Lipids depletion

Subjecting cells to oxidative stress can result in severe metabolic dysfunctions, including peroxidation of membrane lipids, depletion of nicotinamide nucleotides, rises in intracellular free Ca ions, cytoskeletal disruption and DNA damage. The latter is often measured as formation of single-strand breaks, double-strand breaks or chromosomal aberrations. Indeed, DNA damage has been almost invariably observed in a wide range of mammalian cell types exposed to oxidative stress in a number... 

As a second possibility, lipid-protein interaction must be considered. The red shift might be explained in terms of hydrophobic interaction of the hydrocarbon chains of phospholipids with the protein in such a way that the amide chromophores are transferred to a less polar environment (89). Again, the hypothesis can be tested by removal of lipid. The existence of the red shift in lipid-depleted mitochondria and in lipid-free mitochondrial structural protein shows that lipid-protein interaction is not necessary to produce the ORD spectra characteristic of membranes. It is possible that if some molecular rearrangement occurs during the extraction process, a red shift caused by hydrophobic lipid-protein association could be replaced with a red shift arising from hydrophobic protein-protein association. Such an explanation is unlikely, especially in view of the retention of the unit membrane structure in electron micrographs taken of extracted vesicles (30). On the basis of ORD, then, the most reasonable conclusion is that the red shift need not be assigned to lipid-protein association. 

Lenaz, G., Sechi, A. M., Masotti, L., and Parenti-Castelli, G. Lipid-protein interactions in mitochondria. II. On the nature and biochemical significance of the interaction between phospholipids and lipid-depleted mitochondria. Arch. Biochem. Biophys. 141, 89-97 (1970). 

Van Heusden M. C., Van der Horst D. J., Kawooya J. K. and Law J. H. (1991) In vivo and in vitro loading of lipid by artificially lipid-depleted lipophorins evidence for the role of lipophorin as a reusable lipid shuttle. J. Biol. Chem. 264, 17287-17292. 

ER of adrenal, testis, ovary, liver and placenta. It is relatively unstable, being inactivated by freezing, even when pure. A phospholipid environment appears to be an important requirement since, when bovine adrenal microsomal preparations were treated with phospholipase A, 80-85% of phospholipids were hydrolysed with a concomitant loss of 80-90% of enzymic activity [84], Restoration of activity was achieved by adding back to the lipid-depleted membranes aqueous dispersions of microsomal total lipid mixtures [84],... 

Of interest, lipid-containing pellicle was less permeable to lactic acid diffusion in vitro than lipid-depleted pellicle and pellicles from caries-resistant subjects were less permeable than pellicles from caries-susceptible subjects [102], These observations suggest a possible protection mechanism against caries without highlighting the particular lipids responsible. Other studies have indicated that lipids adversely affect the association of calcium with salivary glycoprotein [105]. It has also been speculated that because lipids modify the hydrophobic nature of the pellicle, they may facilitate bacterial adhesion [102,105],... 

Leukocytes from subjects with familial hypercholesterolemia responded to incubation in a lipid-depleted medium with a higher activation of sterol synthesis and an enhanced induction of HMG-CoA reductase compared to leukocytes from controls. This increase in sterol synthesis and HMG-CoA reductase was correlated with a loss of cholesterol into the medium. 

Lipid-depleted serum Hepatoma tissue culture cells + 146... 

In a second mechanism for delivering cholesterol to cells, the receptor SR-BI mediates the selective uptake of cho-lesteiyl esters from high-density lipoprotein, LDL, and very low density lipoprotein. The resulting lipid-depleted lipoprotein particle is subsequently released from the cell and can be reused (see Figure 18-16). 

HDL binding to SR class B type I (SR-BI) on the cell surface mediates the transfer of its cholesteryl esters to the cell and subsequent release of the lipid-depleted HDL into... 

Chou et al. (2005) have investigated CS2-induced skin toxicity in mice and alterations in epidermal permeability leading to physiological and pathological changes from topical exposure to CS2. The authors have postulated two mechanistic pathways to account for CS2-induced epidermal alterations, one involving intercellular lipid depletion and the other with keratinocyte damage. 

Lipids may well be involved in the subunit interactions in the Na-K ATPase complex, since this would explain why the monomeric K -activated phosphatase is less inhibited upon delipidation and is reactivated at lower lipid concentrations than the overall Na-K ATPase activity [117,120]. This requirement of subunit interaction is supported by the finding that in the presence of detergents covalent cross-linking of a-subunits by Cu or Cu -phenanthroline is inhibited and is replaced by cross-linking of an a- to a )8-subunit [121], despite the very low SH-group content of the j8-subunit (Section 3a). In a lipid-depleted enzyme preparation the ATP-dependent phosphorylation level is reduced less than the overall Na-K ATPase activity [122]. Addition of K to the phosphorylated lipid-depleted enzyme did not stimulate Pj production, whereas addition of K to the lipid-reactivated preparation increased hydrolysis. This implies that the P 2 — P conformational transition is blocked in the lipid-depleted preparations, and that this is one of the steps in which subunit interaction is involved. 

