不同蛋白质和脂肪水平对1龄团头鲂生长性能和体组成的影响

试验采用3×3因子设计,探讨了饲料中不同蛋白质和脂肪水平对1龄团头鲂[均重:(50.37±1.27)g]生长性能和体组成的影响。试验设3个蛋白质水平(25%、30%和35%)和3个脂肪水平(3%、6%和9%),共配制9组饲料。试验鱼饲养于网箱(规格为2 m×1 m×1 m)中,每天投喂3次,试验期为8周。结果表明:蛋白质和脂肪之间无交互作用存在(P>0.05)。蛋白质和脂肪水平对存活率无显著影响(P>0.05)。增重率、特定生长率和饵料系数显著受蛋白质和脂肪水平影响(P<0.05)。其中,25%蛋白组的增重率及特定生长率显著低于其他蛋白组(P<0.05),而6%脂肪组显著高于其他脂肪组(P<0.01)。尽管35%蛋白6%脂肪组的饵料系数最低,但与除了25%蛋白3%脂肪和25%蛋白9%脂肪这两组外的其他组相比,差异均不显著(P>0.05)。蛋白效率比和氮保留率随蛋白质水平的升高显著降低(P<0.05)。此外,蛋白效率比显著受脂肪水平的影响(P<0.05),以6%组最高。能量保留率随脂肪水平的升高显著升高(P<0.05)。鱼体肥满度随蛋白质和脂肪水平的升高显著升高(P<0.05)。腹脂率和肝体比随脂肪水平的升高显著升高(P<0.05),而受蛋白质水平的影响较小(P>0.05)。蛋白质水平对全鱼、胴体和肝脏的组成均无显著影响(P>0.05)。脂肪水平对全鱼水分、脂肪和能量有极显著影响(P<0.01),其中,全鱼水分含量随脂肪水平的升高显著降低(P<0.01),而脂肪和能量含量则显著升高(P<0.01)。胴体和肝脏水分、脂肪含量的变化趋势与全鱼基本一致。以上结果表明,1龄团头鲂的适宜蛋白质和脂肪水平分别为30%和6%,适宜蛋能比为18.21 g/MJ。     

Influence of cultivation conditions on lipid production by Cryptococcus albidus

Summary Cryptococcus albidus var. albidus CBS 4517 was able to accumulate lipid under nitrogen-limited as well as excess-nitrogen conditions. The highest lipid-producting capacity was, however, observed in nitrogen-limited cultivations. In nitrogen-limited batch cultures, a lipid content of 34% (w/w) in biomass and a maximum specific lipid productivity of 37 mg lipid/g lipid-free biomass·h, was determined. The yield of lipid from glucose was about 0.15 g/g in nitrogen-limited and 0.11 g/g in excess-nitrogen cultures.In a nitrogen-limited fed-batch culture, 12.4 g/l lipid was produced at 90 h of cultivation and the cells contained 46.3% (w/w) lipid.Higher lipid yield and cellular lipid content were observed when inorganic nitrogen sources were used compared with organic. The choice of carbon source was seen to influence growth as well as lipid production and the highest yields of lipid were obtained when glucose, maltose or mannitol was used.A cultivation temperature of 20°C provided the highest lipid productivity compared to 25°C and 30°C. Addition of citrate to the growth medium was seen to have a stimulating effect on the specific lipid productivity.     

