Vitamin E and the susceptibility of erythrocytes and reconstituted liposomes to oxidative stress in aged diabetics

A remarkable increase in the permeability of erythrocyte ghosts and liposomal membranes composed of erythrocyte lipids from aged diabetics was revealed by measuring [¹⁴C]glucose leakage. There were no significant differences in the contents of free cholesterol or phospholipids, or in the cholesterol/phospholipid ratio between diabetic and normal erythrocyte membranes, but significantly higher amounts of unsaturated fatty acids, arachidonic acid and docosahexaenoic acid were observed in the erythrocyte membranes of diabetics. Reconstituted liposomes prepared from aged diabetic erythrocyte lipids were highly susceptible to superoxide-induced oxidative stress. Vitamin E was highly effective in suppressing the peroxidative lysis of liposomes composed of diabetic erythrocyte lipids. The effect of superoxide dismutase (SOD) on the inhibition of peroxidation of unsaturated lipids within liposomal membranes was less than that of vitamin E.     

Effect of hypothyroidism on the lipid composition of rat plasma and erythrocyte membranes

The effect of hydrothyroidism on plasma and erythrocyte membrane lipid components has been investigated. This pathological state is accompanied by a) a cholesterol increase of about 60% in plasma, and at the same time a 22% reduction in erythroycte membranes; b) 44% and 30% phospholipid level decreases in both plasma and red cell membranes, respectively; and c) almost unaffected phospholipid and fatty acid compositions of both plasma and erythrocyte membranes. All changes were corrected by treatment of the hypothyroid rats with triiodothyronine for two days. These findings suggest that in hypothyroid rats a reduced transfer of cholesterol from plasma to erythrocyte membrane probably takes place. This could explain, at least in part, the increased hematic cholesterol level observed in hypothyroid animals. In red cell membranes, the simultaneous decrease in cholesterol and phospholipid levels does not alter the cholesterol/phospholipid molar ratio, thus avoiding their abnormal function.     

A rapid method for extraction of total lipids from whey protein concentrates and separation of lipid classes with solid phase extraction

A modified procedure for extraction of total lipids from whey protein concentrates was developed such that stable emulsion with extracting solvents was avoided and the solvent system remained monophasic. Nonlipid contaminants from the extract were removed using gel filtration instead of traditional aqueous washing to prevent any loss of polar lipids. The extraction of total lipids by the modified procedure was complete and comparable with a reference procedure. Traditional thin-layer chromatography is tedious and more qualitative than quantitative for lipid class separation. Total lipids were further separated into free fatty acids, phospholipids, cholesterol ester, triacylglycerol, cholesterol, diacylglycerol, and monoacylglycerol, using modified solid phase extraction procedure. Columns with 2 g amino propyl packing allowed separation of up to 80 mg of total lipids into lipid classes gravimetrically. The values for anhydrous milk fat for all lipid classes agreed with those in the literature. Separation of total lipids into lipid classes with solid phase extraction is easy, quantitative, and can also be performed on a preparative scale.     

Quantitative31P nuclear magnetic resonance analysis of the phospholipids of erythrocyte membranes using detergent

³¹P Nuclear magnetic resonance (NMR) spectra of human erythrocyte lysates dissolved in sodium cholate were acquired. The narrow resonances of phospholipids were mostly well resolved, allowing identification and accurate quantitative analysis of phospholipid classes of the erythrocyte membranes. The ether-linked phosphatidylethanolamine components of the erythrocyte membranes were identified, based on the removal of plasmalogens by acidolysis and of diacyl phospholipid species by degradation using phospholipase A₁. It was also shown that the introduction of double bonds on the acyl chains of phosphatidylcholine shifted the³¹P NMR resonances to lower frequencies. Quantitative analyses of phospholipids from the spectra were based on their apparent molar concentrations. The recoveries of phospholipids from erythrocytes were significantly higher than those using conventional extraction procedures.     

