Linoleic acid and linolenic acid: effect on permeability properties of cultured endothelial cell monolayers

High circulating plasma levels of free fatty acids may injure endothelial cells, resulting in decreased barrier function of the vascular endothelium. The effect of media supplementation with varying concentrations of either linoleic (C18:2 omega 6) or linolenic acid (C18:3 omega 3) on albumin transfer across cultured endothelial monolayers was studied. A 24-h cell exposure to linoleic but not linolenic acid resulted in a concentration dependent and largely reversible increase in albumin transfer. Both fatty acids and in particular linolenic acid incorporated into cellular phospholipids. In contrast, only supplementation with linoleic but not linolenic acid resulted in an increased incorporation of this fatty acid into cell triglycerides. Similarly, only total cell triglyceride content increased after incubation with linoleic- but not with linolenic-enriched media. These results indicate that cellular enrichment with linoleic but not linolenic acid causes cellular perturbations that may be implicated in atherosclerosis.     

Mechanisms of action of dietary fatty acids in regulating the activation of vascular endothelial cells during atherogenesis

Dietary long chain omega-3 polyunsaturated fatty acids from fish oil appear to be clearly efficient in regulating endothelial dysfunction (or activation), which is the first stage of atherogenesis. Studies on endothelial cells in vitro have shown that the main dietary PUFA and oleic acid may prevent endothelium activation either by inhibiting the expression of adhesion molecules or by improving the nitric oxide production. Saturated fatty acids and also linoleic acid do not inhibit endothelium activation. The mechanisms involved in this inhibition could be related to endothelial cell membrane characteristics or redox status. However, these findings need to be confirmed in vivo.     

Zinc protects against apoptosis of endothelial cells induced by linoleic acid and tumor necrosis factor alpha

BACKGROUND: Zinc requirements of the vascular endothelium may be increased in inflammatory conditions, ie, atherosclerosis, in which apoptotic cell death is prevalent. OBJECTIVE: We hypothesized that zinc deficiency may potentiate disruption of endothelial cell integrity mediated by fatty acids and inflammatory cytokines by enhancing pathways that lead to apoptosis and up-regulation of caspase genes. DESIGN: Endothelial cells were maintained in low-serum medium or grown in culture media containing selected chelators, ie, diethylenetriaminepentaacetate or N,N,N', N'-tetrakis(2-pyridylmethyl)-ethylenediamine (TPEN), with or without zinc supplementation. Subsequently, cells were treated with linoleic acid, tumor necrosis factor alpha (TNF-alpha), or both. We studied the effect of zinc deficiency and supplementation on the induction of apoptosis by measuring caspase-3 activity, cell binding of annexin V, and DNA fragmentation. RESULTS: Our results indicated that linoleic acid and TNF-alpha independently, but more markedly in concert, up-regulated caspase-3 activity and induced annexin V binding and DNA fragmentation. Zinc deficiency, especially when induced by TPEN, dramatically increased apoptotic cell death induced by cytokines and lipids compared with control cultures. Supplementation of low-serum- or chelator-treated endothelial cells with physiologic amounts of zinc caused a marked attenuation of apoptosis induced by linoleic acid and TNF-alpha. Morphologic changes of cells observed during zinc deficiency were prevented by zinc supplementation. Media supplementation with other divalent cations (eg, calcium and magnesium) did not mimic the protective role of zinc against apoptosis. CONCLUSIONS: Our data indicate that zinc is vital to vascular endothelial cell integrity, possibly by regulating signaling events to inhibit apoptotic cell death.     

Zinc nutrition and apoptosis of vascular endothelial cells: implications in atherosclerosis.

