Influence of an increased intake of linoleic acid on the incorporation of dietary (n-3) fatty acids in phospholipids and on prostanoid synthesis in rat tissues

Complexity of understanding the role of dietary and erythrocyte docosahexaenoic acid (DHA) on the cognitive performance of school-age children

Background

Early childhood is a period of rapid brain development, with increases in synapses rich in the omega-3 (ω-3) fatty acid, DHA (22:6ω-3) continuing well beyond infancy. Despite the importance of DHA to neural phospholipids, the requirement of dietary DHA for neurodevelopment remains unclear.

Objectives

The aim was to assess the dietary DHA and DHA status of young children, and determine the association with cognitive performance.

Methods

This was a cross-sectional study of healthy children (5-6 y), some of whom were enrolled in a follow-up of a clinical trial (NCT00620672). Dietary intake data (n = 285) were assessed with a food-frequency questionnaire (FFQ) and three 24-h recalls. Family characteristics were collected by questionnaire, and anthropometric data measured. Venous blood was collected, cognitive performance assessed using several age-appropriate tools including the Kaufman Assessment Battery for Children. The relation between dietary DHA, RBC DHA, and child neurodevelopment test scores was determined using Pearson's correlation or Spearman's rho, and quintiles of test scores compared by Mann-Whitney U test.

Results

Child DHA intakes were highly variable, with a stronger association between RBC DHA and DHA intake assessed by FFQ (rho = 0.383, P < 0.001) compared with one or three 24-h recalls. Observed ethnic differences in DHA intake status as well as neurodevelopmental test scores led to analysis of the association between DHA intake and status with neurodevelopment test scores for White children only (n = 190). Child RBC DHA status was associated with neurodevelopment test scores, including language (rho = 0.211, P = 0.009) and short-term memory (rho = 0.187, P = 0.019), but only short-term memory was associated with dietary DHA (rho = 0.221, P = 0.003).

Conclusions

Child RBC DHA but not dietary DHA was associated with multiple tests of cognitive performance. In addition, DHA intake was only moderately associated with RBC DHA, raising complex questions on the relation between diet, DHA transfer to membrane lipids, and neural function.

Omega-6 to omega-3 fatty acid ratio and higher-order cognitive functions in 7- to 9-y-olds: a cross-sectional study

BACKGROUND

Biochemical and behavioral evidence has suggested that the ratio of n-6 (omega-6) to n-3 (omega-3) could be an important predictor of executive function abilities in children.

OBJECTIVE

We determined the relation between the ratio of n-6 to n-3 and cognitive function in children. We hypothesized that children with lower ratios of n-6 to n-3 fatty acids would perform better on tests of planning and working memory.

DESIGN

Seventy 7- to 9-y-old children completed three 24-h diet recalls and a subset of the Cambridge Neuropsychological Test Assessment Battery. Parents provided information on their demographics and children's diet histories.

RESULTS

Mean n-3 and mean n-6 intakes were related to the mean time spent on each action taken in the planning problem. The ratio of n-6 to n-3 significantly predicted performance on the working memory and planning problems. There was a significant interaction between the ratio and fatty acid intake; when children had high ratios, a higher intake of n-3 fatty acids predicted a better performance on the planning task than when children had lower n-3 intakes. When children had low ratios, a lower intake of n-3 and lower intake of n-6 predicted better performance than when intakes were higher.

CONCLUSIONS

The relation between cognitive abilities and the ratio of n-6 to n-3 may be mediated by an enzymatic affinity for n-3 fatty acids. The ratio of n-6 to n-3 should be considered an important factor in the study of fatty acids and cognitive development. This trial was registered at clinicaltrials.gov as NCT01823419.

A randomized placebo-controlled study on high-dose oral algal docosahexaenoic acid supplementation in children with cystic fibrosis

Low plasma concentrations of docosahexaenoic acid (DHA) are reported in unsupplemented cystic fibrosis (CF) patients. Forty-one CF patients aged from 6 to 12 years were randomized to receive high-dose DHA (100 mg/kg/day in the first month and 1g per day thereafter through a 12-month supplementation) or placebo (germ oil). Primary outcome was percentage change in plasma AA:DHA ratio. Secondary outcomes were changes in the number of pulmonary exacerbations compared to previous year, lung function, BMI, skinfold thicknesses, and body composition assessed by DXA and in serum concentrations of C-reactive protein, cytokines and vitamin (α-tocopherol and retinol). Compared to the control group plasma AA:DHA ratio decreased in the intervention group after 6 months (median percentage changes: -73% in the intervention group vs. -10% in the control group, P=0.001). No differences were detected between groups for secondary outcomes. Despite a decrease of the AA/DHA ratio, DHA supplementation for one year did not induce any significant biochemical and clinical improvement in CF patients.

