Cholesterol cholesteryl esters

Loading of guests within the SCKs (for potential delivery) is modeled after lipoproteins, which are composites of cholesterol, cholesteryl ester, phospholipids, and protein forming biological structures of core-shell morphology... 

Most of the mention of cholesterol in the popular press positions this molecule as a threat to human health. Many foods are proudly labeled cholesterol-free. People are properly warned to pay attention to their plasma cholesterol level, particnlarly that carried in the low-density lipoproteins, LDLs, commonly known, with pretty good reason, as bad cholesterol. LDLs are lipoprotein particles containing a large protein known as B-100 associated with cholesterol, cholesteryl esters, phospholipids, and some triglycerides. 

Cholesterol and cholesteryl esters are carried in the blood as plasma lipoproteins. VLDL carries cholesterol, cholesteryl esters, and triacylglycerols from the liver to other tissues, where the triacylglycerols are degraded by lipoprotein lipase, converting VLDL to LDL. 

Cholesterol and cholesteryl ester synthesis acetyl-CoA----> cholesterol----> cholesteryl esters... 

An adult ingests about 60 to 150 g of lipids per day, of which more than n nety percent is normally triacylglycerol (formerly called triglyceride). Uhe remainder of the dietary lipids consists primarily of cholesterol, cholesteryl esters, phospholipids, and unesterified ("free") fatty acids. "The digestion of dietary lipids is summarized in Figure 15.2. 

Most plasma cholesterol is in an esterified form (with a fatty add attached at C-3, see Figure 18.2), which makes the structure sen more hydrophobic than free cholesterol. Cholesteryl esters are rot found in membranes, and are normally present only in low levels in most cells. Because of their hydrophobicity, cholesterol and ils esters must be transported in association with protein as a compo nent of a lipoprotein particle (see p. 225) or be solubilized by phos pholipids and bile salts in the bile (see p. 223). 

Digestion of dietary lipids Dietary lipids DIGESTION OF DIETARY LIPIDS (p. 171) Dietary lipids consist primarily of triacylglycerol, with some cholesterol, cholesteryl esters, phospholipids, and free (nonesterified) fatty acids. 

Protein Phospholipid Cholesterol Cholesteryl esters Triacylglycerol... 

The plasma lipoproteins are made mainly in the liver and intestine. In the rat, approximately 80% of the plasma apoproteins originate from the liver the rest are derived from the intestine. The components of chylomicrons, including apoproteins A-I, A-IV, and B-48 phospholipid cholesterol cholesteryl ester and triacylglycerols, are products of the intestinal cells. Chylomicrons are secreted into lymphatic capillaries, which eventually enter the bloodstream. The liver is the major source of VLDLs and HDLs. 

The lipids of the diet include triglycerides, phospholipids, cholesterol, cholesteryl esters, and fat-soluble vitamins. Lipids are soluble in water, but only at extremely low concentrations many thousands of times lower than those attainable by water-soluble nutrients. Lipids are called fat-soluble because they tend to adhere to, migrate into, or be easily dispersed into fats and oils. (The term oil-soluble also may be used to describe lipids.) A lipid that is solid at room temperature generally is called a fat one that is liquid at room temperature is called an oil. 

Protein Phospho- lipid Trigly- ceride Free cholesterol Cholesteryl ester... 

Protein Major Apoproteins Phospholipid Cholesterol Cholesteryl Ester Triacylglycerol Diameter (nm)... 

