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

Antioxidant role of selenium against maneb-induced cardiotoxicity in mice

The current study was conducted to assess the beneficial effect of selenium (Se) on maneb-induced cardiotoxicity and fatty acid alterations in adult mice. Swiss albino male mice were assigned into four experimental groups. The first group consisted of negative controls. The second group represented the positive controls where mice received daily, via the diet, sodium selenite at a dose of 0.2 mg/kg. For the third group, mice were subjected to intraperitoneal injections of maneb (30 mg/kg BW). The fourth group (MB+Se) received daily the same dose of maneb as group 3 along with sodium selenite at the same dose as group 2. Mice exposure to maneb caused cardiotoxicity as indicated by an increase in malondialdehyde, hydrogen peroxide, and protein carbonyl levels, and an alteration of the antioxidant defense system (catalase, glutathione peroxidase, superoxide dismutase, glutathione, and vitamin C). Plasma lactate dehydrogenase activity and total cholesterol, triglyceride, and low-density lipoprotein cholesterol levels increased, while high-density lipoprotein cholesterol level decreased. Results showed also a decrease in the amount of n-3 PUFA, docosahexaenoic, docosapentaenoic, and eicosapentaenoic acids. However, an increase in the levels of MUFA, cis-vaccenic, and palmitoleic acids was observed. Co-administration of Se restored the parameters indicated above to near control values. The histopathological findings confirmed the biochemical results. Selenium could be a useful and efficient agent against maneb-induced cardiotoxicity.

Comparative Effects of the Fat Extracted from Raw and Fried Sardines Upon Rat Growth and Zinc Bioavailability

Three diets containing 8% olive oil, fresh sardine (Clupea pilchardus) oil and oil from sardines fried in olive oil were prepared. After in vitro digestion, soluble (dialysed and non-dialysed) and insoluble zinc fractions were determined. Fresh sardine oil and oil from sardines fried in olive oil provided more dialysed zinc and less insoluble zinc than 8% olive oil. Three groups of growing rats consumed the diets for 28 days. Food intake and body weight values of rats fed 8% olive oil were significantly higher than those fed fresh sardine oil and slightly lower than those fed oil from sardines fried in olive oil. Animals fed fresh sardine oil exhibited the lowest apparent zinc retention during days 5-12, but absorption efficiency increased during days 21-28 and all groups had similar final zinc absorption and retention values. Animals fed oil from sardines fried in olive oil displayed higher (days 5-12) or similar (days 21-28) apparent zinc absorption and retention values than rats fed 8% olive oil and fresh sardine oil. Hepatic zinc concentrations were higher in rats fed oil from sardines fried in olive oil than fed fresh sardine oil, while all groups showed similar spleenic concentrations. Zinc accumulation in skin was significantly higher in animals fed fresh sardine oil than in those fed oil from sardines fried in olive oil, and their total erythrocyte zinc concentrations were also higher than in rats fed oil from sardines fried in olive oil or on 8% olive oil. In conclusion, a diet high in raw sardine fatty acids can cause excessive zinc accumulation in skin and erythrocytes. However, these negative effects of sardine oil disappear after frying in olive oil.

Dietary methods and biomarkers of omega 3 fatty acids: a systematic review

The aims of the present study were to review the validity of dietary methods used to measure the usual long chain (LC) omega-3 polyunsaturated fatty acid (n-3 PUFA) intake of a population and to assess the usefulness of different biomarkers of n-3 PUFA in healthy humans. Two systematic literature searches were conducted until May 2011 to update previous systematic reviews. The first literature search aimed to find studies validating the methodology used for measuring the dietary intake of n-3 PUFA. The second search aimed to find human intervention studies in which n-3 PUFA status changed after 2 weeks of n-3 PUFA supplementation. Sixteen studies were identified for inclusion in the first review. Correlation coefficients between fatty acids in subcutaneous fat or blood lipids and dietary intake of n-3 PUFA from different questionnaires were similar. Subcutaneous fat has been reported as the best reference method for some authors, and these studies showed moderate correlation coefficients with no dietary intake method being superior to any other. As for the evaluation of biomarkers of docosahexaenoic acid (DHA, 22 : 6 n-3) and eicosapentaenoic acid (EPA, 20 : 5n-3) status in response to supplementation, the new search reaffirmed and reinforced the evidence supporting that plasma phospholipid DHA, erythrocyte DHA, and platelet DHA were all effective and robust biomarkers of DHA status. Our findings only confirmed earlier studies and did not provide evidence for reaching new conclusions.

