The control of fatty acid composition in glycerolipids

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.

The Function and Mechanism of Lipid Molecules and Their Roles in The Diagnosis and Prognosis of Breast Cancer

Lipids are essential components of cell structure and play important roles in signal transduction between cells and body metabolism. With the continuous development and innovation of lipidomics technology, many studies have shown that the relationship between lipids and cancer is steadily increasing, involving cancer occurrence, proliferation, migration, and apoptosis. Breast cancer has seriously affected the safety and quality of life of human beings worldwide and has become a significant public health problem in modern society, with an especially high incidence among women. Therefore, the issue has inspired scientific researchers to study the link between lipids and breast cancer. This article reviews the research progress of lipidomics, the biological characteristics of lipid molecules, and the relationship between some lipids and cancer drug resistance. Furthermore, this work summarizes the lipid molecules related to breast cancer diagnosis and prognosis, and then it clarifies their impact on the occurrence and development of breast cancer The discussion revolves around the current research hotspot long-chain non-coding RNAs (lncRNAs), summarizes and explains their impact on tumor lipid metabolism, and provides more scientific basis for future cancer research studies.

The effect of ethanol on the phase transition temperature and the phase structure of monounsaturated phosphatidylcholines

Previous studies from our laboratories have delineated the relationship between the acyl chain asymmetry of mixed-chain phosphatidylcholines, C(X):C(Y)PC, and the effect of ethanol concentration, [EtOH], on the main phase transition temperature, T(m), and the phase structure of the lipid bilayer composed of C(X):C(Y)PC using differential scanning calorimetry and X-ray diffraction techniques [Huang and McIntosh, Biophys. J. 72 (1997) 2702--2709]. In the present work, we have extended these studies to characterize the effect of [EtOH] on the T(m) and the phase structure of the lipid bilayer composed of sn-1 saturated/sn-2 monounsaturated phosphatidylcholines with various positions of the cis double bond. Specifically, five positional isomers of 1-eicosanoyl-2-eicosenoyl-sn-glycero-3-phosphocholines, C(20):C(20:1 Delta(n))PC with n=5, 8, 11, 13 and 17, were synthesized and studied. For C(20):C(20:1 Delta(n))PC with n=5 and 8, results from the calorimetric experiments showed that in response to various concentrations of ethanol, the change in T(m) of the lipid bilayer composed of monounsaturated lipids was characterized by a sigmoidal or biphasic profile in the plot of T(m) versus [EtOH]. In contrast, a continuous depression of the T(m) by ethanol was observed calorimetrically for C(20):C(20:1 Delta(n))PC with n> or =11. The X-ray diffraction experiments further demonstrated that C(20):C(20:1 Delta(5))PC and C(20):C(20:1 Delta(8))PC can undergo the ethanol-induced gel-to-fully interdigitated phase transition at T<T(m). Such a transition, however, was not observed for C(20):C(20:1 Delta(13))PC even at a very high ethanol concentration of 100 mg/ml. These distinct different effects of [EtOH] on the phase transition temperature and the phase structure can be attributed to various positions of the cis double bond in these monounsaturated phosphatidylcholines. And the different effects of ethanol can, in fact, be explained based on the molecular structures of these monounsaturated lipids packed in the gel-state bilayer as generated by molecular mechanics simulations. To the best of our knowledge, this is the first time that the ethanol-induced fully interdigitated bilayers are observed at T<T(m) for unsaturated phospholipids with well defined double bond positions in their sn-2 acyl chains.