Low linoleic acid may facilitate Δ6 desaturase activity and docosahexaenoic acid accretion in human fetal development

The n-3 and n-6 fatty acids are transferred across the placenta with consistently higher 22:6n-3 and lower 18:2n-6 in fetal than maternal plasma. This study sought to determine whether maternal and fetal cord blood red blood cell (RBC) phospholipid fatty acids show similar saturation with 22:6n-3, and also addressed the relationship between 18:2n-6 and Δ6 desaturase product/precursor ratios for 97 mothers and newborns. Despite higher fetal than maternal plasma phospholipid 22:6n-3, the maternal and fetal RBC phospholipid 22:6n-3 showed similar curvilinear relationships to the plasma phospholipid 22:6n-3. Risk of failure to achieve high RBC phospholipid 22:6n-3 increased sharply below a plasma phospholipid 22:6n-3 of 6.5g/100g fatty acids. Higher maternal and fetal 18:2n-6 was associated with lower RBC phospholipid 22:6n-3/22:5n-3, 22:5n-6/22:4n-6 and 18:3n-6/18:2n-6. These findings suggest low placental transfer of 18:2n-6 may be a specific mechanism to prevent inhibition of fetal Δ6 desaturase and facilitate fetal cellular phospholipid 22:6n-3 accretion.

Erythrocyte fatty acids and prostate cancer risk: a comparison of methods

The role of fatty acids (FA) in prostate carcinogenesis is unclear. Interest in the inter-relationship among different types of FA has resulted in new analytic approaches to FA and their role in cancer development. We evaluated the association between erythrocyte FA and prostate cancer in 127 prostate cancer patients and 183 screen negative controls. We present three approaches to the analyses of the FA and prostate cancer association; (1) individual or common groups of FA, (2) biologically meaningful FA ratios and (3) principal components analysis. Monounsaturated FA and the alpha-linolenic:eicosapentaenoic ratio were associated with reduced risk of prostate cancer. However, Factor 1, which was strongly correlated with some long chain saturated FA, was associated with an increased risk of prostate cancer. We provide an example of modeling FA and their inter-relationships on the risk of prostate cancer. Comparing three approaches suggests the importance of considering the impact of the entire fatty acid profile in disease prevention.

Gene and protein expression profiling of the fat-1 mouse brain

Polyunsaturated fatty acids (PUFAs) are essential structural components of all cell membranes and, more so, of the central nervous system. Several studies revealed that n-3 PUFAs possess anti-inflammatory actions and are useful in the treatment of dyslipidemia. These actions explain the beneficial actions of n-3 PUFAs in the management of cardiovascular diseases, inflammatory conditions, neuronal dysfunction, and cancer. But, the exact molecular targets of these beneficial actions of n-3 PUFAs are not known. Mice engineered to carry a fat-1 gene from Caenorhabditis elegans add a double bond into an unsaturated fatty acid hydrocarbon chain and convert n-6 to n-3 fatty acids. This results in an abundance of n-3 eicosapentaenoic acid and docosapentaenoic acid specifically in the brain and a reduction in n-6 fatty acids of these mice that can be used to evaluate the actions of n-3 PUFAs. Gene expression profile, RT-PCR and protein microarray studies in the hippocampus and whole brain of wild-type and fat-1 transgenic mice revealed that genes and proteins concerned with inflammation, apoptosis, neurotransmission, and neuronal growth and synapse formation are specifically modulated in fat-1 mice. These results may explain as to why n-3 PUFAs are of benefit in the prevention and treatment of diseases such as Alzheimer's disease, schizophrenia and other diseases associated with neuronal dysfunction, low-grade systemic inflammatory conditions, and bronchial asthma. Based on these data, it is evident that n-3 PUFAs act to modulate specific genes and formation of their protein products and thus, bring about their various beneficial actions.

The effects of fish oil and high or low linoleic acid intake on fatty acid composition of human peripheral blood mononuclear cells

Dietary intake of 18: 2n-6 and 18: 3n-3 may affect endogenous production and incorporation of n-3 long-chain PUFA (LCPUFA) from fish oils (FO). This double-blinded controlled 2 x 2-factorial 8-week intervention investigates the effects of high and low 18: 2n-6 intake in combination with FO-supplementation on tissue fatty acid composition. Healthy young men (n 64) were randomized to capsules with FO or olive oil (control) (4.4 (2.0-5.6) ml/d) and to either sunflower oil and margarine (S/B) or rapeseed oil and a butter spread (R/K) to provide a high or a low 18: 2n-6 intake. Diet was measured by 4-d weighed dietary records at baseline, during and 8 weeks after the intervention and tissue incorporation as fatty acid composition of peripheral blood mononuclear cells (PBMC). The fat intervention gave a mean difference in the 18: 2n-6 intake of 7.3 g/d (95 % CI 4.6, 10.0) and a similar 18: 3n-3 intake in the groups. The R/K groups had a 0.2 % fatty acid (FA%) (95 % CI 0.0, 0.4, P = 0.02) higher content of 22: 5n-3 in the PBMC, a tendency of slightly higher 20: 5n-3 (P = 0.06), but no more 22: 6n-3 (P = 0.83) than the S/B groups. FO effectively raised the PBMC content of all n-3 LCPUFA (P < 0.001). The fat intervention did not markedly influence the effect of FO; the mean PBMC content of n-3 LCPUFA was 10.3 (sem 0.3) FA% in the FO+S/B group and 10.6 (sem 0.2) FA% in the FO+R/K group. In conclusion, increasing the 18: 2n-6 intake did not have any pronounced effect on incorporation of n-3 LCPUFA in PBMC, either alone or with simultaneous FO supplementation.

