Polar Lipid Biosynthesis Research Articles

Lipidomic analysis of diatoms cultivated with silica nanoparticles

Polar lipids from the diatoms Diadesmis gallica and Navicula atomus were separated and their structures were determined using high resolution tandem MS HILIC-LC/ESI. This method allowed us to identify 34 classes of lipids, each containing dozens of molecular species, including regioisomers. The largest differences were found in two sulfur-containing lipids, sulfoquinovosyldiacylglycerol and phosphatidylsulfocholine caused probably by the remodeling of lipid species. These diatoms have been found to use several mechanisms to resolve growth in extreme environments, i.e. silica starvation. The presence of insoluble nano-SiO2 leads to the replacement of cellular phospholipids with sulfolipids. Regioisomer ratios also vary depending on the concentration of nano-SiO2 in the culture medium, i.e. the biosynthesis of polar lipids via the prokaryotic (plastidial) and/or eukaryotic (explastidial) pathways. Complex analyses of polar lipids using high resolution HILIC-LC/ESI-tandem, as used for diatoms, can also be used for other photosynthetic microorganisms.

Quercetin inhibition of SREBPs and ChREBP expression results in reduced cholesterol and fatty acid synthesis in C6 glioma cells.

Quercetin (Que), a widely distributed flavonoid in the human diet, exerts neuroprotective action because of its property to antagonize oxidative stress. Here, we investigated the effects of Que on lipid synthesis in C6 glioma cells. A rapid Que-induced inhibition of cholesterol and, to a lesser extent, of fatty acid synthesis from [1-14C]acetate was observed. The maximum decrease was detected at the level of palmitate, the end product of de novo fatty acid synthesis. The effect of Que on the enzyme activities of acetyl-CoA carboxylase 1 (ACC1) and fatty acid synthase (FAS), the two enzymes of this pathway, was investigated directly in situ in permeabilized C6 cells. An inhibitory effect on ACC1 was observed after 4 h of 25 μM Que treatment, while FAS activity was not affected. A reduction of polar lipid biosynthesis was also detected. A remarkable decrease of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) activity, regulatory enzyme of cholesterol synthesis, was evidenced. Expression studies demonstrated that Que acts at transcriptional level, by reducing the mRNA abundance and protein amount of ACC1 and HMGCR. Deepening the molecular mechanism, we found that Que decreased the expression of SREBP-1 and SREBP-2, transcriptional factors representing the main regulators of de novo fatty acid and cholesterol synthesis, respectively. Que also reduced the nuclear content of ChREBP, a glucose-induced transcription factor involved in the regulation of lipogenic genes. Our results represent the first evidence that a direct and rapid downregulatory effect of Que on cholesterol and de novo fatty acid synthesis is elicited in C6 cells.

Oleic Acid and Hydroxytyrosol Inhibit Cholesterol and Fatty Acid Synthesis in C6 Glioma Cells

Recently, the discovery of natural compounds capable of modulating nervous system function has revealed new perspectives for a healthier brain. Here, we investigated the effects of oleic acid (OA) and hydroxytyrosol (HTyr), two important extra virgin olive oil compounds, on lipid synthesis in C6 glioma cells. OA and HTyr inhibited both de novo fatty acid and cholesterol syntheses without affecting cell viability. The inhibitory effect of the individual compounds was more pronounced if OA and HTyr were administered in combination. A reduction of polar lipid biosynthesis was also detected, while triglyceride synthesis was marginally affected. To clarify the lipid-lowering mechanism of these compounds, their effects on the activity of key enzymes of fatty acid biosynthesis (acetyl-CoA carboxylase-ACC and fatty acid synthase-FAS) and cholesterologenesis (3-hydroxy-3-methylglutaryl-CoA reductase-HMGCR) were investigated in situ by using digitonin-permeabilized C6 cells. ACC and HMGCR activities were especially reduced after 4 h of 25 μM OA and HTyr treatment. No change in FAS activity was observed. Inhibition of ACC and HMGCR activities is corroborated by the decrease of their mRNA abundance and protein level. Our results indicate a direct and rapid downregulatory effect of the two olive oil compounds on lipid synthesis in C6 cells.

