Thin-layer chromatography of human platelet phospholipids with fatty acid analysis

A new update of MALDI-TOF mass spectrometry in lipid research

Matrix-assisted laser desorption and ionization (MALDI) mass spectrometry (MS) is an indispensable tool in modern lipid research since it is fast, sensitive, tolerates sample impurities and provides spectra without major analyte fragmentation. We will discuss some methodological aspects, the related ion-forming processes and the MALDI MS characteristics of the different lipid classes (with the focus on glycerophospholipids) and the progress, which was achieved during the last ten years. Particular attention will be given to quantitative aspects of MALDI MS since this is widely considered as the most serious drawback of the method. Although the detailed role of the matrix is not yet completely understood, it will be explicitly shown that the careful choice of the matrix is crucial (besides the careful evaluation of the positive and negative ion mass spectra) in order to be able to detect all lipid classes of interest. Two developments will be highlighted: spatially resolved Imaging MS is nowadays well established and the distribution of lipids in tissues merits increasing interest because lipids are readily detectable and represent ubiquitous compounds. It will also be shown that a combination of MALDI MS with thin-layer chromatography (TLC) enables a fast spatially resolved screening of an entire TLC plate which makes the method competitive with LC/MS.

A 65-Day Fumonisin B Exposure at High Dietary Levels Has Negligible Effects on the Testicular and Spermatological Parameters of Adult Rabbit Bucks

A 65-day study was undertaken to test the effects of two doses (10 and 20 mg/kg) of dietary fumonisin Bs (FB) on the rabbit male reproduction system. Body and testicular weight was not affected by the intoxication, neither the fatty acid composition of the testicular total phospholipids; the testis histological analysis failed to reveal any toxic effect. The FBs increased the testicular concentration and activity of reduced glutathione and glutathione peroxidase and decreased initial phase lipid peroxidation (conjugated dienes and trienes) in a dose dependent manner. Sperm morphology and chromatin condensation were monitored on Feulgen-stained smears. No significant differences were observed between the treatment groups and between sampling time points. The live cell ratio in the sperm (as assessed with flow cytometry) was not different among groups at any of the five sampling timepoints and was also identical within groups. Similarly, the spermatozoa membrane lipid profile was also identical in all three groups after the total intoxication period. In summary, it was demonstrated that FBs in an unrealistic and unjustified high dose still do not exert any drastic harmful effect on the leporine, male reproduction system, meanwhile slightly augmenting testicular antioxidant response.

Proto-oncogene Src links lipogenesis via lipin-1 to breast cancer malignancy

Increased lipogenesis has been linked to an increased cancer risk and poor prognosis; however, the underlying mechanisms remain obscure. Here we show that phosphatidic acid phosphatase (PAP) lipin-1, which generates diglyceride precursors necessary for the synthesis of glycerolipids, interacts with and is a direct substrate of the Src proto-oncogenic tyrosine kinase. Obesity-associated microenvironmental factors and other Src-activating growth factors, including the epidermal growth factor, activate Src and promote Src-mediated lipin-1 phosphorylation on Tyr398, Tyr413 and Tyr795 residues. The tyrosine phosphorylation of lipin-1 markedly increases its PAP activity, accelerating the synthesis of glycerophospholipids and triglyceride. Alteration of the three tyrosine residues to phenylalanine (3YF-lipin-1) disables lipin-1 from mediating Src-enhanced glycerolipid synthesis, cell proliferation and xenograft growth. Re-expression of 3YF-lipin-1 in PyVT;Lpin1-/- mice fails to promote progression and metastasis of mammary tumours. Human breast tumours exhibit increased p-Tyr-lipin-1 levels compared to the adjacent tissues. Importantly, statistical analyses show that levels of p-Tyr-lipin-1 correlate with tumour sizes, lymph node metastasis, time to recurrence and survival of the patients. These results illustrate a direct lipogenesis-promoting role of the pro-oncogenic Src, providing a mechanistic link between obesity-associated mitogenic signaling and breast cancer malignancy.

Eicosapentaenoic acid-containing polar lipids from seaweed Susabinori (Pyropia yezoensis) alleviate hepatic steatosis in obese db/db mice

Nonalcoholic fatty liver disease (NAFLD) is emerging as the most common liver disease in industrialized countries. Because hepatic steatosis is an early pathogenesis of NAFLD, the discovery of food components that could ameliorate hepatic steatosis is of interest. Susabinori (Pyropia yezoensis) is recognized as one of the most delicious edible brown algae, and we prepared lipid component of susabinori (SNL), which is rich in eicosapentaenoic acid (EPA)-containing polar lipids. In this study, we tested whether feeding SNL to db/db mice protects them from developing obesity-induced hepatic steatosis. After four weeks of feeding, hepatomegaly, hepatic steatosis, and hepatic injury were markedly alleviated in SNL-fed db/db mice. These effects were partly attributable to the suppression of activities and mRNA expressions of lipogenic enzymes and enhanced levels of adiponectin due to the SNL diet. Additionally, mRNA expression of monocyte chemoattractant protein-1, an inflammatory chemokine, was markedly suppressed, and the mRNA levels of PPARδ, the anti-inflammatory transcription factor, were strongly enhanced in the livers of db/db mice by the SNL diet. We speculate that the development and progression of obesity-induced hepatic steatosis was prevented by the suppression of chronic inflammation due to the combination of bioactivities of EPA, phospholipids, and glycolipids in the SNL diet.

Phospholipids containing ether-bound hydrocarbon-chains are essential for efficient phagocytosis and neutral lipids of the ester-type perturb development in Dictyostelium

Lipids are the building blocks for cellular membranes; they provide signalling molecules for membrane dynamics and serve as energy stores. One path of their synthesis is initiated by glycerol-3-phosphate acyltransferase (GPAT), which in Dictyostelium resides on the endoplasmic reticulum. When an excess of fatty acids is present, it redistributes to storage organelles, the lipid droplets. Mutants, where the GPAT was eliminated by homologous recombination, produce fewer lipid droplets and are almost devoid of triacylglycerols (TAG), rendering them more resistant to cell death and cell loss in the developmental stages preceding fruiting body formation. The enzyme most closely related to GPAT is called FARAT, because it combines a fatty acyl-reductase (FAR) and an acyltransferase (AT) domain in its sequence. The protein is confined to the lumen of the peroxisome, where it transfers a fatty acid to dihydroxyacetone-phosphate initiating the synthesis of ether lipids, later completed at the endoplasmic reticulum. A mutant lacking FARAT produces lipid droplets that are devoid of the storage lipid monoalkyl-diacyl-glycerol (MDG), but the efficiency of spore formation in the developmental cycle is largely unaltered. Instead, these mutants are strongly impaired in phagocytosis of yeast particles, which is attributed to reduced synthesis of membrane phospholipids containing ether-linked chains.