Solubilization, partial purification and photolabeling of the integral membrane protein lysophospholipid:acyl-CoA acyltransferase (LAT)

In the present study, we defined experimental conditions that allowed the extraction of the integral membrane protein lysophospholipid:acyl-CoA acyltransferase (LAT, EC 2.3.1.23) from membranes while maintaining the full enzyme activity using the nonionic detergent n-octyl glucopyranoside (OGP) and solutions of high ionic strength. We found that the optimal OGP concentration depended on the ionic strength of the solubilization buffer. Fluorescence measurements with 1,6-diphenyl-1,3,5-hexatriene indicated that the critical micellar concentration (CMC) of OGP decreased with increasing salt concentrations. Analogous studies revealed that the zwitterionic detergent Chaps was ineffective in extracting LAT from membranes in the absence of salt, whereas its solubilization efficiency increased with increasing salt concentrations. Detailed lipid analysis of the different protein/lipid/detergent mixed micelles showed that the protein/lipid/OGP mixed micelles were relatively enriched with sphingomyelin (SPM) compared to protein/lipid/Chaps mixed micelles, indicating that the differences in the solubilization efficiency may be due to the ability to extract more SPM from membranes. When the protein/lipid/OGP mixed micelles were dissociated into protein/detergent and lipid/detergent complexes by the addition of increasing Chaps concentrations, one-tenth of the LAT enzyme activity was preserved making the enzyme accessible to protein purification. Analysis by native PAGE revealed that in the presence of excess Chaps a high molecular mass protein complex migrated into the gel which could be photolabeled by 125I-labelled-18-(4'-azido-2'-hydroxybenzoylamino)-oleyl-CoA. This fatty acid analogue has been shown to be a competitive inhibitor of LAT enzyme activity in the dark, and an irreversible inhibitor after photolysis. Therefore, this protein complex is assumed to contain the LAT enzyme.

Calorimetric and molecular mechanics studies of the thermotropic phase behavior of membrane phospholipids

In this review, we summarize the results of recent studies on the main phase transition behavior of phospholipid bilayers using the combined approaches of molecular mechanics simulations and high-resolution differential scanning calorimetry. Following a brief overview of the phase transition phenomenon exhibited by the lipid bilayer, we begin with the review by showing how several structural parameters underlying various phospholipids including phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol are defined and determined. Specifically, these structural parameters are obtained with saturated lipids packed in the gel-state bilayer using computer-based molecular mechanics calculations. Then we proceed to present the calorimetric data obtained with the lipid bilayer composed of saturated phospholipids as it undergoes the gel-to-liquid-crystalline phase transition in excess water. The general equations that can correlate the gel-to-liquid-crystalline phase transition temperature (T(m)) of the lipid bilayer with the structural parameters of the lipid molecule constituting the lipid bilayer are subsequently presented. From these equations, two tables of predicated T(m) values for well over 400 molecular species of saturated phosphatidylcholine and saturated phosphatidylethanolamine are generated. We further review the structure and chain-melting behavior of a large number of sn-1 saturated/sn-2 unsaturated phospholipids. Two T(m)-diagrams are shown, from which the effects of the number and the position of one to five cis carbon-carbon double bonds on T(m) can be viewed simultaneously. Finally, in the last part of this review, simple molecular models that have been invoked to interpret the characteristic T(m) trends exhibited by lipid bilayers composed of unsaturated lipids with different numbers and positions of cis carbon-carbon double bonds as seen in the T(m)-diagram are presented.

Phase transition behavior and molecular structures of monounsaturated phosphatidylcholines. Calorimetric studies and molecular mechanics simulations

