Dietary n-3 fatty acid effects on neutrophil lipid composition and mediator production. Influence of duration and dosage

Mobilization efficiency is critically regulated by fat via marrow PPARδ

The mobilization efficiency of hematopoietic stem/progenitor cells from bone marrow (BM) to circulation by granulocyte colony-stimulating factor (G-CSF) is dramatically dispersed in humans and mice with no mechanistic lead for poor mobilizers. The regulatory mechanism for mobilization efficiency by dietary fat was assessed in mice. Fat-free diet (FFD) for 2 weeks greatly increased mobilization compared to normal diet (ND). The BM mRNA level of peroxisome proliferator-activated receptor δ (PPARδ), a receptor for lipid mediators, was markedly up-regulated by G-CSF in mice fed with ND and displayed strong positive correlation with widely scattered mobilization efficiency. It was hypothesized that BM fat ligand for PPARδ might inhibit mobilization. The PPARδ agonist inhibited mobilization in mice fed with ND and enhanced mobilization by FFD. Treatment with the PPARδ antagonist and chimeric mice with PPARδ+/- BM showed enhanced mobilization. Immunohistochemical staining and flow cytometry revealed that BM PPARδ expression was enhanced by G-CSF mainly in mature/immature neutrophils. BM lipid mediator analysis revealed that G-CSF treatment and FFD resulted in the exhaustion of ω3-polyunsaturated fatty acids such as eicosapentaenoic acid (EPA). EPA induced the up-regulation of genes downstream of PPARδ, such as carnitine palmitoyltransferase-1α and angiopoietin-like protein 4 (Angptl4), in mature/immature neutrophils in vitro and inhibited enhanced mobilization in mice fed with FFD in vivo. Treatment of wild-type mice with the anti-Angptl4 antibody enhanced mobilization together with BM vascular permeability. Collectively, PPARδ signaling in BM mature/immature neutrophils induced by dietary fatty acids negatively regulates mobilization, at least partially, via Angptl4 production.

Pharmacokinetics of omega-3 fatty acids in patients with severe sepsis compared with healthy volunteers: A prospective cohort study

BACKGROUND

Pharmacokinetics (PK) of pharmaceuticals and pharmaconutrients are poorly understood in critically ill patients, and dosing is often based on healthy subject data. This might be particularly problematic with enteral medications due to metabolic abnormalities and impaired gastrointestinal tract absorption common in critically ill patients. Utilizing enteral fish oil, this study was undertaken to better understand and define PK of enteral omega-3 fatty acids (eicospentaenoic acid [EPA] and docosahexaenoic acid [DHA]) in critically ill patients with severe sepsis.

MATERIALS AND METHODS

Healthy volunteers (n = 15) and mechanically ventilated (MV) adults with severe sepsis (n = 10) were recruited and received 9.75 g EPA and 6.75 g DHA daily in two divided enteral doses of fish oil for 7 days. Volunteers continued their normal diet without other sources of fish oil, and sepsis patients received standard enteral feeding. Blood was collected at frequent intervals during the 14-day study period. Peripheral blood mononuclear cells (PMBCs) and neutrophils were isolated and analyzed for membrane fatty acid (FA) content. Mixed linear models and t-tests were used to analyze changes in FA levels over time and FA levels at individual time points, respectively. PK parameters were obtained based on single compartment models of EPA and DHA kinetics.

RESULTS

Healthy volunteers were 41.1 ± 10.3 years; 67% were women. In patients with severe sepsis (55.6 ± 13.4 years, 50% women), acute physiologic and chronic health evaluation (APACHE) II score was 27.2 ± 8.8 at ICU admission and median MV duration was 10.5 days. Serum EPA and DHA were significantly lower in sepsis vs. healthy subjects over time. PBMC EPA concentrations were generally not different between groups over time, while PBMC DHA was higher in sepsis patients. Neutrophil EPA and DHA concentrations were similar between groups. The half-life of EPA in serum and neutrophils was significantly shorter in sepsis patients, whereas other half-life parameters did not vary significantly between healthy volunteers and sepsis patients.

CONCLUSIONS

While incorporation of n-3 FAs into PBMC and neutrophil membranes was relatively similar between healthy volunteers and sepsis patients receiving identical high doses of fish oil for one week, serum EPA and DHA were significantly lower in sepsis patients. These findings imply that serum concentrations and EPA and DHA may not be the dominant driver of leukocyte membrane incorporation of EPA and DHA. Furthermore, lower serum EPA and DHA concentrations suggest that either these n-3 FAs were being metabolized rapidly in sepsis patients or that absorption of enteral medications and pharmaconutrients, including fish oil, may be impaired in sepsis patients. If enteral absorption is impaired, doses of enteral medications administered to critically ill patients may be suboptimal.