Fruit seeds and their oils as promising sources of value-added lipids from agro-industrial byproducts: oil content, lipid composition, lipid analysis, biological activity and potential biotechnological applications

Thousands of tons of fruit seeds are discarded every year worldwide as agro-industrial byproducts. Fruit seeds have a high oil content, are rich in monounsaturated fatty acids (FA) and in n-6 and n-3 polyunsaturated essential FA. Sterols, phospholipids, glycolipids, carotenoids, tocopherols and polyphenols are other seed phytochemicals that make them interesting from a commercial viewpoint. Fruit seeds have high potential as raw material for several industries, but their lipid profile remains poorly studied. Current analytical approaches for the analysis of lipids that are based on high-performance liquid chromatography and high-resolution mass spectrometry allow the separation and analysis of compounds with the accurate identification and structural characterization of molecular species in very small quantities. Even though lipidomic analysis of fruit seeds' lipids is still in its infancy, it will bring a new look over these value-added byproducts. This review covers the following topics: (a) the lipid content of various fruit seed oils; (b) their lipid composition (FA, triacylglycerol, sterol, phospholipid and glycolipid profiles), (c) current and future analytical methodologies for the analysis of lipids in fruit seeds; (d) biological activities of fruit seeds' extracts; and (e) potential biotechnological applications of fruit seed oils for their commercial valorization based on lipids.

Conversion of dietary trans-vaccenic acid to trans11,cis13-conjugated linoleic acid in the rat lactating mammary gland by Fatty Acid Desaturase 3-catalyzed methyl-end Δ13-desaturation

In vitro, the rat Fatty Acid Desaturase 3 (FADS3) gene was shown to code for an enzyme able to catalyze the unexpected Δ13-desaturation of trans-vaccenic acid, producing the trans11,cis13-conjugated linoleic acid (CLA) isomer. FADS3 may therefore be the first methyl-end trans-vaccenate Δ13-desaturase functionally characterized in mammals, but the proof of this concept is so far lacking in vivo. The present study therefore aimed at investigating further the putative in vivo synthesis of trans11,cis13-CLA from dietary trans-vaccenic acid in rodents. During one week of pregnancy and two weeks post-partum, Sprague-Dawley female rats were fed two diets either high (10.0% of fatty acids and 3.8% of energy intake) or low (0.4% of fatty acids and 0.2% of energy intake) in trans-vaccenic acid. The trans11,cis13-CLA was specifically detected, formally identified and reproducibly quantified (0.06% of total fatty acids) in the mammary gland phospholipids of lactating female rats fed the high trans-vaccenic acid-enriched diet. This result was consistent with FADS3 mRNA expression being significantly higher in the lactating mammary gland than in the liver. Although the apparent metabolic conversion is low, this physiological evidence demonstrates the existence of this new pathway described in the lactating mammary gland and establishes the FADS3 enzyme as a reliable mammalian trans-vaccenate Δ13-desaturase in vivo.

Metabolomic and lipidomic analysis of the effect of pioglitazone on hepatic steatosis in a rat model of obese Type 2 diabetes

BACKGROUND AND PURPOSE

Thiazolidinediones, acting as PPAR-γ ligands, reduce hepatic steatosis in humans and animals. However, the underlying mechanism of this action remains unclear. The purpose of this study was to investigate changes in hepatic metabolites and lipids in response to treatment with the thiazolidinedione pioglitazone in an animal model of obese Type 2 diabetes.

EXPERIMENTAL APPROACH

Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats were orally administered either vehicle (control) or pioglitazone (30 mg·kg^-1 ) and fed a high-fat diet (60% kcal fat) for 12 weeks. Hepatic metabolites were analysed via metabolomic and lipidomic analyses. Gene expression and PLA₂ activity were analysed in livers from pioglitazone-treated and control rats.

KEY RESULTS

OLETF rats that received pioglitazone showed decreased fat accumulation and improvement of lipid profiles in the liver compared to control rats. Pioglitazone treatment significantly altered levels of hepatic metabolites, including free fatty acids, lysophosphatidylcholines and phosphatidylcholines, in the liver. In addition, pioglitazone significantly reduced the expression of genes involved in hepatic de novo lipogenesis and fatty acid uptake and transport, whereas genes related to fatty acid oxidation were up-regulated. Gene expression and enzyme activity of PLA₂ , which hydrolyzes phosphatidylcholines to release lysophosphatidylcholines and free fatty acids, were significantly decreased in the livers of pioglitazone-treated rats compared to control rats.

CONCLUSIONS AND IMPLICATIONS

Our results present evidence for the ameliorative effect of pioglitazone on hepatic steatosis, largely due to the regulation of lipid metabolism, including fatty acids, lysophosphatidylcholines, phosphatidylcholines and related gene-expression patterns.

Feeding wet distillers grains plus solubles contributes to sarcoplasmic reticulum membrane instability

Feeding wet distillers grains plus solubles (WDGS) increases polyunsaturated fatty acid (PUFA) levels in beef. It was hypothesised that WDGS in feedlot diets increases PUFA concentration in the sarcoplasmic reticulum (SR) membrane, thereby altering membrane integrity, resulting in more rapid intracellular calcium leakage and improved tenderness. The objective of this study was to evaluate this hypothesis. Ninety-six crossbred steers were fed either a corn-based diet with 0% WDGS or 50% WDGS. Fifteen strip loins per treatment were collected, fabricated into steaks, aged and placed under retail display conditions. Steaks were used to measure tenderness, proteolysis, free calcium concentrations, lipid oxidation, sarcomere length and SR membrane fatty acid, phospholipid lipid, neutral lipid and total lipid profiles. Compared with steaks from steers fed 0% WDGS, steaks from steers fed 50% WDGS were more tender (P < 0.05) and had greater (P < 0.05) free calcium concentrations early post-mortem. Feeding 50% WDGS also tended to increase (P < 0.10) total PUFA concentrations, decrease (P < 0.10) total phospholipid concentration and increase (P < 0.10) total neutral lipid concentration for SR membrane. Steaks from steers fed 0% WDGS had greater (P < 0.05) lipid oxidation (TBARS values) than steaks from steers fed 50% WDGS after extended aging. Although differences in tenderness between the two treatments were detected, there were no corresponding differences (P > 0.10) in sarcomere length or proteolysis. This study showed that feeding WDGS may increase tenderness, possibly by increasing free calcium in muscle early post-mortem. However, the true mechanism that contributes to these differences is still unclear.