High resolution differential scanning calorimetric studies were performed to investigate the thermotropic phase behavior of 26 molecular species of sn-1 saturated/sn-2 monounsaturated phosphatidylcholines. In parallel with calorimetric studies, the energy-minimized structures and steric energies of the diglyceride moieties of these monoenoic lipids were determined using a molecular mechanics approach. The combined calorimetric and computational studies led to the following results and conclusions. (i) When a single cis-carbon-carbon double bond (delta) is incorporated into a saturated diacylphosphatidylcholine molecule at any position within the central segment of the long sn-2 acyl chain, the resulting monoenoic lipid molecules will, in excess water, exhibit reduced phase transition temperature (Tm) and transition enthalpy (delta H) as they undergo the gel to liquid-crystalline phase transition. The Tm and delta H-lowering effects of the delta bond can be attributed to a decrease in the chain length of the sn-2 acyl chain, a change in the chain length difference between the sn-1 and sn-2 acyl chains, and a local perturbation of the chain-chain van der Waals interaction in the vicinity of the delta bond. (ii) For a series of positional isomers of 1-stearoyl-2-cis-octadecenoylphosphatidylcholine, C(18):C(18:1 delta n)PC, with a delta bond at different positions along the sn-2 acyl chain, the Tm value depends critically on the position of the delta bond. Specifically, the Tm value is minimal as the delta bond is located at the geometric center of the linear segment of the sn-2 acyl chain, and the Tm value is progressively increased as the delta bond migrates toward either end of the sn-2 acyl chain. (iii) The various monoenoic phosphatidylcholines under study can be divided into two groups. The Tm values of most lipids in each group can be correlated in an identical manner with their structural parameters, yielding a common Tm-structure relationship.

Cholesterol condensation of alpha-linolenic and gamma-linolenic acid-containing phosphatidylcholine monolayers and bilayers

Cholesterol is demonstrated to condense phosphatidylcholine (PC) monolayers and bilayers containing stearic acid in the sn-1 position and alpha-linolenic acid in the sn-2 position (18:0, alpha-18:3 PC) but has no effect when gamma-linolenic acid occupies the sn-2 position (18:0,gamma-18:3 PC). Cholesterol-induced condensation is measured by area/molecule determinations made on monolayers using a Langmuir trough, while condensation in bilayers is followed by the fluorescent dyes merocyanine (MC540) and dansyllysine. Permeability to erythritol is also demonstrated to be diminished by cholesterol for the condensable 18:0,alpha-18:3 PC bilayer membranes but not the 18:0,gamma-18:3 PC membranes. alpha- and gamma-linolenic acid are isomers containing 18 carbons and three unsaturations. Both fatty acids have unsaturations at positions 9 and 12 and differ only in the location of the third unsaturation, at either position 6 for gamma-linolenic acid (an omega-6 fatty acid) and at position 15 for alpha-linolenic acid (an omega-3 fatty acid). Here lipid-cholesterol interaction is used to distinguish the effect of position of unsaturation on membrane structure.

Quantitative effects of dietary polyunsaturated fats on the composition of fatty acids in rat tissues

A method combining data on fatty acid composition into subsets is used to illustrate general relative competitive selectivities in the metabolic and transport events that maintain fatty acid compositions in tissue lipids and to minimize differences among tissues or species in the amount of individual fatty acids. Fatty acid compositions of triglycerides and phospholipids in several tissues of the rat were maintained with simple relationships between the exogenous n-3 and n-6 dietary polyunsaturated fatty acids and the endogenous n-7 and n-9 types of fatty acid. The general pattern of fatty acids in triglycerides was similar for liver, plasma and adipose tissue, averaging about 30% as saturated acids, 67% as 16- and 18-carbon unsaturated acids and only about 2% as 20- and 22-carbon highly unsaturated acids. The tissues maintained a linear relationship between the amount of 18-carbon polyunsaturated fatty acids in the diet and in the tissue triglycerides, with the proportionality constant for 18:3n-3 being 60% of that for 18:2n-6. The total phospholipids of liver, plasma and red blood cells maintained about 45% of the fatty acids in the form of saturated fatty acids and 20-30% as 20- and 22-carbon highly unsaturated fatty acids irrespective of very different proportions of n-3, n-6 and n-9 types of fatty acids. In all three tissues, the 20-carbon highly unsaturated fatty acids of the n-3, n-6 and n-9 type were maintained in a competitive hyperbolic relationship with apparent EC50 values for dietary 18:2n-6 and 18:3n-3 near 0.1% of dietary calories. The consistent quantitative relationships described in this study illustrate an underlying principle of competition among fatty acids for a limited number of esterification sites. This approach may be useful in predicting the influence of diet upon tissue levels of the substrates and antagonists of eicosanoid biosynthesis.

