Plasma membrane enrichment with cis-unsaturated fatty acids enhances LDL metabolism in U937 monocytes

Direct Membrane Penetration and Cytosolic Delivery of Nanoparticles via Electrostatically Bound Amphiphiles

Nanoparticles usually enter cells through energy-dependent endocytosis that involves their cytosolic entry via biomembrane-coated endosomes. In contrast, direct translocation of nanoparticles with straight access to cytosol/subcellular components without any membrane coating is limited to very selective conditions/approaches. Here we show that nanoparticles can switch from energy-dependent endocytosis to energy-independent direct membrane penetration once an amphiphile is electrostatically bound to their surface. Compared to endocytotic uptake, this direct cell translocation is faster and nanoparticles are distributed inside the cytosol without any lysosomal trafficking. We found that this direct cell translocation option is sensitive to the charges of both the nanoparticles and the amphiphile. We propose that an electrostatically bound amphiphile induces temporary opening of the cell membrane, which allows direct cell translocation of nanoparticles. This approach can be adapted for efficient subcellular targeting of nanoparticles and nanoparticle-based drug delivery application, bypassing the endosomal trapping and lysosomal degradation.

Effects of 3FTx Protein Fraction from Naja ashei Venom on the Model and Native Membranes: Recognition and Implications for the Mechanisms of Toxicity

Three-finger toxins are naturally occurring proteins in Elapidae snake venoms. Nowadays, they are gaining popularity because of their therapeutic potential. On the other hand, these proteins may cause undesirable reactions inside the body's cells. A full assessment of the safety of Naja ashei venom components for human cell application is still unknown. The aim of the study was to determine the effect of the exogenous application of three-finger toxins on the cells of monocytes (U-937) and promyelocytes (HL-60), with particular emphasis on the modification of their membranes under the influence of various doses of 3FTx protein fraction (0-120 ng/mL). The fraction exhibiting the highest proportion of 3FTx proteins after size exclusion chromatography (SEC) separation was used in the experiments. The structural response of cell membranes was described on the basis of single-component and multi-component Langmuir monolayers that mimicked the native membranes. The results show that the mechanism of protein-lipid interactions depends on both the presence of lipid polar parts (especially zwitterionic type of lipids) and the degree of membrane saturation (the greatest-for unsaturated lipids). The biochemical indicators reflecting the tested cells (MDA, LDH, cell survival, induction of inflammation, LD50) proved the results that were obtained for the model.

Effects of vegetable oils on biochemical and biophysical properties of membrane retinal pigment epithelium cells

The aim of this study was to investigate the effect of vegetable oil enrichment of retinal pigment epithelial (RPE) cells on their biochemical and biophysical properties. For this, RPE cells were incubated with 4 different vegetables oils (olive oil, corn oil, argan oil, and camelina oil). The cytotoxicity of these vegetable oils was assessed in vivo on 8-week-old mice and in vitro by using the neutral red and YO-PRO-1 tests. Membrane fluidity was evaluated by fluorescence anisotropy using the fluorescent probe diphenylhexatriene, and membrane fatty acid composition was assessed by gas chromatography. None of the oils tested displayed cytotoxic effects. In vitro, omega-3 rich oils improved membrane fluidity by 47% compared with the control cells. The omega-3 PUFA content within membranes decreased by 38% to 55% when cells were incubated separately with olive oil, corn oil, or argan oil, and increased when cells were incubated with a mixture of those oils, or with camelina oil alone (50% and 103% increase, respectively). Our results show that the fatty acids in vegetable oil incorporate into retinal cells and increase the plasma membrane fluidity.

Molecular characterization of gel and liquid-crystalline structures of fully hydrated POPC and POPE bilayers

