A shift from phospholipid to triglyceride synthesis when cell division is inhibited by trans-fatty acids

Lipid nutrition: "In silico" studies and undeveloped experiments

This review examines lipids and lipid-binding sites on proteins in relation to cardiovascular disease. Lipid nutrition involves food energy from ingested fatty acids plus fatty acids formed from excess ingested carbohydrate and protein. Non-esterified fatty acids (NEFA) and lipoproteins have many detailed attributes not evident in their names. Recognizing attributes of lipid-protein interactions decreases unexpected outcomes. Details of double bond position and configuration interacting with protein binding sites have unexpected consequences in acyltransferase and cell replication events. Highly unsaturated fatty acids (HUFA) have n-3 and n-6 motifs with documented differences in intensity of destabilizing positive feedback loops amplifying pathophysiology. However, actions of NEFA have been neglected relative to cholesterol, which is co-produced from excess food. Native low-density lipoproteins (LDL) bind to a high-affinity cell surface receptor which poorly recognizes biologically modified LDLs. NEFA increase negative charge of LDL and decrease its processing by "normal" receptors while increasing processing by "scavenger" receptors. A positive feedback loop in the recruitment of monocytes and macrophages amplifies chronic inflammatory pathophysiology. Computer tools combine multiple components in lipid nutrition and predict balance of energy and n-3:n-6 HUFA. The tools help design and execute precise clinical nutrition monitoring that either supports or disproves expectations.

Inhibition of blood platelet aggregation by dioxo-ene compounds

Compounds with a conjugated oxo-ene-oxo system were tested for inhibition of blood platelet aggregation. All compounds with this structure in trans configuration were effective inhibitors of aggregation induced by thrombin and by arachidonic acid. While the oxo-trans-ene-oxo system is prerequisite for such activity, other structural features of the compounds may be varied without loss of activity. Inhibition is exemplified by 9,12-dioxo-trans-10- and 10,13-dioxo-trans-11-octadecenoic acids and their methyl esters, by 11,14-dioxo-trans-12- eicosenoic acid, by 4,7-dioxo-trans-5- decene and by trans- dibenzoylethylene . The half-inhibition concentrations are in the order of 2-6 microM, with complete inhibition at 8-20 microM. According to experiments with the inhibiting 9,12-dioxo-trans-10-octadecenoic acid, the normal oxygenation of exogenous arachidonic acid by platelets is not affected but the thrombin-induced internal release of this acid seems to be abolished by the inhibitor. The inhibition of aggregation in the presence of exogenous arachidonic acid and its products suggests that the inhibitor also interferes with other events leading to aggregation. By implication from other properties of the oxo-trans-ene-oxo system, reaction with SH groups may be a mechanism for inhibition.

Lipid metabolism in fungi

So far, reviews that have appeared on fungal lipids present data mainly on the lipid composition of these organisms and the influence of lipids on their physiology. These reviews provide little information about the enzymes of lipid metabolism in these organisms and it is assumed, by most workers, that lipid synthesis in all fungi takes place as in Saccharomyces cervesiae, the only fungus in which the complete pathways of phospholipid biosynthesis have been worked out. During the last few years, literature has accumulated on lipid metabolic enzymes of other fungi, as investigators became increasingly interested in this area of research. The present review, after an introduction, will be divided into different sections and each section will deal, comparatively, with various aspects of fungal lipid metabolism and physiology. This review will, therefore, bring out the differences or similarities of lipid metabolism in diverse fungal species.

Possible regulation of phospholipase C activity in human platelets by phosphatidylinositol 4',5'-bisphosphate