The effects of dietary phospholipids enriched with phosphatidylethanolamine on bile and red cell membrane lipids in humans

The role of phospholipids in biliary cholesterol solubilization and crystallization has only recently begun to be appreciated. Phospholipid vesicles are believed to be the metastable carrier from which cholesterol nucleates. Cholesterol crystallization is influenced by the phospholipid species in bile. Feeding rats and hamsters with diets enriched in phospholipids or their precursors, especially ethanolamine, resulted in reduced cholesterol saturation of bile. Although whole phospholipids are normal dietary constituents, the effects and safety of phospholipid components have not been tested in humans. In the present study, we have evaluated the effects of a dietary phospholipid mixture, enriched with phosphatidylethanolamine, on human bile and red blood cell membrane lipid composition. Five ambulatory volunteers having a chronic indwelling T-tube, with an intact enterohepatic circulation, were investigated. Thirty-six grams of phospholipids (54% phosphatidylethanolamine, 54% linoleyl acyl chains) were added to their daily diet for fourteen days. Biliary nucleation time, cholesterol carriers, as well as plasma, red blood cell membrane, and bile lipid compositions, were monitored. Following phospholipid supplementation, the proportion of linoleyl chains (18:2) in biliary phospholipids increased significantly from 31.1±1.2 to 37.7±5.3%, while that of oleyl chains (18:1) decreased from 11.4±1.6 to 9.6±1.1%. These changes were accompanied by an increase of linoleate and its metabolite, arachidonate, in red cell membranes. Phospholipid feeding did not cause any side effects, and no significant changes in biliary nucleation time, cholesterol, phospholipid, or bile salt concentrations, or in the distribution of cholesterol within micelles or vesicles. We conclude that phospholipid feeding is safe, and can be effective as a vehicle for lecithin fatty acyl chain modulation of bile and lipid membranes. These findings may provide a basis for a controlled modulation of biliary phospholipids to increase cholesterol solubility in bile.     

Composition of milk fat globules with increased linoleic acid

Comparisons were made of the composition and distribution of the lipids in fat globules from conventional milks and polyunsaturated milks produced by cows fed protected lipid supplement. Washed creams were prepared from the milks of three individual cows fed a conventional ration, and three fed a protected sunflower-soybean supplement rich in linoleic acid. The washed creams were fractionated by treatment with sodium deoxycholate and centrifugation. Each washed cream and four fractions (designated as outer globule membrane, inner membrane, pellet, and globule core) were analyzed for protein, lipid, phospholipid, cholesterol, tocopherols, carotenoids, and fatty acid composition. The outer and inner membrane fractions were further fractionated into neutral and polar (phospholipid) lipid classes by thin layer chromatography. For both types of washed cream the approximate weight distribution of total solids was: outer membrane, 1%; inner membrane, 2%; pellet, 0.1%; and core, 96%. The percentages of protein, phospholipid, cholesterol, and carotenoids were all lower in the polyunsaturated than in the conventional creams. In the polyunsaturated creams, the percentages of both saturated and unsaturated C₁₈ acids were higher, and of acids of C₁₆ and shorter chain length lower, than in the conventional creams. The phospholipids in the outer and inner membranes from the polyunsaturated milks had larger proportions of linoleic acid than did the phospholipids from the conventional milks. However, this increase in unsaturation was less than that of the core neutral lipids. Pancreatic lipase hydrolysis of the core fractions showed that the increased linoleic acid was introduced preferentially at the 2-position of the triglycerides. In general, the observed changes in physical properties and in susceptibility of polyunsaturated milk to the development of oxidized flavor are consistent with the differences in the relative proportions of the various classes of lipids in the conventional and polyunsaturated milks. Data from thesis of D.H. Bianco submitted in partial fulfillment of the requirements for the M.S. Degree in Food Science, University of California, Davis. Presented in part at the AOCS Meeting, New Orleans, April, 1976.     