Resveratrol inhibition of lipid peroxidation

To define the molecular mechanism(s) of resveratrol inhibition of lipid peroxidation we have utilized model systems that allow us to study the different reactions involved in this complex process. Resveratrol proved (a) to inhibit more efficiently than either Trolox or ascorbate the Fe²⁺ catalyzed lipid hydroperoxide-dependent peroxidation of sonicated phosphatidylcholine liposomes; (b) to be less effective than Trolox in inhibiting lipid peroxidation initiated by the water soluble AAPH peroxyl radicals; (c) when exogenously added to liposomes, to be more potent than α-tocopherol and Trolox, in the inhibition of peroxidation initiated by the lipid soluble AMVN peroxyl radicals; (d) when incorporated within liposomes, to be a less potent chain-breaking antioxidant than α-tocopherol; (e) to be a weaker antiradical than α-tocopherol in the reduction of the stable radical DPPH^·. Resveratrol reduced Fe³⁺ but its reduction rate was much slower than that observed in the presence of either ascorbate or Trolox. However, at the concentration inhibiting iron catalyzed lipid peroxidation, resveratrol did not significantly reduce Fe³⁺, contrary to ascorbate. In their complex, our data indicate that resveratrol inhibits lipid peroxidation mainly by scavenging lipid peroxyl radicals within the membrane, like α-tocopherol. Although it is less effective, its capacity of spontaneously entering the lipid environment confers on it great antioxidant potential.     

The NADPH- and iron-dependent lipid peroxidation in human placental microsomes

In pregnant females, placenta is the most important source of lipid hydroperoxides and other reactive oxygen species (ROS). The increased production of lipid peroxides is often linked to preeclampsia. In our study, we revealed that NADPH- and iron-dependent lipid peroxidation in human placental microsomes (HPM) occurred. In the presence of Fe²⁺ ion, HPM produced small amounts of thiobarbituric acid-reactive substances (TBARS) – a final product of lipid peroxidation. NADPH caused a strong increase of iron stimulated TBARS formation. TBARS formation was inhibited by superoxide dismutase, butylated hydroxytoluene and α-tocopherol but not by mannitol or catalase. TBARS and superoxide radical production was inhibited in similar manner by cytochrome P450 inhibitors. The results obtained led us to the following conclusions: (1) microsomal lipid peroxidation next to mitochondrial lipid peroxidation may by an important source of lipid hydroperoxides in blood during pregnancy and (2) superoxide radical released by microsomal cytochrome P450 is an important factor in NADPH- and iron-dependent lipid peroxidation in HPM.     

The roles of C-terminal helices of human apolipoprotein A-I in formation of high-density lipoprotein particles

Apolipoprotein A-I (apoA-I) accepts cholesterol and phospholipids from ATP-binding cassette transporter A1 (ABCA1)-expressing cells to form high-density lipoprotein (HDL). Human apoA-I has two tertiary structural domains and the C-terminal domain (approximately amino acids 190–243) plays a key role in lipid binding. Although the high lipid affinity region of the C-terminal domain of apoA-I (residues 223–243) is essential for the HDL formation, the function of low lipid affinity region (residues 191–220) remains unclear. To evaluate the role of residues 191–220, we analyzed the structure, lipid binding properties, and HDL formation activity of Δ191–220 apoA-I, in comparison to wild-type and Δ223–243 apoA-I. Although deletion of residues 191–220 has a slight effect on the tertiary structure of apoA-I, the Δ191–220 variant showed intermediate behavior between wild-type and Δ223–243 regarding the formation of hydrophobic sites and lipid interaction through the C-terminal domain. Physicochemical analysis demonstrated that defective lipid binding of Δ191–220 apoA-I is due to the decreased ability to form α-helix structure which provides the energetic source for lipid binding. In addition, the ability to form HDL particles in vitro and induce cholesterol efflux from ABCA1-expressing cells of Δ191–220 apoA-I was also intermediate between wild-type and Δ223–243 apoA-I. These results suggest that despite possessing low lipid affinity, residues 191–220 play a role in enhancing the ability of apoA-I to bind to and solubilize lipids by forming α-helix upon lipid interaction. Our results demonstrate that the combination of low lipid affinity region and high lipid affinity region of apoA-I is required for efficient ABCA1-dependent HDL formation.     