n-3 fatty acids as precursors for active metabolic substances: dissonance between expected and observed events

It may be hypothesized that many diseases are associated with an overproduction of eicosanoids from the n-6 acid, arachidonic acid (20:4n-6), and the formation and function of these n-6 eicosanoids can be antagonized by dietary n-3 fats. This hypothesis provides a basis for evaluating the benefits and risks of including various amounts of n-3 and n-6 fats in the diet. Understanding the impact of dietary polyunsaturated fats leads inevitably to a reappraisal of what is 'normal' in terms of what is typical and what is desirable for the fatty acid composition of tissue lipids, the magnitude of eicosanoid-mediated responses, and the frequency and severity of certain diseases.

The role of polyunsaturated fatty acids in fish

The physical properties of polyunsaturated and saturated fatty acids are compared in relation to melting points and fluidity. The role of polyunsaturated fatty acids on membrane fluidity and membrane bound enzyme activity is discussed. The influence of the environment, particularly temperature, on poikilothermic animals is considered in relation to membrane fatty acid composition and metabolism. The metabolic role of polyunsaturated fatty acids of the (n-3) series and their interaction with arachidonate metabolism is discussed.

Molecular species composition of phosphatidylcholines during the development of the avian embryo brain

A comparative approach has been used to investigate the molecular species composition of phosphatidylcholine (PC) and its age variation throughout several developmental stages of chick and duck embryo brains. The brain PC consist of 15 major molecular species which do not undergo appreciable variation in their relative abundance either during embryonic development or between equivalent stages of maturation in the 2 avian species. In fact, a highly invariable molecular architecture of PC is shown in the developing organ. Molecular species containing saturated or monounsaturated fatty acids were dominant in all stages of development of the avian embryo brain. Among these molecular species, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine accounted for 75-80% of the total PC.

Metabolism of different monoacylphospholipids in isolated hepatocytes and the intact rat

The 1-[3H] palmitoyl, 2-[3H] oleoyl, and 2-[14C] linoleoyl derivatives of sn-glycero-3-phosphoethanolamine and the corresponding derivatives of sn-glycero-3-phosphocholine were injected intraportally to rats and their incorporation into liver lipids was studied 15 min thereafter. Both the uptake by the liver and the degree of acylation was higher for the unsaturated compounds. The uptake of lysophosphatidylethanolamine was higher than that of lysophosphatidlycholine. The metabolism of 1-lysophosphatidylethanolamine was also studied in isolated hepatocytes. The degree of hydrolysis was much more prominent than in vivo. After injecting 2-[14C] linoleoyl derivatives, a large part of the 14C was recovered in the dienoic phospholipids. Subfractionation by reversed-phase partition chromatography showed that the isotope was located in the palmitoyllinoleoyl and stearoyl-linoleoyl fraction. The 100 X stearoly/(palmitoyl + stearoyl) ratio was 84 in dienoic phosphatidylethanolamine and 59 in dienoic phosphatidylcholine. This preference for stearic acid is significantly larger than in other pathways yielding dienoic phospholipids. It can be concluded that the monoacylphospholipid acyltransferase reactions operating at positions 1 or 2 yield different saturated acyl chain profiles in phosphatidylethanolamine and phosphatidylcholine of a specific unsaturation. This may be important in the regulation of the fatty acid composition of the membrane phospholipids.