Lipidomic analysis of the extremophilic red alga Galdieria sulphuraria in response to changes in pH

Analysis of polar lipids from the red micro-alga Galdieria sulphuraria by means of the HILIC-LC/high resolution ESI-tandem MS determined 14 classes of lipids including identification of tens of molecular species of lipids and their regioisomers. The extremophilic alga G. sulphuraria uses several mechanisms for adaptation to low pH and high temperature, the major change being a replacement of cellular phospholipids by betaine lipids. We also found a change in the ratio of regioisomers of the polar lipids, i.e. phospho-, glyco- and betaine lipids, in dependence on the culture medium pH. We hypothesize that biosynthesis of polar lipids via the prokaryotic and/or eukaryotic pathway is dependent on ambient pH.

The effect of cadmium on lipid and fatty acid biosynthesis in tomato leaves

AbstractThis research aims to examine the effect of cadmium uptake on lipid composition and fatty acid biosynthesis, in young leaves of tomato treated seedlings (Lycopersicon esculentum cv. Ibiza F1). Results in membrane lipids investigations revealed that high cadmium concentrations affect the main lipid classes, leading to strong changes in their composition and fatty acid content. Thus, the exposure of tomato plants to cadmium caused a concentration-related decrease in the unsaturated fatty acid content, resulting in a lower degree of fatty acid unsaturation. The level of lipid peroxides was significantly enhanced at high Cd concentrations. Studies of the lipid metabolism using radioactive labelling with [1-14C]acetate as a major precursor of lipid biosynthesis, showed that levels of radioactivity incorporation in total lipids as well as in all lipid classes were lowered by Cd doses. In total lipid fatty acids, [1-14C]acetate incorporation was reduced in tri-unsaturated fatty acids (C16:3 and C18:3); While it was enhanced in the palmitic (C16:0), palmitoleic (C16:1), stearic (C18:0) and linoleic (C18:2) acids. [1-14C]acetate incorporation into C16:3 and C18:3 of galactolipids [monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG)] and some phospholipids [phosphatidylcholine (PC) and phosphatidylglycerol (PG)] was inhibited by Cd stress. Our results showed that in tomato plants, cadmium stress provoked an inhibition of polar lipid biosynthesis and reduced fatty acid desaturation process.

Characterization of the precursor of tetraether lipid biosynthesis in the thermoacidophilic archaeon Thermoplasma acidophilum.

Polar lipid biosynthesis in the thermoacidophilic archaeon Thermoplasma acidophilum was analyzed using terbinafine, an inhibitor of tetraether lipid biosynthesis. Cells of T. acidophilum were labeled with [(14)C]mevalonic acid, and their lipids were extracted and analyzed by two-dimensional thin-layer chromatography. Lipids labeled with [(14)C]mevalonic acid, [(14)C]glycerol, and [(32)P]orthophosphoric acid were extracted and hydrolyzed under different conditions to determine the structure of polar lipids. The polar lipids were estimated to be archaetidylglycerol, glycerophosphatidylcaldarchaetidylglycerol, caldarchaetidylglycerol, and beta- l-gulopyranosylcaldarchaetidylglycerol, the main polar lipid of T. acidophilum. Pulse and chase experiments with terbinafine revealed that one tetraether lipid molecule is synthesized by head-to-head condensation of two molecules of archaetidylglycerol and that a sugar group of tetraether phosphoglycolipid is expected to attach to the tetraether lipid core after head-to-head condensation in T. acidophilum. A precursor accumulated in the presence of terbinafine with a fast-atom-bombardment mass spectrometry peak m/z 806 was compatible with archaetidylglycerol. The relative height of the peak m/z 806 decreased after removal of the inhibitor. The results suggest that most of the precursor, archaetidylglycerol, is in fully saturated form.

Inhibition of phytosterol biosynthesis in elicitor-treated cultures of Ammi majus

