Total sialic acid content of glycophorins during senescence of human red blood cells.

Glycophorins extracted from membranes of young and old human red blood cells have within an error of +/- 1.5% the same sialic acid content when referred to a relative measure of the number of glycophorins. The degree of surface iodination in glycophorins, which was shown to be the same in young and old cells, served as this relative measure. This finding implies that senescent human red blood cells hardly reveal desialylated surface proteins (less than or equal to 3%). However, the sialic acid content per cell was repeatedly reported to be 10 to 15% lower in old than in young cells. Therefore, we conclude 1) that human red blood cells lose intact glycophorin together with membrane during red blood cell senescence, and 2) that removal of desialylated and senescent red blood cells from the circulation proceeds by different routes.     

A meta-analysis of blood fatty acids in people with learning disorders with particular interest in arachidonic acid

Small individual studies report that people with learning disorders have lower than normal blood concentrations of docosahexaenoic acid and arachidonic acid. The origin and consequence of the subnormal docosahexaenoic acid have been much speculated. However, relatively little attention has been paid to the significance of the low arachidonic acid concentration. Studies were identified through a literature search including subjects with various learning disorders or symptoms thereof and age-matched controls. A meta-analysis of pooled data from the red blood cell and plasma/serum showed that red blood cell arachidonic acid and docosahexanoic acid concentrations were significantly lower than normal [−3.93 and −18.92, respectively (weighted mean difference as a % of weighted mean control)]. Plasma/serum arachidonic acid and docosahexaenoic acid concentrations were also significantly lower than normal [−6.99 and −15.66, respectively (weighted mean difference as a % of weighted mean control)]. However, in absolute amounts the arachidonic acid was as severely depressed as docosahexanoic acid within red blood cells 0.57 mg/100 mg of fatty acid below normal verses 0.59 mg/100 mg for docosahexaenoic acid. Plasma/serum arachidonic acid was even lower; 0.71 mg/100 mg of fatty acid below normal verses 0.34 mg/100 mg for docosahexaenoic acid. The origin, consequences and relative importance of subnormal arachidonic acid to brain function bears further investigation.     

Phospholipid hydroperoxide glutathione peroxidase activity and vitamin E level in the liver microsomal membrane: effects of age and dietary alpha-linolenic acid deficiency

Age and diet-induced variations of phospholipid hydroperoxide glutathione peroxidase (PHGPx) activity and alpha-tocopherol concentration in the liver microsomal membrane were studied in male Wistar rats fed a semipurified diet either balanced in n-6 and n-3 polyunsaturated fatty acids (PUFA) (Control) or deprived of alpha-linolenic acid, i.e. n-3 PUFA (Deficient) over two generations. The animals were studied at the age of 6 months (adult) or 24 months (old). Both PHGPx activity and vitamin E level were significantly higher in 24-month old rats as compared to 6-month old rats. By contrast, the thiobarbituric acid reactive substances (TBARS) following stimulated in vitro peroxidation of membrane lipids were markedly lower (P < 0.01) with aging. The fatty acid composition of microsomal membrane phospholipids (PL) was also considerably modified by age. In particular, the levels of arachidonic acid and total n-6 PUFA were lower (P < 0.001) whereas n-3 PUFA levels were higher (P < 0.001) in most PL main classes. The alpha-linolenic acid deficiency markedly influenced these age-related changes. The higher PHGPx activity in the old rats as compared to the adult rats was only significant in those fed the control diet. In the 6-month old rats (but not in the 24-month old rats), the deficient diet led to a higher membrane vitamin E level and to lower TBARS production than the control diet. The results suggest that the nature of dietary PUFA may influence the age-related variations in this pair of membrane antioxidants and also in the fatty acid composition of microsomes.     

Specific oxygenation of plasma membrane phospholipids by Pseudomonas aeruginosa lipoxygenase induces structural and functional alterations in mammalian cells