Phospholipidomic Analysis Reveals Changes in Sphingomyelin and Lysophosphatidylcholine Profiles in Plasma from Patients with Neuroborreliosis

In recent years, the number of patients suffering from Lyme Disease (LD) has significantly increased. The most dangerous manifestation of LD is neuroborreliosis associated with invasion of the central nervous system by Borrelia burgdorferi. Phospholipids (PL) and their metabolites are involved in inflammation, which plays a dominant, but still unclear, role in the pathogenesis of neuroborreliosis. We analyzed the plasma PL profiles of neuroborreliosis patients (n = 8) and healthy volunteers (n = 8) using a lipidomic approach. Significant increases in the lysophosphatidylcholines LysoPtdCho 16:0 and LysoPtdCho 18:2 were observed. The plasma of neuroborreliosis patients appeared to have an increased relative abundance of sphingomyelin CerPCho d18:1/24:1 and a decrease in CerPCho d18:0/18:0. Principal components analysis of the relative abundances of all PL class species distinguished between neuroborreliosis patients and healthy subjects. This is the first report comparing PL classes and their molecular species in neuroborreliosis patients and healthy subjects.

Variation in human cancer cell external phosphatidylserine is regulated by flippase activity and intracellular calcium

Viable cancer cells expose elevated levels of phosphatidylserine (PS) on the exoplasmic face of the plasma membrane. However, the mechanisms leading to elevated PS exposure in viable cancer cells have not been defined. We previously showed that externalized PS may be used to monitor, target and kill tumor cells. In addition, PS on tumor cells is recognized by macrophages and has implications in antitumor immunity. Therefore, it is important to understand the molecular details of PS exposure on cancer cells in order to improve therapeutic targeting. Here we explored the mechanisms regulating the surface PS exposure in human cancer cells and found that differential flippase activity and intracellular calcium are the major regulators of surface PS exposure in viable human cancer cells. In general, cancer cell lines with high surface PS exhibited low flippase activity and high intracellular calcium, whereas cancer cells with low surface PS exhibited high flippase activity and low intracellular calcium. High surface PS cancer cells also had higher total cellular PS than low surface PS cells. Together, our results indicate that the amount of external PS in cancer cells is regulated by calcium dependent flippase activity and may also be influenced by total cellular PS.

In vitro antifungal activity of different components of Centratherum anthelminticum and Ocimum sanctum seed oils and their synergism against oral pathogenic fungi

Background. Opportunistic fungal infections like candidiasis are common in the oral cavity. In recent years Candida species have shown resistance against a number of synthetic drugs. This study assessed the antifungal activity of Centratherum anthelminticum and Ocimum sanctum seed oils against six common pathogenic Candida strains. Synergistic activity of the major oil components was also studied.

Methods. Antifungal activity of Centratherum anthelminticum and Ocimum sanctum seed oils were tested against six oral fungal pathogens, Candida albicans ATCC 90028, Candida krusei 6258, Candida tropicalis 13803, Candida parapsilosis22019, Candida glabrata 90030 and Candida dubliniensis MYA 646, by disc diffusion and broth microdilution methods to determine the diameter of inhibition zone (DIZ) and minimum inhibitory concentration (MIC), respectively. The oil was extracted using Soxhlet apparatus from seeds subjected to columnchromatography (CC) and thin layer chromatography (TLC) and major components were separated and quantified.

Results. All the six Candida strains showed growth inhibition to a variable degree when tested with both seed oils. Both seed oils showed antifungal activity. For Centratherum anthelminticum seed oil maximum DIZ at 7 μL was recorded at 75.7 mm for Candida albicans ATCC 90028, and the least DIZ was 45.7 mm for Candida dubliniensis MYA 646. For Ocimum sanctum seed oil maximum DIZ at 7 μL was 61.0 mm for Candida krusei ATCC 6258 and the least DIZ was 46.7 mm for Candida tropicalis ATCC 13803. The mixtures of phospholipids and unsaponifiable matter exhibitedMIC values at 1.25 μL for both oils, whereas neutral lipids fraction and unsaponifiable matter exhibited similar MIC at 2.5 μL against Candida albicans and Candida krusei.

Conclusion.Centratherum anthelminticum and Ocimum sanctumseed oils exhibited strong antifungal activity against six different species of Candida and this may be attributed to various active components in the oil and their synergistic activity.

The protective effect of vitamin E against changes in fatty acid composition of phospholipid subclasses in gill tissue of Oreochromis niloticus exposed to deltamethrin

The effects of deltamethrin on the fatty acid composition of phospholipid subclasses (phosphatidylchlonine (PC), phosphatidylethanolamine (PE), phosphatidylinositole (PI) and phosphatidylserine (PS)) in gill tissue of Oreochromis niloticus (Perciformes: Cichlidae) and the possible protective effect of vitamin E against deltamethrin were determined by gas chromatography. The changes in the fatty acid profile were analysed after 14 d of exposure. Treatments included Group I (fed with basal diet only), Group II (fed with vitamin E-supplemented diet), Group III (fed with basal diet and exposed to deltamethrin) and Group IV (fed with vitamin E-supplemented diet and exposed to deltamethrin). The effects of deltamethrin on PI, PE and PS were valid for the total saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs). The effect on PC was detected in total SFAs and total PUFAs. The vitamin E-supplemented diet did not show complete protective effect on fatty acid composition of the fish exposed to deltamethrin. However, the protective effect was observed in total SFAs, total MUFAs and total PUFAs in PC. In PI, protective effect was only recorded on total PUFAs. There was no protective effect in PS and PE. The results of the present study demonstrated that deltametrin exposure had harmful effects on cell membrane and treatment with vitamin E could only partially protect fish gills.

Body mass related variations in the polar lipid fatty acyl chain composition of the mammalian lung and alveolar surfactant

In nine mammalian species (mouse - cattle: 21.5 g-503 kg) lung total phospholipids (PL), alveolar surfactant phosphatidylcholine (PC) and sphingomyelin (SM) fatty acyl (FA) chain composition was tested relating to body mass (BM) and resting respiratory rate (RRR) associated adaptations. In PL, PC and SM oleic acid (C18:1 n9) provided negative correlations with RRR. Palmitic acid (C16:0) was strongly, positively correlated with RRR in the pulmonary PLs, and myristic (C14:0) acid correlated positively with RRR in the surfactant PCs. In pulmonary PLs negative allometry was found for myristic, palmitic, palmitoleic (C16:1 n7) and docosahexaenoic (C22:6 n3) acids and total saturation, while oleic (C18:1 n9), alpha-linolenic (C18:3 n3) and gondoic (C20:1 n9) acids, total n9 FA s and monounsaturation increased allometrically. In surfactant PC FA s palmitic acid provided negative, while oleic acid and monounsaturation positive allometry; the average FA chain length (ACL) was identical in all species. Surfactant SM FA composition was fully species independent for palmitic and arachidonic acids, total saturation, monounsaturation and ACL. The in vivo lipid peroxidation rate was species independent. The variability of lung PLs was consonant with the "membrane pacemakers theory", while surfactant PC composition was mostly related to RRR.