Polyunsaturated Fatty Acid Composition of Cerebrospinal Fluid Fractions Shows Their Contribution to Cognitive Resilience of a Pre-symptomatic Alzheimer's Disease Cohort

Alzheimer’s disease (AD) pathology is characterized by an early and prolonged decrease in the amyloid peptide (Aβ) levels concomitant with a later increase in phospho-tau concentrations in cerebrospinal fluid (CSF). We propose that changes in lipid metabolism can contribute to the abnormal processing of Aβ₄₂ in AD. Our aim was to determine if polyunsaturated fatty acid (PUFA) metabolism can differentiate pre-symptomatic AD from normal aging and symptomatic AD. Using neuropsychology measures and Aβ₄₂/T-tau in cerebrospinal fluid (CSF), we classify three groups of elderly study participants: cognitively healthy with normal Aβ₄₂/T-tau (CH-NAT), cognitively healthy with pathological Aβ₄₂/T-tau (CH-PAT), and AD individuals. We determined the size distribution and the concentration of CSF particles using light scattering and quantified PUFA composition in the nanoparticulate (NP) fraction, supernatant fluid (SF), and unesterified PUFA levels using gas chromatography combined with mass spectrometry. Four PUFAs (C20:2n-6, C20:3n-3, C22:4n-6, C22:5n-3) were enriched in NP of AD compared with CH-NAT. C20:3n-3 levels were higher in the NP fraction from AD compared with CH-PAT. When normalized to the number of NPs in CSF, PUFA levels were significantly higher in CH-NAT and CH-PAT compared with AD. In the SF fractions, only the levels of docosahexaenoic acid (DHA, C22:6n-3) differentiated all three clinical groups. Unesterified DHA was also higher in CH-NAT compared with the other clinical groups. Our studies also show that NP PUFAs in CH participants negatively correlate with CSF Aβ₄₂ while C20:4n-6, DHA, and n-3 PUFAs in the SF fraction positively correlate with T-tau. The profile of PUFAs in different CSF fractions that correlate with Aβ₄₂ or with T-tau are different for CH-NAT compared with CH-PAT. These studies show that PUFA metabolism is associated with amyloid and tau processing. Importantly, higher PUFA levels in the cognitively healthy study participants with abnormal Aβ₄₂/T-tau suggest that PUFA enhances the cognitive resilience of the pre-symptomatic AD population. We propose that interventions that prevent PUFA depletion in the brain may prevent AD pathology by stabilizing Aβ₄₂ and tau metabolism. Further studies to determine changes in PUFA composition during the progression from pre-symptomatic to AD should reveal novel biomarkers and potential preventive approaches.

Dietary DHA amplifies LXA4 circuits in tissues and lymph node PMN and is protective in immune-driven dry eye disease

Recently identified regulatory PMN control immune-driven dry eye disease (DED) in females by producing the arachidonic acid (ω-6)-derived specialized pro-resolving mediator (SPM), LXA4, in lymph nodes. Dietary ω-3 docosahexaenoic acid (DHA) is protective in DED but mechanisms of action remain elusive. DHA is converted to ω-3 SPMs by PMN via the same lipoxygenases (LOX) that generate LXA4. We investigated if dietary DHA amplifies SPM formation and affects T effector cell function and/or regulatory PMN in DED. DED was induced in mice on a DHA-enriched or ω-3-deficient diet. DHA deficiency amplified DED with marked sex-specific differences. Dietary DHA protection against dry eye disease correlated with increased PMN levels in lymph nodes, ocular tissues, and unexpectedly, selective amplification of LXA4 tissue levels. Dietary DHA increased 12/15-LOX and decreased 5-LOX expression in lymph nodes and isolated lymph node PMN, which correlated with amplified LXA4 formation. Acute DHA treatment rescued DHA-deficient females from exaggerated DED by amplifying lymph node LXA4 formation, increasing Treg and decreasing TH1 and TH17 effector cells. Our results identify DHA regulation of LXA4 producing PMN in ocular tissues and lymph nodes in health and immune disease as novel mechanism and determinant for T-cell responses to routine ocular injury or stress signals.