Pseudomonas aeruginosa is a gram-negative pathogen, which causes life-threatening infections in immunocompromized patients. These bacteria express a secreted lipoxygenase (PA-LOX), which oxygenates free arachidonic acid to 15S-hydro(pero)xyeicosatetraenoic acid. It binds phospholipids at its active site and physically interacts with lipid vesicles. When incubated with red blood cells membrane lipids are oxidized and hemolysis is induced but the structures of the oxygenated membrane lipids have not been determined. Using a lipidomic approach, we analyzed the formation of oxidized phospholipids generated during the in vitro incubation of recombinant PA-LOX with human erythrocytes and cultured human lung epithelial cells. Precursor scanning of lipid extracts prepared from these cells followed by multiple reaction monitoring and MS/MS analysis revealed a complex mixture of oxidation products. For human red blood cells this mixture comprised forty different phosphatidylethanolamine and phosphatidylcholine species carrying oxidized fatty acid residues, such as hydroxy-octadecadienoic acids, hydroxy- and keto-eicosatetraenoic acid, hydroxy-docosahexaenoic acid as well as oxygenated derivatives of less frequently occurring polyenoic fatty acids. Similar oxygenation products were also detected when cultured lung epithelial cells were employed but here the amounts of oxygenated lipids were smaller and under identical experimental conditions we did not detect major signs of cell lysis. However, live imaging indicated an impaired capacity for trypan blue exclusion and an augmented mitosis rate. Taken together these data indicate that PA-LOX can oxidize the membrane lipids of eukaryotic cells and that the functional consequences of this reaction strongly depend on the cell type.     

Sheep Erythrocyte Membrane Binding and Transfer of Long-Chain Fatty Acids

We have studied binding and membrane transfer rates of unsaturated long-chain fatty acids in sheep red cells, as previously done for human red cells, in order to elucidate the transport mechanism. Observed differences must be assigned to the different composition of the membrane in the two species. Equal surface areas of the membranes of the two species have similar binding capacities and affinities for palmitic-, linoleic-, oleic- and arachidonic acid at 37°C. The competitive bindings of linoleic- and arachidonic acid as well as the distribution of bound arachidonic acid on the two sides of the membrane are not different in the two species. However, the rate constants for membrane transfer in sheep are less than half of those measured previously for human ghosts. This finding is confirmed by the exchange efflux kinetics of ghosts containing albumin-bound fatty acid. Studies of sheep ghost membranes with oleic-, arachidonic- and linoleic acid reveal a proportionality between the membrane transfer rate constants and the number of fatty acid double bonds, as found previously for human ghost membrane, and the effect of double bonds is in harmony with a large negative activation entropy for diffusion through the membrane. The established replacement of lecithin by sphingomyelin with a low unsaturation fatty acid index in sheep membranes probably causes a lower transversal lipid phase fluidity. Double bonds diminish the flexibility of hydrocarbon chains and thus the large negative activation entropy of diffusion across the membrane. The smaller transfer rate constants of the three unsaturated fatty acids in sheep membranes support the hypothesis that the transfer is diffusion in protein defined annular lipid domains and not carrier mediated. Received: 24 February 1999/Revised: 10 June 1999     

Antioxidant modulation of oxidant-stimulated uptake and release of arachidonic acid in eicosapentaenoic acid-supplemented human lymphoma U937 cells

Omega-3 polyunsaturated fatty acids (PUFA) are increasingly finding use as treatments for a variety of medical conditions. PUFA supplementation can, however, result in increased oxidative stress causing elevated turnover rate of membrane phospholipids, impairment of membrane integrity and increased formation of inflammatory mediators. The aim of this study was to determine which antioxidant compounds were most effective in ameliorating the stimulation of phospholipid turnover by oxidative stress. U937 cells were supplemented with eicosapentaenoic acid and either ascorbic acid, alpha-tocopherol, beta-carotene or astaxanthin prior to being challenged with oxidant. Although all antioxidants were found to be effective in decreasing oxidant-stimulated peroxide formation, only alpha-tocopherol significantly decreased oxidant-stimulated release of 3H-labeled arachidonic acid (AA), while ascorbic acid markedly increased release. All antioxidants except alpha-tocopherol decreased oxidant-stimulated 3H-AA uptake. Our data suggest that antioxidants are not equally effective in combating the effects of oxidative stress upon membrane phospholipid turnover, and that optimal protection will require mixtures of antioxidants.     

老化红细胞肌醇磷脂代谢的探讨

本文用密度梯度离心法,将红细胞分成年轻及老化两部分,分别测定了膜磷脂、甘油二酯及磷酸肌醇的含量,蛋白激酶C在膜内及胞浆内的分布及其对膜蛋白的磷酸化。实验结果表明老化及年轻红细胞磷脂含量,除磷脂酰胆碱明显降低外,其他均无差异。老化红细胞甘油二酯含量低于(P<0.01)年轻者,而磷酸肌醇两者含量相似。老化红细胞膜内蛋白激酶C活性远比年轻者高,而在胞浆内活性则相反。说明老化红细胞膜蛋白激酶C活性增高,可使红细胞膜蛋白4.1、4.2、4.5和4.9进行磷酸化,这些膜蛋白与维持红细胞形态及功能有关,可能它们的磷酸化是老化红细胞变形性降低,脆性增加的因素之一。     

