Structure- and configuration-dependent effects of C18 unsaturated fatty acids on the chicken and sheep erythrocyte membrane

Hemolytic activity and platelet aggregation inhibitory effect of vipoxin's basic sPLA2 subunit

In the present study we evaluated the effect of secreted phospholipase A₂ (sPLA₂) (the toxic subunit of the heterodimeric neurotoxin vipoxin, isolated from the Bulgarian long-nosed viper Vipera ammodytes meridionalis) on hemolysis, erythrocyte morphology and platelet aggregation. Hemolytic activity of sPLA₂ was examined in the presence of saturated (palmitic) and unsaturated (oleic) fatty acids and it was found that oleic acid increased the hemolytic activity of sPLA₂ in a concentration-dependent manner, compared to the effect of palmitic acid and controls. The addition of heparin to red blood cells (RBC) suspension containing sPLA₂ or mixture of sPLA₂ and the corresponding fatty acid led to an inhibition of hemolytic activity. The effect of sPLA₂ on RBC morphology resulted in formation of echinocytes (spherocyte subtype), suggesting that RBC could be the possible targets attacked by sPLA₂. Vipoxin sPLA₂ inhibited (in a dose-dependent manner) platelet aggregation when arachidonic acid and collagen were used as inducers, while in the case of ADP its inhibitory effect was inappreciable.

Trans fat involvement in cardiovascular disease

Coronary heart disease is becoming a worldwide epidemic and diet and lifestyle are well known contributing factors. Identifying the kinds of foods that may have a cardioprotective or cardiotoxic effect and understanding their molecular mechanisms of action has become of increasing importance. Through largely epidemiological evidence, trans fatty acid (TFA) intake has been associated with a variety of cardiovascular complications including atherosclerosis. Traditionally, industrial TFAs (iTFAs) have been associated with these deleterious cardiovascular effects. However, there is a current body of research that suggests that ruminant trans fats (rTFAs) may have a cardioprotective role within the heart. The molecular mechanisms whereby TFAs are delivering their effects are largely unknown. In the following review, we discuss recent in vitro, animal and epidemiological research to better understand the effect of TFAs in the diet on cardiovascular disease, particularly atherosclerosis.

Hemolysis and antihemolysis induced by amino acid-based surfactants

Surfactants have the special ability to interact with the lipid bilayer of cell membranes. The red blood cell is one of the most used cellular membrane models to study the mechanisms underlying surfactant-induced osmotic cell resistance. To increase our knowledge regarding the mechanisms of surfactant membrane interaction, we studied the action of five lysine-derivative anionic and three arginine-derivative cationic amino acid-based surfactants on hypotonic hemolysis. Results showed two different antihemolytic behaviors among amino acid-based surfactants, both related to the maximal protective concentration. How the physico-chemical properties and structure of these compounds determine the protection against hypotonic hemolysis is discussed in detail. We found a good correlation between the CMC and the concentrations resulting in maximum protection against hypotonic hemolysis for the cationic surfactants, but no correlation for the anionic surfactants. In the case of lysine derivative surfactants, which only differ in their counterions, the counterion is implicated in the differences in the antihemolytic potency and the hemolytic activities of this.

Membrane transformation during malaria parasite release from human red blood cells

Three opposing pathways are proposed for the release of malaria parasites from infected erythrocytes: coordinated rupture of the two membranes surrounding mature parasites; fusion of erythrocyte and parasitophorus vacuolar membranes (PVM); and liberation of parasites enclosed within the vacuole from the erythrocyte followed by PVM disintegration. Rupture by cell swelling should yield erythrocyte ghosts; membrane fusion is inhibited by inner-leaflet amphiphiles of positive intrinsic curvature, which contrariwise promote membrane rupture; and without protease inhibitors, parasites would leave erythrocytes packed within the vacuole. Therefore, we visualized erythrocytes releasing P. falciparum using fluorescent microscopy of differentially labeled membranes. Release did not yield erythrocyte ghosts, positive-curvature amphiphiles did not inhibit release but promoted it, and release of packed merozoites was shown to be an artifact. Instead, two sequential morphological stages preceded a convulsive rupture of membranes and rapid radial discharge of separated merozoites, leaving segregated internal membrane fragments and plasma membrane vesicles or blebs at the sites of parasite egress. These results, together with the modulation of release by osmotic stress, suggest a pathway of parasite release that features a biochemically altered erythrocyte membrane that folds after pressure-driven rupture of membranes.

