Storage in lipids

Of the various lipid components of the lipoproteins, only the biosynthesis of cholesteryl esters has not yet been mentioned. Cholesteryl ester is the storage form of cholesterol in cells. It is synthesized from cholesterol and acyl-CoA by acyl-CoA cholesterol acyltransferase (ACAT) (fig. 20.13), which is located on the cytosolic surface of hepatic endoplasmic reticulum. Acylation of the 3 hydroxyl group of cholesterol eliminates the polarity of cholesterol and facilitates the packing of cholesterol as its ester in the core of the lipoprotein or for storage in lipid droplets within cells. 

Even though chemicals with long half-lives and high storage in lipid tend to have stable concentrations, they may not be at steady state. For example, dioxin body burdens apparently increased in the early part of the 20th century and then declined over the last 2 decades. That pattern repre-... 

Apart from storage in lipid tissue, certain drugs can be preferentially taken up or sequestered into other tissues. 

Flick, G.J., Hong, G.-P, and Knobl, G.M., 1992, Lipid oxidation of seafood during storage, in Lipid Oxidation in Food, St. Angelo, A.J., Ed., ASC Symposium Series 500, Am. Chem. Soc., Washington, Chapter 11. 

Alcoholic beverages are quite often consumed during lunchtime or after work, and since the excretion of xylene is delayed by its high solubility and storage in lipid-rich tissues, the simultaneous presence of xylene and alcohol in the body is probably not uncommon and could result in enhancement of the toxicity of xy lene. ... 

I. Lundstrom and M. Stenberg, Charge Injection and Charge Storage in Lipid Multilayers, Chem. Phys. Lipids 12, 287-302 (1974). 

Hurst (19) discusses the similarity in action of the pyrethrins and of DDT as indicated by a dispersant action on the lipids of insect cuticle and internal tissue. He has developed an elaborate theory of contact insecticidal action but provides no experimental data. Hurst believes that the susceptibility to insecticides depends partially on the cuticular permeability, but more fundamentally on the effects on internal tissue receptors which control oxidative metabolism or oxidative enzyme systems. The access of pyrethrins to insects, for example, is facilitated by adsorption and storage in the lipophilic layers of the epicuticle. The epicuticle is to be regarded as a lipoprotein mosaic consisting of alternating patches of lipid and protein receptors which are sites of oxidase activity. Such a condition exists in both the hydrophilic type of cuticle found in larvae of Calliphora and Phormia and in the waxy cuticle of Tenebrio larvae. Hurst explains pyrethrinization as a preliminary narcosis or knockdown phase in which oxidase action is blocked by adsorption of the insecticide on the lipoprotein tissue components, followed by death when further dispersant action of the insecticide results in an irreversible increase in the phenoloxidase activity as a result of the displacement of protective lipids. This increase in phenoloxidase activity is accompanied by the accumulation of toxic quinoid metabolites in the blood and tissues—for example, O-quinones which would block substrate access to normal enzyme systems. The varying degrees of susceptibility shown by different insect species to an insecticide may be explainable not only in terms of differences in cuticle make-up but also as internal factors associated with the stability of oxidase systems. 

Fat absorbed from the diet and lipids synthesized by the liver and adipose tissue must be transported between the various tissues and organs for utilization and storage. Since lipids are insoluble in water, the problem of how to transport them in the aqueous blood plasma is solved by associating nonpolar lipids (triacylglycerol and cholesteryl esters) with amphipathic hpids (phospholipids and cholesterol) and proteins to make water-miscible hpoproteins. 

The concentrations of [14C]-radiolabel were very low in the adipose deposits of mice, rats, and dogs at 1, 2, and 3 days after administration of a single dose of diisopropyl methylphosphonate (Hart 1976). This demonstrates lack of storage in body lipids. 

STORAGE OF LIPID MESSENGERS IN NEURAL MEMBRANE PHOSPHOLIPIDS 576... 

The general rules that should therefore be observed include the use of a blanket of nitrogen whenever possible and evaporation of solvents at the lowest feasible temperatures, which must not exceed 50°C. The addition of an antioxidant such as butylated hydroxytoluene (2,6-di-/-butyl-4-methylphenol) to the extraction solvents (0.1 g 1 ) might be necessary to prevent deterioration of unsaturated lipids but it is essential for storage of lipid extracts at about 0.1% of the weight of lipid. Inactivation of lipolytic enzymes may usually be achieved by addition of an alcohol such as methanol or, in some cases, isopropanol. The latter is recommended for some more stable enzymes sometimes found in plant tissues. Alternatively the plant may be briefly immersed in boiling water. 

Ethanol-related high levels of NADH+H and acetyl-CoA in the liver lead to increased synthesis of neutral fats and cholesterol. However, since the export of these in the form of VLDLs (see p. 278) is reduced due to alcohol, storage of lipids occurs (fatty liver). This increase in the fat content of the liver (from less than 5% to more than 50% of the dry weight) is initially reversible. However, in chronic alcoholism the hepatocytes are increasingly replaced by connective tissue. When liver cirrhosis occurs, the damage to the liver finally reaches an irreversible stage, characterized by progressive loss of liver functions. 

Hellerer, T., Axang, C., Brackmann, C., Hillertz, R, Pilon, M., and Enejder, A. 2007. Monitoring lipid storage in Caenorhabditis elegans using coherent anti-Stokes Raman scattering microscopy. Proc. Natl. Acad. Sci. USA 104 14658-63. 

The effects of storage on lipids depend on potato variety (Mondy et al., 1963). Tuber storage at 4°C resulted in an initial small increase in total fatty acid content (Dobson et al., 2004). Prolonged storage resulted in a fall to the initial values detected close to harvest. The content... 

Studies conducted by different authors on the release of chemical substances from medical devices, mainly those used for infusing solutions, show that these are potential sources of contamination for pharmaceutical formulations. One of the most studied is diethylhexyl phthalate, the same plasticizer found in PVC infusion bags to give flexibility. The same concerns about the use of PVC bags for the storage of lipids or lipophilic formulations are valid for tubing. 

Under proper processing conditions minimal alterations in the structure and bioavailability of food lipids take place. However, excessive heat and/or improper storage conditions can result in a number of degradative changes in lipids. These chemical changes have a much greater effect upon palatability than upon nutritive value. 

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