Effect of n−3 fatty acid supplementation on lipid peroxidation and protein aggregation in rat erythrocyte membranes

Human erythrocytes in the circulation undergo dynamic oxidative damage involving membrane lipid peroxidation and protein aggregation during aging. The present study was undertaken to determine the effect of n−3 fatty acid supplementation on lipid peroxidation and protein aggregation in the circulation and also the in vitro susceptibility of rat erythrocyte membranes to oxidative damage. Wistar male rats were fed a diet containing n−6 fatty acid-rich safflower oil or n−3 fatty acid-rich fish oil with an equal amount of vitamin E for 6 wk. n−3 Fatty acid content in erythrocyte membranes of rats fed fish oil was significantly higher than that of rats fed safflower oil. The degree of membrane lipid peroxidation and protein aggregation of rats fed fish oil was not significantly higher than that of rats fed safflower oil when the amounts of phospholipid hydroper-oxides, thiobarbituric acid-reactive substances, and detergent-insoluble protein aggregates were measured. When isolated erythrocytes were oxidized under aerobic conditions in the presence of Fe(III), the degree of membrane lipid peroxidation of erythrocytes from rats fed fish oil was increased to a greater extent than that of rats fed safflower oil, whereas the degree of membrane protein aggregation of both groups was increased in a similar extent. Hence, n−3 fatty acid supplementation did not affect lipid peroxidation and protein aggregation in membranes of circulating rat erythrocytes, and the supplementation increased the susceptibility of isolated erythrocytes to lipid peroxidation, but not to protein aggregation, under the aerobic conditions. If a sufficient amount of vitamin E is supplied, n−3 fatty acid supplementation may give no undesirable oxidative effects on rat erythrocytes in the circulation.     

The lipid composition of erythrocytes in european cattle and buffalo steers

This study compared the lipid composition of the red blood cells of European cattle and of buffalo steers at the same level of feed intake in a thermoneutral evironment. The mean volumes of the erythrocytes and their lipid content were greater in buffalo than those in cattle. However, the amounts of phospholipid and cholesterol in cells of equal volume were higher in buffalo than in cattle. In contrast, the phospholipid level at a given cholesterol level was higher in cattle than in buffalo. The distribution of the different molecular species of phospholipids in the red cells of the two breeds were similar, but there were significant distinctions in their fatty acid patterns, notably in the levels of 24∶0 and 24∶1 in the sphingomyelin fractions. The proportion of total monounsaturated acids in the erythrocytes were similar from both breeds. However, there was a higher percentage of polyunsaturated fatty acids with a corresponding lower content of total saturated fatty acids in the red cells from buffalo than in those from cattle. The breed differences in erythrocyte lipid composition are discussed in relation to breed differences in red cell characters and could lead to a better understanding of the mechanisms of environmental adaptation.     

Differential uptake of cholesterol and plant sterols by rat erythrocytes in vitro

The in vitro uptake of radioactively labeled cholesterol and the plant sterol β-sitosterol has been examined in rat erythrocytes. From mixed micellar solutions containing egg yolk phospholipid and sodium taurocholate, the erythrocytes showed a nonlinear uptake of the two sterols. The uptake leveled off after about 45 min with the attainment of a 1∶1 total sterol-to-phospholipid ratio within the cell membrane, as determined on a mass basis. From soltuions containing egg yolk phospholipid, or purified egg yolk phosphatidylcholine, a preference for cholesterol over the plant sterol was observed, increasing with time from a cholesterol/β-sitosterol uptake ratio of unity (the media ratio) to a maximum of 2 after a 60-min incubation. Correction of the data for nonspecifically bound sterol increased the ratio to a maximum of 5 at the 30-min time point. The increase in the cholesterol/β-sitosterol uptake ratio with time, following an initial nonspecific association, showed that penetration of the plasma membrane by the sterol was required for the selectivity to be expressed. The presence of lysophosphatidylcholine or bovine serum albumin did not exert any noticeable influence over the extent of selectivity of absorption. Replacement of the egg yolk phospholipid with synthetic dipalmitoyl-phosphatidylcholine led to a loss of the sterol selectivity. No evidence was found to support a selective extraction of sterol from the erythrocyte membrane to account for the observed effects, nor was there any sign of a mass accumulation of phospholipid during the incubation. It is suggested that the media phospholipid influences the membrane permeability toward cholesterol and β-sitosterol. Presented in part at the 72nd annual meeting of the American Oil Chemists' Society, New Orleans, LA, May 1981.     