Prostaglandin synthesis in rat brain astrocytes is under the control of the n-3 docosahexaenoic acid, released by group VIB calcium-independent phospholipase A2

In the current study, we reveal that in astrocytes the VIB Ca(2+)-independent phospholipase A(2) is the enzyme responsible for the release of docosahexaenoic acid (22:6n-3). After pharmacological inhibition and siRNA silencing of VIB Ca(2+)-independent phospholipase A(2), docosahexaenoic acid release was strongly suppressed in astrocytes, which were acutely stimulated (30 min) with ATP and glutamate or after prolonged (6 h) stimulation with the endotoxin lipopolysaccharide. Docosahexaenoic acid release proceeds simultaneously with arachidonic acid (20:4n-6) release and prostaglandin liberation from astrocytes. We found that prostaglandin production is negatively controlled by endogenous docosahexaenoic acid, since pharmacological inhibition and siRNA silencing of VIB Ca(2+)-independent phospholipase A(2) significantly amplified the prostaglandin release by astrocytes stimulated with ATP, glutamate, and lipopolysaccharide. Addition of exogenous docosahexaenoic acid inhibited prostaglandin synthesis, which suggests that the negative control of prostaglandin synthesis observed here is likely due to competitive inhibition of cyclooxygenase-1/2 by free docosahexaenoic acid. Additionally, treatment of astrocytes with docosahexaenoic acid leads to the reduction in cyclooxygenase-1 expression, which also contributes to reduced prostaglandin production observed in lipopolysaccharide-stimulated cells. Thus, we identify a regulatory mechanism important for the brain, in which docosahexaenoic acid released from astrocytes by VIB Ca(2+)-independent phospholipase A(2) negatively controls prostaglandin production.

Decreasing linoleic acid with constant alpha-linolenic acid in dietary fats increases (n-3) eicosapentaenoic acid in plasma phospholipids in healthy men

High linoleic acid (LA) intakes have been suggested to reduce alpha-linolenic acid [ALA, 18:3(n-3)] metabolism to eicosapentaenoic acid [EPA, 20:5(n-3)] and docosahexaenoic acid [DHA, 22:6(n-3)], and favor high arachidonic acid [ARA, 20:4(n-6)]. We used a randomized cross-over study with men (n = 22) to compare the effect of replacing vegetable oils high in LA with oils low in LA in foods, while maintaining constant ALA, for 4 wk each, on plasma (n-3) fatty acids. Nonvegetable sources of fat, except fish and seafoods, were unrestricted. We determined plasma phospholipid fatty acids at wk 0, 2, 4, 6, and 8, and triglycerides, cholesterol, serum CRP, and IL-6, and platelet aggregation at wk 0, 4, and 8. LA and ALA intakes were 3.8 +/- 0.12% and 1.0 +/- 0.05%, and 10.5 +/- 0.53% and 1.1 +/- 0.06% energy with LA:ALA ratios of 4:0 and 10:1 during the low and high LA diets, respectively. The plasma phospholipid LA was higher and EPA was lower during the high than during the low LA diet period (P < 0.001), but DHA declined over the 8-wk period (r = -0.425, P < 0.001). The plasma phospholipid ARA:EPA ratios were (mean +/- SEM) 20.7 +/- 1.52 and 12.9 +/- 1.01 after 4 wk consuming the high or low LA diets, respectively (P < 0.001); LA was inversely associated with EPA (r = -0.729, P < 0.001) but positively associated with ARA:EPA (r = 0.432, P < 0.001). LA intake did not influence ALA, ARA, DPA, DHA, or total, LDL or HDL cholesterol, CRP or IL-6, or platelet aggregation. In conclusion, high LA intakes decrease plasma phospholipid EPA and increase the ARA:EPA ratio, but do not favor higher ARA.

α-Synuclein gene ablation increases docosahexaenoic acid incorporation and turnover in brain phospholipids

Previously, we demonstrated that ablation of alpha-synuclein (Snca) reduces arachidonate (20:4n-6) turnover in brain phospholipids through modulation of an endoplasmic reticulum-localized acyl-CoA synthetase (Acsl). The effect of Snca ablation on docosahexaenoic acid (22:6n-3) metabolism is unknown. In the present study, we examined the effect of Snca gene ablation on brain 22:6n-3 metabolism. We determined 22:6n-3 uptake and incorporation into brain phospholipids by infusing awake, wild-type and Snca-/- mice with [1-14C]22:6n-3 using steady-state kinetic modeling. In addition, because Snca modulates 20:4n-6-CoA formation, we assessed microsomal Acsl activity using 22:6n-3 as a substrate. Although Snca gene ablation does not affect brain 22:6n-3 uptake, brain 22:6n-3-CoA mass was elevated 1.5-fold in the absence of Snca. This is consistent with the 1.6- to 2.2-fold increase in the incorporation rate and turnover in ethanolamine glycerophospholipid, phosphatidylserine, and phosphatidylinositol pools. Increased 22:6n-3-CoA mass was not the result of altered Acsl activity, which was unaffected by the absence of Snca. While Snca bound 22:6n-3, Kd = 1.0 +/- 0.5 micromol/L, it did not bind 22:6n-3-CoA. These effects of Snca gene deletion on 22:6n-3 brain metabolism are opposite to what we reported previously for brain 20:4n-6 metabolism and are likely compensatory for the decreased 20:4n-6 metabolism in brains of Snca-/- mice.