Molecular dynamics simulations were used for a comprehensive study of the structural properties of monounsaturated POPC and POPE bilayers in the gel and liquid-crystalline state at a number of temperatures, ranging from 250 to 330 K. Though the chemical structures of POPC and POPE are largely similar (choline versus ethanolamine headgroup), their transformation processes from a gel to a liquid-crystalline state are contrasting. In the similarities, the lipid tails for both systems are tilted below the phase transition and become more random above the phase transition temperature. The average area per lipid and bilayer thickness were found less sensitive to phase transition changes as the unsaturated tails are able to buffer reordering of the bilayer structure, as observed from hysteresis loops in annealing simulations. For POPC, changes in the structural properties such as the lipid tail order parameter, hydrocarbon trans-gauche isomerization, lipid tail tilt-angle, and level of interdigitation identified a phase transition at about 270 K. For POPE, three temperature ranges were identified, in which the lower one (270-280 K) was associated with a pre-transition state and the higher (290-300 K) with the post-transition state. In the pre-transition state, there was a significant increase in the number of gauche arrangements formed along the lipid tails. Near the main transition (280-290 K), there was a lowering of the lipid order parameters and a disappearance of the tilted lipid arrangement. In the post-transition state, the carbon atoms along the lipid tails became less hindered as their density profiles showed uniform distributions. This study also demonstrates that atomistic simulations of current lipid force fields are capable of capturing the phase transition behavior of lipid bilayers, providing a rich set of molecular and structural information at and near the main transition state.

Macrophage colony-stimulating factor reduces tert-butyl hydroperoxide induced oxidative injury to monocytes/macrophages

The transformation of macrophages into foam cells is an important event in the development of atherosclerosis, and the oxidative injury caused by oxidized low density lipoprotein (Ox-LDL) plays an essential role in that process. It has been proved that macrophage colony-stimulating factor (M-CSF) could prevent the progression of atherosclerosis in Watanabe heritable hypercholesterolemic (WHHL) rabbits. We proposed that the anti-atherogenic effect of M-CSF was partly associated with its protective effect on monocyte-derived macrophages from Ox-LDL induced oxidative injury. In order to prove this, we investigated the effect of M-CSF on the oxidative injury caused by tert-butyl hydroperoxide (tbOOH) to mouse peritoneal macrophages and U937/J774 cell lines. The results showed that M-CSF could protect mouse peritoneal macrophages from oxidative injury (presented by cell morphology and cell survival rate); L929 cell-conditioned medium (L929-CM) had the same effect as M-CSF; and anti-M-CSF monoclonal antibody could mostly block the protective effect of L929-CM on macrophages. L929-CM was proved to be also able to decrease the impact of plasma membrane fluidity in U937 and J774 cells treated with tbOOH. Incubation with tbOOH caused DNA fragmentation in U937 cells. The presence of L929-CM greatly reduced the number of apoptotic U937 cells characterized by DNA fragmentation. From these results, we concluded that M-CSF could protect monocytes/macrophages from oxidative injury. It may be one of the mechanisms which explain the anti-atherogenic effect of exogenous M-CSF in WHHL rabbits.

Free fatty acids modulate LDL receptor activity in BHK-21 cells

It has been shown that dietary fatty acids affect serum low density lipoprotein (LDL) levels, but the mechanism responsible for this effect is still under debate. Here we investigate the effect of different free fatty acids on LDL receptor activity in BHK-21 cells. These cells possess a classical LDL receptor strongly regulated by substances like 25-OH-cholesterol or lovastatin. Preincubation of cells for 24 h with both oleic (cis 18:1) and its trans counterpart, elaidic acid, enhanced 125I-LDL binding, internalization and degradation, being oleic acid more effective than elaidic acid. Among polyunsaturated fatty acids (PUFA) of the n-6 series arachidonic acid (20:4) enhanced LDL receptor activity more than linoleic acid (18:2), and among PUFA of the n-3 series docosahexaenoic (22:6) and eicosapentaenoic acids (20:5) were more effective compared to alpha-linolenic acid (18:3). Conversely, preincubation of cells with saturated fatty acids, palmitic (16:0) and stearic (18:0) acids, decreased binding, internalization and degradation of 125I-LDL. Scatchard analysis of binding data obtained with palmitic and oleic acids showed that these two fatty acids affect LDL receptor number without altering receptor affinity. The regulatory effect of free fatty acids on LDL receptor activity in BHK-21 cells is consistent with the hypothesis that the ability of fatty acids to modulate LDL-cholesterol levels in vivo is mediated, at least in part, by an action on receptor-dependent uptake of LDL.