Changes in mitochondrial and microsomal lipid peroxidation and fatty acid profiles in adrenal glands, testes, and livers from alpha-tocopherol-deficient rats

Studies were done to evaluate the effects of alpha-tocopherol deficiency in rats on the fatty acid composition and sensitivity to lipid peroxidation (LP) of mitochondria and microsomes from adrenal glands, testes, and livers. In control (alpha-tocopherol-sufficient) animals, adrenal concentrations of alpha-tocopherol were approximately 10 times greater than those in livers and testes. Dietary deficiency of alpha-tocopherol for 8 weeks decreased adrenal and hepatic concentrations by 80-90% and testicular concentrations by approximately 60-70%. Incubation of testicular or hepatic mitochondria and microsomes from control rats with FeSO(4) (1.0 mM) caused a time-dependent stimulation of LP as indicated by the formation of thiobarbituric acid reactive substances (TBARS); the rate of TBARS production increased in preparations from alpha-tocopherol-deficient animals. TBARS formation was not demonstrable in adrenal mitochondria or microsomes from alpha-tocopherol sufficient rats, but reached high levels in alpha-tocopherol-deficient preparations. The fatty acid composition of mitochondria and microsomes was tissue-dependent. In particular, arachidonic acid comprised approximately 40% of the total fatty acids in adrenal membranes, but only 20-25% in testes and livers. alpha-Tocopherol deficiency increased oleic acid concentrations in adrenal and hepatic mitochondria and microsomes but not in testes. In all three tissues, linoleic acid concentrations decreased by approximately 50%, but arachidonic acid levels were unaffected by alpha-tocopherol deficiency. The results indicate a close relationship between tissue sensitivity to LP in vitro and alpha-tocopherol concentrations. Nonetheless, any oxidative stress in vivo caused by alpha-tocopherol deficiency seems to spare arachidonic acid in mitochondria and microsomes but decreases linoleic acid concentrations. It is possible that because of the important physiological functions of arachidonic acid, metabolic adaptations serve to maintain membrane content during periods of oxidative stress.     

Inhibition of arachidonic acid oxidation by beta-carotene, retinol and alpha-tocopherol

Prostaglandin and hydroxyeicosatetraenoic acid (HETE) production from arachidonic acid in bovine seminal vesicles and kidney as influenced by the addition of beta-carotene, retinol or alpha-tocopherol was studied. The major product formed was prostaglandin E2 (approximately 85% prostaglandin E2 of control), and its proportion decreased with increasing concentration of the additives, while the proportion of HETE increased. Prostaglandin and HETE production was considerably inhibited by beta-carotene and retinol, and to a lesser extent by alpha-tocopherol; HETE production was inhibited less than that of prostaglandin. It appears that beta-carotene, retinol and alpha-tocopherol influence both the cyclooxygenase and lipoxygenase pathways; this modulation of arachidonic acid oxidation by physiological compounds may have important in vivo implications.     

In vivo survival of selected murine carrier red blood cells after separation by density gradients or aqueous polymer two-phase systems.

In order to explore possibilities of using erythrocytes as carrier systems for delivery of pharmacological agents, we have studied the in vivo survival of murine carrier red blood cell populations enriched in young or old cells. Hypotonic-isotonic dialysis has been used to modify the cells as carrier systems and Percoll/albumin density gradients or counter-current distribution in aqueous polymer two-phase systems to separate them according to age. Hypotonic-isotonic dialysis produces a decrease in the red blood cell populations in vivo survival rate (from 9.5 to 7.8 days). Among the cells modified as carriers, the enriched young red blood cell populations show a higher in vivo survival (half-life 6.5-7.4 days) than populations made up of predominantly old red blood cells (half-life 4.7-6.2 days). Half-life of young or old circulating red blood cells was approximately one day longer when these cells were separated by counter-current distribution rather than by Percoll density gradients. Based on these results, hypotonic-isotonic dialysis of whole and enriched young or old red blood cell populations, with higher or lower survival rates, can be considered as a useful tool for modification of these cells as carriers. The final outcome of such changes can be translated into better control of plasma drug delivery during therapy.     