Maize meal predisposes to endemic squamous cancer of the oesophagus in Africa: breakdown of esterified linoleic acid to the free form in stored meal leads to increased intragastric PGE2 production and a low-acid reflux

Endemic cancer of the oesophagus in Africa is associated with the use of maize as the staple. In one African community endemic cancer of the oesophagus has been shown to have a strong statistical association with the consumption of foods based on maize in the meal form. A strong association with consumption of maize meal has also been shown in a region of Italy. It has been argued in the past that the association with maize consumption is due to a fortuitous association; or due to the nutritional deficiencies of maize meal; or due to fungal contamination. We argue that maize meal is a distinctly different food from whole maize, and that nutritional content as much as deficiency is responsible for predisposition of the oesophagus to carcinogenesis. An important factor is the breakdown of esterified linoleic acid to the free form in stored maize meal. This leads to excess production of prostaglandin E2 in the stomach. The excess Prostaglandin E2 causes a low-acid duodenogastro-oesophageal reflux, which predisposes to carcinogenesis. Supporting evidence is available that the steps of this mechanism occur in endemic areas, and that they are associated with the carcinogenic process. Health measures including poverty alleviation, health education, and monitoring and control of maize meal storage and content may be required to reduce the incidence of this disease in Africa.

Neuroprotection of rat hippocampal slices exposed to oxygen–glucose deprivation by enrichment with docosahexaenoic acid and by inhibition of hydrolysis of docosahexaenoic acid-containing phospholipids by calcium independent phospholipase A2

Polyunsaturated fatty acids play an important role in the development of pathological states in brain after hypoxia/ischemia. Here, we investigated the role of docosahexaenoic acid (22:6n-3) in brain phospholipids for neuronal survival. We used organotypic cultures of rat brain hippocampal slices exposed to 40 min of oxygen-glucose deprivation, to study the consequences of experimental ischemia. In [14C]docosahexaenoic acid-labeled cultures, oxygen-glucose deprivation induced significant release of radioactive docosahexaenoic acid. This release could be blocked by the selective inhibitor of the Ca2+-independent phospholipase A2, 4-bromoenol lactone (10 microM), when it was added 30 min prior to oxygen-glucose deprivation. Addition of 4-bromoenol lactone at 30 min prior to oxygen-glucose deprivation markedly decreased the neuronal damage induced by oxygen-glucose deprivation. The protective effect was substantially higher in dentate gyrus than in CA1 and CA3 areas. Enrichment of the hippocampal tissue with docosahexaenoic acid by incubation with 10 microM docosahexaenoic acid for 24 h exerted the same neuroprotective effect, which was observed after treatment with 4-bromoenol lactone. In contrast to the 24 h-preincubation, simultaneous addition of docosahexaenoic acid with the onset of oxygen-glucose deprivation had no protective effect. This suggests that incorporation of docosahexaenoic acid into phospholipids is required for the protective effect observed. Then the possible involvement of arachidonic acid metabolism in docosahexaenoic acid-induced neuroprotection was tested. Inhibition of prostaglandin production by ibuprofen produced no change in neuroprotection after 24-h incubation of the hippocampal slices with docosahexaenoic acid. Simultaneous inhibition of Ca2+-independent and Ca2+-dependent phospholipases A2 by treatment with the general phospholipase A2 inhibitor methyl arachidonyl fluorophosphonate (3 microM, 30 min prior to oxygen-glucose deprivation) resulted in significant enhancement of the neuroprotective effect in the dentate gyrus, but not in the CA1 and CA3 areas. In summary, the results reported here indicate that docosahexaenoic acid and docosahexaenoic acid-containing phospholipids provide potent protection against neurodegeneration after hypoxia/hypoglycemia. Furthermore, our data suggest that Ca2+-independent phospholipase A2, the isoform, which has been largely ignored so far, is a possible target for treatment of ischemia-related pathologies in brain.

