Chylomicrons analysis

Fasted blood samples have to be analyzed for this analysis. When non-fasting samples are analyzed, the triglyceride-rich chylomicrons will be included in the VLDL fraction during this procedure, which will lead to false results. 

Apolipoprotein C-II can also be isolated from VLDL or HDL (H20, L5, N3). It contains 78 residues (J3) and has been shown by Chou-Fasman analysis to bind phospholipids (M26, M40), with three predicted helical sequences (M26). ApoC-II has attracted a great deal of attention because it activates one of the most important enzymes in plasma lipid metabolism, lipoprotein lipase, responsible for the hydrolysis of triglyceride in chylomicrons and VLDL. Sparrow and Gotto have summarized a number of studies on structure-function relationships (S52). These, taken together, indicate that there are separate functional domains in apoC-II, in that lipoprotein lipase activation is mediated by residues 55-78 and phospholipid binding by... 

Lipid analysis revealed low plasma cholesterol. A fasting lipid profile showed total cholesterol was 1 mmol/L (normal is 3.5-5.0 mmol/L). On fractionation, HDL was found to be normal while LDL was undetectable. Postprandial electrophoresis of plasma lipoproteins demonstrated the presence of HDL, but absence of chylomicrons, VLDL, and LDL. Plasma levels of apolipoprotein B (apoB) were well below the sensitivity of the test used for their measurement... 

Three disorders of lipoprotein metabolism share these characteristics familial hypobetal-ipoproteinemia, chylomicron retention disease, and ABL (Table 27-2). The presence or absence of specific plasma apoB lipoproteins, as well as their mode of inheritance, can be useful when attempting to differentiate between these disorders. Symptoms associated with familial hypo-betalipoproteinemia are usually milder than for the other two and are inherited as dominant traits, that is, symptoms are observed in at least one parent of an affected offspring. Chylomicron retention disease is an autosomal recessive disorder with a severe phenotype commonly presenting soon after birth. Plasma lipoprotein analysis from affected individuals shows a specific absence of chylomicrons (apoB48) but normal amounts of VLDL and LDL (apoB 100). In our patient, evidence of recessive inheritance and absence of all apoB-containing lipoproteins implicates ABL as the most likely diagnosis. 

Fig. 11. Analysis of protein (A280) and total cholesterol A55Q) for human serum. Column G5000PW+G3000SW+G3000SW. Sample (A), normal female (B), liver cirrhosis (C), hyperlipidemia. Loaded volume 20 pi of whole serum. Peaks 1, chylomicrons 2, VLDL 3, LDL 4, HDL2 5, HDL3 6, VHDL 7, r-globul1n 8, albumin. Other HPLC conditions as in Fig. 10.

Lipids circulate in blood as constituents of the lipoproteins or bound to albumin (free fatty acids). Electrophoretic separation of plasma proteins on paper is a relatively easy and convenient method for the semi-quantitative analysis of lipoproteins. Staining the strips with dyes which only respond to lipids reveals three well-defined bands when normal plasma or serum is analyzed. The a-lipoprotein migrates the farthest from the origin. The pre-j8, previously called the a-2-hpoprotein, and the jS-Hpoprotein, are closer to the origin. In the post-prandial normal serum, and in some hyperlipemic sera, after fasting, a fourth band can be seen at the origin. This band is due to neutral fat particles with a small protein content (i.e. chylomicron fraction). 

Shortly after the consumption of a fatty meal, the presence of chylomicrons is very apparent in a sample of plasma (lipaemia). The very large particles scatter light giving the plasma an opalescent appearance. The particles can be isolated as a floating layer after a short low speed centrifugation and can be withdrawn from the top of the tube with a Pasteur pipette for analysis. 

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