Erythrocyte hemolysis and shape changes induced by new lysine-derivate surfactants

The effects of new synthetic lysine-derived anionic surfactants on human and rat erythrocytes were studied. The surfactants were salts of Nalpha,Nepsilon-dioctanoyl lysine with different counterions: lysine (77KK), tris (trishydroxymethyl amminomethane) (77KT), sodium (77KS), and lithium (77KL). 77KK and 77KT showed a biphasic hemolytic behavior in the erythrocytes. The surfactants 77KS and 77KL showed concentration-dependent hemolysis with a CH50 of about 3.4 and 2.6 mmol/l, respectively. 77KK and 77KT induced protection against hypotonic hemolysis in rat erythrocytes at the concentration which showed the least hemolytic activity under isotonic conditions. With human erythrocytes, 77KT did not show biphasic behavior in isotonic medium, but under hypotonic conditions biphasic behavior was present. Changes in shape of the erythrocyte, from discocytic to stomatocytic were observed after incubation with the anionic surfactants studied. Such shape changes occurred progressively over time, with total alteration in shape occuring after about 20 min of incubation.

Hemolytic action of anionic surfactants of the diacyl lysine type

Amphiphiles induce hemolysis at a given concentration and that would be dependent on their structure. To know this, we have synthesized anionic surfactants derived from lysine and differing in their chain length and we have studied their hemolytic action. The chain length of the surfactants affects their hemolytic behaviour. Surfactants with two chains of 7 or 9 carbons presented biphasic behaviour at a concentration below or above 50 mg/100 ml. However, only the surfactant with two chains of 7 carbons has a protective effect against hypotonic hemolysis. The maximum protection was exerted when the surfactant was added to a 150 mOsmol/L solution. The surfactant is assumed to intercalate into the membrane in an orientated fashion and prevent the hypotonic hemolysis. For this hemolytic behaviour the presence of two chains of 7 carbons seems to be necessary.

Effect of non-lytic concentrations of Brij series detergents on the metabolism-independent ion permeability properties of human erythrocytes

Subcritical micellar concentrations (sub-CMC) of Brij-series detergents alter ion movements between human erythrocytes and their environment when metabolism has been slowed down by incubation at zero degrees centigrade. The effect of nonhemolytic concentrations of detergents on the erythrocyte K+ and Na+ movements is described. Results indicate a significant difference in monovalent cation movements, depending on the number of hydrophilic polyoxyethylene units (n). There is an increasing loss of K+ and gain of Na+ as n increases from 4 to 20. Where n > or = 21, ion movements are not significantly different from those found in erythrocytes not exposed to detergents. The carbon chain length of the detergent fatty acid residue (10-18 carbons) appears to be relatively unimportant, but detergents with unsaturated (oleic acid) hydrophobic regions potentiate K+ release and Na+ uptake when compared to the corresponding saturated fatty acid (stearic acid). The erythrocyte stabilizing effect of detergents against hypo-osmotic shock correlates well with the increase of monovalent ion traffic and the mobility of membrane lipids revealed by fluorescence anisotropy measurements.