Exchange of free cholesterol between plasma and erythrocytes from hyperthyroid and hypothyroid ratsin Vitro

In our previous studies, we found that circulating thyroid hormone levels alter cholesterol partition between plasma and erythrocytes by changing the phospholipid content of erythrocytes (Ruggiero, F.M.,et al. (1984)Horm. Metabol. Res. 16, 37–40; Ruggiero, F.M.,et al. (1987)Lipids 22, 148–151). As an extension of this work, we now followed the exchange of free cholesterol between plasma and erythrocytes in control, hyperthyroid and hypothyroid rats under various experimental conditionsin vitro. In control rats, erythrocytes incubated with plasma at 37°C for 4 hr lose 10% of cholesterol which was esterified by lecithin: cholesterol acyltransferase (LCAT) present in the plasma. In hyperthyroid rats, erythrocytes incubated with plasma lose 30% of cholesterol within the same time. By contrast, in the case of hypothyroid rats incubation for 4 hr was necessary to transfer 24% of free cholesterol from plasma to erythrocytes. Inhibition of cholesterol esterification did not affect the loss of erythrocyte cholesterol in control and in hyperthyroid rats. Ca²⁺ increased the LCAT activity in the plasma of these rats. The findings shed light on the role of thyroid hormones in regulating cholesterol levels in plama through active cholesterol transfer between plasma and erythrocytes.     

Compensatory mechanisms in erythrocyte lipids in patients with atherosclerosis

The quantitative coposition of phospholipids and fatty acids of erythrocytes was investigated in patients with atherosclerosis. It was stated that the erythrocyte lipids of atherosclerotic patients contained smaller quantitities of phosphatidylcholine and phosphatidylinositol, a significantly larger quantity of sphingomyelin, and higher sphingomyelin/phosphatidylcholine and cholesterol/phospholipid ratios. The existence of compensatory changes was stated, which was evident in the reduction of palmitic and stearic acids and the increase of linoleic and eicosatrienoic acids in erythrocyte phospholipids. These changes in fatty acid composition probably cause minimal changes in the membrane fluidity indiced by an increased cholesterol/phospholipid and sphingomyelin/phosphatidylcholine ratios. This paper was the first evidence of occurrence of those changes in erythrocytes during spontaneous atherosclerosis in human     

Oral polyunsaturated phosphatidylcholine reduces platelet lipid and cholesterol contents in healthy volunteers

The effects of orally administered polyunsaturated phosphatidylcholine (PPC) on plasma lipids, lipoproteins and platelet function and composition were studied in seven healthy male volunteers. PPC (Nattermann & Cie, GmbH, Cologne, Federal Republic of Germany), 10 g/day, was given for a 6-week period after a 4-week wash out; laboratory tests were repeated after a further 4-week period after the end of treatment. PPC did not appear, during treatment, to modify the levels of plasma total cholesterol and triglycerides. High density lipoprotein (HDL) cholesterol levels were, however, increased after six weeks of PPC. The most dramatic changes occurred in platelet membrane composition: the total lipid/total protein and the cholesterol/protein ratios were reduced significantly, whereas increases of the phospholipid/total lipid ratio and of the linoleic acid membrane content were observed. Platelet function tests, both in whole blood and in platelet rich plasma, were not modified. Similarly, the thromboxane B₂ formation after standard stimuli and the sensitivity to exogenous prostaglandin I₂ also were unchanged. During the final wash out period following treatment, a reduction of plasma total and low density lipoprotein (LDL) cholesterol levels also was recorded. PPC appears to be capable of modulating lipid exchanges between cell membranes and the plasma compartment.     