Lipidomic analysis of phospholipids from human mammary epithelial and breast cancer cell lines

Alterations of phospholipid (PL) profiles have been associated to disease and specific lipids may be involved in the onset and evolution of cancer; yet, analysis of PL profiles using mass spectrometry (MS) in breast cancer cells is a novel approach. Previously, we reported a lipidomic analysis of PLs from mouse mammary epithelial and breast cancer cells using off-line thin layer chromatography (TLC)-MS, where several changes in PL profile were found to be associated with the degree of malignancy of cells. In the present study, lipidomic analysis has been extended to human mammary epithelial cells and breast cancer cell lines (MCF10A, T47-D, and MDA-MB-231), using TLC-MS, validated by hydrophilic interaction liquid chromatography-MS. Differences in phosphatidylethanolamine (PE) content relative to total amount of PLs was highest in non-malignant cells while phosphatidic acid was present with highest relative abundance in metastatic cells. In addition, the following differences in PL molecular species associated to cancer phenotype, metastatic potential, and cell morphology were found: higher levels of alkylacyl PCs and phosphatidylinositol (PI; 22:5/18:0) were detected in migratory cells, epithelial cells had less unsaturated fatty acyl chains and shorter aliphatic tails in PE and sphingomyelin classes, while PI (18:0/18:1) was lowest in non-malignant cells compared to cancer cells. To date, information about PL changes in cancer progression is scarce, therefore results presented in this work will be useful as a starting point to define possible PLs with prospective as biomarkers and disclose metabolic pathways with potential for cancer therapy.

A new look at the lipid composition of the plasma membrane of human blood platelets relative to the GPIIb/IIIa (integrin cxIIβ3) content

The total lipids of the human platelet plasma membrane (HPPM) from 50 ml of blood of healthy subjects were extracted, quantified and related to the mass content of the major intrinsic membrane protein, the glycoprotein IIb/IIIa (GPIIb/IIIa). The HPPM total lipid/GPIIb/IIIa weight ratio determined was 5.40 ± 0.20, independently of the membrane washing procedure used, with the cholesterol/GPIIb/IIIa and phospholipid/GPIIb/IIIa molar ratios of 800 ± 50 and 1200 ± 40, respectively. If the distribution of lipids around each intrinsic protein were proportional to its mass, the lipids around a molecule of GPIIb/IIIa will occupy about 120 nm(2) of the membrane plane, which is about one and a half times the cross-sectional area of the extracellular head of GPIIb/IIIa, as estimated by electron microscopy. The lipid extracts were further subjected to thin-layer chromatography to separate and quantify the different phospholipid fractions, the free fatty acids and the neutral lipid fraction and the distribution of fatty acids in each fraction was determined by gas chromatography after methanolysis. The phospholipid molar distribution was SPM(22.3 ± 0.9%), PC(36.2 ± 1.0%), PE(24.9 ± 0.9%), PS(12.1 ± 0.6%) and PI(4.5 ± 0.4%) and the free fatty acid fraction represented 2.9 ± 0.4% of the total fatty acids in HPPM. The fatty acid chain length ranged from 14 to 24 carbons, comprising unsaturated fatty acids (47.3% molar per cent of the total) of which 40.7 ± 2.0% were monosaturated and 40.7 ± 0.9% tetraunsaturated. Palmitic, stearic, oleic and arachidonic acids represent 66% of the total fatty acids of HPPM, being: 68.9 ± 5.3% of palmitic acid and 63.3 ± 6.9% of oleic acid in PC; 50.9 ± 3.8% of arachidonic acid in PE; and 30.5 ± 2.4% of stearic acid in PS. We discuss the methodological modifications and the new data in relation with the major differences in HPPM lipid composition found in the literature. The data obtained provides a comprehensive and accurate description of the lipid composition of HPPM on which to rely as a reference for basic and medical studies.

A decreased n-6/n-3 ratio in the fat-1 mouse is associated with improved glucose tolerance

A reduction in skeletal muscle fatty acid oxidation (FAO), manifested as a reduction in mitochondrial content and (or) FAO within mitochondria, may contribute to the development of insulin resistance. n-3 polyunsaturated fatty acids (PUFA) have been observed to increase the capacity for FAO and improve insulin sensitivity. We used the fat-1 mouse model, a transgenic animal capable of synthesizing n-3 PUFA from n-6 PUFA, to examine this relationship. Fat-1 mice exhibited a approximately 20-fold decrease in the n-6/n-3 ratio in skeletal muscle, and plasma glucose and the area under the glucose curve were significantly (p < 0.05) lower in fat-1 mice during a glucose challenge test. The improvement in whole-body glucose tolerance in the fat-1 mouse was associated with a approximately 21% (p < 0.05) decrease in whole-muscle citrate synthase (CS) activity (in red muscle only), without alterations in CS activity of isolated mitochondria (either red or white muscle; p > 0.05). These data suggest that the fat-1 mouse has decreased skeletal muscle mitochondrial content. However, the intrinsic ability of mitochondria to oxidize fatty acids was not altered in the fat-1 mouse, as rates of palmitate oxidation in isolated mitochondria from both red and white muscle were unchanged. Overall, this study demonstrates that a decrease in the n-6/n-3 ratio can enhance glucose tolerance in healthy animals, independent of changes in mitochondrial content.

Lipid analysis by thin-layer chromatography--a review of the current state

High-performance thin-layer chromatography (HPTLC) is a widely used, fast and relatively inexpensive method of separating complex mixtures. It is particularly useful for smaller, apolar compounds and offers some advantages over HPLC. This review gives an overview about the special features as well as the problems that have to be considered upon the HPTLC analysis of lipids. The term "lipids" is used here in a broad sense and comprises fatty acids and their derivatives as well as substances related biosynthetically or functionally to these compounds. After a short introduction regarding the stationary phases and the methods how lipids can be visualized on an HPTLC plate, the individual lipid classes will be discussed and the most suitable solvent systems for their separation indicated. The focus will be on lipids that are most abundant in biological systems, i.e. cholesterol and its derivates, glycerides, sphingo- and glycolipids as well as phospholipids. Finally, a nowadays very important topic, the combination between HPTLC and mass spectrometric (MS) detection methods will be discussed. It will be shown that this is a very powerful method to investigate the identities of the HPTLC spots in more detail than by the use of common staining methods. Future aspects of HPTLC in the lipid field will be also discussed.

Mitochondrial fatty acid synthesis is required for normal mitochondrial morphology and function in Trypanosoma brucei

Trypanosoma brucei use microsomal elongases for de novo synthesis of most of its fatty acids. In addition, this parasite utilizes an essential mitochondrial type II synthase for production of octanoate (a lipoic acid precursor) as well as longer fatty acids such as palmitate. Evidence from other organisms suggests that mitochondrially synthesized fatty acids are required for efficient respiration but the exact relationship remains unclear. In procyclic form trypanosomes, we also found that RNAi depletion of the mitochondrial acyl carrier protein, an important component of the fatty acid synthesis machinery, significantly reduces cytochrome-mediated respiration. This reduction was explained by RNAi-mediated inhibition of respiratory complexes II, III and IV, but not complex I. Other effects of RNAi, such as changes in mitochondrial morphology and alterations in membrane potential, raised the possibility of a change in mitochondrial membrane composition. Using mass spectrometry, we observed a decrease in total and mitochondrial phosphatidylinositol and mitochondrial phosphatidylethanolamine. Thus, we conclude that the mitochondrial synthase produces fatty acids needed for maintaining local phospholipid levels that are required for activity of respiratory complexes and preservation of mitochondrial morphology and function.