Phospholipase C from human platelets was found to catalyze the Ca2+-dependent degradation of phosphatidylinositol (PI), phosphatidylinositol 4'-phosphate (DPI), and phosphatidylinositol 4',5'-bisphosphate (TPI) at Ca2+ concentrations from 150 microM to 5 mM. Both DPI and TPI inhibited the hydrolysis of [2-3H]inositol-labeled PI (250 microM) in a concentration-dependent manner. The use of DPI and TPI from beef brain, both of which have fatty acid compositions different from that of soybean PI, permitted an assessment of the inhibitory effect of polyphosphoinositides on the hydrolysis of PI by phospholipase C. Fatty acid analysis of the diacylglycerols formed demonstrated that DPI and TPI, when incubated in mixture with PI, were competitive substrates for PI hydrolysis. Increasing the DPI/PI ratio from 0 to 0.3 caused a shift in the degradation of PI to DPI without greatly affecting the formation of 1,2-diacylglycerol. TPI alone, or in mixture with PI, was a poor substrate for phospholipase C. Increasing the TPI/PI ratio from 0 to 0.21, on the other hand, inhibited both PI degradation (greater than or equal to 95%) and overall formation of 1,2-diacylglycerol (greater than or equal to 82%). Kinetic analysis revealed that TPI acts as a mixed-type inhibitor with a Ki of about 10 microM. The Ka for Ca2+ in PI hydrolysis was profoundly increased from 5 to 180 microM when TPI (36 microM) was included with PI (250 microM). Optimum PI degradation under these conditions was only attained when the calcium concentration approached 4 mM. Analysis of phospholipids from unstimulated human platelets from five different donors revealed DPI/PI and TPI/PI ratios of 0.42 and 0.16, respectively. These findings, combined with the observed inhibition of PI hydrolysis by TPI at a TPI/PI ratio of 0.16, would suggest that in unstimulated platelets phospholipase C activity may be inhibited by greater than or equal to 75%. Changes in 33P-prelabeled phospholipids of intact platelets upon stimulation with thrombin indicated a transient decline in 33P label of both TPI and DPI (15 s) followed by an increase in [33P]phosphatidic acid but no change in [33P]PI. The finding that DPI is selectively degraded by phospholipase C in mixture with PI at DPI/PI ratios determined to be present in unstimulated platelets indicates that DPI may be more important than PI in the formation of 1,2-diacylglycerol which is believed to serve as precursor of arachidonic acid for thromboxane biosynthesis. Furthermore, the results suggest that in human platelets TPI may serve as modulator for the formation of 1,2-diacylglycerol from inositol phospholipids.

Selective loss of mitochondrial genome can be caused by certain unsaturated fatty acids

Various unsaturated fatty acids had different effectiveness for maintaining the continued replication of functional mitochondria in an unsaturated fatty acid auxotroph of Saccharomyces cerevisiae (KD115). Certain isomers of octadecenoic acid (i.e., cis-9) and eicosatrienoic acid (i.e.,cis-8,11,14) permitted continued replication of mitochondria and provided cultures that contained only 4 to 5% cells that formed petite colonies. On the other hand, cultures grown with cis-12- or cis-13-octadecenoic acid or cis-11,14,17-eicosatrienoic acid, produced a 12- to 16-fold greater frequency of petite mutants (50-60%) after 8 to 10 generations of growth. The production of the petite mutants occurred despite adequate incorporation of these unsaturated fatty acids into cellular phospholipids and an apparently normal ability to undergo the initial steps in the induction of cellular respiration. The evidence suggests that some cellular processes necessary for continued mitochondrial replication depend on the structural features of the fatty acyl chains as well as the overall content of unsaturated fatty acids in membrane phospholipids. Impairment of that process by certain inadequate fatty acids or by an inadequate supply of a suitable fatty acid leads to a permanent loss of the mitochondrial genome from the cells of subsequent generations.

Effects of unsaturated fatty acid deprivation on neutral lipid synthesis in Saccharomyces cerevisiae

The effects of unsaturated fatty acid deprivation on lipid synthesis in Saccharomyces cerevisiae strain GL7 were determined by following the incorporation of [14C]acetate. Compared to yeast cells grown with oleic acid, unsaturated fatty acid-deprived cells contained 200 times as much 14C label in squalene, with correspondingly less label in 2,3-oxidosqualene and 2,3;22,23-dioxidosqualene. Cells deprived of either methionine or cholesterol did not accumulate squalene, demonstrating that the effect of unsaturated fatty acid starvation on squalene oxidation was not due to an inhibition of cell growth. Cells deprived of olefinic supplements displayed additional changes in lipid metabolism: (i) an increase in 14C-labeled diacylglycerides, (ii) a decrease in 14C-labeled triacylglycerides, and (iii) increased levels of 14C-labeled decanoic and dodecanoic fatty acids. The changes in squalene oxidation and acylglyceride metabolism in unsaturated fatty acid-deprived cells were readily reversed by adding oleic acid. Pulse-chase studies demonstrated that the [14C]squalene and 14C-labeled diacylglycerides which accumulated during starvation were further metabolized when cells were resupplemented with oleic acid. These results demonstrate that unsaturated fatty acids are essential for normal lipid metabolism in yeasts.