Enriching Islet Phospholipids With Eicosapentaenoic Acid Reduces Prostaglandin E2 Signaling and Enhances Diabetic β-Cell Function

Prostaglandin E₂ (PGE₂) is derived from arachidonic acid, whereas PGE₃ is derived from eicosapentaenoic acid (EPA) using the same downstream metabolic enzymes. Little is known about the impact of EPA and PGE₃ on β-cell function, particularly in the diabetic state. In this work, we determined that PGE₃ elicits a 10-fold weaker reduction in glucose-stimulated insulin secretion through the EP3 receptor as compared with PGE₂ We tested the hypothesis that enriching pancreatic islet cell membranes with EPA, thereby reducing arachidonic acid abundance, would positively impact β-cell function in the diabetic state. EPA-enriched islets isolated from diabetic BTBR Leptin^ob/ob mice produced significantly less PGE₂ and more PGE₃ than controls, correlating with improved glucose-stimulated insulin secretion. NAD(P)H fluorescence lifetime imaging showed that EPA acts downstream and independently of mitochondrial function. EPA treatment also reduced islet interleukin-1β expression, a proinflammatory cytokine known to stimulate prostaglandin production and EP3 expression. Finally, EPA feeding improved glucose tolerance and β-cell function in a mouse model of diabetes that incorporates a strong immune phenotype: the NOD mouse. In sum, increasing pancreatic islet EPA abundance improves diabetic β-cell function through both direct and indirect mechanisms that converge on reduced EP3 signaling.

Endogenous Production of Long-Chain Polyunsaturated Fatty Acids and Metabolic Disease Risk

Long chain polyunsaturated fatty acids (PUFAs) are important structural components of cellular membranes and are converted into eicosanoids which serve various biological roles. The most common dietary n-6 and n-3 PUFAs are linoleic acid and α-linoleic acid, respectively. These 18-carbon chain fatty acids undergo a series of desaturation and elongation steps to become the 20-carbon fatty acids arachidonic acid and eicosapentaenoic acid, respectively. Evidence from genome wide association studies has consistently demonstrated that plasma and tissue levels of the n-6 long-chain PUFA arachidonic acid and to a lesser extent the n-3 long-chain PUFA eicosapentaenoic acid, are strongly influenced by variation in fatty acid desaturase-1,-2, and elongation of very long chain fatty acid genes. Studies of functional variants in these genes, as well as studies in which desaturase activity has been indirectly estimated by fatty acid product-to -precursor ratios, have suggested that endogenous capacity to synthesize long-chain PUFAs may be associated with metabolic diseases such as diabetes mellitus. Interventional studies are starting to tease out the complicated relationship between dietary intakes of specific fatty acids, variation in desaturase and elongase genes and tissue levels of long chain PUFAs. Thus future studies of dietary PUFA interventions designed to reduce inflammatory and metabolic diseases will need to carefully consider how an individual's genetically-determined endogenous long-chain PUFA synthesis capacity might modify therapeutic response.

Marine omega-3 fatty acids and inflammatory processes: Effects, mechanisms and clinical relevance

Inflammation is a condition which contributes to a range of human diseases. It involves a multitude of cell types, chemical mediators, and interactions. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are omega-3 (n-3) fatty acids found in oily fish and fish oil supplements. These fatty acids are able to partly inhibit a number of aspects of inflammation including leukocyte chemotaxis, adhesion molecule expression and leukocyte-endothelial adhesive interactions, production of eicosanoids like prostaglandins and leukotrienes from the n-6 fatty acid arachidonic acid, production of inflammatory cytokines, and T-helper 1 lymphocyte reactivity. In addition, EPA gives rise to eicosanoids that often have lower biological potency than those produced from arachidonic acid and EPA and DHA give rise to anti-inflammatory and inflammation resolving mediators called resolvins, protectins and maresins. Mechanisms underlying the anti-inflammatory actions of marine n-3 fatty acids include altered cell membrane phospholipid fatty acid composition, disruption of lipid rafts, inhibition of activation of the pro-inflammatory transcription factor nuclear factor kappa B so reducing expression of inflammatory genes, activation of the anti-inflammatory transcription factor peroxisome proliferator activated receptor γ and binding to the G protein coupled receptor GPR120. These mechanisms are interlinked, although the full extent of this is not yet elucidated. Animal experiments demonstrate benefit from marine n-3 fatty acids in models of rheumatoid arthritis (RA), inflammatory bowel disease (IBD) and asthma. Clinical trials of fish oil in RA demonstrate benefit, but clinical trials of fish oil in IBD and asthma are inconsistent with no overall clear evidence of efficacy. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Generation and dietary modulation of anti-inflammatory electrophilic omega-3 fatty acid derivatives

Dietary ω-3 polyunsaturated fatty acids (PUFAs) decrease cardiovascular risk via suppression of inflammation. The generation of electrophilic α,β-unsaturated ketone derivatives of the ω-3 PUFAs docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA) in activated human macrophages is catalyzed by cyclooxygenase-2 (Cox-2). These derivatives are potent pleiotropic anti-inflammatory signaling mediators that act via mechanisms including the activation of Nrf2-dependent phase 2 gene expression and suppression of pro-inflammatory NF-κB-driven gene expression. Herein, the endogenous generation of ω-3 PUFAs electrophilic ketone derivatives and their hydroxy precursors was evaluated in human neutrophils. In addition, their dietary modulation was assessed through a randomized clinical trial.