Gel-phase microdomains and lipid rafts in monolayers affect the redox properties of ubiquinone-10

The redox properties of ubiquinone-10 (UQ) were examined in monolayers of mixtures of dioleoylphosphatidylcholine, palmitoylsphingomyelin, and cholesterol of different compositions, self-assembled on a mercury electrode, over the pH range from 7.5 to 9.5. A detailed analysis of the cyclic voltammograms of UQ in the above lipid environments points to a mechanism consisting of an elementary electron transfer step followed by two protonation (or deprotonation) steps in quasiequilibrium and by a further electron transfer step. In a lipid environment of solid-ordered (s_o) microdomains in a liquid-disordered (l_d) matrix, electron transport across the lipid monolayer takes place in the l_d phase. In a pure s_o phase, UQ tends to segregate into UQ-rich pools, exhibiting reversible electron transfer steps. In a lipid environment consisting of liquid-ordered (l_o) microdomains (lipid rafts) in an l_d matrix, UQ molecules tend to localize along the edge of the lipid rafts. However, in a lipid environment consisting exclusively of l_o and s_o microdomains, UQ molecules tend to segregate into UQ-rich pools. In all lipid environments, electron transport by UQ occurs with the quinone moiety localized on the solution side with respect to the ester linkages of the dioleoylphosphatidylcholine molecules.     

Amphotericin B interactions with a DOPC monolayer. Electrochemical investigations

A model lipid membrane consisting of a monolayer of dioleoyl phosphatidylcholine (DOPC) adsorbed onto a Hg electrode has been used to study the interaction between the lipid and different formulations of Amphotericin B (AmB) [Fungizone® (FZ), Heated Fungizone (HFZ), and Abelcet®]. The lipid organizational order was measured by electrochemical methods [capacitance and metal ion (Tl⁺) reduction], characterizing the change in lipid order due to interaction with the drug. The mean size and number density of pores formed in the monolayer were estimated by fitting the reduction current transients to a random array of microelectrode model. This method was shown sensitive for investigation of the interaction of drugs with the DOPC monolayer. Abelcet was found to have a smaller disruptive effect on lipid order than FZ and HFZ. The formulations used to solubilize the AmB were also studied. Sodium deoxycholate used as a solubilizer in FZ displayed significant influence on lipid order similar to that observed for Abelcet. The lipid complex, used in Abelcet, did not significantly perturb the DOPC monolayer order. The lipid complex used in Abelcet may have an annealing or healing effect that buffers the disruption possible due to AmB.     

Functional biodiversity of lipids in Antarctic zooplankton: Calanoides acutus, Calanus propinquus, Thysanoessa macrura and Euphausia crystallorophias

Zooplankton samples were collected in January 1993 off Dronning Maud Land along a transect from open waters to the marginal ice zone close to the Antarctic ice shelf. Thysanoessa macrura was caught in open waters while Calanoides acutus and Calanus propinquus were mainly sampled between ice floes in the marginal ice zone. The “ice-krill”Euphausia crystallorophias was found over the shelf directly associated with ice floes. T. macrura had a lipid content up to 36% of its dry weight with the dominant lipid class, wax ester, accounting for 45–50% of the total lipid. The predominance of 18:1 fatty alcohols is the striking characteristic of the wax esters. Small specimens of E. crystallorophias had lipid levels up to 26% of their dry weight with, unexpectedly, triacylglycerols being the dominant lipid (up to 41% of total lipid). The small levels of wax esters in these animals (3–6% of total lipid) had phytol as a major constituent. Large specimens of E. crystallorophias had up to 34% of their dry weight as lipid, with wax esters (47% of total lipid) dominated by 16:0 and 14:0 fatty alcohols as the major lipid. Calanus propinquus had lipid levels of up to 34% of their dry weight, with triacylglycerols (up to 63% of total lipid) being the dominant lipid. High levels of 22:1 (n-9) fatty acid were present in the triacylglycerols. Calanoides acutus had lipid levels up to 35% of the dry weight with wax esters accounting for up to 83% of total lipid. High levels of (n-3) polyunsaturated fatty acids were recorded with 20:5(n-3), 22:6(n-3) and 18:4(n-3) being the dominant moieties. On the basis of their lipid compositions we deduce that: (1) Calanoides acutus is the strictest herbivore among the four species studied, heavily utilizing the typical spring bloom; (2) T. macrura is essentially omnivorous, probably utilizing the less defined bloom situations found in oceanic waters; (3) E. crystallorophias is an omnivore well adapted to utilize both a bloom situation and to feed on ice algae and micro-zooplankton associated with the ice; (4) Calanus propinquus seems to be the most opportunistic feeder of the four species studied, probably grazing heavily on phytoplankton during a bloom and, during the rest of the year, feeding on whatever material is available, including particulates, flagellates and other ice-associated algae. We conclude that the different biochemical pathways generating large oil reserves of different compositions, enabling species to utilize different ecological niches, are major determinants of biodiversity in polar zooplankton. Accepted: 22 June 1998     