Preparation of phosphatidyl[2-3H]inositol from yeast grown in medium containing myo[2-3H]inositol

Phosphatidyl[2-3H]inositol was prepared from Saccharomyces cerevisiae (YSC-2), grown in synthetic medium containing myo[2-3H]inositol. Over 44 microCi (or 81%) of the radiolabeled inositol was taken up by the organism, with 34 microCi incorporated into phosphatidylinositol. Upon purification by silicic acid pressure liquid chromatography (MPLC), a final yield of 24 to 26 microCi of phosphatidyl[2-3H]inositol with a specific radioactivity of 40 X 10(3) dpm/nmole was obtained. The purified phosphatidyl[2-3H]inositol was found to be a suitable for phospholipase C from human platelets.

Chaulmoogric acid: assimilation into the complex lipids of mycobacteria

Lipid analysis of Mycobacterium vaccae, grown in the presence of chaulmoogric acid, demonstrates that this cyclopentenyl fatty acid is taken up by the organism and incorporated into cellular phospholipids and triacylglycerols. As cell growth is retarded by the addition of chaulmoogric acid to the growth medium, it is possible that the antimicrobial properties of this compound results from a perturbation of membrane processes.

Manipulation of alkylglycerolipid levels in cultured cells. Fatty alcohol versus alkylglycerol supplements

Ehrlich ascites cells and monolayers of L-M cell fibroblasts were grown in medium containing either long-chain fatty alcohols or alkylglycerols. The cells were then analyzed to determine the contribution of these lipid precursors to the synthesis of complex lipids for the purpose of defining the most efficient system to elevate the levels of ether phospholipids. Label from high specific activity [1-14C]hexadecanol, [1-14C]octadecanol, and [1-14C]octadecenol was incorporated into alkyl linkages (C-18 : 1 greater than C-16 : 0 greater than C-18 : 0); however, similar labeling of acyl groups occurred. Increasing the amount of hexadecanol in the growth medium resulted in a higher percentage of 14C-labeled acyl groups than alkyl linkages at all concentrations of the alcohol supplement. Supplements of rac-[1-14C]hexadecylglycerol to the growth media were assimilated into phospholipids, which significantly increased as a function of the amounts added. Mass determinations of the alkyl ether phospholipid content in L-M cells incubated for 24 h with an alkylglycerol mixture (10.8 microgram/ml) showed an approximate 70% increase over control levels; supplementation had only a slight effect on the alk-1-enyl content. The systems described will be useful for investigating biophysical and biochemical effects of alkyl ether enrichment in membranes.

Cell growth with trans fatty acids is affected by adenosine 3',5'-monophosphate and membrane fluidity

Two positional isomers (9 and 11) of trans octadecenoates did not support growth on glucose of an Escherichia coli mutant that requires unsaturated fatty acids. However, the trans fatty acids provided sufficient fluidity to produce much higher cell yields when the concentration of adenosine 3',5'-monophosphate was raised. The effectiveness of the trans acids rose from 0 to 1 cell per femtomole to 15 to 20 cells per femtomole as the concentration of adenosine 3',5'-monophosphate was increased. The corresponding cis positional isomers supported high yields (35 to 40 cells per femtomole) independent of supplementation. The enhanced growth with adenosine 3',5'-monophosphate supplementation is not due to an increased uptake and incorporation of the trans isomers relative to the cis isomers, since the 9-trans isomer was incorporated more rapidly than the 9-cis isomer into the membrane phospholipids under all growth conditions and represented 21 +/- 2 mole percent of the acids. The finding that cells growing with trans fatty acid isomers have a higher requirement for adenosine 3',5'-monophosphate may indicate that some fatty acids can alter the metabolic regulation normally exerted by the cyclic nucleotide.

Triaglycerol metabolism in Saccharomyces cerevisiae. Relation to phospholipid synthesis

The acylglycerol content of Saccharomyces cerevisiae has been examined during cellular growth. The cells maintained a constant amount of phospholipid and diacylglycerol throughout growth. Triacylglycerol content fell in the early exponential phase of growth and then increased sharply upon entry of the culture into the stationary growth phase. Pulse-chase experiments with [1-14C]oleic acid and [2-3H]- and [1-14C]glycerol indicated that the triacylglycerol molecule was utilized for phospholipid synthesis in early exponential phase probably through a diacylglycerol intermediate. A substantial turnover of phospholipid during growth was also apparent. No role for the triacylglycerol could be found in regulating the fatty acid species of the phospholipid nor in the storage of fatty acid for energy metabolism.