Little is known about the requirements and function of zinc in maintaining endothelial cell integrity, especially during stressful conditions, such as the inflammatory response in cardiovascular disease. There is evidence that zinc requirements of the vascular endothelium are increased during inflammatory conditions such as atherosclerosis, where apoptotic cell death is also prevalent. Apoptosis is a morphologically distinct mechanism of programmed cell death which involves the activation of a cell-intrinsic suicide program, and there is evidence that factors such as inflammatory cytokines (e.g., tumor necrosis factor [TNF]) and pure or oxidized lipids are necessary to induce the cell death pathway. Because of its constant exposure to blood components, including prooxidants, diet-derived fats, and their derivatives, the endothelium is very susceptible to oxidative stress and to apoptotic injury mediated by blood lipid components, prooxidants, and cytokines. Thus, it is likely that the cellular lipid environment, primarily polyunsaturated fatty acids, can potentiate the overall endothelial cell injury by increasing cellular oxidative stress and cytokine release in proximity to the endothelium, which then could further induce apoptosis and disrupt endothelial barrier function. Our data suggest that zinc deficiency exacerbates the detrimental effects of specific fatty acids (e.g., linoleic acid) and inflammatory cytokines, such as TNF, on vascular endothelial functions. We propose that a major mechanism of zinc protection against disruption of endothelial cell integrity during inflammatory conditions, is by the ability of zinc to inhibit the pathways of signal transduction leading to apoptosis and especially mechanisms that lead to upregulation of caspase genes.     

Conjugated linoleic acid isomers inhibit platelet-derived growth factor-induced NF-κB transactivation and collagen formation in human vascular smooth muscle cells

Background Atherosclerosis is characterized by extensive thickening of the arterial intima partially resulting from deposition of collagen by vascular smooth muscle cells (SMCs). Polyunsaturated fatty acids stimulate collagen formation through NF-κB activation. Aim of the study The present study aimed to explore the effect of conjugated linoleic acids (CLAs) which are known to inhibit NF-κB activation on collagen formation by SMCs. Methods Vascular SMCs were cultured with 50 μmol/l of CLA isomers (c9t11-CLA, t10c12-CLA) or linoleic acid (LA) and analysed for collagen formation and NF-κB p50 transactivation. Results Treatment with CLA isomers but not LA significantly reduced PDGF-stimulated [³H] proline incorporation into cell layer protein of SMCs without altering cell proliferation. Simultaneous treatment with the PPARγ inhibitor T0070907 abrogated this effect. Treatment of SMCs with c9t11-CLA and t10c12-CLA significantly reduced PDGF-induced NF-κB p50 activation. Conclusions CLA isomers inhibit PDGF-stimulated collagen production by vascular SMCs, which is considered to be a hallmark of atherosclerosis, in a PPARγ-dependent manner. Whether inhibition of the NF-κB-pathway is of significance for the reduction of collagen formation by CLA isomers needs further investigation.     

Effect of essential fatty acids on glucose-induced cytotoxicity to retinal vascular endothelial cells

ABSTRACT: BACKGROUND: Diabetic retinopathy is a major complication of dysregulated hyperglycemia. Retinal vascular endothelial cell dysfunction is an early event in the pathogenesis of diabetic retinopathy. Studies showed that hyperglycemia-induced excess proliferation of retinal vascular endothelial cells can be abrogated by docosahexaenoic acid (DHA, 22:6 omega-3) and eicosapentaenoic acid (EPA, 20:5 omega-3). The influence of dietary omega-3 PUFA on brain zinc metabolism has been previously implied. Zn2+ is essential for the activity of Delta6 desaturase as a co-factor that, in turn, converts essential fatty acids to their respective long chain metabolites. Whether essential fatty acids (EFAs) alpha-linolenic acid and linoleic acid have similar beneficial effect remains poorly understood. METHODS: RF/6A cells were treated with different concentrations of high glucose, alpha-linolenic acid and linoleic acid and Zn2+. The alterations in mitochondrial succinate dehydrogenase enzyme activity, cell membrane fluidity, reactive oxygen species generation, SOD enzyme and vascular endothelial growth factor (VEGF) secretion were evaluated. RESULTS: Studies showed that hyperglycemia-induced excess proliferation of retinal vascular endothelial cells can be abrogated by both linoleic acid (LA) and alpha-linolenic acid (ALA), while the saturated fatty acid, palmitic acid was ineffective. A dose-response study with ALA showed that the activity of the mitochondrial succinate dehydrogenase enzyme was suppressed at all concentrations of glucose tested to a significant degree. High glucose enhanced fluorescence polarization and microviscocity reverted to normal by treatment with Zn2+ and ALA. ALA was more potent that Zn2+. Increased level of high glucose caused slightly increased ROS generation that correlated with corresponding decrease in SOD activity. ALA suppressed ROS generation to a significant degree in a dose dependent fashion and raised SOD activity significantly. ALA suppressed high-glucose-induced VEGF secretion by RF/6A cells. CONCLUSIONS: These results suggest that EFAs such as ALA and LA may have beneficial action in the prevention of high glucose-induced cellular damage.     