Methods

Endogenous generation of electrophilic omega-3 PUFAs and their hydroxy precursors was evaluated by mass spectrometry in neutrophils isolated from healthy subjects, both at baseline and upon stimulation with calcium ionophore. For the clinical trial, participants were healthy adults 30–55 years of age with a reported EPA+DHA consumption of ≤300 mg/day randomly assigned to parallel groups receiving daily oil capsule supplements for a period of 4 months containing either 1.4 g of EPA+DHA (active condition, n = 24) or identical appearing soybean oil (control condition, n = 21). Participants and laboratory technicians remained blinded to treatment assignments.

Results

5-lypoxygenase-dependent endogenous generation of 7-oxo-DHA, 7-oxo-DPA and 5-oxo-EPA and their hydroxy precursors is reported in human neutrophils stimulated with calcium ionophore and phorbol 12-myristate 13-acetate (PMA). Dietary EPA+DHA supplementation significantly increased the formation of 7-oxo-DHA and 5-oxo-EPA, with no significant modulation of arachidonic acid (AA) metabolite levels.

Conclusions

The endogenous detection of these electrophilic ω-3 fatty acid ketone derivatives supports the precept that the benefit of ω-3 PUFA-rich diets can be attributed to the generation of electrophilic oxygenated metabolites that transduce anti-inflammatory actions rather than the suppression of pro-inflammatory AA metabolites.

Trial Registration

ClinicalTrials.gov NCT00663871

Docosahexaenoic acid (DHA) production by Thraustochytrium sp. ATCC 20892

Thraustochytrium sp. ATCC 20892 produced high yields of docosahexaenoic acid (DHA), more than four other strains of Thraustochytrium and Schizochytrium tested, but insignificant amounts of other polyunsaturated fatty acids. Glucose and sodium glutamate were the preferred carbon and nitrogen sources, respectively, and the optimum conditions for growth and DHA production were pH 7.0 at 25°C with 40 g glucose 1(-1) for 4 days. Temperature profiling under these optimum conditions further enhanced the yield and volumetric productivity of DHA.

Enteral omega-3 fatty acid, gamma-linolenic acid, and antioxidant supplementation in acute lung injury

CONTEXT

The omega-3 (n-3) fatty acids docosahexaenoic acid and eicosapentaenoic acid, along with γ-linolenic acid and antioxidants, may modulate systemic inflammatory response and improve oxygenation and outcomes in patients with acute lung injury.

OBJECTIVE

To determine if dietary supplementation of these substances to patients with acute lung injury would increase ventilator-free days to study day 28.

DESIGN, SETTING, AND PARTICIPANTS

The OMEGA study, a randomized, double-blind, placebo-controlled, multicenter trial conducted from January 2, 2008, through February 21, 2009. Participants were 272 adults within 48 hours of developing acute lung injury requiring mechanical ventilation whose physicians intended to start enteral nutrition at 44 hospitals in the National Heart, Lung, and Blood Institute ARDS Clinical Trials Network. All participants had complete follow-up.

INTERVENTIONS

Twice-daily enteral supplementation of n-3 fatty acids, γ-linolenic acid, and antioxidants compared with an isocaloric control. Enteral nutrition, directed by a protocol, was delivered separately from the study supplement.

MAIN OUTCOME MEASURE

Ventilator-free days to study day 28.

RESULTS

The study was stopped early for futility after 143 and 129 patients were enrolled in the n-3 and control groups. Despite an 8-fold increase in plasma eicosapentaenoic acid levels, patients receiving the n-3 supplement had fewer ventilator-free days (14.0 vs 17.2; P = .02) (difference, -3.2 [95% CI, -5.8 to -0.7]) and intensive care unit-free days (14.0 vs 16.7; P = .04). Patients in the n-3 group also had fewer nonpulmonary organ failure-free days (12.3 vs 15.5; P = .02). Sixty-day hospital mortality was 26.6% in the n-3 group vs 16.3% in the control group (P = .054), and adjusted 60-day mortality was 25.1% and 17.6% in the n-3 and control groups, respectively (P = .11). Use of the n-3 supplement resulted in more days with diarrhea (29% vs 21%; P = .001).