Another consequence of partial lipid depletion is that the residual K -stimulated phosphatase is not inhibited by Na nor undergoes stimulation by Na" " -I-ATP at low K concentrations [117,124]. This has led to the suggestion that the K" -stimulated phosphatase activity in preparations containing a full lipid complement is a monomeric enzyme function by virtue of a K -induced dissociation of the dimer into monomers. Na would inhibit the phosphatase by inducing dimerization. In lipid-depleted preparations, having only one of the monomers saturated with lipid as a prerequisite for phosphatase activity to occur, Na would be unable to cause dimerization. Hence, it does neither inhibit the phosphatase activity nor stimulate Na-K ATPase activity for which dimerization is essential. As a consequence, the Na -dependent reactions (ATP-phosphorylation and the ADP-ATP exchange) would be expressions of the dimer and the -dependent reactions (K -stimulated dephosphorylation and phosphatase) expressions of the monomer. However, thimerosal, which would inhibit monomer interaction, does not inhibit any of these partial reactions, but increases the affinities for K" " [125,126] and lipid depletion reduces the Na -dependent phosphorylation less than the overall Na-K ATPase activity [122]. It is clear from these studies that an unequivocal answer as to the monomeric and dimeric nature of the partial reactions in the overall Na-K ATPase reaction and their lipid dependence must await determination of their functional molecular weights. 

The effects of sodium chlorite on membrane components and antioxidant depletion have been studied in rabbit corneal epithelial cells, human conjunctival epithelial cells, phospholipid vesicles prepared from egg yolk and GSH in solution. Incubation of phospholipid vesicles with 3.5 mmol sodium chlorite/l for up to 2 h had no effect, whereas incubation for 48 h resulted in lipid depletion and an increase in lipid oxidation. Sodium chlorite was found to be a very potent GSH oxidizing agent at a GSH/sodium chlorite ratio of 0.5, GSH was depleted after 5 min. GSH depletion was also seen in rabbit corneal epithelial cells and human conjunctival epithelial cells incubated with 3.5 mmol sodium chlorite/l or 0.55 mmol sodium chlorite/l. At 3.5 mmol/l, sodium chlorite caused rapid loss of cell viability in the corneal cells, as assessed by trypan blue staining and loss of adherence. At 0.55 mmol/l, sodium chlorite had very little effect over the first few hours but decreased viability after 24 h. The conjunctival cells appeared to be less sensitive than the corneal cells. No oxidatively modified lipids could be detected in the cells following sodium chlorite treatment, and no effects were seen in levels of cytosolic antioxidants (Ingram et al., 2003). 

Immature HPL Lipid depleted apoAI-contalnIng particle... 

Delipidation of membranes (at least in the case of mitochondria) enhanced the extent of the transference of lipid from liposomes to membrane protein. Partial delipidation of mitochondria was also accomplished by extracting the organelles with 50% (v/v) aqueous acetone. This treatment inactivated many enzymes, but they could be reactivated by incubating the lipid-depleted organelles with liposomes made from the extracted lipids (Jolliot and Mazliak, 1973). 

The antistaphylococcal activity of 4-n-alkylphenols increases with increasing alkyl chain length from 2 to 6 carbon atoms [95], As the length of the alkyl chain increases so the water solubility falls, the lipid solubility rises, and the molecules become more surface active [95]. Penetration into the lipid-rich interior of the cell membrane therefore appears to be an important step in the antimicrobial action of the alkylphenols. Fattened staphylococci with increased Hpid content display some resistance to the alkylphenols because the molecules are bound to the extra lipid and are thereby denied access to the membrane [95]. Conversely, lipid-depleted cells are more sensitive than normal cells to alkylphenols and other membrane-active agents [96]. 

Krupa Z, Williams JP, and Huner, NPA. The role of aeyl lipids in reconstitution of lipid-depleted light harvesting complex II from cold hardened and nonhardened rye. Plant Physiol. 1992 100 931-938. 

Apoprotein E, which binds to hepatic receptors for uptake of lipid-depleted chylomicron remnants. Chylomicron remnants are taken into the liver by receptor-mediated endocytosis, followed by hydrolysis of the proteins and the residual lipids. 

Thus, one can expect that, due to their different composition in acyl lipids, the two monolayers will be assigned different roles in the thylakoid membrane function. One of the approaches to test this hypothesis has been to use the acyl lipid depletion technique in which special precautions have to be taken to remove all hydrolysis products (free fatty acids and lysoderivatives) which could alter membrane function [6]. Recent evidence concerning the role of phospholipids in sustaining the uncoupled non-cyclic electron flow activity is that several distinct populations of PG and PC have to be considered [3,6]. A first one, which is easily accessible to phospholipase A2, supports only about 15% of the activity. A second phospholipid population which is less accessible to phospholipase A2 sustains the remaining 85% of the activity. Finally, a third population of phospholipids does not seem to be involved in the uncoupled non-cyclic electron flow activity. These results and several other reports using mainly reconstitution procedures [4,5] point to the fact that acyl lipids may sustain the photosynthetic membrane function. 

Membrane vesicles prepared from Thiobacillus ferrooxidans contained three enzymes of the iron oxidation system. Delipidation of these vesicles by aqueous acetone decreased the enzymatic activities. They were restored by incubation of the lipid-depleted vesicles with a dispersion of ornithine-containing lipid together with coenzyme Qg. A possible role of the ornithine-containing lipid in the iron oxidation system has been suggested (25). 

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