Dietary linoleic acid modulates liver plasma membrane unsaturated fatty acid composition,phosphatidylcholine and cholesterol content,as well as glucagon stimulated adenylate cyclase activity

Male Sprague-Dawley rats were fed diets containing 20% (w/w) fat in which linoleic acid was substituted for saturated fatty acids. High or low levels of dietary linoleic acid were fed for 24 days. Liver plasma membranes were isolated for analysis of lipid composition and glucagon stimulated adenylate cyclase activity. Dietary saturated fatty acid content did not affect the saturated fatty acid composition of membrane phospholipids. Increase in dietary linoleic acid increased content of linoleic acid homologues in phosphatidylcholine. Diets low in linoleic acid increased total phosphatidylcholine and cholesterol levels in the plasma membrane, increasing glucagon stimulated and fluoride stimulated adenylate cyclase activity. These observations imply that change in glucagon stimulated adenylate cyclase activity resulted from transitions in membrane phospholipid content of linoleic acid and its homologous fatty acids or from associated changes in membrane phospholipid class content.     

Dietary studies of children from a biracial population: intakes of fat and fatty acids in 10- and 13-year olds

Dietary intakes of fat and fatty acids were examined in children randomly selected from a biracial community, Bogalusa, LA. Between two 10-yr-old groups examined 3 yr apart, temporal trends of 1) higher intakes of polyunsaturated fatty acids, linoleic and linolenic acids, and 2) lower intakes of animal fat, saturated fatty acids, and palmitic acid were documented. No racial differences were found, and the only difference between sexes was for myristic acid (boys greater than girls). Longitudinal comparisons of a cohort of 148 children examined at both 10 and 13 yr showed higher intakes over time of unsaturated fatty acids, polyunsaturated fatty acids, vegetable fat, oleic, linoleic, and linolenic acids, and lower intakes of cholesterol, saturated fatty acids, animal fat, and myristic acid. The percentage of energy intake from fat, saturated fatty acids and polyunsaturated fatty acids was quite similar to other reports of US children and adults. Few children's intakes of cholesterol, fat, and fatty acids were compatible with current recommendations for prudent diets. Patterns of dietary fat and fatty acid intake of Bogalusa children reflect reported food market trends of increased use of vegetable fats.     

Structured lipids improve fat absorption in normal and malabsorbing rats

The presence of medium-chain fatty acids in dietary fatty acid as well as the triacylglycerol structure may influence the absorption and lymphatic transport of fatty acids. We compared the lymphatic transport and recovery of fatty acids from four intragastrically administered fats based on rapeseed oil and decanoic acid in two rat models of normal absorption and malabsorption, respectively. The fats were: 1) a fat with a regiospecific structure, 2) a similar fat but with a random distribution of fatty acids in the triacylglycerol molecule, 3) a physical mixture of tridecanoin and rapeseed oil and 4) rapeseed oil as control. Lymph samples were collected for 24 h. Significantly higher recoveries were observed of total fatty acids, oleic acid, linoleic acid and linolenic acid from the specific oil in malabsorbing rats and of linoleic acid in normal rats fed specific oil compared with those fed rapeseed oil. Furthermore, the recoveries of oleic acid and linolenic acid from the specific oil in normal rats were higher than those from the other oils. In malabsorbing rats, the transport of all fats was approximately 90% less than that of normal rats. The present study demonstrates improved hydrolysis and absorption of the specific oil compared with the other oils examined both in rats with normal absorption and in rats with malabsorption.     

