Between lipoproteins and

Steck TL, Ye J, Lange Y. Probing red cell membrane cholesterol movement with cyclodextrin. Biophys. J. 2002 83 2118-2125. Estronca LMBB, Moreno MJ, Laranjinha JAN, Almeida LM, Vaz WLC. Kinetics and thermodynamics of lipid amphiphiles exchange between lipoproteins and albumin in serum. Biophys. J. 2005 88 557-565. 

Lipoproteins have also been used for studying protein-stimulated phospholipid transfer between lipoproteins (Ihm et al., 1982), and between lipoproteins and vesicles (Damen et al., 1981, 1982). Care must be exercised when high density lipoprotein is used as a substrate in an exchange reaction with vesicles, since vesicles may be disrupted and net transfer of lipid results (Damen et al., 1981). A high density lipoprotein-vesicle assay with appropriate precautions has been employed by Damen et al. (1981). 

Bi-directional flux of free cholesterol between cells and lipoproteins occurs, and rate constants characteristic of influx and efflux can be measured [17]. The direction of any net transfer of free cholesterol is determined by the relative free cholesterol/phospholipid molar ratios of the donor and acceptor particles. Cholesterol diffuses down its gradient of chemical potential generally partitioning to the phospholipid-rich particle. Such a surface transfer process can lead to delivery of cholesterol to cells. This mechanism operates independently of any lipoprotein internalization by the receptor-mediated endocytosis. The influence of enzymes such as lecithin-cholesterol acyltransferase and hepatic lipase on the direction of net transfer of free cholesterol between lipoproteins and cells can be understood in terms of their effects of the pool sizes and the rate constants for influx and efflux. 

Binding of tocopherols and transfer between lipoproteins and tissues Binding of a-tocopherol and inhibition of PKCa Binding of y-tocopherol and inhibition of COX-2... 

The levels of amylase in normal urine and sera have been measured using Phadebas Starch as a substrate. The sera of patients undergoing haemodialysis or treatment with heparin appear to show a rise in the levels of amylase when the amylase is measured by a starch-iodine procedure. A corresponding increase was not observed in in vitro experiments, and it was concluded that interactions between lipoproteins and starch in vivo prevent the starch-iodide complexes from forming, thereby giving a false measurement. 

In the following sections, we will first outline the types of peptides present in lipoproteins and then briefly describe the broad classes of lipoproteins, summarizing their nomenclature, composition, functions and biosynthesis. This will be followed by a more detailed description of the metabolic interrelationships between lipoproteins and how their metabolism is integrated within the body. Methods of isolation and analysis will be described and the section will end with a summary of their clinical relevance, leading to a discussion of the importance of lipoprotein metabolism in some metabolic diseases. 

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... 

FIGURE 4.29 Relation between molecular weight of lipoproteins and elution volume for combination GFC columns. Column 7.5 mm i.d. X 60 cm. Sample Chylomicron, VLDL, LDL, HDLj, HDL3, albumin, and ovalbumin. Elution 0.1 hA Tris—HCI buffer (pH 7.4). Flow rate 1.0 ml/min. 

Plasma lipid transfer proteins, which include the cholesteryl-ester-transfer-protein (CETP previously known as lipid transfer protein I, LTP-I) and the phospholipid-transfer-protein (PLTP previously known as lipid transfer protein II, LTP-II) mediate the transfer of lipids (cholesteryl esters, triglycerides and phospholipids) between lipoproteins present in human plasma. These proteins significantly affect plasma lipoprotein concentration and composition. 

In contrast with the hydrocarbon carotenes primarily located in the cores of the CM particles, xanthophylls are present at the surfaces of the CM particles, making their exchanges with other plasma lipoproteins easier." Therefore, if some exchanges occur between lipoproteins, AUC (or absorption) values of the newly absorbed compound in the TRL fraction will be underestimated. Based on all these considerations, the present approach is more appropriate to determine the relative bioavailability of a compound derived from various treatments within one snbject and/or within one study. 