Methods of assessment of n-3 long-chain polyunsaturated fatty acid status in humans: a systematic review

BACKGROUND

The availability of reliable biomarkers of n-3 (omega-3) long-chain polyunsaturated fatty acid (LCPUFA) status is a prerequisite for linking dietary n-3 LCPUFA status to clinical outcomes.

OBJECTIVE

The objective of this meta-analysis was to assess the usefulness of different biomarkers of n-3 LCPUFA status in healthy humans.

DESIGN

We searched Ovid MEDLINE, EMBASE (Ovid), and Cochrane databases from inception to September 2007 for human intervention studies in which n-3 LCPUFA status changed after > or =2 wk of n-3 LCPUFA supplementation. We used formal inclusion/exclusion criteria and applied standard procedures for data extraction, validity assessment, and meta-analysis.

RESULTS

We included 41 studies (34 randomized controlled trials and 7 before-after studies) reporting on 18 different biomarkers. The data allowed specific evaluation of biomarkers of docosahexaenoic acid (DHA, 22:6n-3) and eicosapentaenoic acid (EPA, 20:5n-3) status in response to supplementation. There were sufficient data to determine that plasma DHA, plasma phospholipid DHA, plasma triacylglycerol DHA, plasma cholesteryl ester DHA, plasma nonesterified DHA, erythrocyte DHA, erythrocyte phospholipid DHA, and platelet DHA were all effective biomarkers of DHA status and that plasma phospholipid EPA was an effective marker of EPA status. Plasma phospholipid DHA appears to be a good marker of DHA status in adult men and women irrespective of DHA baseline status or supplementation dose, but its usefulness in other population subgroups is unclear.

CONCLUSION

There appears to be a range of useful biomarkers of DHA status in humans, but further research is needed to characterize which work best in particular population subgroups.

Elevated concentrations of linoleic acid in erythrocyte membrane phospholipids in patients with inflammatory bowel disease

Inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn disease (CD), is a disorder characterized by diffuse inflammation of the gastrointestinal tract. The immune response and inflammation are mediated by polyunsaturated fatty acids and influenced by dietary fats and lipid metabolism. This study examined the qualitative and quantitative fat intake of IBD patients and healthy controls on plasma phospholipid and erythrocyte membrane phospholipid (EMP) fatty acid content. Measurement of the fatty acid composition of plasma phospholipid and EMP were performed in 29 UC patients, 20 CD patients, and 31 healthy controls. Anthropometric characteristics and data on dietary intake were also collected. We observed significantly lower lipid intake in UC and CD patients vs controls. The UC and CD patients had significantly higher levels of linoleic acid in their EMP than did controls. There were no significant differences in the levels of n-3 polyunsaturated fatty acids, but there were significantly higher levels of the n-6 in the EMP of UC and CD patients compared with controls. The significant differences persisted after the data were adjusted for potential confounders and lipid intake. Higher levels of linoleic acids and n-6 fatty acids, which are involved in production of proinflammatory mediators, were found in IBD patients compared with controls, thereby implicating n-6 fatty acids in the pathophysiology of the disease.

Effects of storage time and added antioxidant on fatty acid composition of red blood cells at -20 degrees C

The stability of PUFA in venous red blood cells (RBC) of women aged 25 to 55 years (n = 12) was investigated during storage at -20 degrees C. The RBC sample from each participant was divided into seven portions: one baseline with the antioxidant BHT, another without BHT, samples without BHT stored for 2, 4, 9, or 17 wk, and samples with BHT stored for 17 wk. No difference was found in proportions of PUFA at baseline and after storage for 2 and 4 wk without BHT, and 17 wk with BHT. After 9 wk without BHT the proportion of 22:6n-3 in RBC was lower, and after 17 wk without BHT proportions of all PUFA were lower than at baseline. High proportion of 22:6n-3 in RBC at baseline was associated with more stable concentration of total FA in RBC without BHT during 17 wk. The findings indicate that PUFA in RBC from healthy women are stable at -20 degrees C for 4 wk without BHT and for at least 17 wk with BHT.