Oleic acid is elevated in cell membranes during rapid cold-hardening and pupal diapause in the flesh fly, Sarcophaga crassipalpis

The integrity of cellular membranes is critical to the survival of insects at low temperatures, thus an advantage is conferred to insects that can adjust their composition of membrane fatty acids (FAs). Such changes contribute to homeoviscous adaption, a process that allows cellular membranes to maintain a liquid-crystalline state at temperatures that are potentially low enough to cause the membrane to enter the gel state and thereby lose its ability to maintain homeostasis. Flesh flies (Sarcophaga crassipalpis) were subjected to two experimental conditions that elicit low temperature tolerance: rapid cold-hardening and diapause. FAs were isolated and analyzed using gas chromatography-mass spectrometry. FAs changed in response to both rapid cold-hardening and diapause. In response to rapid cold-hardening (8 h at 4 degrees C), the proportion of oleic acid (18:1n-9) in pharate adults increased from 30% to 47% of the total FA pool. The proportion of almost every other FA was reduced. By entering diapause, pupae experienced an even greater increase in oleic acid proportion, to 58% of the total FA pool. Oleic acid not only promotes membrane fluidity at low temperature but also allows the cell membrane to maintain a liquid crystalline state if temperatures increase.

Cardiolipin Biosynthesis and Mitochondrial Respiratory Chain Function Are Interdependent

Cardiolipin (CL) is an acidic phospholipid present almost exclusively in membranes harboring respiratory chain complexes. We have previously shown that, in Saccharomyces cerevisiae, CL provides stability to respiratory chain supercomplexes and CL synthase enzyme activity is reduced in several respiratory complex assembly mutants. In the current study, we investigated the interdependence of the mitochondrial respiratory chain and CL biosynthesis. Pulse-labeling experiments showed that in vivo CL biosynthesis was reduced in respiratory complexes III (ubiquinol:cytochrome c oxidoreductase) and IV (cytochrome c oxidase) and oxidative phosphorylation complex V (ATP synthase) assembly mutants. CL synthesis was decreased in the presence of CCCP, an inhibitor of oxidative phosphorylation that reduces the pH gradient but not by valinomycin or oligomycin, both of which reduce the membrane potential and inhibit ATP synthase, respectively. The inhibitors had no effect on phosphatidylglycerol biosynthesis or CRD1 gene expression. These results are consistent with the hypothesis that in vivo CL biosynthesis is regulated at the level of CL synthase activity by the DeltapH component of the proton-motive force generated by the functional electron transport chain. This is the first report of regulation of phospholipid biosynthesis by alteration of subcellular compartment pH.

Cytidine-5'-diphosphocholine affects CTP-phosphocholine cytidylyltransferase and lyso-phosphatidylcholine after transient brain ischemia

Cytidine-5'-diphosphocholine (CDP-choline, also referred as citicoline), the key intermediate in phosphatidylcholine (PtdCho) synthesis, provided significant benefit in experimental central nervous system (CNS) injury including cerebral ischemia. CDP-choline is synthesized by CTP:phosphocholine cytidylyltransferase (CCT), the key rate-limiting enzyme in PtdCho synthesis. Phospholipase A(2) (PLA(2)) hydrolyzes PtdCho to produce free fatty acids and lyso-PtdCho, an inhibitor of CCT. We investigated the status of CCT and lyso-PtdCho after 10-min transient brain ischemia in gerbils with reperfusion up to 2 days. Ischemia with no reperfusion resulted in loss of CCT activity in cytosol (408 +/- 8 pmol/min/mg protein compared to sham 695 +/- 45; P < 0.01) and membrane (383 +/- 61 compared to sham 532 +/- 54; P < 0.05). CCT activity remained low over 24-hr reperfusion, and returned to sham levels at Day 2 in membrane but remained low in cytosol. CDP-choline significantly increased CCT activity in cytosol at 1 hr reperfusion (saline, 339 +/- 35 compared to CDP-choline, 430 +/- 70; P < 0.05) and in membrane at 6 hr (saline, 381 +/- 32 compared to CDP-choline, 489 +/- 50; P < 0.01) and 24 hr (saline, 417 +/- 24 compared to CDP-choline, 594 +/- 45; P < 0.01), but had no effect on CCT activity at Day 2. Lyso-PtdCho increased at 1-hr reperfusion (219 +/- 5 nmol/g tissue compared to sham, 92 +/- 8; P < 0.01), and remained elevated over 2 days. CDP-choline attenuated lyso-PtdCho levels at 1-hr reperfusion (162 +/- 21, P < 0.01 compared to saline). These data indicate that PtdCho synthesis is impaired after brain ischemia, and CDP-choline may increase PtdCho levels by attenuating the loss of CCT activity and lyso-PtdCho formation.

Absence of cardiolipin results in temperature sensitivity, respiratory defects, and mitochondrial DNA instability independent of pet56

Cardiolipin (CL) is a dimeric phospholipid localized primarily in the mitochondrial membrane. Previous studies have shown that yeast cells containing a disruption of CRD1, the structural gene encoding CL synthase, exhibit temperature-sensitive colony formation and multiple mitochondrial defects. A recent report (Zhang, M., Su, X., Mileykovskaya, E., Amoscato, A. A., and Dowhan, W. (2003) J. Biol. Chem. 278, 35204-35210) suggested that defects associated with CL deficiency may result from the reduced expression of PET56 in crd1 Delta mutant backgrounds and should be reevaluated. In the current study, we present evidence that CL deficiency leads to mitochondrial DNA instability, loss of viability, and defects in oxidative phosphorylation at elevated temperatures. The observed mutant phenotypes are characteristic of crd1 Delta mutant cells of both PET56 and pet56 backgrounds and are complemented by an episomal copy of CRD1 but not by expression of the PET56 gene. Phosphatidylglycerol is elevated in crd1 Delta mutant cells when grown in the presence of fermentable and non-fermentable carbon sources, although the extent of the increase is higher in nonfermentable medium. An increase in the ratio of phosphatidylethanolamine to phosphatidylcholine was also apparent in the mutant. These findings demonstrate that CRD1, independent of PET56, is required for optimal mitochondrial function and for an essential cellular function at elevated temperatures.

