Removal Of Oleate Research Articles

Opposite effects of saturated and unsaturated free fatty acids on intracellular signaling and metabolism in neuronal cells

Elevated levels of plasma saturated free fatty acids are a major pathogenic factor in diabetes, cardiovascular and liver diseases. Growing evidence suggests a link between sFFA-induced metabolic impairments and neurodegeneration. Excessive sFFAs in the brain circulation may trigger neuroinflammation and insulin resistance, however the underlying signaling changes have not been clarified in neuronal cells. We recently reported the effects of FFAs on intracellular signaling and metabolism in neuronal cells. We found that palmitate induced both insulin resistance and mitochondrial dysfunction while promoting phosphorylation and nuclear translocation of NF-κB p65 in neuronal cells. The latter is a key event in the inflammatory cascade. Oleate pre-exposure and then removal was sufficient to completely block subsequent palmitate-induced intracellular signaling and metabolic derangements. Interestingly, oleate also prevented ceramide-induced insulin resistance and cytotoxicity. Protein kinase A and triglyceride accumulation were implicated in the mechanism of oleate action. This is the first demonstration showing that oleate has beneficial properties against sFFA and ceramide models of neuronal injury. The lasting effect following oleate removal on preventing palmitate- or ceramide- induced cell damage was striking.

PbSe nanocrystal shape development: oriented attachment at mild conditions and microwave assisted growth of nanocubes

PbSe nanocrystals have been synthesized by conventional hot injection process and also using microwave technique. For PbSe nanocrystals obtained via hot injection process at 160 °C, the quality of the interface between the isolated and purified nanocrystals, after removal of capping ligands, strongly depends on the structure and stoichiometry of the surface. High resolution transmission electron microscopy has been used to investigate the interface between size selected PbSe nanocrystals. Oriented attachment of nanocrystals is achieved by protonation of oleate capping ligands using wet methanol and subsequent solvent evaporation. The removal of oleate from the surface is monitored using infrared spectroscopy. The attachment between preformed PbSe NCs has taken place exclusively through the {100} facets of the rock-salt lattice. In contrast to other related observations, it is found that nanocrystals can also attach through adjacent {100} facets. We have also studied the shape evolution of cubic PbSe NCs during microwave synthesis using transmission electron microscopy. The formation of PbSe nanocubes is attributed to the higher growth rate in the {111} direction compared to that in the {100} direction.

Upregulation of cellular triacylglycerol – free fatty acid cycling by oleate is associated with long-term serum-free survival of human breast cancer cells

We previously showed that exogenous oleate protects human breast cancer cells against palmitate-induced apoptosis in part by increasing esterification of this free fatty acid (FFA) into triacylglycerol (TG). Here, we studied the mechanism whereby oleate protects these cells against apoptosis induced by serum withdrawal. The metabolism of FFA, TG, and glucose, in parallel with long-term cell survival in the absence of serum, was investigated in a panel of human breast cancer cell lines and in nontransformed MCF-10A cells after treatment with exogenous oleate. Short-term (3-24 h) exposure of MDA-MB-231 human breast cancer cells to exogenous oleate resulted in a dose-dependent long-term (10 day) serum-free survival that correlated with the accumulation of TG in lipid droplets and with upregulation of lipolysis. Both effects persisted for several days after oleate removal. Rapid TG lipolysis and FFA re-esterification, supported by high rates of glycolysis that provide the glycerol backbone for TG synthesis, are consistent with the presence of very active TG-FFA cycling in human breast cancer cells. Only the cancer cell lines capable of accumulating TG showed long-term serum-free survival after oleate treatment. The results suggest that upregulation of TG-FFA cycling induced by oleate may be involved in maintenance of human breast cancer cell survival.

Sodium oleate-facilitated reassembly of apolipoprotein A-I with phosphatidylcholine

The influence of sodium oleate (oleate) on complexing of apolipoprotein A-I (apo A-I) with egg yolk phosphatidylcholine (EYPC) was evaluated. Without the use of additional detergent such as sodium cholate, oleate facilitates formation of a single complex of unique stoichiometry, approx. 76:2:20, molar ratio EYPC/apo A-I/oleate, and mean size 7.4 nm with round to ellipsoidal morphology. Near complete reassembly of apo A-I into the complex occurs when the stoichiometry of the mixture approximates that of the complex itself. With increasing content of EYPC in the mixture, the same complex is formed but in decreasing yield; larger complexes are not formed. The rate of complex formation decreases with increase of EYPC in the mixture. Reduction of pH in the reassembly mixture from 8.0 to 5.4 results in a marked reduction in complex formation indicating that ionized oleate facilitates lipidation. Removal of oleate by interaction of the complex with fatty acid-free human serum albumin does not degrade the complex. Incorporation of increasing amounts of unesterified cholesterol into the EYPC-sonicate progressively inhibits oleate-facilitated complex formation. This study shows that oleate, a physiologically relevant lipolysis-derived product, facilitates reassembly of apo A-I with EYPC and promotes formation of a small lipid-poor particle similar to that observed in nascent HDL and during in vivo or in vitro lipolysis of triacylglycerol-rich lipoproteins in the presence of HDL.

Formation and turnover of triglyceride-rich vesicles in the chick liver cell. Effects of cAMP and carnitine on triglyceride mobilization and conversion to ketones.

