BBA - Molecular and Cell Biology of Lipids (v.1631, #2)
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Liver X receptors and the control of cholesterol homeostasis: potential therapeutic targets for the treatment of atherosclerosis by Lesley J Millatt; Virginie Bocher; Jean-Charles Fruchart; Bart Staels (107-118).
The liver X receptors (LXRα and LXRβ) are nuclear receptor transcription factors that are activated by certain oxysterol derivatives of cholesterol. As such, LXR activity may be up-regulated by cellular lipid loading or dietary cholesterol intake. Intensive research interest in the LXRs has led to the identification of an expanding list of LXR target genes. The identity of these genes, and their response to LXR activation, indicates that the LXRs play an important role in the response to excess cholesterol, and that their activation may protect against tissue cholesterol overload. In this review, we highlight the multiple roles of the LXRs in controlling cholesterol homeostasis via their coordinated effects on cholesterol synthesis, dietary cholesterol absorption, reverse cholesterol transport, and bile acid synthesis and excretion. We discuss the therapeutic interest of developing LXR agonists, in view of their apparent protective effects against atherosclerosis. However, we also draw attention to the possible undesirable side-effects of LXR activation, and thus the potential interest of developing target gene-specific LXR agonists, or agonists that are specific for only one LXR isoform.
Keywords: Liver X receptor; Cholesterol; Atherosclerosis; Nuclear receptor; Reverse cholesterol transport;
Phytanic acid alpha-oxidation, new insights into an old problem: a review by Ronald J.A Wanders; Gerbert A Jansen; Matthew D Lloyd (119-135).
Phytanic acid (3,7,10,14-tetramethylhexadecanoic acid) is a branched-chain fatty acid which is known to accumulate in a number of different genetic diseases including Refsum disease. Due to the presence of a methyl-group at the 3-position, phytanic acid and other 3-methyl fatty acids can not undergo β-oxidation but are first subjected to fatty acid α-oxidation in which the terminal carboxyl-group is released as CO2. The mechanism of α-oxidation has long remained obscure but has been resolved in recent years. Furthermore, peroxisomes have been found to play an indispensable role in fatty acid α-oxidation, and the complete α-oxidation machinery is probably localized in peroxisomes. This Review describes the current state of knowledge about fatty acid α-oxidation in mammals with particular emphasis on the mechanism involved and the enzymology of the pathway.
Keywords: Phytanic acid; Peroxisome; Fatty acid;
Characterisation of a potential biomarker of phospholipidosis from amiodarone-treated rats by Gulnahar B Mortuza; William A Neville; Jane Delaney; Catherine J Waterfield; Patrick Camilleri (136-146).
A novel and relatively simple analytical method for the separation, characterisation and semi-quantitation of phospholipids (PLs) from extracts of complex biological samples has been developed. This methodology allows PL extracts from cells and tissues to be analysed by liquid chromatography (LC) coupled to electrospray ionisation mass spectrometry (ESI-MS). Complex mixtures of PLs were separated on a high-performance liquid chromatography (HPLC) system using 0.5% ammonium hydroxide in methanol/water/hexane/formate mixture with UV detection at 205 nm. Identification and structural characterisation of molecular species were carried out utilising ESI-MS and MS/MS in the negative ion mode.The abnormal accumulation of PLs (phospholipidosis) was induced in male Sprague–Dawley rats by administration of the cationic amphiphilic drug (CAD), amiodarone. Analysis of the PL profile of liver and lung tissues, lymphocytes and serum from treated rats was carried out using this analytical procedure (LC-ESI/MS/MS). Differences in PL profiles between treated and untreated animals were highlighted by principal component analysis (PCA). This led to the selection of a potential metabolic marker of phospholipidosis (PLD) identified as a lyso-bis-phosphatidic acid (LBPA) derivative, also known as bis(monoglycero)phosphate (BMP). This PL was absent in control animals but was present in quantifiable amounts in all samples from amiodarone-treated rats.
Keywords: Phospholipidosis (PLD); Lyso-bis-phosphatidic acid (LBPA); Bis(monoglycero)phosphate (BMP); Phosphatidylcholine (PC); Amiodarone; High performance liquid chromatography (HPLC); Electrospray ionisation-mass spectrometry (ESI-MS); Cationic amphiphilic drug (CAD);
Accumulation of genistein and lipophilic genistein derivatives in lipoproteins during incubation with human plasma in vitro by Maija Kaamanen; Herman Adlercreutz; Matti Jauhiainen; Matti J Tikkanen (147-152).