A comparison of lipids from liver and hepatoma subcellular membranes

Subcellular fractions of nuclei, mitochondria, endoplasmic reticulum, plasma membrane and cytosol were prepared from liver and hepatoma 72288CTC. Marker enzyme activities, biochemical compositions and electron microscopy were used to establish purity. Hepatoma NADH: cytochrome C reductase and 5′-nucleotidase exhibited abnormal subcellular distributions. The lipids from the subcellular fractions were examined in detail. Mitochondria and plasma membranes were characterized by elevated percentages of diphosphatidylglycrerol and sphingomyelin, respectively, in both tissues. All hepatoma subcellular fractions contained dramatically elevated levels of sphingomyelin and cholesterol, two components that form preferential strong complexes in vitro. The fatty acid composition of hepatoma sphingomyelin differed markedlg from liver and, unlike liver, did not exhibit organelle specific compositions. Some hepatoma lipid classes contained reduced percentages of palmitate while others contained higher levels. Hepatoma phosphatidylcholine and phosphatidylethanolamine from organelles contained lower percentages of long chain polyunsaturated fatty acids than liver. Generally, unique fatty acid profiles exhibited by individual phospholipid classes of liver subcellular fractions were absent or much reduced in the hepatoma. The ratios of oleate to vaccenate were near one for most of the phospholipid classes of most liver fractions, but all hepatoma classes, with few exceptions, contained a much higher percentage of oleate in all subcellular fractions. The hypothesis is proposed that the origin of some acyl moieties for the biosynthesis of various hepatome lipid classes differs from liver sources. The possible changes in acyl pools, sources and compartments for complex lipid biosynthesis could result in change in the quantities of molecular species that could contribute to the abnormal properties of the hepatoma membranes.     

Separation of neutral lipid,free fatty acid and phospholipid classes by normal phase HPLC

Normal phase high performance liquid chromatography methods are described for the separation of neutral lipid, fatty acid and five phospholipid classes using spectrophotometric detection at 206 nm. Separations were accomplished in less than 10 min for each lipid class. A mobile phase consisting of hexane/methyltertiarybutylether/acetic acid (100∶5∶0.02) proved effective in separating cholesteryl ester and triglyceride with recoveries of 100% for radiolabeled cholesteryl oleate and 98% for radiolabeled triolein. Free fatty acid and cholesterol were separated by two different mobile phases. The first, hexane/methyltertiarybutylether/acetic acid (70∶30∶0.02) effectively separated free fatty acids and cholesterol, but did not separate cholesterol from 1,2-diglyceride. A mobile phase consisting of hexane/isopropanol/acetic acid (100∶2∶0.02) effectively separated free fatty acid, cholesterol, 1,2-diglyceride and 1,3-diglyceride. Recoveries of oleic acid and cholesterol were 100% and 97%, respectively. Five phospholipid classes were separated using methylteriarybutylether/methanol/aqueous ammonium acetate (pH 8.6) (5∶8∶2) as the mobile phase. The recoveries of phosphatidylinositol, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin and lysophosphatidylcholine were each greater than 96%.     

Effect of diabetes and insulin replacement on the lipid properties of hepatic smooth endoplasmic reticulum

This study is a characterization of the lipid properties of the smooth and rough endoplasmic reticulum (SER, RER) of liver from streptozotocin-induced diabetic rats. A significant decrease in membrane microviscosity was observed in the SER but not the RER of diabetic rats when compared to that of normal controls. This decrease in SER membrane microviscosity correlated with a decrease in cholesterol/phospholipid ratio of these membranes that could be accounted for solely by a change in the membrane cholesterol content. Changes in phospholipid fatty acyl chain composition were also observed in the SER membranes but these changes were small when compared to the large change in cholesterol content observed. Insulin treatment for only one day did not significantly alter the microviscosity of the SER but after 2, 4 and 6 days of treatment both membrane microviscosity and membrane cholesterol content were restored to values similar to those for normal animals. No significant changes in the RER lipid composition were observed. It is well known that increases in glucose-6-Pase (G-6-Pase) activity of liver ER membranes are associated with diabetic onset. An increase in the specific activity of G-6-Pase was observed in both SER and RER membrane preparations, although the observed increase in the SER membrane is higher. The changes in the G-6-Pase activity of the SER membranes were correlated with the alterations in the microviscosity and lipid composition of these membranes. It is postulated that lipid properties of the SER membranes, may contribute to the regulation of G-6-Pase activity in that membrane.     