Hydrolysis of phosphatidylserine-exposing red blood cells by secretory phospholipase A2 generates lysophosphatidic acid and results in vascular dysfunction

Secretory phospholipase A(2) (sPLA(2)) type IIa, elevated in inflammation, breaks down membrane phospholipids and generates arachidonic acid. We hypothesized that sPLA(2) will hydrolyze red blood cells that expose phosphatidylserine (PS) and generate lysophosphatidic acid (LPA) from phosphatidic acid that is elevated in PS-exposing red blood cells. In turn, LPA, a powerful lipid mediator, could affect vascular endothelial cell function. Although normal red blood cells were not affected by sPLA(2), at levels of sPLA(2) observed under inflammatory conditions (100 ng/ml) PS-exposing red blood cells hemolyzed and generated LPA (1.2 nM/10(8) RBC). When endothelial cell monolayers were incubated in vitro with LPA, a loss of confluence was noted. Moreover, a dose-dependent increase in hydraulic conductivity was identified in rat mesenteric venules in vivo with 5 microM LPA, and the combination of PS-exposing red blood cells with PLA(2) caused a similar increase in permeability. In the presence of N-palmitoyl L-serine phosphoric acid, a competitive inhibitor for the endothelial LPA receptor, loss of confluence in vitro and the hydraulic permeability caused by 5 microM LPA in vivo were abolished. The present study demonstrates that increased sPLA(2) activity in inflammation in the presence of cells that have lost their membrane phospholipid asymmetry can lead to LPA-mediated endothelial dysfunction and loss of vascular integrity.     

Temperature-dependent abnormalities of the erythrocyte membrane in porcine malignant hyperthermia

The temperature dependence of ATPase activities and stearic acid spin label motion in red blood cells of normal and MH-susceptible pigs have been examined. Arrhenius plots of red blood cell ghost Ca-ATPase and calmodulin-stimulable Ca-ATPase activities were identical for both normal and MH erythrocyte ghosts. Arrhenius plots of Mg-ATPase activity exhibited a break (defined as a change in slope) at 24 degrees C in both MH and normal erythrocyte ghosts. However, below 24 degrees C the apparent activation energy for this activity was less in MH than normal ghosts. To determine whether breaks in ATPase Arrhenius plots could be correlated with changes in the physical state of the red blood cell membrane, the spin label 16-doxyl-stearate was introduced into the bilayer of both erythrocyte ghosts and red blood cells. With both ghosts and intact cells, at each temperature examined, the mobility of the probe in the lipid bilayer, as measured by electron paramagnetic resonance, was greater in normal than in MH membranes. While there were no breaks in Arrhenius plots for probe motion in the erythrocyte ghosts, the apparent activation energy for probe motion was significantly greater in normal than in MH ghost membranes. While there was no break in the Arrhenius plot of probe motion in normal intact red blood cell membranes, there were breaks in the Arrhenius plot of probe motion at both 24 and 33 degrees C in intact MH red blood cell membranes. Based on the altered temperature dependence of Mg-ATPase activity and spin probe motion in membranes derived from MH red blood cells, we conclude that there may be a generalized membrane defect in MH pigs which is reflected in the red blood cell as an altered membrane composition or organization.     

Altered enzyme function and premature sequestration of erythrocytes in aged individuals

Experimentation performed to determine the parameters of the life-span of the erythrocyte in hosts of various ages have determined that, in aged individuals, the rate of turnover of cells is considerably increased over that observed in young individuals. These observations are based on studies in humans, rats, mice, and rabbits in which either in situ 59Fe labelling or age-density gradient separation were used. The mechanisms for the recognition of the effete red cell in the aged host and the nature of the membrane alterations that bring about the premature sequestration are not fully understood. However, it has been consistently observed that the red cells of aged individuals have higher levels of IgG bound to their membranes than do young cells, with the most dense cells having the highest levels of immunoglobulin. Studies of most enzymes, particularly those involved in protection against oxidative damage have shown reduced activity as a function of both cell and donor age. Evidence of enzyme damage has been observed even in the youngest circulating red blood cells of old individuals. This fact leads us to hypothesize that the erythrocyte of the aged individual as it differentiates and is released from the bone marrow is less functional and partially damaged. The erythrocytes of both old and young individuals age in the circulation, accumulating subtle alterations that are recognized by the immune and/or reticuloendothelial systems and lead to sequestration. The cells of the elderly individual accumulate a greater degree of damage due to their initially reduced capacity to protect themselves from environmental stress. These alterations eventually bring them to their early sequestration.     