Aberrant cardiolipin metabolism in the yeast taz1 mutant: a model for Barth syndrome

In eukaryotic cells, the acyl species of the phospholipid cardiolipin (CL) are more highly unsaturated than those of the other membrane phospholipids. Defective acylation of CL with unsaturated fatty acids and decreased total CL are associated with Barth syndrome, an X-linked cardio- and skeletal myopathy attributed to a defect in the gene G4.5 (also known as tafazzin). We constructed a yeast mutant (taz1) containing a null mutation in the homologue of the human G4.5 gene. The yeast taz1Delta mutant was temperature sensitive for growth in ethanol as sole carbon source, but grew normally on glucose or glycerol plus ethanol. Total CL content was reduced in the taz1Delta mutant, and monolyso-CL accumulated. The predominant CL acyl species found in wild-type cells, C18:1 and C16:1, were markedly reduced in the mutant, whereas CL molecules containing saturated fatty acids were present. Interestingly, CL synthesis increased in the mutant, whereas expression of the CL structural genes CRD1 and PGS1 did not, suggesting that de novo biosynthetic enzyme activities are regulated by CL acylation. These results indicate that the taz1Delta mutant is an excellent genetic tool for the study of CL remodelling and may serve as a model system for the study of Barth syndrome.

Rat long chain acyl-CoA synthetase 5, but not 1, 2, 3, or 4, complements Escherichia coli fadD

Long chain fatty acids are converted to acyl-CoAs by acyl-CoA synthetase (fatty acid CoA ligase: AMP forming, E.C. 6.2.1.3; ACS). Escherichia coli has a single ACS, FadD, that is essential for growth when fatty acids are the sole carbon and energy source. Rodents have five ACS isoforms that differ in substrate specificity, tissue expression, and subcellular localization and are believed to channel fatty acids toward distinct metabolic pathways. We expressed rat ACS isoforms 1-5 in an E. coli strain that lacked FadD. All rat ACS isoforms were expressed in E. coli fadD or fadDfadR and had ACS specific activities that were 1.6-20-fold higher than the wild type control strain expressing FadD. In the fadD background, the rat ACS isoforms 1, 2, 3, 4 and 5 oxidized [(14)C]oleate at 5 to 25% of the wild type levels, but only ACS5 restored growth on oleate as the sole carbon source. To ensure that enzymes of beta-oxidation were not limiting, assays of ACS activity, beta-oxidation, fatty acid transport, and phospholipid synthesis were also examined in a fadD fadR strain, thereby eliminating FadR repression of the transporter FadL and the enzymes of beta-oxidation. In this strain, fatty acid transport levels were low but detectable for ACS1, 2, 3, and 4 and were nearly 50% of wild type levels for ACS5. Despite increases in beta-oxidation, only ACS5 transformants were able to grow on oleate. These studies show that although ACS isoforms 1-4 variably supported moderate transport activity, beta-oxidation, and phospholipid synthesis and although their in vitro specific activities were greater than that of chromosomally encoded FadD, they were unable to substitute functionally for FadD regarding growth. Thus, membrane composition and protein-protein interactions may be critical in reconstituting bacterial ACS function.

Cardiolipin Stabilizes Respiratory Chain Supercomplexes

Cardiolipin stabilized supercomplexes of Saccharomyces cerevisiae respiratory chain complexes III and IV (ubiquinol:cytochrome c oxidoreductase and cytochrome c oxidase, respectively), but was not essential for their formation in the inner mitochondrial membrane because they were found also in a cardiolipin-deficient strain. Reconstitution with cardiolipin largely restored wild-type stability. The putative interface of complexes III and IV comprises transmembrane helices of cytochromes b and c1 and tightly bound cardiolipin. Subunits Rip1p, Qcr6p, Qcr9p, Qcr10p, Cox8p, Cox12p, and Cox13p and cytochrome c were not essential for the assembly of supercomplexes; and in the absence of Qcr6p, the formation of supercomplexes was even promoted. An additional marked effect of cardiolipin concerns cytochrome c oxidase. We show that a cardiolipin-deficient strain harbored almost inactive resting cytochrome c oxidase in the membrane. Transition to the fully active pulsed state occurred on a minute time scale.

B Cell receptor directs the activation of NFAT and NF-κB via distinct molecular mechanisms

BCR engagement initiates intracellular calcium ([Ca2+]i) mobilization which is critical for the activation of multiple transcription factors including NF-kappaB and NFAT. Previously, we showed that Bruton's tyrosine kinase (BTK)-deficient (btk-/-) B cells, which display a modestly reduced calcium response to BCR crosslinking, do not activate NF-kappaB. Here we show that BTK is also essential for the activation of NFAT following BCR engagement. Pharmacological mobilization of [Ca2+]i in BTK-deficient DT40 B cells (DT40.BTK) does not rescue BCR directed activation of NF-kappaB and only partially that of NFAT, suggesting existence of additional BTK-signaling pathways in this process. Therefore, we investigated a requirement for BTK in the production of diacylglycerol (DAG). We found that DT40.BTK B cells do not produce DAG in response to BCR engagement. Pharmacological inhibition of PKC isozymes and Ras revealed that the BCR-induced activation of NF-kappaB requires conventional PKCbeta, whereas that of NFAT may involve non-conventional PKCdelta and Ras pathways. Consistent with an essential role for BTK in the regulation of NFAT, B cells from btk-/- mice display defective expression of CD5, a gene under the control of NFAT. Together, these results suggest that BCR employs distinct BTK-dependent molecular mechanisms to regulate the activation of NF-kappaB versus NFAT.

Expression of the yeast PIS1 gene requires multiple regulatory elements including a Rox1p binding site

The PIS1 gene is required for de novo synthesis of phosphatidylinositol (PI), an essential phospholipid in Saccharomyces cerevisiae. PIS1 gene expression is unusual because it is uncoupled from the other phospholipid biosynthetic genes, which are regulated in response to inositol and choline. Relatively little is known about regulation of transcription of the PIS1 gene. We reported previously that PIS1 transcription is sensitive to carbon source. To further our understanding of the regulation of PIS1 transcription, we carried out a promoter deletion analysis that identified three regions required for PIS1 gene expression (upstream activating sequence (UAS) elements 1-3). Deletion of either UAS1 or UAS2 resulted in an approximately 45% reduction in expression, whereas removal of UAS3 yielded an 84% decrease in expression. A comparison of promoters among several Saccharomyces species shows that these sequences are highly conserved. Curiously, the UAS3 element region (-149 to -138) includes a Rox1p binding site. Rox1p is a repressor of hypoxic genes under aerobic growth conditions. Consistent with this, we have found that expression of a PIS1-cat reporter was repressed under aerobic conditions, and this repression was dependent on both Rox1p and its binding site. Furthermore, PI levels were elevated under anaerobic conditions. This is the first evidence that PI levels are affected by regulation of PIS1 transcription.