Amphiphile-induced antihaemolysis is not causally related to shape changes and vesiculation

A wide variety of structurally different antihaemolytic amphiphiles were tested for their ability to induce exovesiculation (acetylcholinesterase (AChE) release, transmission electron microscopic (TEM) studies), endovesiculation (fluorescein isothiocyanate conjugated dextran (FITC-dextran) internalization, TEM studies) and shape changes in human erythrocytes at concentrations where they exert maximum protection against hypotonic haemolysis. The results show that vesiculation is a common phenomenon induced by amphiphiles in erythrocytes. Sphero-echinocytogenic amphiphiles induced exovesiculation, whereas stomatocytogenic amphiphiles induced endovesiculation. The antihaemolytic potency of the amphiphiles was not related to their ability to induce exo- or endovesiculation, or to the type or extent of shape changes induced, and it could not be ascribed to any molecular feature of the amphiphiles or to their charge. It is proposed that amphiphiles, when intercalated into the lipid bilayer of the membrane, rapidly induce rearrangements within the bilayer and that these rearrangements are associated with an increase in the permeability of the membrane; it is suggested that a rapid efflux of ions decreases the difference in osmotic pressure between cell interior and hypotonic buffer, thereby protecting cells from being lysed.

Interaction of free fatty acids with the erythrocyte membrane as affected by hyperthermia and ionizing radiation

The interference of hyperthermia and ionizing radiation, respectively, with the effects of capric (10:0), lauric (12:0), myristic (14:0), oleic (cis-18:1) and elaidic (trans-18:1) acids on the osmotic resistance of human erythrocytes was investigated. The results are summarized as follows: (A) not only at 37 degrees, but also at 42 degrees and 47 degrees C lauric acid (12:0) represents the minimum chain length for the biphasic behaviour of protecting against hypotonic hemolysis at a certain lower concentration range and hemolysis promotion at subsequent higher concentrations; (B) with increasing temperatures the protecting as well as the hemolytic effects occur at lower concentrations of the fatty acids; (C) the increase of temperature promotes the extent of hemolysis and reduces the extent of protection against hypotonic hemolysis; (D) Gamma-irradiation of erythrocytes selectively affects the concentration of oleic acid at which maximum protection against hypotonic hemolysis occurs, without altering the minimum concentration for 100% hemolysis.

Chain length-dependent interaction of free fatty acids with the erythrocyte membrane

Free fatty acids protect erythrocytes against hypotonic haemolysis in a certain low concentration range and become haemolytic at higher concentrations. The chain length dependence of this biphasic behaviour was investigated using human erythrocytes. The results can be summarized as follows: (i) A critical minimum chain length is required for both effects. Octanoic acid (C8) and fatty acids with a shorter chain length do not have any effect on the osmotic resistance of erythrocytes. (ii) Decanoic acid (C10) decreases the extent of hypo-osmotic haemolysis and does not become haemolytic at higher concentrations. (iii) Dodecanoic acid (C12) represents the minimum chain length for the typical concentration-dependent biphasic behaviour with protection against hypo-osmotic haemolysis at a certain low concentration range and subsequent haemolysis at higher concentrations. (iv) Tetradecanoic acid (C14) exhibits two concentration ranges of protection against hypo-osmotic haemolysis, each followed by haemolytic concentrations. (v) The observed effects are not correlated with the critical micellar concentrations of the investigated fatty acids.

Critical temperatures for the interaction of free fatty acids with the erythrocyte membrane

Non-esterified long-chain fatty acids reduce the extent of hypotonic hemolysis at a certain low concentration range but cause hemolysis at higher concentrations. This biphasic behavior was investigated at different temperatures (0-37 degrees C) for lauric (12:0), myristic (14:0), palmitoleic (16:1), oleic (cis-18:1) and elaidic (trans-18:1) acids. The results are summarized as follows: (A) the fatty acids examined exhibit a high degree of specificity in their thermotropic behavior; (B) oleic acid protects against hypotonic hemolysis even at the highest concentrations, up to 15 degrees C, when it becomes hemolytic, but only in a limited concentration range; (C) elaidic acid does not affect the osmotic stability of erythrocytes up to 20 degrees C, when it starts protecting: above 30 degrees C, it becomes hemolytic at the highest concentrations; (D) palmitoleic acid is an excellent protecting agent at all temperatures in a certain concentration range, becoming hemolytic at higher concentrations; (E) lauric acid protects up to 30 degrees C and becomes hemolytic only above this temperature; (F) myristic acid exhibits an extremely unusual behavior at 30 and 37 degrees C by having alternating concentration ranges of protecting and hemolytic effects; (G) there is a common critical temperature for hemolysis at 30 degrees C for saturated and trans-unsaturated fatty acids; (H) the initial slope of Arrhenius plots of percent hemolysis at the concentration of maximum protection is negative for cis-unsaturated fatty acids and positive for saturated and trans-unsaturated fatty acids.