Formation of Nepsilon-(succinyl)lysine in vivo: a novel marker for docosahexaenoic acid-derived protein modification

Free radical-catalyzed peroxidation of docosahexaenoic acid (DHA, C22:6/omega-3) generates various lipid peroxidation products that covalently modify biomolecules such as proteins. Under a free radical-generating system, DHA significantly modified lysine residues in bovine serum albumin. Upon incubation of oxidized DHA with an amino-compound pyridoxamine or a lysine-containing peptide, N-propanoyl and N-succinyl adducts were determined to be the major modification products. The hydroperoxide levels in the oxidized DHA closely reflected the formation of the N(epsilon)-(succinyl)lysine (SUL) upon reaction with the peptide, indicating that the hydroperoxides of DHA represent a potential pathway for the formation of SUL. To detect the DHA-derived protein modification in vivo, we developed a monoclonal antibody (mAb2B12) specific to SUL and found that the antibody specifically reacts with the SUL moiety. The formation of SUL was then immunochemically demonstrated in the liver of mice fed with DHA followed by intraperitoneal injection of carbon tetrachloride (CCl(4)), a hepatic lipid peroxidation model. Immunoreactive materials with mAb2B12 were observed in the DHA + CCl(4) group, but were not significant in the control, DHA-alone, and CCl(4)-alone groups. These data suggest that the formation of DHA-derived adducts such as SUL may be implicated in the oxidative damage observed in DHA-enriched tissues.

Effects of combined dietary supplementation on oxidative and inflammatory status in dyslipidemic subjects

BACKGROUND AND AIM

Dyslipidemia is one of the main risk factors for atherosclerosis, usually the underlying cause of cardiovascular diseases which are the major cause of morbidity and mortality in developed countries. The aim of this study was to assess the effects and the advantages of a combined dietary supplementation with PUFA n-3, vitamin E, niacin and gamma-oryzanol on lipid profile, inflammatory status and oxidative balance.

METHODS AND RESULTS

Fifty-seven dyslipidemic volunteers were randomly assigned to receive: placebo (group A, 19 subjects); PUFA n-3 and vitamin E (group B, 18 subjects); the same as B plus gamma-oryzanol and niacin (group C, 20 subjects). Lipid profile, reactive oxygen species (ROS), total antioxidant capacity (TAC), vitamin E, interleukin 1-beta (IL1-beta), tumor necrosis factor (TNF-alpha) and thromboxane B2 (TXB2) were determined at baseline (T0) and after four months (T1). All dyslipidemic subjects showed, at baseline, oxidative stress and, after four months, all biochemical markers improved significantly in groups treated with dietary supplementation. Particularly in group C all lipid patterns improved significantly.

CONCLUSIONS

Our findings demonstrate that the strategy of combining different compounds, which protect each other and act together at different levels of the lipid chain production, improves lipid profile, inflammatory and oxidative status, allowing us to reduce the dose of each compound under the threshold of its side effects.

Subchronic (13-week) oral toxicity study, preceded by an in utero exposure phase, with arachidonate-enriched triglyceride oil (SUNTGA40S) in rats

Polyunsaturated fatty acids (PUFAs), such as arachidonic acid (ARA) and docosahexaenoic acid (DHA) are natural constituents found in human milk, fish oil or egg yolk. Until recently, infant formulas, though providing the essential fatty acid precursors for these PUFAs, did not contain preformed ARA or DHA. In this study the safety of SUNTGA40S as source of ARA, not only for use in infant formulas but also for nutritional products or food supplements, was evaluated in a subchronic study in Wistar rats, preceded by a 4-week pretreatment period of parental (F(0)) rats and exposure of the F(0) dams throughout mating, gestation and lactation. SUNTGA40S was administered at dietary levels of 0.5%, 1.5% and 5% (wt/wt) adjusted with corn oil to 5.76% added fat. An additional group received 3.65% (wt/wt) SUNTGA40S in conjunction with 2.11% (wt/wt) high DHA Tuna oil, providing an ARA:DHA ratio of 2.7:1. High-fat and low-fat controls received basal diet with or without 5.76% corn-oil supplement. The content, stability and homogeneous distribution of the test substances in the diet were confirmed under study conditions. The administration of SUNTGA40S, with or without DHA oil, did not affect health, growth, fertility or reproductive performance of the parental rats, nor pup characteristics (condition, weight gain, viability, number per litter or sex ratio). In the subchronic study with the offspring (F(1)) rats, no significant differences were found in condition, neurobehavioural observations, ophthalmoscopy, growth, urinalysis or macroscopic and microscopic findings between the test groups and the low-fat or the high-fat controls. In males of the 5% SUNTGA40S and the SUNTGA40S/DHA group, red blood cell counts, haemoglobin concentration and packed cell volume were lower and reticulocytes were slightly higher than in the high-fat and low-fat control groups. Cholesterol, triglycerides and phospholipids in plasma were lower than in the high-fat controls in both sexes in the 5% SUNTGA40S and the SUNTGA40S/DHA group and (for triglycerides only) in the 1.5% SUNTGA group. Due to the administration of extra dietary fat, food intake and prothrombin time (males only) were lower and alkaline phosphatase activity was higher in all the high-fat groups, including the corn-oil controls, as compared to the low-fat controls. The weight of the spleen was higher in males of the 5% SUNTGA40S and the SUNTGA40S/DHA group compared to both the low-fat and the high-fat controls. The effects noted in this study at high dose levels of SUNTGA40S are consistent with previously reported physiological responses to dietary intake of high PUFA containing oils. The present results provide evidence that SUNTGA40S is a safe source of arachidonic acid. Except during lactation when the intake in dams doubled, 5% Suntga40S in the diet was equivalent to an overall intake of approximately 3g/kg body weight/day in F(0) and F(1) animals.