Electron spin resonance studies of fatty acid-induced alterations in membrane fluidity in cultured endothelial cells

Endothelial cell dysfunction has been implicated in the development of atherosclerosis. Of vital importance to the maintenance of endothelial cell integrity is the preservation of membrane functional and structural properties, such as membrane fluidity. The aim of this study was to develop a model for studying the relationship between endothelial cell integrity and membrane fluidity alterations in a well-defined cell culture setting. Alterations in membrane fluidity were assessed using electron spin resonance after labeling endothelial cells with the lipid-specific spin labels, CAT-16 and 12-nitroxide stearic acid. Endothelial cells were exposed to various 18-carbon fatty acids, i.e. stearic (18:0), oleic (18:1), linoleic (18:2), or linolenic (18:3), in addition to lipolyzed HDL (L-HDL) and benzyl alcohol. Membrane phospholipid fatty acid composition of endothelial cells supplemented with these fatty acids was analyzed using gas chromatography. All fatty acids, except 18:0, decreased membrane fluidity. A relationship between membrane fluidity and fatty acid compositional alterations in cellular phospholipids was observed. In particular, the arachidonic acid content decreased following exposure to 18:1, 18:2, or 18:3. Exposure of endothelial cells to L-HDL, lipoprotein particles which contain high levels of 18:1 and 18:2, also decreased membrane fluidity. The stabilization of cytoskeletal actin filaments by phalloidin partially prevented 18:2-induced increases in albumin transfer, thus implicating a cytoskeletal involvement in the 18:2-induced membrane fluidity changes involved in endothelial cell dysfunction. The present study shows that the exposure of endothelial cells to various lipids causes membrane fluidity alterations which may contribute to endothelial cell dysfunction and atherosclerosis.

Oleate and other long chain fatty acids stimulate low density lipoprotein receptor activity by enhancing acyl coenzyme A:cholesterol acyltransferase activity and altering intracellular regulatory cholesterol pools in cultured cells

Modification of dietary fatty acid composition results in changes in plasma cholesterol levels in man. We examined the effect of in vitro fatty acid supplementation on low density lipoprotein (LDL) receptor activity in cultured cells and questioned whether changes were related to fatty acid-induced alterations in acyl-CoA: cholesterol acyltransferase (ACAT) activity. Preincubation of cultured cells (i.e. human skin fibroblasts, J774 macrophages, and HepG2 cells) with oleic acid (oleic acid:bovine serum albumin molar ratio 2:1) at 37 degrees C for longer than 2 h resulted in a 1.2- to 1.5-fold increase in LDL cell binding at 4 degrees C and LDL cell degradation at 37 degrees C. Scatchard analysis showed that oleic acid increased LDL receptor number but not LDL affinity (Kd). Fatty acid supplementation of J774 macrophages increased both LDL receptor activity and cholesteryl ester accumulation. The ACAT inhibitor, 58-035, eliminated both effects, and increased ACAT activity preceded stimulation of LDL receptor activity by 1-2 h. Supplementation of macrophages with triolein emulsion particles also increased LDL cell binding and degradation, and addition of cholesterol to the emulsions abolished this effect. Among fatty acids tested, oleate (18:1), arachidonate (20:4), and eicosapentanoate (20:5) demonstrated the greatest effects. We hypothesize that certain fatty acids delivered to cells either in free form, or as triglyceride, first increase cellular ACAT activity, which then causes a decrease in an intracellular free cholesterol pool, signaling a need for increased LDL receptor activity. This mechanism may play a role in the effect of certain dietary fatty acids on LDL metabolism in vivo.

Omega-3 fatty acids in smooth muscle cell phospholipids increase membrane cholesterol efflux

The aim of our work was to determine whether fatty acid modifications in smooth muscle cell phospholipids affect cholesterol efflux and desorption. [3H]Cholesterol was used to label cholesterol pools in the whole cell or selectively in the plasma membrane. Cells were incubated for 12 h in order to increase oleate, linoleate, arachidonate, eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) in phospholipids. Cholesterol efflux was monitored using native or tetranitromethane modified high-density lipoprotein3 (HDL3). When all cholesterol pools were labeled, the efflux from cells treated with different fatty acids were not different. Plasma membrane cholesterol efflux remained unchanged after oleate, linoleate or arachidonate treatments, but was markedly increased after EPA and DHA enrichment, both with native HDL3 and with tetranitromethane-high-density lipoprotein. These results suggest that the positive effects of n-3 fatty acid consumption on the atherosclerotic process could be linked in part to an increase in plasma membrane cholesterol efflux from vascular smooth muscle cells.