Effects of nonionic amphiphiles at sublytic concentrations on the erythrocyte membrane

The interactions of octaethyleneglycol alkylethers (C10-C16), pentaethyleneglycol dodecylether, and dodecyl D-maltoside with the human erythrocyte membrane were studied. All the amphiphiles protected erythrocytes against hypotonic haemolysis. At concentrations where the amphiphiles protected erythrocytes against hypotonic haemolysis they reduced phosphate efflux. The potency of the amphiphiles, at equiprotecting concentrations, was correlated negatively to the length of the alkyl chain. Potassium fluxes were increased by all the amphiphiles at protective concentrations. The relative potency of the amphiphiles varied but it was not simply related to the length of the alkyl chain. The only amphiphile affecting active potassium influx was octaethyleneglycol decylether which induced a slight decrease. It is concluded that the increase in passive cation fluxes caused by the amphiphiles is due to an increased permeability of the lipid bilayer induced through a nonspecific interaction of the amphiphiles with the bilayer. The effect of the amphiphiles on ion transport mediated by membrane proteins is proposed to be due to an alteration of the state of the transporting protein.

Uninfected red cells from malaria-infected blood: alteration of fatty acid composition involving a serum protein: an in vivo and in vitro study

Alteration of uninfected erythrocytes from Plasmodium (the malaria parasite)-infected blood remained an open question. In this study we compared the in vivo fatty acid compositions of control and uninfected monkey erythrocytes. A large (40%) increase in the linoleic acid level was observed, which was recovered mostly in neutral lipids. An in vitro system was developed to study medium-mediated alterations of cultured erythrocytes by Plasmodium falciparum. The increase in the linoleate level was reproduced in vitro and was also localized in the neutral lipid fraction, especially in triacylglycerols. Studies using proteolytic digestion and heat denaturation showed that a heat-labile serum protein is indispensable for the increase in the linoleate level of red cells treated with the supernatant of P. falciparum cultures. Both the function and the mechanism of this modification of uninfected erythrocytes still remain unknown.

Biphasic interaction of Triton detergents with the erythrocyte membrane

Octylphenoxy polyoxyethylene ethers (Triton detergents) interact with the erythrocyte membrane in a biphasic manner, i.e. they stabilize erythrocytes against hypo-osmotic haemolysis at low concentrations (0.0001-0.01%, v/v), but become haemolytic at higher concentrations. This biphasic behaviour was demonstrated with Triton X-114, Triton X-100 and Triton X-102. However, a critical chain length is a prerequisite for the haemolytic effect, because Triton X-45, which differs from the other Tritons only by the shorter chain of the polyoxyethylene residue, does not exhibit this biphasic behaviour, but goes on protecting against osmotic rupture up to saturating concentrations. Even a 1% solution of Triton X-45 does not cause haemolysis. This structural specificity of Triton X-45, namely the lack of haemolysis and efficient stabilization against osmolysis even at higher concentrations of the detergent, is exhibited at 0 degree and 37 degrees C as well as at room temperature. Three conclusions are reached: (i) a critical chain length of the octylphenoxy polyoxyethylene ethers is required for the haemolytic effect; (ii) the different structural requirements would suggest that different mechanisms are responsible for the haemolytic and the stabilizing effect of amphiphilic substances; (iii) the results suggest that haemolysis is not caused simply by dissolution of the membrane by the detergent but is a rather more specific process.