Role of Ca2+-independent phospholipase A2 and n-3 polyunsaturated fatty acid docosahexaenoic acid in prostanoid production in brain: perspectives for protection in neuroinflammation

Various diseases of the central nervous system are characterized by induction of inflammatory events, which involve formation of prostaglandins. Production of prostaglandins is regulated by activity of phospholipases A(2) and cyclooxygenases. These enzymes release the prostaglandin precursor, the n-6 polyunsaturated fatty acid, arachidonic acid and oxidize it into prostaglandin H(2). Docosahexaenoic acid, which belongs to the n-3 class of polyunsaturated fatty acids, was shown to reduce production of prostaglandins after in vivo and in vitro administration. Nevertheless, the fact that in brain tissue cellular phospholipids naturally have a uniquely high content of docosahexaenoic acid was ignored so far in studies of prostaglandin formation in brain tissue. We consider the following possibilities: docosahexaenoic acid might attenuate production of prostaglandins by direct inhibition of cyclooxygenases. Such inhibition was found with the isolated enzyme. Another possibility, which has been already shown is reduction of expression of inducible cyclooxygenase-2. Additionally, we propose that docosahexaenoic acid could influence intracellular Ca(2+) signaling, which results in changes of activity of Ca(2+)-dependent phospholipase A(2), hence reducing the amount of arachidonic acid available for prostaglandin production. Astrocytes, the main type of glial cells in the brain control the release of arachidonic acid, docosahexaenoic acid and the formation of prostaglandins. Our recently obtained data revealed that the release of arachidonic and docosahexaenoic acids in astrocytes is controlled by different isoforms of phospholipase A(2), i.e. Ca(2+)-dependent phospholipase A(2) and Ca(2+)-independent phospholipase A(2), respectively. Moreover, the release of arachidonic and docosahexaenoic acids is differently regulated through Ca(2+)- and cAMP-dependent signal transduction pathways. Based on analysis of the current literature and our own data we put forward the hypothesis that Ca(2+)-independent phospholipase A(2) and docosahexaenoic acid are promising targets for treatment of inflammatory related disorders in brain. We suggest that Ca(2+)-independent phospholipase A(2) and docosahexaenoic acid might be crucially involved in brain-specific regulation of prostaglandins.

Why is psoriasis uncommon in Africans? The influence of dietary factors on the expression of psoriasis

Psoriasis is uncommonly seen in Africans, probably partly due to genetic factors. However, the dietary habits of Africans may provide another explanation, which is explored in this paper. Maize, the staple diet in most parts of Africa, is high in linoleic acid but low in other polyunstaturated fatty acids and riboflavin. Linoleic acid is a precursor of prostaglandin E2 (PGE2) and its high intake, especially in the absence of other polyunsaturated fatty acids (PUFAs) and riboflavin, results in high tissue production of PGE2. PGE2 is known to suppress cellular immunity, resulting in decreased expression of psoriasis.

Dietary n-3 PUFAs affect the blood pressure rise and cardiac impairments in a hyperinsulinemia rat model in vivo

The cardiovascular consequences of eicosapentaenoic acid (EPA)- and docosahexaenoic acid (DHA)-specific intake were evaluated in vivo in a hyperinsulinemia (HI) model induced by dietary fructose intake. Wistar rats were fed a diet containing (or not for control) either EPA or DHA. The rise in blood pressure (BP), heart rate, and ECG were continuously monitored using an intra-abdominal telemetry system. The myocardial phospholipid fatty acid profile was significantly affected by DHA intake but less by EPA intake. The data indicated a reduced rise in BP in both DHA and EPA HI groups compared with controls. This result was confirmed by tail-cuff measurement after 5 wk [133.3 +/- 1.67 and 142.5 +/- 1.12 mmHg in n-3 polyunsaturated fatty acid (PUFA) and control groups, respectively], whereas n-3 PUFA did not affect BP in non-HI rats (116.3 +/- 3.33 mmHg). The heart rate was lower in the HI DHA group than in the other two dietary HI groups. Moreover, DHA induced a significantly shorter QT interval. It is concluded that the cardioactive component of fish oils is DHA through a mechanism that may involve the cardiac adrenergic system.

The modulatory effects of prostaglandin-E on cytokine production by human peripheral blood mononuclear cells are independent of the prostaglandin subtype

The production of inflammatory mediators, relevant to (auto)immune diseases and chronic inflammatory conditions, can be modulated by dietary intake of n-3 and n-6 long chain polyunsaturated fatty acids (PUFAs). It was suggested that these effects are related to the formation of different series of eicosanoids, in particular prostaglandin-E (PGE). In this study we investigated whether prostaglandin subtypes metabolized from arachidonic acid (PGE2), dihomo-gamma-linolenic acid (PGE1) or eicosapentaenoic acid (PGE3) have different effects on T-cell proliferation and cytokine production in vitro. Freshly isolated human peripheral blood mononuclear cells (PBMC) were stimulated with concanavalin A (ConA) or lipopolysaccharide (LPS) in the presence or absence of exogenous PGE1, PGE2 or PGE3. We found that tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma) and to a lesser extent interleukin (IL)-10 production was inhibited by all PGE-subtypes in ConA-stimulated PBMC concomitant with unaffected IL-2 levels. The modulated cytokine production of ConA stimulated cells was independent of T-cell proliferation. PGE2 and PGE1 moderately stimulated proliferation, while PGE3 inhibited the proliferative response to some extent. In LPS-stimulated PBMC, TNF-alpha production was inhibited by all PGE-subtypes, whereas IL-6 remained unaffected and IL-10 production was increased. Time course experiments on the effects of PGE-subtypes on cytokine production after ConA or LPS stimulation showed these effects to be time dependent, but indifferent of the prostaglandin subtype added. Overall, the modulatory effects of PGE on cytokine production were irrespective of the subtype. This may implicate that the immunomodulatory effects of PUFAs, with respect to cytokine production, are not caused by a shift in the subtype of PGE.