Atherosclerosis is initiated by the uptake and retention of oxidized low-density lipoprotein (LDL) into the arterial intima. We have previously shown that dietary isoflavone phytoestrogens inhibit LDL oxidation in vitro. The inhibition could have been caused by undetected isoflavone metabolites associated with lipoproteins. In the present study, we incubated human plasma with [3H]genistein, both with and without the lecithin:cholesterol acyltransferase (LCAT) inhibitor dithionitrobenzoic acid (DTNB). Our results indicated that the 3H-label was attached to both high-density lipoprotein (HDL) and LDL, and that it represented both underivatized genistein and lipophilic derivatives of genistein, part of which were identified as fatty acid monoesters. The latter was demonstrated by the findings that DTNB decreased the HDL and LDL associated radioactivity in the lipophilic fraction isolated by hydrophobic chromatography and that saponification hydrolysis liberated a corresponding part of the 3H-label. Two-dimensional reversed-phase thin-layer chromatography (TLC) demonstrated that a corresponding part of the radioactivity comigrated with genistein monoester standards in the absence of DTNB but was abolished if DTNB had been present in the incubation. In summary, incubation of plasma with [3H]genistein resulted in accumulation of underivatized genistein as well as lipophilic genistein derivatives in lipoproteins. A smaller part of the latter were genistein monoesters, while part remained unidentified. Our results suggest an explanation for the increased oxidation resistance of isolated LDL during intake of soybean isoflavones.
Keywords: Genistein; Isoflavone; Soy; Antioxidant; Phytoestrogen; Lipoprotein;
Two uncommon phospholipase D isoenzymes from poppy seedlings (Papaver somniferum L.) by Marek Oblozinsky; Regina Schoeps; Renate Ulbrich-Hofmann; Lydia Bezakova (153-159).
Phospholipase D (PLD) has been detected in seedlings of Papaver somniferum L. cv. Lazúr (Papaveraceae). Purification of the enzyme revealed the existence of two forms of PLD (named as PLD-A and PLD-B). The two enzymes strongly differ in their catalytic properties. The pH optima were found at pH 8.0 for PLD-A and at pH 5.5 for PLD-B. While both enzymes show hydrolytic activity toward phosphatidylcholine (PC) and phosphatidyl-p-nitrophenol (PpNP), PLD-B only was able to catalyze the exchange of choline in PC by glycerol. Both enzymes were activated by Ca2+ ions with an optimum concentration of 10 mM. In contrast to PLDs from other plants, PLD-B was still more activated by Zn2+ ions with an optimum concentration of 5 mM. The apparent molecular masses of PLD-A and PLD-B, derived from sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), were estimated to be 116.4 and 114.1 kDa. N-terminal protein sequencing indicated N-terminal blockage in both cases. The isoelectric points were found to be 8.7 for PLD-A and 6.7 for PLD-B. Both enzymes were shown to be N-linked glycoproteins. This paper is the first report on PLD in poppy and indicates some important differences of the two enzyme forms to other PLDs known so far.
Keywords: Phospholipase D; Papaver somniferum; Purification; Zn-activation; Transphosphatidylation;
Up-regulation of the peroxisomal β-oxidation system occurs in butyrate-grown Candida tropicalis following disruption of the gene encoding peroxisomal 3-ketoacyl-CoA thiolase by Mitsuyoshi Ueda; Naoki Kanayama; Naomi Kamasawa; Masako Osumi; Atsuo Tanaka (160-168).
In the yeast Candida tropicalis, two thiolase isozymes, peroxisomal acetoacetyl-CoA thiolase and peroxisomal 3-ketoacyl-CoA thiolase, participate in the peroxisomal fatty acid β-oxidation system. Their individual contributions have been demonstrated in cells grown on butyrate, with C. tropicalis able to grow in the absence of either one. In the present study, a lack of peroxisomal 3-ketoacyl-CoA thiolase protein resulted in increased expression (up-regulation) of acetoacetyl-CoA thiolase and other peroxisomal proteins, whereas a lack of peroxisomal acetoacetyl-CoA thiolase produced no corresponding effect. Overexpression of the acetoacetyl-CoA thiolase gene did not suppress the up-regulation or the growth retardation on butyrate in cells without peroxisomal 3-ketoacyl-CoA thiolase, even though large amounts of the overexpressed acetoacetyl-CoA thiolase were detected in most of the peroxisomes of butyrate-grown cells. These results provide important evidence of the greater contribution of 3-ketoacyl-CoA thiolase to the peroxisomal β-oxidation system than acetoacetyl-CoA thiolase in C. tropicalis and a novel insight into the regulation of the peroxisomal β-oxidation system.
Keywords: Peroxisomal acetoacetyl-CoA thiolase; Peroxisomal 3-ketoacyl-CoA thiolase; Cytosolic acetoacetyl-CoA thiolase; Yeast Candida tropicalis; Butyrate; Peroxisomal fatty acid β-oxidation;
Effects of sphingomyelin on apolipoprotein E- and lipoprotein lipase-mediated cell uptake of lipid particles by Shin-ya Morita; Keiichirou Okuhira; Nanoko Tsuchimoto; Aline Vertut-Doı̈; Hiroyuki Saito; Minoru Nakano; Tetsurou Handa (169-176).