Dietary fatty acids, lipoproteins, and cardiovascular disease

Dietary fat quality and quantity significantly affect the metabolism of all the plasma lipoproteins and probably constitute the most significant dietary determinants of plasma lipoprotein levels. Since the major role of the plasma lipoproteins is the transport of exogenous and endogenous fat, this would be expected of a highly regulated, metabolically homeostatic system. The data clearly show that dietary fat saturation affects all aspects of lipoprotein metabolism, from synthesis to intravascular remodeling and exchanges to receptor-mediated and nonspecific catabolism. The experimental data regarding dietary fatty acid effects on lipoprotein metabolism are complicated and at times contradictory due to the large degree of metabolic heterogeneity in the population, which, when coupled with the known abnormalities of lipoprotein metabolism associated with certain types of hyperlipoproteinemia, can present responses from A to Z. It is clear that the same dietary pattern has different effects in different individuals and that complicating factors of individuality raise some concerns regarding generalized dietary recommendations. As new knowledge of the role of dietary factors and CVD risk develops, and our abilities to characterize the individual patient's response to dietary interventions become more refined, it may be possible to specify dietary fat intervention from a patient-oriented concept rather than a single all-purpose diet approach. Thus it would be possible to design dietary interventions to match patient needs and gain both efficacy and compliance. With the spectrum of approaches possible--low fat, moderate fat with MUFA, n-3 PUFA, etc.--we should be able to approach dietary interventions to reduce CVD risk at both a population-based level and a patient-specific level. There remains much to learn regarding the effects of dietary fatty acids on the synthesis, intravascular modifications, and eventual catabolism of the plasma lipoproteins. The area of lipoprotein metabolism in health and disease, of its modifications by diets and drugs, and of the contributions of genetic heterogeneity to these processes is one of notable advances over the past two decades and continues to be an area of intense investigation.

Effect of dietary fat saturation and cholesterol on LDL composition and metabolism. In vivo studies of receptor and nonreceptor-mediated catabolism of LDL in cebus monkeys

The mechanism(s) by which polyunsaturated fats reduce low density lipoprotein (LDL) cholesterol and apolipoprotein (apo) B were investigated in 20 cebus monkeys (Cebus albifrons) fed diets containing corn oil or coconut oil as fat (31% of calories) with or without dietary cholesterol (0.1% by weight) for 3 to 10 years. Coconut-oil feeding compared to corn-oil feeding resulted in significant increases in levels of plasma total cholesterol (176%), very low density lipoprotein (VLDL)-LDL cholesterol (236%), high density lipoprotein (HDL) cholesterol (148%), apo B (78%), and apo A-I (112%). The addition of dietary cholesterol to corn oil compared to corn oil alone resulted in smaller, but significant, increases in levels of total cholesterol (44%), HDL cholesterol (40%), and apo A-I (33%). Although the increases in VLDL-LDL cholesterol were of similar magnitude (52%), they barely failed to reach statistical significance (p less than 0.08), while the changes in apo B levels were negligible. The addition of dietary cholesterol to coconut oil, compared to coconut oil alone, resulted in no significant changes in lipoprotein cholesterol or apoproteins, although levels of VLDL-LDL cholesterol and apo B values increased 22% and 16%, respectively. Although hepatic free cholesterol content was not altered by diet, coconut-oil compared to corn-oil feeding resulted in significant increases in hepatic cholesteryl esters (236%) and triglycerides (325%), the latter increasing still further when dietary cholesterol was added to coconut oil (563%). To further assess the effects of these dietary changes on LDL metabolism, radioiodinated normal and glucosylated LDL kinetics were performed. The production rate of LDL apo B was not altered by diet. With corn-oil feeding, 63% of LDL catabolism was via the receptor-mediated pathway. Coconut-oil compared to corn-oil feeding resulted in a 50% decrease in receptor-mediated LDL apo B fractional catabolic rate (FCR) and a 27% reduction in nonreceptor-mediated LDL apo B FCR. The addition of dietary cholesterol to corn oil, compared to corn oil alone, resulted in no significant effect on LDL apo B catabolism. The addition of dietary cholesterol to coconut oil, compared to coconut oil alone, was associated with no significant change in nonreceptor catabolism of LDL apo B but with a 58% decrease in receptor-mediated catabolism of LDL (p less than 0.059). The diet-induced alterations of LDL catabolism were significantly correlated with hepatic lipids, which were enriched in saturated fatty acids.(ABSTRACT TRUNCATED AT 400 WORDS)