The n-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid increase systemic arterial compliance in humans

BACKGROUND

n-3 Fatty acids influence vascular function, but the effect of individual fatty acids on systemic arterial compliance (SAC) has not been reported. SAC, which reflects arterial elasticity, is emerging as a new cardiovascular risk factor and appears to predict future cardiovascular events.

OBJECTIVE

We tested whether the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) improve SAC in dyslipidemic subjects.

DESIGN

Thirty-eight dyslipidemic subjects were randomly assigned to receive 3 g EPA/d (n = 12), 3 g DHA/d (n = 12), or a placebo (n = 14) in a 7-wk parallel, double-blind trial. Arterial functions were measured at the beginning and end of the interventions. Plasma lipids and plasma fatty acids were also measured.

RESULTS

Consumption of the n-3 fatty acids significantly increased SAC, whereas consumption of the placebo did not (P = 0.043; repeated-measures analysis of variance across the 3 groups); the increase was 36% with EPA and 27% with DHA. The major components contributing to the increase in SAC (systolic and pulse pressures and total vascular resistance) tended to decrease but not significantly. Plasma total and VLDL triacylglycerol were significantly lower in the n-3 fatty acid groups (P = 0.026 and 0.006, respectively; repeated-measures analysis of variance) than in the placebo group.

CONCLUSION

EPA and DHA increase SAC and tend to reduce pulse pressure and total vascular resistance, effects that may reduce the risk of adverse cardiovascular events.

Dietary fat and salivary prostaglandin E2

A study of the relation between dietary fat intake and salivary prostaglandin E2 was undertaken in Transkei, South Africa. Samples of saliva were obtained from (1) Transkeians on a very low fat diet, (2) Transkeians on a low fat diet, (3) Transkeians on a medium fat diet, (4) British patients. Salivary PGE2 means for the groups were (1) 2357 pg/ml, (2) 2020 pg/ml, (3) 733 pg/ml, (4) 312.5 pg/ml. Differences between groups 1 and 3, 1 and 4, and 2 and 4 were significant. Rural Transkeians on a low-fat diet have an elevated level of PGE2 in saliva. As fat increases in the diet, PGE2 in saliva tends towards the level found in those who eat a western diet. An increase in the level of PGE2 production in the upper gastrointestinal tract and in the tissues of the body may be a factor in promoting cancer of the esophagus and diseases favored by Th1 immune dysfunction.

Dietary n-3 polyunsaturated fatty acids affect the development of renovascular hypertension in rats

The consequences of a dietary n-3 PUFA supply was investigated on the blood pressure (BP) increase elicited by left renal artery stenosis in rats distributed in 3 groups (n = 8) fed for 8 weeks a semi-purified diet either as control diet or enriched diets (docosahexaenoic acid, DHA, or eicosapentaenoic acid, EPA). The PUFA intake induced large alterations in heart and kidney phospholipid fatty acid profile, but did not influence body weight, cardiac hypertrophy, renal left atrophy and right hypertrophy. Within 4 weeks, BP raised from 120-180 +/- 2 mm Hg in the control group, but only to 165 +/- 3 mm Hg in the n-3 PUFA groups. After stabilization of BP in the 3 groups, the rats received a short administration of increasing dose of perindopril. The lower dose (0.5 mg/kg) moderately decreased BP only in the control group. With higher doses (1, 5 and 10 mg/kg) BP was normalized in the 3 groups, with a higher amplitude of the BP lowering effect in the control group. A moderate n-3 PUFA intake can contribute to prevent the development of peripheral hypertension in rats by a mechanism that may involve angiotensin converting enzyme.

Modulation of rat platelet activation by vessel wall-derived prostaglandin and platelet-derived thromboxane: effects of dietary fish oil on thromboxane-prostaglandin balance

By dietary manipulation of rats with n-3 polyunsaturated fatty acids (PUFAs), platelets and endothelium-containing aortic tissue were obtained with decreased levels of arachidonate and increased levels of eicosapentaenoate and docosahexaenoate. These diet-induced changes were accompanied by a reduced formation of thromboxane A(2) (TXA(2)) and prostaglandin I(2) (PGI(2)) in platelets and aortic tissue, respectively. When platelets were incubated with autologous, aorta-derived PGI(2), the dietary modulation of PGI(2) generation had a stronger effect on the activation process than the dietary effect on TXA(2) generation. The platelet-inhibiting effect of PGI(2) was independent of the type of agonist and involved both TXA(2)-dependent and -independent activation responses. PGI(2) also inhibited the agonist-induced formation of TXA(2). In addition, the platelet-inhibitory effect of PGI(2) was more prolonged in time than the brief, stimulatory effect of TXA(2). We conclude that, in the thromboxane-prostaglandin balance of platelet activation, PGI(2) plays a more prominent role than TXA(2). Furthermore, dietary n-3 PUFAs appear to influence platelet activation more by reducing formation of endothelial PGI(2) than by decreasing autocrine-produced TXA(2). Thus, in rats, the proposed antithrombotic effect of fish oil is unlikely to be caused by an altered thromboxane-prostaglandin balance.