N-acetyl-9-O-acetylneuraminic acid, the receptor determinant for influenza C virus, is a differentiation marker on chicken erythrocytes

Erythrocytes from chicken of different age were analysed for their agglutinability by influenza C virus, which has been shown recently to use N-acetyl-9-O-acetylneuraminic acid as a high-affinity receptor determinant for the attachment to cells. Only with birds not younger than six days complete agglutination of the erythrocytes was observed. The hemagglutination titer which was initially low reached its maximum value at the age of about 20 days. Sialic acid was isolated from erythrocytes, purified and analysed by colorimetry, thin-layer chromatography, high-performance liquid chromatography, and gas-liquid chromatography-mass spectrometry. The sialic acid content of erythrocytes from one-day old and adult chicken was 21 micrograms and 18 micrograms sialic acid/ml packed erythrocytes, respectively. While N-acetylneuraminic acid was the major type of sialic acid on erythrocytes from both one-day old and adult chicken, N-acetyl-9-O-acetylneuraminic acid was only detected on red blood cells from adult animals accounting for 30-40% of total sialic acid. These results indicate that N-acetyl-9-O-acetylneuraminic acid, in addition to serving as a receptor determinant for influenza C virus, represents a developmental marker on chicken erythrocytes.     

Diet fat composition alters membrane phospholipid composition, insulin binding, and glucose metabolism in adipocytes from control and diabetic animals

The present study was designed to determine if diet fat-induced alteration in the fatty acid composition of the adipocyte plasma membrane alters insulin binding and the insulin responsiveness of glucose metabolism in control and diabetic states. Normal (control) and diabetic (streptozotocin-induced) rats were fed high fat semipurified diets providing a high or low polyunsaturated to saturated fatty acid (P/S) ratio. Feeding a high P/S diet increased the polyunsaturated fatty acid content of major membrane phospholipids of the adipocyte plasma membrane from both normal and diabetic animals. The diabetic state was associated with an elevated content of linoleic acid and a reduced level of arachidonic acid consistent with reduced delta 6-desaturation. Feeding the high P/S diet to diabetic animals increased membrane linoleic acid content and prevented the decrease observed in the arachidonic acid of membrane phospholipids. The high P/S diet was associated with increased insulin binding in nondiabetic animals but did not change the amount of insulin bound by cells from diabetic animals. Significantly (p less than 0.05) increased rates of insulin-stimulated glucose transport and lipogenesis (glucose incorporation into lipids) were observed in control animals fed the high as compared to the low P/S diet. The rates of insulin-stimulated glucose transport, oxidation, and lipogenesis were lower (p less than 0.05) for cells from diabetic as compared to control animals. However, feeding a high P/S diet significantly improved rates for all three of these functions (p less than 0.05). It is concluded that diet-induced alterations in membrane composition may provide a mechanism for improving the cellular response to insulin in cells from diabetic animals.     

Changes in the fatty acid profiles of red blood cell membrane phospholipids in human neonates during the first month of life

We have studied the changes in the fatty acid profiles of red blood cell membrane phospholipids in 47 infants who were exclusively fed human milk from birth to 1 month of life. Twenty blood samples were obtained from cord, 15 at 7 days and 12 at 30 days after birth. Membrane phospholipids were obtained from erythrocyte ghosts by thin-layer chromatography and fatty acid composition was determined by gas liquid chromatography. Phosphatidylcholine showed the most important changes during early life; stearic, w6 eicosatrienoic and arachidonic acids decreased whereas oleic and linoleic acids increased. In phosphatidylethanolamine, palmitic and stearic acid declined and oleic, linoleic and docosahexenoic acids increased with advancing age. Small changes were noted for individual fatty acids in phosphatidylserine. In sphingomyelin stearic acid increased from birth to 1 month and linoleic, arachidonic and nervonic acids decreased. Total polyunsaturated fatty acids of the w6 series greater than 18 carbon atoms increased with advancing age in phosphatidylethanolamine and decreased in choline and serine phosphoglycerides and in sphingomyelin. Long chain fatty acids derived from linoleic acid decreased in phosphatidylcholine but increased in ethanolamine and serine phosphoglycerides. The different behavior in the changes observed in fatty acid patterns for each erythrocyte membrane phospholipid may be a consequence of its different location in the cell membrane bilayer and specific exchange with plasma lipid fractions.     