It has been reported that human plasma sphingomyelin (SM) levels are positively and independently related to coronary artery disease. The lipoprotein surface is mainly formed by phosphatidylcholine (PC) and SM together with cholesterol and apolipoproteins. However, the influence of SM on the cell uptake of triglyceride-rich lipoproteins and remnants is poorly understood. To clarify the role of SM in lipoprotein uptake, we prepared lipid emulsions containing triolein, PC and SM as model particles of lipoproteins. Apolipoprotein E (ApoE) binding studies revealed that incorporation of SM into the emulsion surface reduced the binding capacity of apoE without changing the affinity. Surface SM reduced apoE-mediated uptake of emulsions by HepG2 cells because of the decreased amount of binding apoE. Apolipoproteins C-II and C-III inhibited the apoE-mediated uptake of SM containing emulsions more effectively. The stimulatory effect of lipoprotein lipase (LPL) on emulsion uptake was decreased by replacing surface PC with SM. These results suggest that SM-induced changes in the binding properties of apolipoproteins and LPL correlate with decreased hepatic uptake of lipid particles.
Keywords: Sphingomyelin; Apolipoprotein E; Apolipoprotein C; Lipoprotein lipase; Cell uptake;
Apo A-IV: an update on regulation and physiologic functions by Simona Stan; Edgard Delvin; Marie Lambert; Ernest Seidman; Emile Levy (177-187).
Apolipoprotein (apo) A-IV, first identified 28 years ago as a plasma lipoprotein moiety, is now known to participate in the regulation of various metabolic pathways. It is synthesized primarily in the enterocytes of the small intestine during fat absorption. After entry into the bloodstream, the 46-kDa glycoprotein apo A-IV appears associated with chylomicrons, high-density lipoproteins, and in the lipoprotein-free fraction. It has a role in lipid absorption, transport and metabolism, and may act as a post-prandial satiety signal, an anti-oxidant and a major factor in the prevention of atherosclerosis. After summarizing and discussing these functions for reader's comprehension, the current review focuses on the regulation of apo A-IV by nutrients, biliary components, drugs, hormones and gastrointestinal peptides. The understanding of the involved mechanisms that underline apo A-IV regulation may in the long run allow us to switch on its gene, which may confer multiple beneficial effects, including the protection from atherosclerosis.
Keywords: Lipoprotein; Atherosclerosis; Food intake; Nutrient; Hormone;
The polar lipid composition of Mesorhizobium ciceri by Adam Choma; Iwona Komaniecka (188-196).
The extractable lipid composition of Mesorhizobium ciceri strain HAMBI 1750 grown in a phosphate sufficient medium (79CA) is reported. Cardiolipin (CL—27% of total lipids), phosphatidylglycerol (PG—18%), phosphatidylethanolamine (PE—1%), phosphatidylcholine (PC—30%) and two methylated derivatives of PE, i.e. phosphatidyl-N, N-dimethylethanolamine (DMPE—1%) and phosphatidyl-N-monomethylethanolamine (MMPE—1%), were found to make up the phospholipids of the analysed bacteria. Nonphosphorus, ornithine-containing lipid (OL—10%) was also detected. Polar groups of phospholipids were predominantly acylated with cis-11,12-methyleneoctadecanoyl (lactobacillic) residues, whereas the ornithine lipid contained mainly 3-hexadecanoyloxy-11,12-methyleneoctadecanoic acid bound to the α-amino group.
Keywords: Mesorhizobium ciceri; Phospholipid; Ornithine-containing lipid; 3-hydroxy-11,12-methyleneoctadecanoic acid; Fatty acid;
Highly sensitive active-site titration of lipase in microscale culture media using fluorescent organophosphorus ester by Ryota Fujii; Yuji Utsunomiya; Jun Hiratake; Atsushi Sogabe; Kanzo Sakata (197-205).
The fluorescent organophosphorus esters, diethyl 4-methylumbelliferyl phosphate (1), ethyl hexyl 4-methylumbelliferyl phosphate (2) and ethyl 4-methylumbelliferyl heptylphosphonate (3) have been synthesized and evaluated as a sensitive active-site titrant of lipase. The phosphorus esters 1, 2 and 3 inactivated the lipase from Pseudomonas aeruginosa (LPL-312) with a second-order rate constant for enzyme inactivation (k on) of 1.8, 32 and 5600 s−1 M−1, respectively. The long-chain phosphonate 3 turned out to be the most potent inactivator of the lipase to release a stoichiometric amount of highly fluorescent 4-methylumbelliferone (4MU) as a leaving group. By using the phosphate 3 as an active-site titrant, the low concentration (4.5 nM) of the active lipase was titrated successfully. The highly sensitive active-site titration with 3 enabled the direct determination of the concentration of the active lipase expressed in a microscale culture medium. Although the expression level differed significantly from one culture to another, the titrated concentration of the active lipase was proportional to the apparent activity for all the independent cultures. The molecular activity calculated for the expressed lipase was found to be the same as that of the purified lipase. The present active-site titration method is widely applicable to the biocatalytic engineering of lipases such as directed evolution, site-directed mutagenesis, chemical modification and immobilization.
Keywords: Active-site titration; Lipase; 4-Methylumbelliferyl phosphonate; Microscale titration; Directed evolution;