Abnormal arachidonic acid content of red blood cell membranes and main lithogenic factors in stone formers

BACKGROUND

Increased arachidonic acid content in red blood cell membranes of stone formers (SF) has recently been reported and is hypothesized as representing the underlying causal factor for both hyperoxaluria and hypercalciuria. We performed the present study to see whether we could confirm this finding and to test whether any relationship exists between the fatty acid composition of red blood cell membranes and the main metabolic factors involved in stone formation.

METHODS

In 21 SF and 40 healthy controls subjects the fatty acid composition of red blood cell membranes was assessed. In addition, the following parameters were evaluated in SF: daily and fasting urinary calcium excretion, fractional intestinal calcium absorption, 1,25-dihydroxy-vitamin D, intact parathyroid hormone, hydroxyproline in fasting urine, daily urinary excretion of oxalate, citrate, urate, electrolytes, urea, sulphate, relative supersaturation for calcium oxalate monohydrate.

RESULTS

The red blood cell membrane of SF had a lower content of arachidonic acid, linoleic acid, and docosahexaenoic acid than that of control subjects. Arachidonic acid content was not correlated with any of the parameters studied. However, when patients were grouped according to the degree of oxalate excretion, hyperoxaluric SF had a higher arachidonic acid content and arachidonic/linoleic acid ratio than SF with normal oxalate excretion.

CONCLUSIONS

Our results do not confirm the finding of an increased arachidonic acid content of red blood cell membrane in SF. On the contrary, reduced arachidonic acid levels were found in our patients. However, hyperoxaluric SF had a relatively higher arachidonic acid content than SF with normal urinary oxalate excretion.

Incorporation and metabolism of trans 20:5 in endothelial cells. Effect on prostacyclin synthesis

To study the ability of long-chain trans fatty acids (FA) to be incorporated and metabolized into endothelial cells, bovine aortic endothelial cells were incubated with medium enriched eicosapentaenoic acid (EPA) bound to albumin (M2) or one of its geometrical isomers: 20:5 5c,8c,11t,14c,17c (M3), 20:5 5c,8c,11c,14c,17t (M4), or 20:5 5c,8c,11t,14c,17t (M5). After 48 h of incubation, supernatant and cells were harvested and their lipids were analyzed, including prostacyclin synthesis. EPA and 22:5n-3 of endothelial cells incubated with M2 were, respectively, three and two times higher than in control cells (incubated in M1, without any fatty acid added), whereas 22:6n-3 increased only in the supernatant, suggesting its release after biosynthesis. However, 18:2n-6 and 22:4n-6 decreased (about 30%). Trans 20:5 isomers represented 4.7, 3.9, and 5.2% of total phospholipid FA in endothelial cells incubated with M3, M4, and M5, respectively. They were elongated into trans 22:5 and trans 24:5, as revealed by gas chromatography-mass spectrometry and gas chromatography-Fourier transform infrared analysis. In cells incubated with M2, M3, M4, and M5, prostacyclin synthesis was inhibited by 49.0, 62.5, 60.5, and 72.0%, respectively. This effect may be due to less available arachidonic acid in the cells and to a competition between EPA isomers and AA at the level of cyclooxygenase pathway, as it was demonstrated that 20:5 delta17t was metabolized by this enzyme.

Eicosapentaenoic and docosahexaenoic acid affect mitochondrial and peroxisomal fatty acid oxidation in relation to substrate preference

Decreased triacylglycerol synthesis within hepatocytes due to decreased diacylglycerol acyltransferase (DGAT) activity has been suggested to be an important mechanism by which diets rich in fish oil lower plasma triacylglycerol levels. New findings suggest that eicosapentaenoic acid (EPA), and not docosahexaenoic acid (DHA), lowers plasma triacylglycerol by increased mitochondrial fatty acid oxidation and decreased availability of fatty acids for triacylglycerol synthesis. To contribute to the understanding of the triacylglycerol-lowering mechanism of fish oil, the different metabolic properties of EPA and DHA were studied in rat liver parenchymal cells and isolated rat liver organelles. EPA-CoA was a poorer substrate than DHA-CoA for DGAT in isolated rat liver microsomes, and in the presence of EPA, a markedly lower value for the triacyl[3H]glycerol/diacyl[3H]glycerol ratio was observed. The distribution of [1-14C]palmitic acid was shifted from incorporation into secreted glycerolipids toward oxidation in the presence of EPA (but not DHA) in rat liver parenchymal cells. [1-14C]EPA was oxidized to a much greater extent than [1-14C]DHA in rat liver parenchymal cells, isolated peroxisomes, and especially in purified mitochondria. As the oxidation of EPA was more effective and sensitive to the CPT-I inhibitor, etomoxir, when measured in a combination of both mitochondria and peroxisomes, we hypothesized that both are involved in EPA oxidation, whereas DHA mainly is oxidized in peroxisomes. In rats, EPA treatment lowered plasma triacylglycerol and increased hepatic mitochondrial fatty acid oxidation and carnitine palmitoyltransferase (CPT)-I activity in both the presence and absence of malonyl-CoA. Whereas only EPA treatment increased the mRNA levels of CPT-I, DHA treatment increased the mRNA levels of peroxisomal fatty acyl-CoA oxidase and fatty acid binding protein more effectively than EPA treatment. In conclusion, EPA and DHA affect cellular organelles in relation to their substrate preference. The present study strongly supports the hypothesis that EPA, and not DHA, lowers plasma triacylglycerol by increased mitochondrial fatty acid oxidation.