Polymyxin binding to charged lipid membranes an example of cooperative lipid-protein interaction

The binding of polymyxin-B to lipid bilayer vesicles of synthesis phosphatidic acid was studied using fluorescence, ESR spectroscopy and electron microscopy. 1,6-Diphenylhexatriene (which exhibits polarized fluorescence) and pyrene decanoic acid (which forms excimers) were used as fluorescene probes to study the lipid phase transition.The polymyxin binds strongly to negatively charged lipid layers. As a result of lipid/polymyxin chain-chain interactions, the transition temperature of the lipid. This can be explained in terms of a slight expansion of the crystalline lipid lattice (Lindeman's rule). Upon addition of polymyxin to phosphatidic acid vesicles two rather sharp phase transitions (with ΔT = 5°C) are observed. The upper transition (at T_u) is that of the pure lipid and the lower transition (at T₁) concerns the lipids bound to the peptide. The sharpness of these transitions strongly indicates that the bilayer is characterized by a heterogeneous lateral distribution of free and bound lipid regions, one in the crystalline and the other in the fluid state. Such a domain structure was directly observed by electron microscopy (freeze etching technique). In (1:1) mixtures of dipalmitoyl phosphatidic acid and egg lecithin, polymyxin induces the formation of domains of charged lipid within the fluid regions of egg lecithin.With both fluorescence methods the fraction of lipid bound to polymxin-B as a function of the peptide concentration was determined. S-shaped binding curves were obtained. The same type of binding curve is obtained for the interaction action of Ca²⁺ with phosphatidic acid lamellae, while the binding of polylysine to such membranes is characterized by a linear or Langmuir type binding curve. The S-shaped binding curve can be explained in terms of a cooperative lipid-ligand (Ca²⁺, polymyxin) interaction.A model is proposed which explains the association of polymyxing within the membrane plane in terms of elastic forces caused by the elastic distortion of the (liquid crystalline) lipid layer by this highly asymmetric peptide.     

Effects of dietary protein and lipid levels on growth and feed utilization of wild‐caught striped sea bream,Lithognathus mormyrus

A feeding trial was carried out to determine the effects of dietary protein and lipid levels on the growth performance and feed utilization of wild‐caught striped sea bream (Lithognathus mormyrus). The experimental fish were collected from a local lagoon (Çardak Lagoon, Çanakkale, Turkey), transferred to the Marine Net Cage Unit and fed by hand to apparent satiation with a commercial sea bream feed (Biomar; 42% crude protein, 16% crude lipid). Approximately 4 weeks were needed to acclimate the fish to farming conditions. No pathological signs were observed and no fish losses occurred during the adaptation period. For the test trials four test diets with different levels of protein and lipid were formulated [low protein and low lipid (LP:LL), low protein and high lipid (LP:HL), high protein and low lipid (HP:LL), and high protein and high lipid (HP:HL)] and fed to L. mormyrus (mean weight 85.0 ± 4.6 g SEM) in the net cages (Ø 2 m, depth 2.5 m) for 60 days. During the experiment water temperature varied between 21.1 and 26.4°C; dissolved oxygen 8.4–9.6 mg L^?1; pH 7.2–8.6; and salinity 23.3–25.6‰. Growth performances of fish fed high protein diets were higher compared to fish fed low protein diets, irrespective of the dietary lipid level (P < 0.05). Feed conversion ratio (FCR) and protein efficiency ratio (PER) were not influenced by dietary protein or lipid levels (P > 0.05). Preliminary results indicate that striped sea bream can be easily adapted to farming conditions in net cages, and that a diet containing 50% crude protein and 15% crude lipid (HP:LL) levels with 23.0 g protein MJ^?1 gross energy of protein/energy ratio would be suitable for striped sea bream growth.     

