Lipoprotein Blood

Estrogens are thought to exert their cardiovascular effects by acting on blood lipoproteins or by direct effects on blood vessels. In studies performed in rats, fulvestrant had no effect on plasma cholesterol levels. When administered along with estradiol, however, it blocked the cholesterol-lowering activity of estradiol (Lundeen et al. 1997). 

Lipoprotein (LPLase) is required for the metabolism of both chylomicrons and VLDL. This enzyme is induced by insulin and transported to the luminal surface of capillary endothelium where it is in direct contact with the blood. Lipoprotein lipase hydrolyzes the fiitty adds from triglycerides carried by ch)4oinicrons and VLDL and is activated by apoC-II. 

Type Deficiency Lipid Elevated in Blood Lipoprotein Elevated in Blood Comments... 

As precursors for the biosynthesis of fats (lipogenesis), the adipocytes use triacylglycerols from lipoproteins (VLDLs and chylomicrons see p. 278), which are formed in the liver and intestines and delivered by the blood. Lipoprotein lipase [1], which is located on the inner surface of the blood capillaries, cleaves these triacylglycerols into glycerol and fatty acids, which are taken up by the adipocytes and converted back into fats. 

W2. Werner, M., Estimation of blood lipoproteins by radial immunodiffusion after agarose gel filtration. J. Chromatogr. 28, 59-68 (1967). 

In blood, lipids exist as lipoprotein particles, the main function of which is to transport lipids to and from various tissues and organs of the body. There is considerable interest in blood lipoproteins from the viewpoint of human health, especially obesity and cardiovascular diseases. Lipoproteins are classified into four groups on the basis of density, which is essentially a function of their triglyceride content, i.e. chylomicrons, very low density lipoprotein particles (VLDL), low density lipoprotein (LDL) particles and high density lipoprotein (HDL) particles, containing c. 98, 90, 77 and 45% total lipid, respectively (Figure 3.11). 

A more complex case is the serum lipoprotein (74), shown in Figure 13. When sonicated into water, total lipids from both the low density (/ ) and high density (a) lipoproteins give rise to the high resolution spectra expected of molecules which have a high degree of motion. The spectra of the native lipoproteins show line widths nearly identical to those of the lipids alone, so that no additional motional constraints of the apolar portions of the phospholipids occur when the lipids are bound to the apoproteins of the blood lipoproteins. All the obvious peaks observed in the native lipoproteins can be accounted for by lipid protons, and no upheld shift of the methylene protons occurs. We can conclude that unlike the case of the lysolecithin-serum albumin system, the bonding of lipids to proteins is not apolar. In the serum lipoproteins the NMR results are consistent with a micellar structure and not with extensive apolar association of lipid with protein. 

A third important structural pattern involves extensive use of amphipathic helices that lie partially embedded in a membrane surface. For example, the blood lipoproteins are lipid particles partially coated by amphipathic helices (Chapter 21).200 201... 

A better indication of a person s riidi of heart disease comes from a measurement of blood lipoprotein levels. Lipoproteins arc romfdex mol ecules with both lipid and protein parts that transport lipids through the body. They can be divided into four types ucconbiig to density as shown in 6tble 27.4. People with a high serum level high-density lipoproteins 4 HDL s) seem to have a decreased risk of heart disease. Asa rule of thumb, u person s risk drops about for each increase of 5 mg/dl.. in HDL con-... 

Benveniste X Nunez D, DuriezP, Kocth R, Bidault X Fruchart JC. Preformed PAF-acether and lyso PAF-acether are bound to blood lipoproteins. FEBS Lett 1988 226 371-376... 

Blood lipoproteins. Moderate intake of alcoholic drinks may increase high density hpoprotein and diminish low density lipoprotein, which may account for the observed protective effect against ischaemic heart disease (see below). 

Four-compartment pharmacokinetic models (PFC emulsion in blood, PFC in RES tissues, PFC in non-RES tissues, PFC dissolved in blood lipoproteins)... 

The interaction of amphotericin with serum lipoproteins (6) suggests that manipulations of blood lipids and blood lipoproteins might affect the pharmacokinetics of amphotericin, and therefore also alter its activity, including toxic effects, as suggested in animal studies (17). 

The major classes of blood lipoproteins include chylomicrons, VLDL, IDL, LDL, and HDL. 

The blood lipoproteins serve to transport water-insoluble triacylglycerols and cholesterol from one tissue to another. 

Chylomicrons are the least dense of the blood lipoproteins because they have the most triacylglycerol and the least protein. 

In addition to being an important component of cell membranes and the blood lipoproteins, phosphatidylcholine provides the fatty add for the synthesis of cholesterol esters in HDL by the LCAT reaction and, as the dipalmitoyl derivative, serves as lung surfactant. If choline is deficient in the diet, phosphatidylcholine can be synthesized de novo hum glucose (see Figure 6-14). 

Cholesterol and cholesterol esters are transported in blood lipoproteins. 

B. Because chylomicrons contain the most triacylglycerol, they are the least dense of the blood lipoproteins. VLDL is more dense than chylomicrons. Because LDL is produced by degradation of the triacylglycerols of VLDL, LDL is more dense them VLDL. HDL is the most dense of the blood lipoproteins. 

A woman was told by her physician to go on a low-fat diet. She decided to continue to consume the same number of calories by increasing her carbohydrate intake, while decreasing her fat intake. Which of the following blood lipoprotein levels would be decreased as a consequence of this diet ... 

D. Chylomicrons are blood lipoproteins produced from dietary fat. VLDL are produced mainly from dietary carbohydrate. IDL and LDL are produced from VLDL. 

C. VLDL levels are elevated because the decreased insulin and increased glucagon cause lipolysis of adipose triacylglycerols. The fatty acids and glycerol are repackaged in VLDL, which are secreted by the liver. Therefore, both triacylglycerols and cholesterol are elevated in the blood. Lipoprotein lipase is decreased because its synthesis and secretion by adipose tissue are stimulated by insulin. 

Mitochondrial oxidation of fatty acids is the major source of ATP in mammalian liver cells, and biochemists at one time believed this was true in all cell types. However, rats treated with doflbrate, a drug used to reduce the level of blood lipoproteins, were found to exhibit an increased rate of fatty acid oxidation and a large Increase in the number of peroxisomes in their liver cells. This finding suggested that peroxisomes, as well as mitochondria, can oxidize fatty acids. These small organelles, =0.2-1 pm in diameter, are lined by a single membrane (see Figure 5-21). They are present in all... 

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