This reaction is responsible for formation of most of the cholesteryl ester in plasma. The preferred substrate is phosphatidylcholine, which contains an unsaturated fatty acid residue on the 2-carbon of the glycerol moiety. HDL and LDL are the major sources of the phosphatidylcholine and cholesterol. Apo A-I, which is a part of HDL, is a powerful activator of LCAT. Apo C-I has also been implicated as an activator of this enzyme however, activation may depend on the nature of the phospholipid substrate. LCAT is synthesized in the liver. The plasma level of LCAT is higher in males than in females. The enzyme converts excess free cholesterol to cholesteryl ester with the simultaneous conversion of lecithin to lysolecithin. The products are subsequently removed from circulation. Thus, LCAT plays a significant role in the removal of cholesterol and lecithin from the circulation, similar to the role of lipoprotein lipase in the removal of triacylglycerol contained in chylomicrons and VLDL. Since LCAT regulates the levels of free cholesterol, cholesteryl esters, and phosphatidylcholine in plasma, it may play an important role in maintaining normal membrane structure and fluidity in peripheral tissue cells. 

Proportional (Relative) Number of Cholesterol, Cholesteryl Ester, Phospholipid, and Protein Molecules in Four Major Classes of Plasma Lipoproteins. 

Under most metabolic conditions, apo B is synthesized constitutively and in excess of the amount required for secretion. Thus, the rate of apo B synthesis does not usually determine how much apo B is secreted. The assembly of VLDLs is a complex process in which several types of lipids — including TG, cholesterol, cholesteryl esters, and phospholipids — become non-covalently associated with newly synthesized apo B. When insufficient lipid is available for formation of stable apo B-containing particles, excess apo B, and apo B that has been incompletely assembled with lipids, is not secreted but is targeted for intracellular degradation (Section 7). An increased supply of lipid promotes apo B translocation across the ER membrane and into the secretory pathway, resulting in a larger proportion of the newly synthesized apo B being secreted. 

During a study, there has been evaluated the effect of supplementation with a low dose of co-3, obtained by olive oil, on the oxidative modification of low density lipoprotein (LDL) in a group of healthy volunteers, for 16 weeks. Oxidative modification of LDL was assessed measuring the concentrations of free cholesterol, cholesteryl esters and cholesteryl linoleate hydroperoxide in LDL, following copper-induced lipid peroxidation for 0, 2, 3 and 4 h. LDL eicosapentaenoic acid and docosahexaenoic acid compositions were significantly lower in the group treated with )-3 olive oil than the group treated with w-3 fish oil. 

Diameter (nm) Density (g/ml) Protein Phospholipid Cholesterol Cholesteryl esters Triacylglycerol... 

Triacylglycerols Diacylglycerols Monoacylglycerols Fatty acids Phospholipids Cholesterol Cholesteryl esters Hydrocarbons... 

Asmis, R., Buehler, E., Jelk, J., and Gey, K. F. (1997). Concurrent quantification of cellular cholesterol, cholesteryl esters and triglycerides in small biological samples. Reevaluation of thin layer chromatography using laser densitometry. J. Chromatogr., B Biomed. Sci. Appl. 691 59-66. 

Four main classes of plasma lipoprotein can be recognized from their densities and electrophoretic mobilities. They are all large complexes that contain triglycerides, phospholipids, cholesterol, cholesteryl esters and protein in varying proportions (Table 25.4) and consist of a hydrophobic core surrounded by a shell of proteins and phospholipids. The proteins are known as apolipoproteins or apoproteins. These are formed in the liver and small intestine and are of many different kinds. Some of them act as enzyme activators. 

Sterols are a class of lipids that consist of a steroid and an alcohol. The most physiologically abundant sterol in humans is cholesterol, which is an integral part of the plasma membranes, confaring the fluidity of the lipid bilayer. Due to its amphipathic nature, cholesterol is an important structural component of cell membranes and the outer layer of plasma lipoproteins. Cholesterol plays an essential role both in the structure of cells and as a precursor to corticosteroids, mineral corticoids, bUe acids, vitamin D, and sex hormones such as testosterone, estrogen, and progesterone. As excess free cholesterol has cytotoxicity in cells, it is estrailied to a fatty acid to become a cholesteryl ester, a neutral form of cholesterol. Cholesteryl esters can be stored in the hpid droplets of cells without cytotoxicity, and therefore cholesterol esterification is increased whrai free cholesterol content in cells becomes excessive. 

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