The effects of LXR agonist T0901317 and LXR antagonist GSK2033 on morphogenesis and lipid properties in full thickness skin models

Full thickness models (FTMs) are 3D-cultured human skin models that mimic many aspects of native human skin (NHS). However, their stratum corneum (SC) lipid composition differs from NHS causing a reduced skin barrier. The most pronounced differences in lipid composition are a reduction in lipid chain length and increased monounsaturated lipids. The liver-X-receptor (LXR) activates the monounsaturated lipid synthesis via stearoyl-CoA desaturase-1 (SCD-1). Therefore, the aim was to improve the SC lipid synthesis of FTMs by LXR deactivation. This was achieved by supplementing culture medium with LXR antagonist GSK2033. LXR agonist T0901317 was added for comparison. Subsequently, epidermal morphogenesis, lipid composition, lipid organization and the barrier functionality of these FTMs were assessed. We demonstrate that LXR deactivation resulted in a lipid composition with increased overall chain lengths and reduced levels of monounsaturation, whereas LXR activation increased the amount of monounsaturated lipids and led to a reduction in the overall chain length. However, these changes did not affect the barrier functionality. In conclusion, LXR deactivation led to the development of FTMs with improved lipid properties, which mimic the lipid composition of NHS more closely. These novel findings may contribute to design interventions to normalize SC lipid composition of atopic dermatitis patients.     

Studies on canthaxanthin in lipid membranes

Polar carotenoid pigment - canthaxanthin - has been found to interfere with the organization of biological membranes, in particular of the retina membranes of an eye of primates. The organization of lipid membranes formed with dipalmitoylphosphatidylcholine (DPPC) and egg yolk phosphatidylcholine containing canthaxanthin was studied by means of several techniques including: electronic absorption spectroscopy, linear dichroism, X-ray diffractometry, ¹H-NMR spectroscopy and FTIR spectroscopy. It appears that canthaxanthin present in the lipid membranes at relatively low concentration (below 1 mol% with respect to lipid) modifies significantly physical properties of the membranes. In particular, canthaxanthin (i) exerts restrictions to the segmental molecular motion of lipid molecules both in the headgroup region and in the hydrophobic core of the bilayer, (ii) promotes extended conformation of alkyl lipid chains, (iii) modifies the surface of the lipid membranes (in particular in the gel state, L_β´) and promotes the aggregation of lipid vesicles. It is concluded that canthaxanthin incorporated into lipid membranes is distributed among two pools: one spanning the lipid bilayer roughly perpendicularly to the surface of the membrane and one parallel to the membrane, localized in the headgroup region. The population of the horizontal fraction increases with the increase in the concentration of the pigment in the lipid phase. Such a conclusion is supported by the linear dichroism analysis of the oriented lipid multibilayers containing canthaxanthin: The mean angle between the dipole transition moment and the axis normal to the plane of the membrane was determined as 20 ± 3° at 0.5 mol% and 47 ± 3° at 2 mol% canthaxanthin. The analysis of the absorption spectra of canthaxanthin in the lipid phase and ¹H-NMR spectra of lipids point to the exceptionally low aggregation threshold of the pigment in the membrane environment (∼1 mol%). All results demonstrate a very strong modifying effect of canthaxanthin with respect to the dynamic and structural properties of lipid membranes.     