CONCLUSIONS

Twice-daily enteral supplementation of n-3 fatty acids, γ-linolenic acid, and antioxidants did not improve the primary end point of ventilator-free days or other clinical outcomes in patients with acute lung injury and may be harmful.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00609180.

Effect of dietary fatty acids on inflammatory gene expression in healthy humans

Over the past 100 years, changes in the food supply in Western nations have resulted in alterations in dietary fatty acid consumption, leading to a dramatic increase in the ratio of omega-6 (omega6) to omega3 polyunsaturated fatty acids (PUFA) in circulation and in tissues. Increased omega6/omega3 ratios are hypothesized to increase inflammatory mediator production, leading to higher incidence of inflammatory diseases, and may impact inflammatory gene expression. To determine the effect of reducing the omega6/omega3 ratio on expression of inflammatory pathway genes in mononuclear cells, healthy humans were placed on a controlled diet for 1 week, then given fish oil and borage oil for an additional 4 weeks. Serum and neutrophil fatty acid composition and ex vivo leukotriene B(4) production from stimulated neutrophils were measured at the start and end of the supplementation period and after a 2-week washout. RNA was isolated from mononuclear cells and expression of PI3K, Akt, NFkappaB, and inflammatory cytokines was measured by real-time PCR. A marked increase was seen in serum and neutrophil levels of long-chain omega3 PUFA concomitant with a reduction in the omega6/omega3 PUFA ratio (40%). The ex vivo capacity of stimulated neutrophils to produce leukotriene B(4) was decreased by 31%. Expression of PI3Kalpha and PI3Kgamma and the quantity of PI3Kalpha protein in mononuclear cells was reduced after supplementation, as was the expression of several proinflammatory cytokines. These data reveal that PUFA may exert their clinical effects via their capacity to regulate the expression of signal transduction genes and genes for proinflammatory cytokines.

Effect of dietary supplementation with increasing doses of docosahexaenoic acid on neutrophil lipid composition and leukotriene production in human healthy volunteers

n-3 PUFA supplementation helps in the prevention or treatment of inflammatory diseases and CVD. However, many supplementations reported so far are either a combination of n-3 PUFA or used large daily amounts of n-3 PUFA dosages. The present study investigated the influence of increasing dose intake of DHA on the fatty acid composition of phospholipids in neutrophils and on their capability to produce leukotrienes (LT) B4 and B5in vitro. Twelve healthy volunteers were supplemented with increasing daily doses of DHA (200, 400, 800 and 1600 mg, each dose in TAG containing DHA as the only PUFA and for a 2-week period). At the end of each supplementation period, neutrophil fatty acid composition, and LTB4 and LTB5 production were determined by GC and liquid chromatography–tandem MS, respectively. The DHA/arachidonic acid ratio increased in a dose-dependent manner with respect to the increasing doses of DHA supplementation and was significantly different from baseline after supplementation with either 400, 800 or 1600 mg DHA. The LTB5/LTB4 ratio was significantly increased compared to baseline after supplementation with 800 and 1600 mg DHA. LTB5/LTB4 and DHA/arachidonic acid ratios were correlated (r 0·531, P < 0·0001). The present data suggest that both changes in neutrophil lipid composition and LT production occurred with daily supplementation with 800 and 1600 mg DHA. The clinical benefits associated with these doses of DHA in inflammatory diseases remain to be investigated.

Fish oil before cardiac surgery: neutrophil activation is unaffected but myocardial damage is moderated

Could pre-operative dietary intervention with fish oil reduce neutrophil activation and myocardial damage associated with cardiopulmonary bypass (CPB)? Patients were randomised to receive either 8 g/day fish oil (n=22) or placebo (n=18) for 6 weeks. Neutrophil activation, apoptosis and cardiac damage were measured. Demographics and operative variables were similar. Fish oil diet decreased plasma VLDL from 0.69+/-0.34 to 0.51+/-0.24 mmol/l and triglycerides from 1.68+/-0.70 to 1.39+/-0.54 mmol/l. HDL cholesterol increased from 0.94+/-0.27 to 1.03+/-0.26 mmol/l demonstrating significant treatment effects (P=0.007, 0.02 and 0.0003, respectively) as well as compliance with treatment. There were no significant differences in ex vivo N-formyl-methionyl-leucyl-phenylalanine-stimulated neutrophil superoxide anion generation or myeloperoxidase release at recruitment, pre-operatively and at end-CPB. Apoptosis at end-CPB was equally reduced in both groups from 23+/-9% to 13+/-4% in the fish oil group (P<0.001) and 35+/-14% to 15+/-3% in the placebo group (P=0.001). At end-CPB overall troponin I levels averaged 0.91+/-0.60 ng/ml which clearly exceeded diagnostic levels (0.15 ng/ml). At 24h troponin I fell significantly in the fish oil group to 46+/-23% of end-CPB levels (P=0.0002) whereas it peaked in the placebo group to 107+/-72% (P=0.098 vs. end-CPB); this difference was significant: P=0.013. At 48 h the placebo-treated patients had higher troponins but not significantly so (P=0.059). Area-under-the-curve analysis did not conclusively support this (P=0.068). We conclude that fish oil did not significantly decrease post-CPB neutrophil activation (as detected ex vivo) but may moderate post-operative myocardial damage.