The impact of age, body mass index, and fish intake on the EPA and DHA content of human erythrocytes

n-3 FA are beneficial for cardiovascular health, reducing platelet aggregation, TG levels, and the risk of sudden death from myocardial infarction. The percentage of EPA + DHA in red blood cells (RBC), also known as the Omega-3 Index, has recently been proposed as a risk marker for death from coronary heart disease (CHD). The purpose of this study was to begin to explore the factors that can influence RBC EPA + DHA. We collected information on the number of servings of tuna or nonfried fish consumed per month, as well as on age, gender, ethnicity, smoking status, the presence of diabetes, and body mass index (BMI) in 163 adults in Kansas City who were not taking fish oil supplements. The average RBC EPA + DHA in this population was 4.9 +/- 2.1%. On a multivariate analysis, four factors significantly and independently influenced the Omega-3 Index: fish servings, age, BMI, and diabetes. The Index increased by 0.24 units with each additional monthly serving of tuna or nonfried fish (P < 0.0001), and by 0.5 units for each additional decade in age (P < 0.0001). The Index was 1.13% units lower in subjects with diabetes (P = 0.015) and decreased by 0.3% units with each 3-unit increase in BMI (P = 0.001). Gender or smoking status had no effect, and the univariate relationship with ethnicity vanished after controlling for fish intake. Given the importance of n-3 FA in influencing risk for death from CHD, further studies are warranted to delineate the nondietary factors that influence RBC EPA + DHA content.

Plasma and erythrocyte phospholipid fatty acids composition in Serbian hemodialyzed patients

Dyslipidemia is one of the possible risk factors for advanced atherosclerosis in patients with chronic renal failure. Abnormal phospholipid metabolism may play an important role in the progression of atherosclerosis in patients with renal failure. The aim of this study was to determine specific characteristics of plasma and erythrocyte phospholipid content and fatty acid composition in 37 patients with chronic renal failure on hemodialysis (HD). The results were compared with the characteristics of healthy subjects. Briefly, plasma triglyceride (p < 0.001), total cholesterol (p < 0.05), and total phospholipids (p < 0.01) levels were significantly higher and HDL-cholesterol level significantly lower (p < 0.01) in HD patients. Plasma phosphatidylcholine and phosphatidylethanolamine concentration were significantly higher (p < 0.001) in HD patients. The plasma phospholipid fatty acids composition indicated significantly (p < 0.01) higher level of oleic (18:1 n-9) and lower levels of eicopentaenoic (20:5 n-3 EPA) and docosahexaenoic (22:6 n-3 DHA) acids (p < 0.05). However, in HD patients, the relative concentration of plasma phospholipid n-6 polyunsaturated fatty acid (PUFA) was significantly lower (p < 0.05). The fatty acid composition of erythrocyte phospholipid in HD patients was modified with EPA and DHA levels significantly lowered (p < 0.05). Our results demonstrate an abnormal phospholipid metabolism and deficiency of n-3 PUFA in plasma and erythrocyte phospholipids in hemodialyzed patients.

Structural and oxidative modifications of erythrocyte ghosts in patients with primary biliary cirrhosis: relation with the disease stage and effect of bile acid treatment

BACKGROUND

Erythrocyte membrane modifications in patients with cholestasis are supposed to reflect those of hepatocytes.