Determination of alpha-tocopherol in erythrocytes by gas-liquid chromatography

A method is described for the determination of submicrogram amounts of alpha-tocopherol in 0.5 ml of packed erythrocytes. The alpha-tocopherol in a lipid extract is oxidized to alpha-tocopherylquinone which is separated by thin-layer chromatography, eluted, and quantitated by gas-liquid chromatography. Calculation is based on the recovery of added alpha-tocopherol-(3)H. Erythrocytes from stock rats had an average alpha-tocopherol concentration of 344 micro g/100 ml of packed cells, while for human cells the average was 235 micro g/100 ml. The ratio of red cell to plasma alpha-tocopherol was 0.482 for rat blood, and 0.244 for human blood.     

Alpha-tocopherol protection of erythrocytes from hemolysis induced by thermal injury

It is shown that skin burn is accompanied by activation of lipid peroxidation (accumulation of TBA-reactive substances and of fluorescent end-products) in the blood of experimental animals. The decrease in red blood cell membrane stability was demonstrated exerting as increase in the rate of spontaneous hemolysis, content of extraerythrocyte++ haemoglobin and increased sensitivity to exogenous oleic acid. It is estimated that alpha-tocopherol possesses protective stabilizing effect on red blood cell membrane. This stabilizing action is observed when alpha-tocopherol was injected both before the skin burn and immediately after it. It is concluded that two different mechanisms are responsible for stabilizing effect of tocopherol, namely: 1) antiradical, realized via inhibition of lipid peroxidation, and 2) non-antioxidant, caused by interaction of tocopherol with phospholipid hydrolysis products by phospholipases A2 (free fatty acids and lysophospholipids).     

Bicarbonate permeability and immunological evidence for an anion exchanger-like protein in the red blood cells of the sea lamprey,Petromyzon marinus

Physiological and immuno-blotting experiments were used to determine whether the red blood cell membrane of a primitive vertebrate, the sea lamprey Petromyzon marinus, contained a counterpart similar to the vertebrate anion exchange protein known as AE1 or band 3. Results of the physiological experiments which measured CO₂ production after adding H¹⁴CO ₃ ^- to the extracellular saline, indicated significant transmembrane bicarbonate movement in lamprey blood which unlike that in most vertebrates, was insensitive to inhibition by 4,4 diisothiocyanatostilbene-2,2 disulfonic acid. The present study also showed that lamprey red blood cells possess acetazolamide-sensitive carbonic anhydrase which is an important component of CO₂ production by vertebrate red blood cells. Polyclonal immunoglobulins against a 12 amino acid domain in the C-terminus of the mouse AE1 recognized a trout red blood cell membrane protein with a relative molecular mass of 97 kDa, but failed to immunoreact with any membrane proteins from the red blood cells of lamprey. Antibodies against trout AE1 immunoreacted with trout red blood cell membrane proteins of approximately 97 kDa, 200 kDa and >200 kDa. Interestingly, only a 200-kDa membrane protein from the red blood cells of the primitive lamprey immunoreacted with the trout anti-AE1 immunoglobulin proteins. Therefore, lamprey red blood cells appear to possess an AE1-like protein that may be physiologically different than that in most other vertebrates.     

Stories about acyl chains

The effect of dietary polyunsaturated fatty acids and alpha-tocopherol supplementation on erythrocyte lipid peroxidation and immunocompetent cells in mice was studied comparatively using seven dietary oils (15% oil/diet, w/w) including fish oil rich in eicosapentaenoic acid (EPA, 20:5, n-3) and docosahexaenoic acid (DHA, 22:6, n-3). A 43% increase in spleen weight, about twice as many spleen cells and no change in the subpopulations of spleen cells, as well as a significant depression of mitogen-induced blastogenesis of both T and B cells in the spleen were observed in mice fed fish oil for 30 days in comparison with soybean oil diet-fed mice. In the fish oil diet-fed mice, membranous lipid hydroperoxide (hydroperoxides of phosphatidylcholine and phosphatidylethanolamine) accumulation as a marker of oxidative senescence in red blood cells (RBC) was 2.7-3.5 times higher than that in mice fed soybean oil, although there was no difference in the plasma phosphatidylcholine hydroperoxide concentration. In spite of the supplementation of alpha-tocopherol to up to 10 times the level in the basal diet, the degeneration of spleen cells and the stimulated oxidative senescence of RBC found by the fish oil feeding could not be prevented. The results suggest that oral intake of excess polyunsaturated fatty acids, i.e. EPA and DHA, in a fish oil diet can lead to acceleration of membrane lipid peroxidation resulting in RBC senescence linked to the lowering of immune response of spleen cells, and that supplementation of alpha-tocopherol as antioxidant does not always effectively prevent such oxidative degeneration as observed in spleen cells and RBC in vivo.