SYNTHESIS OF POLYUNSATURATED FATTY ACIDS IN VITRO

Dehydrogenation and chain elongation of linoleic acid (18:2w6) by rat liver microsomes in vitro was inhibited by linolenic acid (18:3w3) and oleic acid (18:1w9). These results support the hypothesis, based on nutritional experiments, of a competition among linoleic, linolenic, and oleic acids in the reactions leading to the synthesis of more highly unsaturated fatty acids.     

Relation between dietary linolenic acid and coronary artery disease in the National Heart, Lung, and Blood Institute Family Heart Study.

BACKGROUND: Epidemiologic studies suggest that a higher consumption of eicosapentaenoic acid and docosahexaenoic acid is associated with a reduced risk of cardiovascular disease. Studies in humans and animals also reported an inverse association between alpha-linolenic acid and cardiovascular disease morbidity and mortality. OBJECTIVE: We examined the relation between dietary linolenic acid and prevalent coronary artery disease (CAD). DESIGN: We studied 4584 participants with a mean (+/-SD) age of 52.1 +/- 13.7 y in the National Heart, Lung, and Blood Institute Family Heart Study in a cross-sectional design. Participants' diets were assessed with a semiquantitative food-frequency questionnaire. For each sex, we created age- and energy-adjusted quintiles of linolenic acid, and we used logistic regression to estimate prevalent odds ratios for CAD. RESULTS: From the lowest to the highest quintile of linolenic acid, the prevalence odds ratios of CAD were 1.0, 0.77, 0.61, 0.58, and 0.60 for the men (P for trend = 0.012) and 1.0, 0.57, 0.52, 0.30, and 0.42 for the women (P for trend = 0.014) after adjustment for age, linoleic acid, and anthropometric, lifestyle, and metabolic factors. Linoleic acid was also inversely related to the prevalence odds ratios of CAD in the multivariate model (0.60 and 0.61 in the second and third tertiles, respectively) after adjustment for linolenic acid. The combined effect of linoleic and linolenic acids was stronger than the individual effects of either fatty acid. CONCLUSIONS: A higher intake of either linolenic or linoleic acid was inversely related to the prevalence odds ratio of CAD. The 2 fatty acids had synergistic effects on the prevalence odds ratio of CAD.     

Adipose tissue fatty acid composition and its relations to diet and plasma lipid concentrations in hemodialysis patients

Adipose tissue fatty acid composition, serum lipid profile, and dietary intake of 37 patients on maintenance hemodialysis were studied. In August 1982, 1984, and 1986, analyses were carried out in 15 normotriglyceridemic (NTG) and 22 hypertriglyceridemic (HTG; type IV hyperlipidemia) patients. No correlations were found between dietary intake of polyunsaturated fatty acids (PUFAs), ratio of polyunsaturated to saturated fatty acids (P-S ratio), and carbohydrate content on the one hand and serum lipid concentrations on the other in the two groups. Adipose tissue linolenic acid correlated negatively with serum cholesterol in both groups. Strong correlations were found between dietary intake of PUFAs and adipose tissue linoleic acid content, between PUFAs and the double-bond index, between P-S ratio and adipose tissue linoleic acid content, and between P-S ratio and the double-bond index. No significant differences in dietary intake or adipose tissue fatty acid composition were observed between NTG and HTG patients. Thus, no evidence was found for exogenous dietary influences on serum lipid concentrations. The adipose tissue linoleic acid content did reflect the dietary intake of PUFAs.