Age differences in the positional distribution of phosphoglycerides and molecular species of choline phosphoglycerides during development of the chick embryo liver

The total fatty acid composition and the distribution of acyl groups in the positions 1 and 2 of 1,2-diacyl-sn-glycero-3-phosphocholine and 1,2-diacyl-sn-glycero-3-phosphoethanolamine as well as in the molecular species of 1,2-diacyl-sn-glycero-3-phosphocholine from the chick embryo liver have been investigated at various stages of development. The fatty acid content of the main lipid classes from the yolks was also evaluated. The relative percentages of total saturated fatty acids in 1,2-diacyl-sn-glycero-3-phosphocholine remained constant during liver development; however, the levels of both main saturated acids, palmitic and stearic acids, were reciprocally counterbalanced as the age of the embryo proceeded. On the other hand, arachidonic acid decreased with time whereas linoleic acid and docosahexaenoic acid doubled their proportions during development. The relative amounts of total saturated fatty acids from liver 1,2-diacyl-sn-glycero-3-phosphoethanolamine were also constant during all stages of development; however, palmitic/stearic acid ratio did not change with time in this phosphoglyceride. Fatty acid composition of the yolk phosphoglycerides did not change during embryonic development. It should be noted that marked differences between fatty acid composition of choline and ethanolamine phosphoglycerides from the embryo liver and those of the yolk phosphoglycerides were demonstrated. The general patterns of the positional distribution of the acyl groups in choline phosphoglycerides differed from those of ethanolamine phosphoglycerides. Palmitic and stearic acids were only positioned at position 1 in 1,2-diacyl-sn-glycero-3-phosphoethanolamine whereas both fatty acids did not acylate exclusively the position 1 in 1,2-diacyl-sn-glycero-3-phosphocholine.

Quantitative measurement of the effectiveness of unsaturated fatty acids required for the growth of Saccharomyces cerevisiae

The growth response of a mutant of Saccharomyces cerevisiae which is unable to synthesize unsaturated fatty acids has been measured in the presence of variable concentrations of exogenous unsaturated fatty acids. Final cell yields, doubling times, and lag times were all found to vary as a function of the initial concentration of the added unsaturated acid. The cell yield was found to be a convenient quantitative measurement to use in comparing the effectiveness of various unsaturated acids. Values for the acids ranged from 1.7 to 11 cells per femtomole with values for oleate and palmitoleate at 2.7 and 4.3 cells per femtomole, respectively. In general, the effectiveness of unsaturated acids was found to increase with an increasing number of double bonds. Saturated fatty acids of a chain length of 5 to 18 carbon atoms were completely ineffective. The varied efficiencies of different unsaturated fatty acids indicate that unsaturation per se was not the basis of the nutritional requirement and indicate certain acids that would be useful in further studies of the role of unsaturated acids in cell function.

Synthesis of C-18 mixed acid diacyl-sn-glycerol enantiomers

Procedures have been developed for the synthesis of both enantiomeric forms of mixed fatty acid, saturated and polyunsaturated 1,2-diacyl-sn-glycerols and 2,3-diacyl-sn-glycerols from D-mannitol as starting material. The following diacyl-sn-glycerols have been synthesized: 1-Stearoyl-2-linoleoyl-sn-glycerol, 1-stearoyl-2-linolenoyl-sn-glycerol, 2-linoleoyl-3-stearoyl-sn-glycerol and 2-linolenoyl-3-oleoyl-sn-glycerol. Their specific rotations, refractive indices, densities, solubilities, carbon and hydrogen analysis and iodine values have been reported.

The incorporation of14C-glycerol into different species of diglycerides and triglycerides in rat liver slices

The relative rates of de novo synthesis of species of diglycerides and triglycerides from(14)C-glycerol were examined in rat liver slices. Diglycerides containing one or two double bonds per molecule and triglycerides containing four or more double bonds per molecule represented 70% and 60% respectively of the newly synthesized diglycerides and triglycerides. The newly synthesized triglycerides were more unsaturated than the endogenous triglycerides. Our results suggest that a nonrandom synthesis of species of diglycerides occurred followed by an almost random utilization of the various diglyceride species for the biosynthesis of triglycerides.