METHODS

Erythrocyte membrane composition (cholesterol, phospholipids, fatty acids, protein sulphydrils and carbonyls) was assessed and related to the stage of liver disease in patients with primary biliary cirrhosis before and after 1 year of ursodeoxycholate treatment.

RESULTS

Compared with controls, patients showed lower levels of protein sulphydrils (28.9 +/- 7.1 vs. 65.6 +/- 1.8 nmol mg(-1) prot) and accumulation of carbonyls (4.7 +/- 1.7 vs. 1.4 +/- 0.1 nmol mg(-1) prot). Phosphatidylethanolamine level was lower in stage III-IV cirrhosis while phosphatidylcholine and cholesterol levels were higher; as a consequence the phosphatidylcholine/sphingomyelin ratio was higher than in controls (4.25 +/- 0.55 in the I-II stage and 2.89 +/- 0.44 in the stage III-IV vs. 1.61 +/- 0.30). These changes were particularly evident in patients with more advanced stages of liver disease. Protein sulphydrils and carbonyls, phosphatidylethanolamine and cholesterol levels correlated (P<0.05) with the histological stage of the liver disease, serum and membrane cholesterol levels were significantly related (r=0.66, P<0.05). One year of ursodeoxycholate administration was accompanied by major changes of the membrane lipid composition, partial reversal of protein oxidation, and improvement of serum parameters.

CONCLUSIONS

This study indicates that major alterations in protein status and lipid composition occur in erythrocyte membrane of patients with primary biliary cirrhosis. These changes were more pronounced in patients with advanced liver disease. Ursodeoxycholate was able to revert in part serum and erythrocyte alterations, especially in patients with early stages of liver disease.

Moderate intake of n-3 fatty acids is associated with stable erythrocyte resistance to oxidative stress in hypertriglyceridemic subjects

BACKGROUND

The important triacylglycerol-lowering capacity of n-3 fatty acids is counterbalanced by their inherent sensitivity to oxidation. Inconsistent results about the latter have been reported in hypertriglyceridemic individuals. After incorporation into cell membranes, n-3 fatty acids may alter membrane-related functions. In view of the distinct composition of hypertriglyceridemic membranes and the prooxidant status in this condition, it can be surmised that cell enrichment with the oxidizable n-3 fatty acids will be associated with an increased hemolytic process.

OBJECTIVE

We sought to evaluate the effect of fish oil consumption on n-3 fatty acid incorporation into erythrocyte membranes and subsequent ex vivo oxidative-stress-induced hemolysis in normotriglyceridemic and hypertriglyceridemic subjects.

DESIGN

Sixteen normotriglyceridemic and 12 hypertriglyceridemic subjects were given 6 g fish oil/d for 8 wk. Blood samples were collected before and 4 and 8 wk after treatment. Resistance to 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced hemolysis was assayed in fresh erythrocyte suspensions, and erythrocyte samples were stored at -70 degrees C for later analysis of cholesterol, hemoglobin, fatty acids, vitamin E, and glutathione peroxidase activity.

RESULTS

Fish oil supplementation induced n-3 fatty acid incorporation in normotriglyceridemic and hypertriglyceridemic erythrocyte membranes without decreasing their resistance to AAPH. n-3 Fatty acids significantly protected normotriglyceridemic but not hypertriglyceridemic erythrocytes against hemolysis. In normotriglyceridemic subjects only, the higher resistance to hemolysis correlated with changes in cell vitamin E.

CONCLUSION

Although they exhibit a high susceptibility to oxidation, n-3 fatty acids may preserve membrane integrity and represent an added benefit in the treatment of hypertriglyceridemic patients.

Docosahexaenoic acid supplementation-increased oxidative damage in bone marrow DNA in aged rats and its relation to antioxidant vitamins