Effect of essential fatty acid deficiency on lipid composition of basolateral plasma membrane of pig intestinal mucosal cells

The effect of essential fatty acid (EFA) deficiency on the lipid composition of basolateral plasma membranes (BPM) from intestinal mucosal cells was investigated in weaning pigs fed control or EFA-deficient diets for 12 weeks. The phospholipid and cholesterol contents relative to protein were similar in both groups, showing a cholesterol/phospholipid molar ratio of 0.6. The distribution of phospholipid classes was also unaffected by the diet. In contrast, fatty acid profiles of the two phospholipid main classes, phosphatidylcholine and phosphatidylethanolamine were altered by EFA deficiency. Linoleic acid (18∶2n−6) was largely reduced, whereas arachidonic acid (20∶4n−6) only slightly decreased in EFA-deficient pigs. The unsaturation index was essentially maintained by high levels of oleic acid (18∶1n−9) and by conversion of oleic acid to 5,8,11-eicosatrienoic acid (20∶3n−9). Finally, during the period of EFA deficiency, the lipid composition of BPM of the intestinal mucosal cells was little affected, suggesting a preferential uptake of 20∶4n−6 and (or) precursor mobilized from other tissues. However, an effect of dietary treatment on the function of membrane-associated proteins cannot be ruled out.     

Dissolution of Soap Scum by Surfactants. Part III. Effect of Chelant Type on Equilibrium Solubility and Dissolution Rate of Calcium and Magnesium Soap Scums in Various Surfactant Systems

Soap scum can be effectively removed by using an appropriate surfactant with a chelating agent at a high solution pH. The equilibrium solubilities and dissolution rates of two model soap scums [calcium stearate and magnesium stearate: Ca(C₁₈)₂ and Mg(C₁₈)₂] were investigated in aqueous solutions containing three different types of surfactants [methyl ester sulfonate (MES) as an anionic surfactant; alcohol ethoxylate (EO9) as a nonionic surfactant; and dimethyldodecylamine oxide (DDAO) as an amphoteric surfactant] in the presence of different biodegradable chelants: trisodium ethylenediamine disuccinic acid (Na₃EDDS) and tetrasodium glutamate diacetic acid (Na₄GLDA) compared with disodium ethylenediamine tetraacetate (Na₂EDTA), a chelant with poor biodegradability. The highest equilibrium solubility and dissolution rate of either soap scum were observed at high pH in the DDAO system with Na₄GLDA. In addition, the calcium soap scum had a similar to higher equilibrium solubility and a higher dissolution rate constant as compared with the magnesium soap scum.     

Dietary fatty acids,membrane transport,and oxidative sensitivity in human erythrocytes

This study examined effects of dietary n−3 fatty acids on age-related changes in erythrocyte anion transport and susceptibility to oxidation. Blood was drawn from healthy adult volunteers before and after six weeks' supplementation (nine/group) with 4.0 g/day of safflower oil (containing 2.9 g n−6 fatty acids) or fish oil (containing 1.2 g long-chain n−3 fatty acids). Following density separation of young and old erythrocytes, membrane anion transport and cell membrane lipid composition were measured. Oxidative damage was measured in erythrocyte ghosts exposed to a free radical generator. Fish oil significantly increased 16∶0 and 20∶5n−3 in ghosts of both young and old cells, and 22∶5n−3 and 22∶6n−3 in old cells alone. Safflower oil increased 16∶0, 18∶0, 18∶1n−9, and 22∶5n−6 in ghosts of young cells only. The age-dependent increase in membrane anion transport (P<0.01) was decreased by dietary fish oil supplementation, but not by safflower oil supplementation. Safflower oil and fish oil increased the susceptibility of both young and old erythrocytes to oxidative damage by free radical generation (P<0.001).     