The elicitor-mediated induction of coumarin phytoalexin production by cell-suspension cultures of Ammi majus is accompanied by the inhibition of both biomass production and phytosterol biosynthesis [from mevalonic acid (MVA)]. However, cell-free preparations of cells from elicitor-treated cultures are able to support the synthesis of squalene from MVA, isopentenyl diphosphate (IPP) or (2 E, 6 E)-farnesyl diphosphate (FPP), even though radioactive squalene is not found following administration of [2- 14C]MVA to elicitor-treated cultures. The preparations, as expected, also exhibit umbelliferone:O-dimethylallyl transferase activity. These results indicate that in vivo there is a specific inhibition of one of the enzymes on the MVA to dimethylallyl diphosphate (DMAPP) span of the cytosolic microsomal pathway of terpenoid biosynthesis in elicitor-treated cultures, and that in cell-free preparations this deficiency is made good by the corresponding plastid enzyme. The finding that the coumarin phytoalexins are not labelled on feeding either [2- 14C]acetate or [2- 14C]MVA to elicitor-treated cultures precluded us from establishing whether the inhibition of phytosterol biosynthesis is a means of increasing the input of cytosolic IPP into the plastid for coumarin phytoalexin biosynthesis (in which case cytosolic IPP isomerase would be the enzyme inhibited in elicitor-treated cultures) or whether the cytosolic and plastid pathways of terpenoid biosynthesis are not linked and the site of inhibition (between MVA and DMAPP) is unrelated to the provision of plastid IPP for phytoalexin biosynthesis. The feeding experiments with [2- 14C]acetate suggested that, somewhat unexpectedly, polar lipid biosynthesis is not repressed in elicitor-treated cultures.

Effects of vanadium, nickel and sulphur dioxide on polar lipid biosynthesis in jack pine

Biosynthesis of polar lipids (phospho- and glycolipids) from [1- 14C]acetate was observed in mature needles from hydroponically grown jack pine seedlings. Treatment of the seedlings with vanadium (V) or nickel (Ni) produced marked concentration-dependent inhibitions in the biosynthesis of all polar lipids. Nickel appeared to be more inhibitory than V at 10 ppm. Fumigation of seedlings with gaseous SO 2 (0.34 ppm) also resulted in reduced biosynthesis of polar lipids. Combined treatment of plant seedlings with metal (V or Ni) and SO 2 produced inhibitory effects that were very similar to those produced by metal alone; however, SO 2 did produce an additive inhibitory effect at 10 ppm V.

Total polar lipid biosynthesis during growth of Crotalaria juncea pollen tubes

[1- 14C]-Acetate incorporation into total and polar lipids was studied in the growing pollen tubes of Crotalaria juncea. Ungerminated pollen had phosphatidyl inositol, phosphatidyl serine, phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl glycerol, monogalactosyl diglyceride, digalactosyl diglyceride, sulpholipid and steryl glycosides. In the growing pollen tubes considerable [1- 14C]-acetate incorporation was observed into the individual polar lipids. The exogenous carbon source significantly influenced lipid biosynthesis. Boric acid (20mg/l.) promoted both pollen tube growth and acetate incorporation into phospholipids. In comparison to 5′-adenosine monophosphate, cyclic-3′,5′-adenosine monophosphate (cAMP) promoted tube growth and also enhanced phospho-and glycolipid biosynthesis. The regulation of membrane component biosynthesis by cAMP is suggested.

Effect of irrigation on lipid biosynthesis in maturing sunflower seeds

AbstractThe effect of irrigation on lipid biosynthesis in maturing sunflower (Helianthus annuus L.) seeds has been studied. Restricted irrigation adversely affected the biosynthesis of polar lipids during initial stages and triglycerides at the later stages of seed development. The fatty acid composition remained unaffected by irrigation. A de novo synthesis of triglycerides and fatty acids has also been observed.

Total and Polar Lipid Biosynthesis duringCrotalaria junceaLinn. Pollen Tube Growth: Effect of Gibberellic Acid, Indoleacetic Acid and (2-Chloroethyl)-phosphonic Acid

Total and Polar Lipid Biosynthesis during<i>Crotalaria juncea</i>Linn. Pollen Tube Growth: Effect of Gibberellic Acid, Indoleacetic Acid and (2-Chloroethyl)-phosphonic Acid

An unusual lipid in the human pathogenic fungus Epidermophyton floccosum

The dermatophyte Epidermophyton floccosum contains an unusual lipid characterized as 1(3),2-diacylglyceryl-3(1)- O-4′-( N, N, N-trimethyl)homoserine. Its concentration in E. floccosum is approx. 15% of the polar lipids. The role of this lipid in the biosynthesis of polar lipids and fatty acids is not yet known. However, it is interesting from a chemotaxonomic viewpoint that the lipids from two other genera of dermatophyte, Microsporum cookei and Trichophyton rubrum do not contain this novel lipid.