Refractile cytoplasmic vesicles are formed in less than 10 h when chick liver cell monolayers are incubated with serum-free medium containing 0.9 mM oleate. These vesicles are identical in microscopic appearance to those formed in monolayers by de novo fatty acid synthesis (Tarlow, D. M., Watkins, P. A., Reed, R. E., Miller, R. S., Zwergel, E. E., and Lane, M. D. (1977) J. Cell Biol. 73, 332-353), but require about one-seventh the incubation time to achieve comparable size. After release from the cells by lysis in hypotonic medium, the vesicles can be isolated by flotation at 27,000 X g. Electron microscopy reveals that the isolated vesicles are rimmed by a membrane. Analysis of vesicles isolated from cells labeled with [14C]oleate or [14C]acetate showed that greater than 95% of their 14C content was in the form of triglyceride and that most cellular [14C]triglyceride was contained in the triglyceride-rich vesicles. Exposure of cells to dibytyryl-cAMP after removal of oleate from the medium caused the disappearance of triglyceride-rich vesicles within 36 h. In the absence of cyclic nucleotide, the vesicles persist. Consistent with this morphological change, dibutyryl-cAMP caused a 5.5-fold activation of the apparent rate of mobilization of cellular [14C]triglyceride from cells previously labeled with [14C]oleate. L-(--)-Carnitine alone had no effect; however, when added with dibutyryl-cAMP, cellular triglyceride mobilization was activated 7.4-fold. Although [14C]triglyceride was the principal 14C-labeled product secreted in the absence of cyclic nucleotide and comprised 90% of the total, [14C]acetoacetate and [14C] beta-hydroxybutyrate became major products when cells were treated with dibutyryl-cAMP. Thus, dibytyryl-cAMP activated ketogenesis from cellular [14C]triglyceride by 200-fold and when added with L-(--)-carnitine, by 400-fold. Cells containing triglyceride-rich vesicles labeled with [2-glyceryl-3H]triglyceride were generated by incubation with medium containing [2-3H]glycerol. A comparison of the rates of loss of cellular [1-oleoyl-14C- and [2-glyceryl-3H]triglyceride revealed that substantial re-esterification, i.e. recycling, of 14C-fatty acid released by lipolysis occurred. Under conditions where recycling of 3H label ws minimal, it was determined that 15% of the cellular [2-glyceryl-3H]triglyceride was secreted "en bloc," i.e. without prior lipolysis. En bloc secretion was not affected by dibutyryl-cAMP. The rate of lipolysis of vesicle-associated [2-glyceryl-3H]triglyceride was increased 2.2-fold in the presence of dibutyryl-cAmP. Chloroquine markedly inhibited the dibutyryl-cAMP-dependent lipolysis suggesting the participation of lysosomes in the mobilization of triglyceride-rich vesicles. Mechanisms are presented which could account for the effects of cAMP and carnitine on the turnover of vesicle triglyceride both at the level of lipolysis and the utilization of the released fatty acids by mitochondria...

Effects of vasopressin, glucagon and dibutyryl cyclic AMP on the activities of enzymes of fatty acid esterification in rat hepatocytes

Vasopressin and glucagon have a number of similar actions in rat liver. Both stimulate glycogenolysis and phosphorylase a activity (reviewed in [ 11) and inhibit de novo lipogenesis [2-4]. In other respects, their actions are divergent. Thus vasopressin inhibits ketogenesis from oleate and stimulates oleate esterification, whereas glucagon opposes these effects [5]. The actions of glucagon are probably mediated via the CAMP system. Current opinion suggests that the hepatic effects of vasopressin are not mediated by changes in [CAMP] [ 1,6]. A requirement for Ca2* in the action of the hormone has been indicated [ 1,7]. Stimulation of oleate esterification in hepatocytes could result from increases in the concentration of the substrates of esterlfication (fatty acyl-CoA, glycerol-3-phosphate, dihydroxyacetone phosphate). Vasopressin in the presence of oleate stimulated glycolytic flux and oleate removal in hepatocytes [5]. Another explanation is that the stimulation of oleate esteritication is caused by an increase in the specific activity of the enzymes of esterification (GPAT and DHAPAT). The activity of GPAT (and possibly DHAPAT) is decreased in fat cells by starvation or adrenaline and is increased by insulin (reviewed in [S]). In the whole liver, GPAT activity is decreased by streptozotocin-diabetes, anti-insulin serum and

Effects of Oleate Starvation in a Fatty Acid Auxotroph of Escherichia coli K-12

The effects of oleate starvation on an oleate auxotroph of Escherichia coli K-12 were investigated. Following removal of oleate from the mutant growing in a minimal glycerol-peptone medium, the cells stopped making deoxyribonucleic acid, ribonucleic acid, protein, and phospholipids; they began to die exponentially and finally lysed. During oleate starvation in minimal medium minus peptone, inhibition of macromolecular syntheses and death occurred; however, lysis did not follow. When growth ceased, no further dying was observed. It is shown that none of the early effects (inhibition of macromolecular syntheses and death) can be due to leakiness of the cells, induction of a prophage or a colicin, or lack of energy sources. The cause of inhibition of macromolecular syntheses remained unknown. Since the rate of death was the same as the generation time under different conditions, it appears that death is due to the defective synthesis of some cellular structure (quite possibly, cytoplasmic membrane) during phospholipid deficiency. Lysis was found to require protein synthesis; electron microscopy revealed a peculiar type of "lysis from within"; i.e., the shape of the cells did not change but fragmentation of the inner layer of the cell envelope occurred. The murein was found to be unaltered. Most likely, lysis was a consequence of the cell's attempt to synthesize cytoplasmic membrane with altered phospholipid composition or during phospholipid deficiency. Several membrane functions (respiration, adenosine triphosphate formation, permeability) existing before oleate removal were not lost during starvation. Therefore, general damage to the membrane did not occur, and it could be that most, if not all, described effects were due to defective de novo membrane synthesis.