Dietary linoleic acid, immune inhibition and disease

Review of the evidence available in published literature supports a radical change in viewpoint with respect to disease in countries where maize is the predominant dietary component. In these countries, the pattern of disease is largely determined by a change in immune profile caused by metabolites of dietary linoleic acid. High intake of linoleic acid in a diet deficient in other polyunsaturated fatty acids and in riboflavin results in high tissue production of prostaglandin E2, which in turn causes inhibition of the proliferation and cytokine production of Th1 cells, mediators of cellular immunity. Tuberculosis, measles, hepatoma, secondary infection in HIV and kwashiorkor are all favoured by this reduction in cellular immunity. Diet-associated inhibition of the Th1 subset is a major contributor to the high prevalence of these diseases found in areas of sub-Saharan Africa where maize is the staple.

Diet, reflux and the development of squamous cell carcinoma of the oesophagus in Africa

BACKGROUND

Squamous cancer of the oesophagus has reached epidemic proportions in Africa in the past few decades. There are many known associations but as yet no well established theory of causation.

METHODS

Relevant literature was found by manual review of appropriate journals and literature, Medline searches and cross-referencing. Published theories of causation of endemic cancer of the oesophagus were assessed in the light of available evidence. A hypothesis based on that evidence was formulated.

RESULTS AND CONCLUSION

A predominantly maize-based diet is high in linoleic acid, a precursor for gastric prostaglandin synthesis. In combination with low intake of other fatty acids and riboflavin, high levels of prostaglandin E2 are produced in gastric mucosa, leading to reduced gastric acid secretion, relaxation of the pylorus and a reduction in lower oesophageal sphincter pressure. These events result in combined reflux of duodenal and gastric juices low in acidity into the oesophagus. Resulting dysplasia strongly predisposes to local squamous carcinogenesis. This is now a fertile area for research, which may open the way for preventive action.

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.

Fatty acid composition of breast adipose tissue in breast cancer patients and in patients with benign breast disease

Fatty acid composition of triglycerides (TGs) and phospholipids (PLs) in breast adipose tissue was analyzed in 73 female breast cancer patients and 55 patients with benign breast disease. No differences were observed in the dietary intake of the major fatty acids (i.e., palmitic, stearic, oleic, and linoleic acids) or in the proportion of TGs and PLs in breast adipose tissue between the two groups. In postmenopausal women, however, the dietary intake of eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) was significantly lower in the breast cancer patients than in patients with benign breast disease. Accordingly, the percentage of docosahexaenoic acid of PLs in breast adipose tissue was significantly lower in breast cancer patients than in patients with benign breast disease among postmenopausal women. The stage of the breast cancer did not contribute to the observed alterations of fatty acid composition of PLs. Consonant with the previous epidemiologic data, the present results suggest that intake of the long-chain n-3 fatty acids (mainly derived from fish) may have a protective effect against breast cancer, particularly in postmenopausal women.

Effects of Polyunsaturated Fatty Acids on Glial Cell Activation. A Study Using Primary Cultures

The aim of this study was to examine the effects of essential fatty acids (gammalinolenic acid [18:3 n-6; GLA] and alpha-linolenic acid [18:3 n-3; Lin]) on the activation of glial cells, using lipopolysaccharides as the activating agent. Primary cultures of mixed glial cells from rat brain were used as the model. The morphological activation of microglia was the most significant response to the exposure. This activation was followed by an increase in 5’-nucleotidase (5’-NT) activity. The 5’-NT activity was increased by GLA or Lin alone to 250–350% of the control value and further increased by co-incubation with lipoteichoic acid (a lipopolysaccharide) to 500–600% of the control value.

The lipopolysaccharide-induced activation of glial cells was also followed by an augmented release of prostaglandin E2. GLA increased the release of prostaglandin E2 in a dose-dependent manner, whereas Lin had no effect on its release.

The results show that this model system is useful for studies on factors affecting the activation of glial cells. GLA and Lin did not reverse glial activation induced by lipopolysaccharides under these experimental conditions.