s):

Apolipoprotein B ◽

Low Density Lipoprotein ◽

Ldl Receptor ◽

Density Lipoprotein ◽

Low Density ◽

Critical Aspect ◽

Lipoprotein Particles ◽

Ldl Particles ◽

Plasma Compartment

The objectives of this analysis are to re-examine the foundational studies of the in vivo metabolism of plasma LDL (low-density lipoprotein) particles in humans and, based on them, to reconstruct our understanding of the governance of the concentration of plasma LDL and the maintenance of cholesterol homoeostasis in the hepatocyte. We believe that regulation of cholesterol homoeostasis within the hepatocyte is demonstrably more complex than envisioned by the LDL receptor paradigm, the conventional model to explain the regulation of plasma LDL and the fluxes of cholesterol into the liver, a model which was generated in the fibroblast but has never been fully validated in the hepatocyte. We suggest that the LDL receptor paradigm should be reconfigured as the apoB (apolipoprotein B) paradigm, which states that the rate at which LDL particles are produced is at least an important determinant of their concentration in plasma as the rate at which they are cleared from plasma and that secretion of cholesterol within VLDL (very-low-density lipoprotein) particles is an important mechanism of maintaining cholesterol homoeostasis within the hepatocyte. These two paradigms are not mutually exclusive. The LDL receptor paradigm, however, includes only one critical aspect of the regulation of plasma LDL, namely the rate at which LDL particles are cleared through the LDL receptor pathway, but ignores another – the rate at which LDL particles are added to the plasma compartment. The apoB paradigm includes both and points to a different model of how the hepatocyte achieves cholesterol homoeostasis in a complex metabolic environment.

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Monoclonal antibodies can precipitate low-density lipoprotein. II. Radioimmunoassays with single and combined monoclonal antibodies for determining apolipoprotein B in serum of patients with coronary artery disease.

Clinical Chemistry ◽

10.1093/clinchem/31.10.1659 ◽

1985 ◽

Vol 31 (10) ◽

pp. 1659-1663 ◽

Cited By ~ 9

Author(s):

S Marcovina ◽

B A Kottke ◽

S J Mao

Keyword(s):

Coronary Artery Disease ◽

Monoclonal Antibody ◽

Monoclonal Antibodies ◽

Coronary Artery ◽

Apolipoprotein B ◽

Low Density Lipoprotein ◽

Density Lipoprotein ◽

Low Density ◽

Apo B ◽

Artery Disease

Abstract We have established four lines of monoclonal antibodies against human low-density lipoproteins (LDL) that, mixed in equal proportions, can precipitate LDL in gel and so can be used for apolipoprotein (apo) B determination in plasma. One monoclonal antibody (clone A), with a relatively low binding affinity to LDL (ka = 0.6 X 10(9) L/mol) and recognizing only two species of apo B, significantly underestimated the concentration of apo B in 74 patients with and 27 without coronary artery disease (CAD). High-affinity monoclonal antibody C (Ka = 3.8 X 10(9) L/mol), which recognized all four apo B species, gave the same value for apo B as determined with the mixture of monoclonal antibodies. The latter results (by radioimmunoassay, y) correlated well with those by radial immunodiffusion (chi): y = 0.994 chi + 0.003 (r = 0.987). The CAD patients showed an increased concentration of apo B as compared to the angiographically documented CAD-negative patients. Except for the values determined by clone B (p = 0.07), the increase was statistically significant (p = 0.002-0.018) for values determined by use of the other clones or their mixture.

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