Lipoprotein Solubility

Cholesterol is biosynthesized in the liver trans ported throughout the body to be used in a va riety of ways and returned to the liver where it serves as the biosynthetic precursor to other steroids But cholesterol is a lipid and isn t soluble in water How can it move through the blood if it doesn t dis solve in if The answer is that it doesn t dissolve but IS instead carried through the blood and tissues as part of a lipoprotein (lipid + protein = lipoprotein) The proteins that carry cholesterol from the liver are called low density lipoproteins or LDLs those that return it to the liver are the high-density lipoproteins or HDLs If too much cholesterol is being transported by LDL or too little by HDL the extra cholesterol builds up on the walls of the arteries caus mg atherosclerosis A thorough physical examination nowadays measures not only total cholesterol con centration but also the distribution between LDL and HDL cholesterol An elevated level of LDL cholesterol IS a risk factor for heart disease LDL cholesterol is bad cholesterol HDLs on the other hand remove excess cholesterol and are protective HDL cholesterol IS good cholesterol... 

Cholesterol is biosynthesized in the liver, transported throughout the body to be used in a variety of ways, and returned to the liver where it serves as the biosynthetic precursor to other steroids. But cholesterol is a lipid and isn t soluble in water. How can it move through the blood if it doesn t dissolve in it The answer is that it doesn t dissolve, but is instead carried through the blood and tissues as part of a lipoprotein (lipid + protein = lipoprotein). 

Cholesterol, which is water-insoluble, is transported through the blood in the form of soluble protein complexes known as lipoproteins. 

After uptake, lipophilic pollutants tend to move into hydrophobic domains within animals or plants (membranes, lipoproteins, depot fat, etc.), unless they are biotransformed into more polar and water soluble with compounds having low Metabolism of lipophilic compounds proceeds in two stages ... 

Vitamin E is the Major Lipid-Soluble Antioxidant in Cell Membranes Plasma Lipoproteins... 

This approach can be used only for fat-soluble compounds that follow the same lymphatic route to be transported to the liver as carotenoids. The bioavailability of the compound of interest is determined by monitoring the appearance of the compound and its newly formed intestinal metabolites in the postprandial chylomicron fraction of plasma [also called the density < 1.006 kg/L fraction or triglyceride-rich lipoprotein (TRL) fraction because it is generally a mixture of chylomicrons (CMs) and very low density lipoproteins (VLDLs)] as a function of the time after ingestion. 

Esterbauer et al. (1991) have demonstrated that /3-carotene becomes an effective antioxidant after the depletion of vitamin E. Our studies of LDL isolated from matched rheumatoid serum and synovial fluid demonstrate a depletion of /8-carotene (Section 2.2.2.2). Oncley et al. (1952) stated that the progressive changes in the absorption spectra of LDL were correlated with the autooxidation of constituent fatty acids, the auto-oxidation being the most likely cause of carotenoid degradation. The observation that /3-carotene levels in synovial fluid LDL are lower than those of matched plasma LDL (Section 2.2.2) is interesting in that /3-carotene functions as the most effective antioxidant under conditions of low fOi (Burton and Traber, 1990). As discussed above (Section 2.1.3), the rheumatoid joint is both hypoxic and acidotic. We have also found that the concentration of vitamin E is markedly diminished in synovial fluid from inflamed joints when compared to matched plasma samples (Fairburn etal., 1992). This difference could not be accounted for by the lower concentrations of lipids and lipoproteins within synovial fluid. The low levels of both vitamin E and /3-carotene in rheumatoid synovial fluid are consistent with the consumption of lipid-soluble antioxidants within the arthritic joint due to their role in terminating the process of lipid peroxidation (Fairburn et al., 1992). 

Kempen et al. [176] synthesized a water-soluble cho-lesteryl-containing trigalactoside, Tris-Gal-Chol (I), which when incorporated in lipoproteins allows the utilization of active receptors for galactose-terminated macromolecules as a trigger for the uptake of lipoproteins. The effect of increasing concentrations of Tris-Gal-Chol on the removal of LDL and HDL from serum and their quantitative recovery in the liver is shown in Fig. 13. These data show that lipoproteins containing Tris-Gal-Chol can be used as a liver-specific drug-carrier system. 

These data suggest that one of possible mechanisms of carotenoid delivery to the neural retina may involve lipoprotein uptake from the basal side of the RPE followed by its retro-endocytosis on the apical site (Lorenzi et al., 2008). Alternatively, the endocytosed lipoprotein may be degraded in the RPE followed by secretion of certain lipophilic components from the lipoprotein at the apical site. Due to low solubility of carotenoids in aqueous solutions, it may be suggested that they are secreted already bound to a protein or that an acceptor protein is available in the interphotoreceptor matrix and/or POS. 