Valproate disrupts regulation of inositol responsive genes and alters regulation of phospholipid biosynthesis

Valproate (VPA) is one of the two drugs approved by the Food and Drug Administration (FDA) for the treatment of bipolar disorder. The therapeutic mechanism of VPA has not been established. We have shown previously that growth of the yeast Saccharomyces cerevisiae in the presence of VPA causes a decrease in intracellular inositol and inositol-1-P, and a dramatic increase in expression of INO1, which encodes the rate limiting enzyme for de novo inositol biosynthesis. To understand the underlying mechanism of action of VPA, INO1, CHO1 and INO2 expression, intracellular inositol and phospholipid biosynthesis were studied as a function of acute and chronic exposure of growing cells to the drug. A decrease in intracellular inositol was apparent immediately after addition of VPA. Surprisingly, expression of genes that are usually derepressed during inositol depletion, including INO1, CHO1 and INO2 (that contain inositol-responsive UASINO sequences) decreased several fold during the first hour, after which expression began to increase. Incorporation of 32Pi into total phospholipids was significantly decreased. Pulse labelling of CDP-DG and PG, shown previously to increase during inositol depletion, increased within 30 min. However, pulse labelling of PS, which normally increases during inositol depletion, was decreased within 30 min. PS synthase activity in cell extracts decreased with time, although VPA did not directly inhibit PS synthase enzyme activity. Thus, in contrast to the effect of chronic VPA treatment, short-term exposure to VPA abrogated the normal response to inositol depletion of inositol responsive genes and led to aberrant synthesis of phospholipids.

Ca2+-independent phospholipases A2 and production of arachidonic acid in nuclei of LA-N-1 cell cultures: a specific receptor activation mediated with retinoic acid

The LA-N-1 cell nucleus contains Ca2+-independent phospholipase A2 (PLA2) activity hydrolyzing plasmenylethanolamine (PlsEtn) and 1,2-diacyl-sn-glycero-3-phosphoethanolamine (PtdEtn). These enzymes hydrolyze glycerophospholipids to produce arachidonic acid and lysoglycerophospholipids. The treatment of LA-N-1 cell cultures with all-trans retinoic acid (atRA) results in time- and dose-dependent stimulation of PlsEtn-PLA2 and PtdEtn-PLA2 activities in the nuclear fraction. PLA2 activities in the non-nuclear fraction (microsomes) are not affected by atRA, whilst the pan retinoic acid receptor (RAR) antagonist, BMS493, blocks the PLA2 activities in the nuclear fraction. This indicates that the stimulation of PLA2 activities is a receptor-mediated process. Treatment of LA-N-1 cell cultures with cycloheximide has no effect on basal PLA2 activities. However, atRA-mediated stimulation of PLA2 activities in LA-N-1 cell nuclei is partially inhibited by cycloheximide indicating that this decrease in PLA2 activity is due to a general decreased protein synthesis. Our results also support earlier studies in which atRA induces morphologic differentiation through the stimulation of PLA2-generated second messengers such as arachidonic acid and eicosanoids.

Annexin A1 processing is associated with caspase-dependent apoptosis in BZR cells

Annexins are widely distributed and have been described in lung as well as in other cells and tissues. Annexin I (ANX AI) is a member of the calcium-dependent phospholipid binding protein family. Besides its anti-inflammatory function, ANX AI has been involved in several mechanisms such as the Erk repression pathway or apoptosis. To investigate the role of ANX AI on apoptosis in broncho-alveolar cells, we have constructed a plasmid containing the ANX AI full length cDNA. Transfected BZR cells displayed a higher level of both forms of ANX AI (37 and 33 kDa) as well as a decrease in cell viability (two-fold versus cells transfected with an empty vector). In order to analyse the endogenous ANX AI processing during stimulus-induced apoptosis, BZR cells were treated with a commonly used inducer, i.e. C2 ceramides. In these conditions, microscopic analysis revealed chromatin condensation in dying cells and the Bcl-2, Bcl-x(L)/Bax mRNA balance was altered. Caspase-3 is one of the key executioners of apoptosis, being responsible for the cleavage of many proteins such as the nuclear enzyme poly(ADP-ribose) polymerase (PARP). We demonstrate that caspase-3 was activated after 4 h treatment in the presence of ceramide leading to the cleavage of PARP. Dose-response experiments revealed that cell morphology and viability modifications following ceramide treatment were accompanied by an increase in endogenous ANX AI processing. Interestingly, in both ceramide and transfection experiments, the ANX AI cleaved form was enhanced whereas pre-treatment with the caspase inhibitor Z-VAD-fmk abolished ANX AI cleavage. In conclusion, this study demonstrates a complex regulatory role of caspase-dependent apoptosis where ANX AI is processed at the N-terminal region which could give susceptibility to apoptosis upon ceramide treatment.

A possible role of cholesterol-sphingomyelin/phosphatidylcholine in nuclear matrix during rat liver regeneration

BACKGROUND/AIMS

Phospholipids and cholesterol in chromatin have been previously demonstrated. The lipid fraction changes during cell proliferation in relation to activation of enzymes of phospholipid metabolism. The aim of the present work is to clarify if chromatin lipids may derive or not from nuclear matrix and if they have different roles.

METHODS

The subnuclear fractions were isolated from rat hepatocyte nuclei and the lipid fraction was extracted and analysed by chromatography in normal and regenerating liver. The phosphatidylcholine-sphingomyelin metabolism enzymes activity was assayed, by using radioactive substrates.

RESULTS

In nuclear matrix, cholesterol and sphingomyelin are respectively five and three times higher than those present in chromatin; the amount of phosphatidylcholine, which it is enriched in saturated fatty acids, is lower, thus indicating a less fluid structure. The lower content in phosphatidylcholine may be justified by the phosphatidylcholine-dependent phospholipase C activity, which increases during liver regeneration, reaching a peak at the beginning of S-phase, when also cholesterol and sphingomyelin increase.

CONCLUSIONS

The nuclear matrix lipids are independent from chromatin lipids; the ratio cholesterol-sphingomyelin/phosphatidylcholine is higher and, as a consequence, nuclear matrix is less fluid in relation to DNA synthesis, suggesting a specific role of nuclear matrix as a structure involved in DNA duplication.