Lipid bodies and lipid body formation in an oleaginous fungus, Mortierella ramanniana var. angulispora

Mortierella ramanniana var. angulispora accumulates triacylglycerol (TG) in lipid bodies. Studies on lipid transport into lipid bodies are essential for elucidating mechanisms of lipid body formation. We used fluorescent dyes and fluorescent lipid analogs to visualize lipid body formation with a confocal laser scanning microscope. Different sizes of lipid bodies were stained by Nile red, a lipid body marker – one with a diameter of about 1 μm and the other with a diameter of about 2–3 μm. Lipid bodies matured into larger ones with culture. To metabolically monitor lipid bodies, we used 1-palmitoyl, 2-[5-(5,7-dimethyl boron dipyrromethene difluoride)-1-pentanoyl]-phosphatidic acid (C₅-DMB-PA), and C₅-DMB-phosphatidylcholine (C₅-DMB-PC). These were taken up into fungal cells and incorporated into intracellular organelles at 30°C. C₅-DMB-PA was quickly incorporated into lipid bodies while C₅-DMB-PC was initially incorporated into internal membranes, presumably endoplasmic reticulum membranes, and fluorescence was then gradually transported into lipid bodies. The transport of fluorescent lipids accompanied their metabolism into diacylglycerol (DG) and TG, which, taken together with the fluorescence distribution, suggested that conversion to TG was not necessary for transport into lipid bodies. It is likely that the synthesized DG was mainly located in lipid bodies and the conversion to TG took place in lipid bodies. C₅-DMB-PA and C₅-DMB-PC were converted to DG and TG in the membrane and lipid body fractions of this fungus, which agreed with in vivo metabolism of these fluorescent lipids and in vitro enzyme activity related to PA and PC metabolism. These results indicate that transport and metabolism of C₅-DMB-PA and C₅-DMB-PC represent two different routes for lipid body formation in this fungus.     

Binding of bovine seminal plasma protein BSP-A1/-A2 to model membranes: Lipid specificity and effect of the temperature

Bovine seminal plasma (BSP) contains a family of phospholipid-binding proteins. The affinity of the protein BSP-A1/-A2 for lipid membranes composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and POPC containing 30% (mol/mol) 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) or cholesterol, has been investigated by the isothermal titration calorimetry (ITC). This study confirms the association of these proteins to lipid bilayers, and provides a direct characterization of this exothermic process, at 37 °C. The measurements indicate that the protein affinity for lipid bilayers is modulated by the lipid composition, the lipid/protein ratio, and the temperature. The saturation lipid/protein ratio was increased in the presence of cholesterol and, to a lesser extent, of phosphatidylethanolamine, suggesting that it is modulated by the lipid acyl chain order. For all the investigated systems, the binding of BSP-A1/-A2 could not be modeled using a simple partitioning of the proteins between the aqueous and lipid phases. The existence of "binding sites", and lipid phase separations is discussed. The decrease of temperature, from 37 to 10 °C, converts the exothermic association of the proteins to the POPC bilayers to an endothermic process. A complementary 1-D and 2-D infrared spectroscopy study excludes the thermal denaturation of BSP-A1/-A2 as a contributor in the temperature dependence of the protein affinity for lipid bilayers. The reported findings suggest that changes in the affinity of BSP-A1/-A2 for lipid bilayers could be involved in modulating the association of these proteins to sperm membranes as a function of space and time; this would consequently modulate the extent of lipid extraction, including cholesterol, at a given place and given time.     

Apolipoprotein A-I localization and dipalmitoylphosphatidylcholine dynamics in reconstituted high density lipoproteins