Egg yolk contains mainly lipids (32 34%), proteins (16%), saccharides, mineral compounds, vitamins, dyes and water (48%). It is formed by two distinguishable fractions plasma and granules. The plasma contains mostly lipids (90% of total solids) and proteins. Granules contain mainly acidic phosphoproteins (fosvitin, lipovitellins and low-density lipoproteins), which are soluble only in higher ionic strength water solutions. 

New insights into the analysis of hydrophobically post-translational modified proteins could be achieved by the construction of lipidated proteins in a combination of bioorganic synthesis of activated lipopeptides and bacterial expression of the protein backbone (Fig. 19). The physico-chemical properties of such artificial lipoproteins differ substantially from those of the corresponding lipopeptides. The pronounced dominance of the hydrophilic protein moiety (e.g., for the Ras protein 181 amino acids) over a short lipopeptide with one or two hydrophobic modifications provides solubility up to 10 4 mol/1, while the biotinylated or fluorescence labeled lipopeptides exhibit low solubility in aqueous solutions and can be applied in the biophysical experiments only in vesicle integrated form or dissolved in organic solvent. 

Lee YT, Chiang LY, Chen WJ, Hsu HC (2000) Water-soluble Hexasulfobutyl[60]fullerene inhibit low-density lipoprotein oxidation in aqueous and lipophilic phases. C. Proc. Soc. Exp. Biol. Med. 224 69-75. 

Fernandez, M. L., Vergara-Jimenez, M., Conde, K., Behr, T., and Abdel-Fattah, G. (1997). Regulation of apolipoprotein B-contammg lipoproteins by dietary soluble fiber in guinea... 

Sola, R., Godas, G., Ribalta, J., Vallve, J. C., Girona, J., Anguera, A., Ostos, M., Recalde, D., Salazar, J., Caslake, M., Martin-Lujan, E., Salas-Salvado, J., et al. (2007). Effects of soluble fiber Plantago ovata huak) on plasma lipids, lipoproteins, and apoUpoproteins in men with ischemic heart disease. Am. ]. Clin. Nutr. 85,1157-1163. 

Glycerophospholipids are used for membrane synthesis and for producing a hydrophilic surface layer on lipoproteins such as VLDL. In cell membranes, they also serve as a reservoir of second messengers such as diacylglycerol, inositol 1,4,5-triphosphate, and arachidonic acid. Their structure is similar to triglycerides, except that the last fatty acid is replaced by phosphate and a water-soluble group such as choline (phosphatidylcholine, lecithin) or inositol (phosphatidyl-inositol). 

Ab, Antibody BBB, Blood Brain Barrier CNS, Central Nervous System HIV, Human Immunodeficiency Virus HSA, Human Serum Albumin IGF, Insulin Growth Factor I/R, Ischaemia/Reperfusion MW, Molecular Weight OxLDL, Oxidized Low Density Lipoprotein -R, -receptor sCD4, soluble CD4 VEGF, Vascular Endothelial Growth Factor. 

The table also lists important globulins in blood plasma, with their mass and function. The a- and p-globulins are involved in the transport of lipids (lipoproteins see p. 278), hormones, vitamins, and metal ions. In addition, they provide coagulation factors, protease inhibitors, and the proteins of the complement system (see p. 298). Soluble antibodies (immunoglobulins see p. 300) make up the y-globulin fraction. 

Most lipids are barely soluble in water, and many have amphipathic properties. In the blood, free triacylglycerols would coalesce into drops that could cause fat embolisms. By contrast, amphipathic lipids would be deposited in the blood cells membranes and would dissolve them. Special precautions are therefore needed for lipid transport in the blood. While long-chain fatty acids are bound to albumin and short-chain ones are dissolved in the plasma (see p. 276), other lipids are transported in lipoprotein complexes, of which there several types in the blood plasma, with different sizes and composition. 

Lipoproteins are classified into five groups. In order of decreasing size and increasing density, these are chylomicrons, VLDLs (very-low-density lipoproteins), IDLs (inter-mediate-density lipoproteins), LDLs (low-density lipoproteins), and HDLs (high-density lipoproteins). The proportions of apoproteins range from 1 % in chylomicrons to over 50% in HDLs. These proteins serve less for solubility purposes, but rather function as recognition molecules for the membrane receptors and enzymes that are involved in lipid exchange. 

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