Aluminum accumulation and membrane fluidity alteration in synaptosomes isolated from rat brain cortex following aluminum ingestion: effect of cholesterol

In the present work, we studied the effect of cholesterol/phospholipid (CH/PL) molar ratio on aluminum accumulation and aluminum-induced alteration of membrane fluidity in rat brain cortex synaptosomes. We observed that sub-acute (daily supply of 1.00 g of AlCl(3) during 10 days) and chronic (daily supply of 0.03 g of AlCl(3) during 4 months) exposure to dietary aluminum leads to a synaptosomal aluminum enrichment of 45 and 59%, respectively. During chronic exposure to AlCl(3), the enhancement of aluminum content was prevented by administration of colestipol (0.31 g/day), which decreased the synaptosomal membrane CH/PL molar ratio (nmol/nmol) from 1.2 to 0.4. Fluorescence anisotropy analysis, using 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-(trimethylamino)phenyl)-6-phenylhexa-1,3,5-triene (TMA-DPH), showed that after treatment with colestipol a decrease in membrane order occurs at the level of hydrophilic lipid-water surface and deeper hydrophobic region of the synaptosomal membrane. When the rats were exposed to aluminum, it was observed a significant enhancement of membrane fluidity, which was more pronounced at the level of the membrane hydrophilic regions. Meanwhile, when chronic exposure to dietary AlCl(3) was accompanied by treatment with colestipol, the aluminum-induced decrease in membrane order was negligible when compared to TMA-DPH and DPH anisotropy values measured upon colestipol treatment. In contrast, in vitro incubation of synaptosomes (isolated from control rats) with AlCl(3) induced a concentration-dependent rigidification of this more hydrophilic membrane region. The opposite action of aluminum on synaptosomal membrane fluidity, during in vivo and in vitro experiments, appears to be explained by alteration of synaptosomal CH/PL molar ratio, since a significant reduction (approximately 80%) of this parameter occurs during in vivo exposure to aluminum. In conclusion, during in vivo exposure to aluminum, fluidification of hydrophilic regions and reduction of CH/PL molar ratio of presynaptic membranes accompany the accumulation of this cation, which appear to restrict aluminum retention in brain cortex nerve terminals.

The presence and the role of chromatin cholesterol in rat liver regeneration

BACKGROUND/AIMS

It has been shown that cholesterol is necessary in early G1 phase during cell duplication. In the present research we have studied the presence of cholesterol in the hepatocyte chromatin lipid fraction and its behaviour in liver regeneration.

METHODS

Hepatocyte nuclei and chromatin were isolated from normal and regenerating rat liver. The lipid fraction was extracted and analysed by chromatography. The activity of sphingomyelin-synthase in the chromatin was evaluated using labelled phosphatidylcholine.

RESULTS

In the chromatin, the amount of cholesterol is similar to that of sphingomyelin, and it increases in chromatin digested with exogenous sphingomyelinase or proteinase K. It may be concluded that a complex, formed by cholesterol, sphingomyelin and proteins, is present in the chromatin. The particular affinity between sphingomyelin and cholesterol in chromatin with respect the nuclear membrane may be tentatively explained as due to the enrichment in saturated fatty-acids of the chromatin sphingomyelin. Moreover the cholesterol inhibits the chromatin sphingomyelin-synthase activity. During liver regeneration, an increase in chromatin cholesterol is observed between 6 and 18 h after hepatectomy, when the neutral-sphingomyelinase activity increases and the sphingomyelin-synthase is inhibited.

CONCLUSIONS

The cholesterol is present in the chromatin and its amount changes in relation to cell proliferation in regenerating liver.

Platelet phospholipids are differentially protected against oxidative degradation by plasmalogens

The oxidative degradation of phospholipids in the presence and absence of plasmalogens (plasmenyl phosphatidylethanolamine: PPE) was followed by chemical analysis. Human platelet phospholipids, either intact or after removal of PPE by acid treatment, were oxidized with 28 mM 2,2'-azobis(2-amidinopropane di-HCl in Triton X-100 micelles (detergent/phospholipid 5:1, mol/mol). PPE (12% of all phospholipids, mol/mol) disappeared about three times more rapidly than glycerophospholipids, whereas sphingomyelin remained unaltered and the lysophosphatidylethanolamine (lysoPE) generated became progressively more unsaturated. After 60 min oxidation, the FA compositions of PS, PC, and PI were similar in extracts with or without plasmalogens. In contrast, diacyl phosphatidylethanolamine (DPE) became more saturated in the absence of PPE. The rate of phospholipid destruction was always unique to each class, but for all phospholipids slowed down in the presence of PPE. This protective effect increased in the order DPE < PS < PC < PI and did not seem to be simply related to the class unsaturation. Alpha-tocopherol had no influence on the time courses of the quantities and compositions of the phospholipids, even at a molar ratio of alpha-tocopherol to phospholipids four times higher than in platelet membranes. Thus, PPE protected phospholipids efficiently but differentially against peroxidative attack, whereas the contribution of alpha-tocopherol appeared to be negligible even at a concentration four times greater than in platelet membranes.

Effect of dietary restriction on age-related increase of liver susceptibility to peroxidation in rats

Dietary restriction (DR) increases life span and decreases age-related diseases in experimental animals. It has received a great deal of attention in connection with the relationship between aging, nutrition, and oxidative stress because oxidative injury in several organ systems is a prominent feature in aging. We investigated the possibility that DR can protect vulnerable liver lipids against age-related increases of peroxidation. Male Fischer 344 rats fed ad libitum (AL) or dietarily restricted (maintained on 60% of AL food intake) were killed by decapitation at 4 (young) or 12 mon (adult) of age. Phosphatidylcholine hydroperoxide (PCOOH) concentration of liver was determined using a chemiluminescent high-performance liquid chromatographic method. Liver PCOOH increased with age in adult rats, but less of an increase of PCOOH was seen in DR rats, which is consistent with results on production of thiobarbituric acid-reactive substances and oxygen-derived free radicals. No significant differences were found in liver superoxide dismutase and catalase activity between AL and DR groups of young and adult rats. Liver triglyceride and cholesterol contents were lower in DR than AL rats at 12 mon. Fatty acid compositions of phosphatidylcholine and phosphatidylethanolamine indicated that the ratio of (20:3n-6 + 20:4n-6)/18:2n-6, an index of linoleic acid (18:2n-6) desaturation, was lower in DR than in AL rats. We concluded that DR suppresses age-related oxidative damage in liver by modulating the amount of lipid as well as fatty acid composition.

A role for hormone-sensitive lipase in the selective mobilization of adipose tissue fatty acids

The mobilization of fatty acids from rat and human fat cells is selective according to molecular structure, and notably carbon atom chain length. This study aimed at examining whether the release of individual fatty acids from triacylglycerols (TAG) by hormone-sensitive lipase (HSL) plays a role in the selectivity of fatty acid mobilization. Recombinant rat and human HSL were incubated with a lipid emulsion. The hydrolysis of 18 individual fatty acids, ranging in chain length from 12 to 24 carbon atoms and in unsaturation degree from 0 to 3 double bond(s), was measured by comparing the composition of non-esterified fatty acids (NEFA) to that of the original TAG. The relative hydrolysis (% in NEFA/% in TAG) differed between fatty acids, being about 5-fold and 3-fold higher for the most (18:1n-7) than for the least (24:0) readily released fatty acid by recombinant rat and human HSL, respectively. Relationships were found between the chain length of fatty acids and their relative hydrolysis. Among 12-24 carbon atom saturated fatty acids, the relative hydrolysis markedly decreased (by about 5- and 3-times for recombinant rat and human HSL, respectively) with increasing chain length. We conclude that fatty acids are selectively released from TAG by HSL according to carbon atom chain length. These data provide insight on the mechanism by which fatty acids are selectively mobilized from fat cells.