The structure and molecular dynamics of recombinant high density lipoproteins (rHDL) were studied by non-radiative energy transfer (NRET), fluorescence anisotropy and intensity measurements. The rHDL particles contained human plasma apolipoprotein (apo) A-I and dipalmitoylphosphatidylcholine (DPPC). Fluorescent cis- and trans-parinaric acids were used both as probes of molecular motion in the particle lipid phase and as acceptors in the Forster's energy transfer from apo A-I tryptophan residues to determine particle dimensions, apolipoprotein localization and lipid dynamics. The probes are sensitive to thermal wobbling (macromobility) and conformational deformations (micromobility) of phospholipid acyl chains. The experimental data fitted to various models of the particle structure are compatible with the following: (a) at T < Tt the particles appeared as lens-like discs with a radius of the lipid phase of 5 nm and a mean thickness of 4 nm, the value being more by 20% in the particle centre, the alpha-helices of about 1 nm thickness were located around the edge of the lipid core. Compared to liposomes, both macro- and micromobility of DPPC molecules in rHDL were more rapid due to a significant disorder of the boundary lipid molecules close to the apo A-I molecule. This disorder led to the increase of the specific surface area per one lipid molecule, S(o). The lipid phase can be divided into three regions: (i) zone I of the most tightly packed lipid (0-1.7 nm from the disc axis) with a S(o) value small as 0.5 nm2; (ii) intermediate zone II (from 1.7 to 4.0 nm); and (iii) boundary lipid zone III (4-5 nm) of significantly disordered lipid with a S(o) value large as 0.65 nm2. (b) at T> Tt the S(o) heterogeneity disappeared, the radius of the lipid phase did not increase significantly, not exceeding 5.2-5.4 nm, but protein-induced immobilization of lipid molecules which affected about half or more of the total lipid, became remarkable. The overall effect was the suppression of the transition amplitude in rHDL compared to liposomes. The structural inhomogeneity might underlie the function of the native plasma HDL as the key component of the transport and metabolism of plasma lipids.     

Protein-lipid interactions in antipodal plasma membranes of rat colonocytes

The isolation of apical membranes from rat proximal colonic epithelial cells is described. Differential centrifugation yielded a ‘crude’ membrane fraction which was further purified using sucrose density centrifugation. The final membrane fraction was enriched 20–28-fold over homogenate in alkaline phosphatase and cysteine-sensitive alkaline phosphatase specific activities. Lipid-protein interactions and lipid dynamics examined in apical and basolateral membranes prepared from colonocytes demonstrated: (1) apical membrane, as assessed by steady-state fluorescence polarization studies have a low lipid fluidity; (2) colonic basolateral membranes possess a greater lipid fluidity than apical membranes; (3) compositional differences in these antipodal membranes appear to explain these differences in lipid fluidity; (4) fluorescence polarization studies using diphenylhexatriene detect a thermotropic transition at 21–23°C in apical membranes and liposomes prepared from lipid extracts of these membranes; (5) alkaline phosphatase and l-cysteine-sensitive alkaline phosphatase activities appear to be functionally dependent on the physical state of the apical membrane's lipid.     

Lipid peroxidation in mitochondrial inner membranes. I. An integrative kinetic model

An integrative mathematical model was developed to obtain an overall picture of lipid hydroperoxide metabolism in the mitochondrial inner membrane and surrounding matrix environment. The model explicitly considers an aqueous and a membrane phase, integrates a wide set of experimental data, and unsupported assumptions were minimized. The following biochemical processes were considered: the classic reactional scheme of lipid peroxidation; antioxidant and pro-oxidant effects of vitamin E; pro-oxidant effects of iron; action of phospholipase A₂, glutathione-dependent peroxidases, glutathione reductase and superoxide dismutase; production of superoxide radicals by the mitochondrial respiratory chain; oxidative damage to proteins and DNA. Steady-state fluxes and concentrations as well as half-lives and mean displacements for the main metabolites were calculated. A picture of lipid hydroperoxide physiological metabolism in mitochondria in vivo showing the main pathways is presented. The main results are:(a) perhydroxyl radical is the main initiation agent of lipid peroxidation (with a flux of 10⁻⁷Ms⁻¹); (b) vitamin E efficiently inhibits lipid peroxidation keeping the amplification (kinetic chain length) of lipid peroxidation at low values (10); (c) only a very minor fraction of lipid hydroperoxides escapes reduction via glutathione-dependent peroxidases; (d) oxidized glutathione is produced mainly from the reduction of hydrogen peroxide and not from the reduction of lipid hydroperoxides.     