Cell membranes and multilamellar vesicles: Influence of pH on solvent induced damage

Pigment leakage from sheep and horse erythrocytes and from red beet tissue induced by non-polar solvents was determined as a function of pH. The results were compared to disruption of multilamellar vesicles (MLV) composed of phospholipids with equimolar cholesterol under identical conditions of solvent exposure and pH. Solvent access to cholesterol was used to measure vesicle disruption. MLV were made from 1,2-dioleoyl phosphatidylethanolamine sphingomyelin (SP) and various phosphatidylcholines to simulate the major lipid components of membranes. Pigment leakage from erythrocytes caused by petroleum hydrocarbon (b.p. 60–80°C) was maximal at pH 2–4 and at pH 10, but minimal at pH 6.8; alcohols caused less pigment leakage than petroleum hydrocarbon. Betacyanin leakage from beet tissue induced by petroleum hydrocarbon was maximal at pH 2, with very little leakage at pH 4, 6.6 and pH 10. Alcohols caused minimal damage to beet tissue above pH 2. Cholesterol removal by petroleum hydrocarbon from MLV of mixed lipid composition was maximal at pH 2–4, reduced at pH 6.8 and minimal at pH 10. Lipid mixtures in which fatty acyl side chains of one phospholipid were of a different length than the other lost more sterol than mixtures in which the acyl side chains were of identical chain length. MLV with more than 25% SP lost more sterol than those with less or no SP. Results show that in mixtures of phospholipids, SP exposes the hydrocarbon phase of a bilayer to solvent extraction, a property that was also observed in native membranes. Erythrocyte membranes, which contain SP, were more severely damaged by petroleum hydrocarbon than beet cells, which have none. Membranes from erythrocytes were more prone to solvent disruption at pH 10 than MLV, but they were more resistant at physiological pH. It is suggested that conformational changes in membrane proteins due to shifts in pH cause exposure of hydrophobic portions of surrounding lipids to the environment. At neutral pH, the native conformation of proteins is expected to stabilize the bilayer of membranes.     

Incorporation of n-3 fatty acids into plasma lipid fractions, and erythrocyte membranes and platelets during dietary supplementation with fish, fish oil, and docosahexaenoic acid-rich oil among healthy young men

The effects of n-3 fatty acid supplementation in the form of fresh fish, fish oil, and docosahexaenoic acid (DHA) oil on the fatty acid composition of plasma lipid fractions, and platelets and erythrocyte membranes of young healthy male students were examined. Altogether 59 subjects (aged 19–32 yr, body mass index 16.8–31.3 kg/m²) were randomized into the following diet groups: (i) control group; (ii) fish diet group eating fish meals five times per week [0.38±0.04 g eicosapentaenoic acid (EPA) and 0.67±0.09 g DHA per day]; (iii) DHA oil group taking algae-derived DHA oil capsules (1.68 g/d DHA oil group taking algae-derived DHA oil capsules (1.68 g/d DHA in triglyceride form); and (iv) fish oil group (1.33 g EPA and 0.95 g DHA/d as free fatty acids) for 14 wk. The fatty acid composition of plasma lipids, platelets, and erythrocyte membranes was analyzed by gas chromatography. The subjects kept 4-d food records four times during the study to estimate the intake of nutrients. In the fish diet, in DHA oil, and in fish oil groups, the amounts of n-3 fatty acids increased and those of n-6 fatty acids decreased significantly in plasma lipid fractions and in platelets and erythrocyte membranes. A positive relationship was shown between the total n-3 polyunsaturated fatty acids (PUFA) and EPA and DHA intake and the increase in total n-3 PUFA and EPA and DHA in all lipid fractions analyzed. DHA was preferentially incorporated into phospholipid (PL) and triglyceride (TG) and there was very little uptake in cholesterol ester (CE), while EPA was preferentially incorporated into PL and CE. The proportion of EPA in plasma lipids and platelets and erythrocyte membranes increased also by DHA supplementation, and the proportion of linoleic acid increased in platelets and erythrocyte membranes in the DHA oil group as well. These results suggest retroconversion of DHA to EPA and that DHA also interferes with linoleic acid metabolism.