Effect of dietary fat intake and exercise on inflammatory mediators of the immune system in sedentary men and women

OBJECTIVE

Dietary fat intake and exercise affect the immune system. This study determined the changes in inflammatory components of the immune system in response to maximal exercise with three levels of dietary fat intake: 19%, 30%, and 50% of total calories.

METHODS

Five men and six women were randomly assigned to consume diets with 19% and 50% calories from fat for three weeks each, with a one-week washout. The habitual and washout diets were 30% calories from fat. At the beginning and the end of each diet, body composition and maximal exercise tests were performed. Blood samples were collected before and after exercise to determine the immunological parameters.

RESULTS

The subject's energy intake was balanced to expenditure on the 30% and 50% diets, but was in negative balance on the 19% diet. Exercise led to significant increases in the concentrations of leukocytes, neutrophils, lymphocytes, monocytes, plasma tumour necrosis factor (TNF)-alpha, plasma interleukin (IL)-2, plasma soluble vascular cell adhesion molecule (sVCAM)-1, and the production of IL-1beta and IL-6 by peripheral blood mononuclear (PBMN) cells stimulated with lipopolysaccharide (LPS), irrespective of diets (p < 0.05). The 19% fat diet resulted in increased plasma soluble intercellular adhesion molecule (sICAM)-1 after exercise. Leukotriene (LT) B4 concentration released by neutrophils stimulated with LPS was higher in the 50% fat diet, compared to the lower fat diets, and the sICAM-1 production of neutrophils stimulated with LPS was significantly increased after exercise only with 30% fat diet.

CONCLUSION

While a short, intense bout of exercise increased pro-inflammatory mediators of the immune system, decreasing fat intake to 19% on a caloric deficient diet caused a greater increase in plasma TNF-alpha, sVCAM-1 and sICAM-1 concentration than the 30% and 50% fat diets in male and female subjects. Increasing fat calories to 50% with caloric balance did not exacerbate pro-inflammatory mediators compared to a 30% fat diet.

Nutrient supplementation with polyunsaturated fatty acids and micronutrients in rheumatoid arthritis: clinical and biochemical effects

OBJECTIVE

To investigate in a double-blind placebo-controlled, parallel group study, the effects of a nutrient supplement, containing, among other ingredients, the omega-3 fatty acids eicosapentaenoic acid (1.4 g EPA), docosahexaenoic acid (0.211 g DHA), omega-6 fatty acid gamma-linolenic acid (0.5 g GLA) and micronutrients in patients with active rheumatoid arthritis (RA).

DESIGN, SUBJECTS AND INTERVENTION

RA patients were randomized to receive either daily liquid nutrient supplementation or placebo for 4 months. The primary end point was the change in tender joint count at 2 and 4 months. Other clinical variables included swollen joint count, visual analogue scales for pain and disease activity, grip strength, functionality score and morning stiffness. Biochemical parameters included plasma concentrations of PUFA and vitamins C and E.

SETTING

Outpatient university clinic.

RESULTS

In all, 66 patients enrolled, 55 completed the study. No significant change from baseline in tender joint count or any of the other clinical parameters was detected in either group. Patients receiving nutrient supplementation, but not those receiving placebo, had significant increases in plasma concentrations of vitamin E (P=0.015), and EPA, DHA and docosapentaenoic acid concomitant with decreases of arachidonic acid (P=0.01). Intergroup differences for PUFA and vitamin E were significantly different (P=0.01 and 0.03, respectively).

CONCLUSIONS

This double-blind, placebo-controlled study in RA patients did not show superior clinical benefit of daily nutrient supplementation with EPA, GLA and micronutrients at the doses tested as compared to placebo. The study adds information regarding doses of omega-3 fatty acids, below which anti-inflammatory effects in RA are not seen.

Diet and asthma: has the role of dietary lipids been overlooked in the management of asthma?