We compared the influence of docosahexaenoic acid (DHA) supplementation on oxidative DNA damage in bone marrow between young and aged rats. As a marker of oxidative DNA damage, 8-hydroxydeoxyguanosine (8-OHdG) in DNA was analyzed. Young (5-week-old) and aged (100-week-old) female Wistar rats were given DHA (300mg/kg body weight/day) or vehicle (control) orally for 12 weeks. The 8-OHdG in the bone marrow in the aged DHA group was significantly higher than that in the other groups. Vitamin E concentrations, however, did not differ among the groups regardless of the DHA supplementation. Vitamin C (ascorbic acid) concentrations in the aged control group were approximately 1/2 those in the young control group. The concentrations of vitamin C tended to be higher in the young DHA group and lower in the aged DHA group when compared to their respective control groups. Changes in the concentrations of vitamin C and vitamin E in plasma were similar to those in the bone marrow. The activity of hepatic l-gulono- gamma -lactone oxidase, an enzyme responsible for vitamin C synthesis, corresponded well to the concentrations of vitamin C in the bone marrow and the plasma. These results suggest that in aged rats, but not young rats, excess supplementation of DHA induces oxidative DNA damage in bone marrow and that the decrease in vitamin C synthesis in aged rats is involved in the mechanisms of DNA damage.

Fish oil diet affects on oxidative senescence of red blood cells linked to degeneration of spleen cells in mice

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.

Low-dose eicosapentaenoic or docosahexaenoic acid administration modifies fatty acid composition and does not affect susceptibility to oxidative stress in rat erythrocytes and tissues

In view of the promising future for use of n-3 polyunsaturated fatty acids (PUFA) in the prevention of cancer and cardiovascular diseases, it is necessary to ensure that their consumption does not result in detrimental oxidative effects. The aim of the present work was to test a hypothesis that low doses of eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) do not induce harmful modifications of oxidative cell metabolism, as modifications of membrane fatty acid composition occur. Wistar rats received by gavage oleic acid, EPA, or DHA (360 mg/kg body weight/day) for a period of 1 or 4 wk. Fatty acid composition and alpha-tocopherol content were determined for plasma, red blood cell (RBC) membranes, and liver, kidney, lung, and heart microsomal membranes. Susceptibility to oxidative stress induced by tert-butylhydroperoxide was measured in RBC. EPA treatment increased EPA and docosapentaenoic acid (DPA) content in plasma and in all the membranes studied. DHA treatment mainly increased DHA content. Both treatments decreased arachidonic acid content and n-6/n-3 PUFA ratio in the membranes, without modifying the Unsaturation Index. No changes in tissue alpha-tocopherol content and in RBC susceptibility to oxidative stress were induced by either EPA or DHA treatment. The data suggest that EPA and DHA treatments can substantially modify membrane fatty acids, without increasing susceptibility to oxidative stress, when administered at low doses. This opens the possibility for use of low doses of n-3 PUFA for chemoprevention without risk of detrimental secondary effects.

Copper toxicity towards Saccharomyces cerevisiae: dependence on plasma membrane fatty acid composition

One major mechanism of copper toxicity towards microorganisms is disruption of plasma membrane integrity. In this study, the influence of plasma membrane fatty acid composition on the susceptibility of Saccharomyces cerevisiae to Cu2+ toxicity was investigated. Microbial fatty acid composition is highly variable, depending on both intrinsic and environmental factors. Manipulation was achieved in this study by growth in fatty acid-supplemented medium. Whereas cells grown under standard conditions contained only saturated and monounsaturated fatty acids, considerable incorporation of the diunsaturated fatty acid linoleate (18:2) (to more than 65% of the total fatty acids) was observed in both whole-cell homogenates and plasma membrane-enriched fractions from cells grown in linoleate-supplemented medium. Linoleate enrichment had no discernible effect on the growth of S. cerevisiae. However, linoleate-enriched cells were markedly more susceptible to copper-induced plasma membrane permeabilization. Thus, after addition of Cu(NO3)2, rates of cellular K+ release (loss of membrane integrity) were at least twofold higher from linoleate-supplemented cells than from unsupplemented cells; this difference increased with reductions in the Cu2+ concentration supplied. Levels of cellular Cu accumulation were also higher in linoleate-supplemented cells. These results were correlated with a very marked dependence of whole-cell Cu2+ toxicity on cellular fatty acid unsaturation. For example, within 10 min of exposure to 5 microM Cu2+, only 3% of linoleate-enriched cells remained viable (capable of colony formation). In contrast, 100% viability was maintained in cells previously grown in the absence of a fatty acid supplement. Cells displaying intermediate levels of linoleate incorporation showed intermediate Cu2+ sensitivity, while cells enriched with the triunsaturated fatty acid linolenate (18:3) were most sensitive to Cu2+. These results demonstrate for the first time that changes in cellular and plasma membrane fatty acid compositions can dramatically alter microbial sensitivity to copper.