In fasting hnman sernm, the hydrocarbon carotenes (P-carotene and lycopene) are fonnd primarily in LDL, while the xanthophylls (Intein, zeaxanthin, and P-cryptox-anthin) are more evenly distribnted between LDLs and HDLs. As mentioned earlier and contrary to the carotenes, the xanthophylls are primarily located at the surfaces of lipoprotein particles, making them more likely to exchange between plasma lipoproteins. This hypothesis may explain their eqnal distribntion (or apparent equilibrinm) between LDLs and HDLs. 

Chin et al. (1992) have su ested that oxidized LDL and high-density lipoprotein (HDL) inactivate endothelial cell-derived NO. NO inactivation was due to the oxidized lipids within the lipoprotein particles and was thought to be explained by a chemical reaction between the lipoproteins and NO. Other investigators have shown that relaxation of vascular smooth muscle by acetylcholine or bradykinin (endothelium-dependent vasodilators) is inhibited by LDL (Andrews etal., 1987). The role of NO in the modification of LDL is discussed in full detail in Chapter 2. 

Vaarala, O., Alfthan, G., Jauhiainen, M., Leirisalo-Repo, M., Aho, K. and Palosuo, T. (1993). Cross-reaction between antibodies to oxidised low-density lipoprotein and to cardiolipin in systemic lupus erythematosus. Lancet 341, 923-925. 

Webb, NR, Connell, PM, Graf, GA, Smart, EJ, de Villiers, WJ, de Beer, FC, and van der Westhuyzen, DR, 1998. SR-BII, an isoform of the scavenger receptor BI containing an alternate cytoplasmic tail, mediates lipid transfer between high density lipoprotein and cells. J Biol Chem 273, 15241-15248. 

Attachment There is a high specificity in the interaction between virus and host. The most common basis for host specificity involves the attachment process. The virus particle itself has one or more proteins on the outside which interact with specific cell surface components called receptors. The receptors on the cell surface are normal surface components of the host, such as proteins, polysaccharides, or lipoprotein-polysaccharide complexes, to which the virus particle attaches. In the absence of the receptor site, the virus cannot adsorb, and hence cannot infect. If the receptor site is altered, the host may become resistant to virus infection. However, mutants of the virus can also arise which are able to adsorb to resistant hosts. 

Figure 21 shows the distribution of wine-derived antioxidants between apo B-containing lipoproteins and other high-molecular-weight components of... 

Only nine years after its discovery in plasma as an antigenic trait, a relationship was suggested between lipoprotein(a) and coronary heart disease (CHD) (B6, D2). Moreover, an interesting relationship between longevity and Lp(a) concentrations was reported by Berg (B10) The frequency of higher Lp(a) levels in very old persons (>83 years) was lower than in the reference population. The same observation was made by Knapp (K18) in black American men. This... 

The discovery of Lp(a) by Berg in 1962 (B6) relied on the production of rabbit antisera against beta-lipoprotein and on the selective absorption of these antisera with individual human sera. When certain human sera were used for absorption, the antisera retained precipitation capacity in radial immunodiffusion with 30-35% of individual human sera, which obviously contained a previous unknown antigen. The particle carrying the new antigen shared antigenic properties with beta-lipoprotein, but had an additional antigenic structure. This was evidenced from the only partial fusion of the precipitin bands formed between a positive human serum, the antibeta lipoprotein antiserum and the new absorbed antiserum. 

D9. De Pergola, G., Giorgino, F., Cospite, M. R., Giagulli, V. A., Cignarelli, M., Ferri, G., and Giorgino, R., Relation between sex hormones and semm lipoprotein and lipoprotein(a) concentrations in premenopausal obese women. Arterioscier. Thromb. 13, 675-679 (1993). 

G17. Giavarina, D., Dorizzi, R., Giavarina, M., and Schiavon, R., Age-related correlations between weight and lipoprotein(a) concentrations. Clin. Chem. (Winston-Salem, NC) 38, 1386... 

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