OBJECTIVE

This article discusses the role of diet in the management of asthma. Readers will gain an understanding of how evolution of the western diet has contributed to increased asthma prevalence and how dietary modification that includes management of dietary lipids may reduce symptoms of asthma.

DATA SOURCES

Relevant studies published in English were reviewed.

STUDY SELECTION

Medline search to identify peer-reviewed abstracts and journal articles.

RESULTS

Asthma and obesity, which often occur together, have increased in prevalence in recent years. Studies suggest adaption of a western diet has not only contributed to obesity, but that increased intake of specific nutrients can cause changes in the frequency and severity of asthma. Increased asthma prevalence has also been proposed to arise from increased exposure to diesel particles or lack of exposure to infectious agents or endotoxins during childhood, generating a biased Th2 immune response, and increased cytokine and leukotriene production. Antagonists directed against these pro-inflammatory mediators include anticytokines and antileukotrienes. A reduction in the levels of inflammatory mediators associated with asthma has also been seen with dietary interventions, such as the administration of oils containing gamma-linolenic acid and eicosapentaenoic acid.

CONCLUSIONS

Evidence suggests elevated body mass index and dietary patterns, especially intake of dietary lipids, contribute to symptoms of asthma. Dietary modification may help patients manage their asthma as well as contribute to their overall health.

Regulatory potential of n-3 fatty acids in immunological and inflammatory processes

Over the last few years immunonutrition has gained increasing importance. Among other compounds lipids, especially n-3 polyunsaturated fatty acids, were shown to influence the immune response. The anti-inflammatory effects they exert can be induced by free fatty acids, triglyceride fatty acids, after incorporation into the membrane phopspholipid bilayer or following metabolism to eicosanoids. n-3 Fatty acids influence inflammatory cell activation processes from signal transduction to protein expression even involving effects at the genomic level. n-3 Fatty acid-mediated mechanisms decreased cytokine-induced adhesion molecule expression, thereby reducing inflammatory leucocyte-endothelium interactions and modified lipid mediator synthesis, thus influencing the transendothelial migration of leucocytes and leucocyte trafficking in general. Even the metabolic repertoire of specific immunocompetent cells such as cytokine release or proliferation is modified by n-3 fatty acids. Beyond this they regulate lipid homeostasis shifting the metabolic pathways towards energy supply thus optimizing the function of immune cells. Due to the regulatory impact on different processes of inflammatory and immune cell activation n-3 fatty acids provide positive effects on various states of immune deficiencies and diseases with a hyperinflammatory character, among which selected examples are presented.

Addition of eicosapentaenoic acid to gamma-linolenic acid-supplemented diets prevents serum arachidonic acid accumulation in humans

Previous studies reveal that supplementation of human diets with gamma-linolenic acid (GLA) reduces the generation of lipid mediators of inflammation and attenuates clinical symptoms of chronic inflammatory disorders such as rheumatoid arthritis. However, we have shown that supplementation with this same fatty acid also causes a marked increase in serum arachidonate (AA) levels, a potentially harmful side effect. The objective of this study was to design a supplementation strategy that maintained the capacity of GLA to reduce lipid mediators without causing elevations in serum AA levels. Initial in vitro studies utilizing HEP-G2 liver cells revealed that addition of eicosapentaenoic acid (EPA) blocked Delta-5-desaturase activity, the terminal enzymatic step in AA synthesis. To test the in vivo effects of a GLA and EPA combination in humans, adult volunteers consuming controlled diets supplemented these diets with 3.0 g/d of GLA and EPA. This supplementation strategy significantly increased serum levels of EPA, but did not increase AA levels. EPA and the elongation product of GLA, dihomo-gamma-linolenic acid (DGLA) levels in neutrophil glycerolipids increased significantly during the 3-wk supplementation period. Neutrophils isolated from volunteers fed diets supplemented with GLA and EPA released similar quantities of AA, but synthesized significantly lower quantities of leukotrienes compared with their neutrophils before supplementation. This study revealed that a GLA and EPA supplement combination may be utilized to reduce the synthesis of proinflammatory AA metabolites, and importantly, not induce potentially harmful increases in serum AA levels.