Modification of the fatty acid composition of individual phospholipids and neutral lipids after infection of the simian erythrocyte by Plasmodium knowlesi

Using capillary gas-liquid chromatography, we have analyzed the alteration in the total fatty acid, phospholipid and neutral lipid compositions of the monkey erythrocyte, after infection by the malarial parasite Plasmodium knowlesi. Data based on fatty acid quantitation show that the phospholipid composition is altered, with particularly large increases in phosphatidylcholine (PC) and phosphatidylethanolamine (PE), the most abundant phospholipids in normal and P. knowlesi-schizont-infected cells. Unesterified fatty acids were found to be less abundant in infected cells. The total fatty acid content of the cell is increased 6-fold during infection, and total fatty acid composition is also changed: the infected cells are richer in palmitate (+23%), oleate (+29%) and linoleate (+89%), but contained less stearate (-27%) and arachidonate (-40%). The determination of the fatty acid composition of individual phospholipids, neutral lipids and unesterified fatty acids showed that choline-containing phospholipids (PC and sphingomyelin) were not as altered in their fatty acid pattern as anionic phospholipids (PE, phosphatidylserine (PS) and phosphatidylinositol (PI) and lysophosphatidylcholine (lysoPC). Specific alterations in the fatty acid compositions of individual phospholipids were detected, whereas the rise in linoleic acid was the only change during infection that was recovered in each phospholipid (except PC), neutral lipid and unesterified fatty acids. The fatty acid composition of the neutral lipids and unesterified fatty acids was particularly modified: the only rise in arachidonic acid level was observed in these lipid classes after infection. The total plasmalogen level of the erythrocyte is decreased in infected cells (-60%), but their level is increased in PI.

Temperature-dependent specificity of cis-trans isomeric fatty acid interaction with the erythrocyte membrane

Stabilization of red cells against hypotonic haemolysis by cis-trans isomeric free C18 fatty acids occurs with pronounced specificity which is strongly temperature-dependent, but in a distinctly different manner for the two configurational isomers. Oleic acid (cis-18:1) stabilizes very efficiently at 0 degrees C, even at the highest concentrations. Elaidic acid (trans-18:1) causes neither stabilization nor haemolysis at this temperature. At room temperature (23 degrees C), elaidic acid acquires the ability to protect, without turning haemolytic at high concentrations. At 37 degrees C elaidic acid also becomes haemolytic. The protecting effect of oleic acid at 0 degrees C is the result of a rapid reaction. The characteristic, temperature-dependent specificity of cis-trans isomeric C18 fatty acid interaction with the red cell membrane appears to be a general phenomenon, since it was observed alike with erythrocytes of different species.

Quantitative analysis of fatty acid methyl esters and dimethyl acetals on a polar (free fatty acid phase) capillary column

Separation of fatty acid methyl esters and dimethyl acetals from complex biological samples has been achieved by gas-liquid chromatography on a capillary column coated with free fatty acid phase. Response-correcting factors were determined, showing rather large variations with fatty acid length. Polyunsaturated fatty acid methyl esters were shown to have lower responses than saturated species, whereas dimethyl acetals and equivalent methyl esters were found to give similar responses. Total fatty acid and aldehyde compositions of human and simian erythrocytes were determined and compared, showing a somewhat higher level of linoleate and arachidonate, and a lower level of plasmalogens in simian erythrocytes.

Activation of bovine platelets induced by long-chain unsaturated fatty acids at just below their lytic concentrations, and its mechanism

The effects of long-chain unsaturated fatty acids such as linoleic acid on bovine platelets were examined. Not only linoleic acid, but also oleic and linolenic acid, at just below the concentrations causing marked cell lysis, induced an absorbance decrease of the platelet suspension in the presence of Ca2+. Since this absorbance decrease was reversed by the addition of EDTA and moreover aggregate formation was found by macroscopic and microscopic observation, it was concluded that unsaturated fatty acids at just below their lytic concentrations caused platelet aggregation. Unsaturated fatty acids also caused release of adenine nucleotides, but there was a lag time between the release and the aggregation, just as with ADP-induced release, suggesting that the aggregation was independent of the release of ADP. It was revealed that this activation of platelets by unsaturated fatty acids was caused by marked Ca2+ uptake into the cytoplasm, resulting from significant membrane perturbation.