Resveratrol inhibition of lipid peroxidation

To define the molecular mechanism(s) of resveratrol inhibition of lipid peroxidation we have utilized model systems that allow us to study the different reactions involved in this complex process. Resveratrol proved (a) to inhibit more efficiently than either Trolox or ascorbate the Fe2+ catalyzed lipid hydroperoxide-dependent peroxidation of sonicated phosphatidylcholine liposomes; (b) to be less effective than Trolox in inhibiting lipid peroxidation initiated by the water soluble AAPH peroxyl radicals; (c) when exogenously added to liposomes, to be more potent than alpha-tocopherol and Trolox, in the inhibition of peroxidation initiated by the lipid soluble AMVN peroxyl radicals; (d) when incorporated within liposomes, to be a less potent chain-breaking antioxidant than alpha-tocopherol; (e) to be a weaker antiradical than alpha-tocopherol in the reduction of the stable radical DPPH*. Resveratrol reduced Fe3+ but its reduction rate was much slower than that observed in the presence of either ascorbate or Trolox. However, at the concentration inhibiting iron catalyzed lipid peroxidation, resveratrol did not significantly reduce Fe3+, contrary to ascorbate. In their complex, our data indicate that resveratrol inhibits lipid peroxidation mainly by scavenging lipid peroxyl radicals within the membrane, like alpha-tocopherol. Although it is less effective, its capacity of spontaneously entering the lipid environment confers on it great antioxidant potential.     

Complex biomembrane mimetics on the sub-nanometer scale

Biomimetic lipid vesicles are indispensable tools for gaining insight into the biophysics of cell physiology on the molecular level. The level of complexity of these model systems has steadily increased, and now spans from domain-forming lipid mixtures to asymmetric lipid bilayers. Here, we review recent progress in the development and application of elastic neutron and X-ray scattering techniques for studying these systems in situ and under physiologically relevant conditions on the nanometer to sub-nanometer length scales. In particular, we focus on: (1) structural details of coexisting liquid-ordered and liquid-disordered domains, including their thickness and lipid packing mismatch as a function of a size transition from nanoscopic to macroscopic domains; (2) membrane-mediated protein partitioning into lipid domains; (3) the role of the aqueous medium in tuning interactions between membranes and domains; and (4) leaflet-specific structure in asymmetric bilayers and passive lipid flip-flop.     

Plasma Lipidomic Profiling of Treated HIV-Positive Individuals and the Implications for Cardiovascular Risk Prediction

Background

The increased risk of coronary artery disease in human immunodeficiency virus (HIV) positive patients is collectively contributed to by the human immunodeficiency virus and antiretroviral-associated dyslipidaemia. In this study, we investigate the characterisation of the plasma lipid profiles of treated HIV patients and the relationship of 316 plasma lipid species across multiple lipid classes with the risk of future cardiovascular events in HIV- positive patients.

Methods

In a retrospective case-control study, we analysed plasma lipid profiles of 113 subjects. Cases (n = 23) were HIV-positive individuals with a stored blood sample available 12 months prior to their diagnosis of coronary artery disease (CAD). They were age and sex matched to HIV-positive individuals without a diagnosis of CAD (n = 45) and with healthy HIV-negative volunteers (n = 45).

Results

Association of plasma lipid species and classes with HIV infection and cardiovascular risk in HIV were determined. In multiple logistic regression, we identified 83 lipids species and 7 lipid classes significantly associated with HIV infection and a further identified 74 lipid species and 8 lipid classes significantly associated with future cardiovascular events in HIV-positive subjects. Risk prediction models incorporating lipid species attained an area under the receiver operator characteristic curve (AUC) of 0.78 (0.775, 0.785)) and outperformed all other tested markers and risk scores in the identification of HIV-positive subjects with increased risk of cardiovascular events.

Conclusions

Our results demonstrate that HIV-positive patients have significant differences in their plasma lipid profiles compared with healthy HIV-negative controls and that numerous lipid species were significantly associated with elevated cardiovascular risk. This suggests a potential novel application for plasma lipids in cardiovascular risk screening of HIV-positive patients.