Effect of low-to-moderate amounts of dietary fish oil on neutrophil lipid composition and function

Although essential to host defense, neutrophils are also involved in numerous inflammatory disorders including rheumatoid arthritis. Dietary supplementation with relatively large amounts of fish oil [containing >2.6 g eicosapentaenoic acid (EPA) plus 1.4 g docosahexaenoic acid (DHA) per day] can attenuate neutrophil functions such as chemotaxis and superoxide radical production. In this study, the effects of more moderate supplementation with fish oil on neutrophil lipid composition and function were investigated. The rationale for using lower supplementary doses of fish oil was to avoid adverse gastrointestinal problems, which have been observed at high supplementary concentrations of fish oil. Healthy male volunteers aged <40 yr were randomly assigned to consume one of six dietary supplements daily for 12 wk (n = 8 per treatment group). The dietary supplements included four different concentrations of fish oil (the most concentrated fish oil provided 0.58 g EPA plus 1.67 g DHA per day), linseed oil, and a placebo oil. The percentages of EPA and DHA increased (both P < 0.05) in neutrophil phospholipids in a dose-dependent manner after 4 wk of supplementation with the three most concentrated fish oil supplements. No further increases in EPA or DHA levels were observed after 4 wk. The percentage of arachidonic acid in neutrophil phospholipids decreased (P < 0.05) after 12 wk supplementation with the linseed oil supplement or the two most concentrated fish oil supplements. There were no significant changes in N-formyl-met-leu-phe-induced chemotaxis and superoxide radical production following the dietary supplementations. In conclusion, low-to-moderate amounts of dietary fish oil can be used to manipulate neutrophil fatty acid composition. However, this may not be accompanied by modulation of neutrophil functions such as chemotaxis and superoxide radical production.

Modulation of PAF production by incorporation of arachidonic acid and eicosapentaenoic acid in phospholipids of human leukemic monocyte-like cells THP-1

Stimulated leukocytes generate platelet-activating factor (PAF) from membrane 1-O-alkyl-2-acyl-sn-glycerophosphocholine through hydrolysis of fatty acid and subsequent acetylation at the sn2 position of glycerol. Since the enzymes involved in the hydrolysis step of PAF biosynthesis have relative selectivity for arachidonic acid (AA), the fatty acid composition of PAF precursors might modulate PAF production. We studied the effect of AA and eicosapentaenoic acid (EPA) incorporation on PAF biosynthesis, by measuring the incorporation of [(3)H]acetate, in Ca(2+) ionophore (A23187)-stimulated human leukemic monocyte-like cells, THP-1. Supplementation of THP-1 with AA (25 microM, 1 week) or EPA (25 microM, 1 week) led to their efficient incorporation, in comparable quantities and with similar distributions, into phosphatidylcholine and phosphatidylethanolamine, and to a lesser extent into phosphatidylinositol. THP-1 cells supplemented with AA or with EPA synthetized similar amounts of PAF and of acyl analog of PAF under resting condition. However, AA-supplemented cells responded to A23187 stimulation by important raises of PAF (+125.71%) and of acyl analog of PAF (+381.75%) productions, whereas the same stimulation had little effect or no effect at all in cells supplemented with EPA. These results show that both EPA and AA may influence PAF production through their incorporation into PAF precursors, indicating that PAF production might be modulated by the fatty acid composition of its precursors.

Role of arachidonyl triglycerides within lipid bodies in eicosanoid formation by human polymorphonuclear cells

Increasing evidence suggests that the subcellular and glycerolipid localization of esterified arachidonic acid (AA) is a key factor in regulating its availability to lipases. The goal of the current study was to determine the potential of AA stored in triglycerides (TG) to serve as a substrate for lipases and 5-lipoxygenase during neutrophil (polymorphonuclear leukocytes, PMN) activation. PMN containing high concentrations of AA in TG were generated by culturing PMN in vitro with high concentrations of exogenous AA (eAA) for 12 h. Cellular AA increased 2- and 4-fold in PMNs incubated with 5 and 20 microM AA, respectively, and this increase was almost exclusively observed in neutral lipids (NL). Further analysis revealed that 88% of the AA in the NL fraction was associated with TG. Subsequent experiments were designed to determine whether this AA in TG could be mobilized and metabolized to eicosanoids during cell activation. TG pools of AA were increased as previously described and then PMN were stimulated with ionophore, A23187. In contrast to the 43-fold increase in TG AA after eAA loading (20 microM), free AA increased by only 1.9-fold after cell stimulation. Similarly, leukotriene (LT)B(4) production increased only 2-fold after loading TG with large quantities of AA. The magnitude of increase in free AA released and in LTB(4) formation was similar to the magnitude of increase in AA mass in phospholipase (PL), suggesting that PL, and not TG, served as the source of released AA and subsequent product generation. To confirm that AA in TG did not serve as a source for eicosanoid production, cellular pools of AA were differentially labeled with [(14)C]AA and [(3)H]AA, and the [(3)H]AA-to-[(14)C]AA ratio of LTB(4) and 20-hydroxyl LTB(4) produced during cell stimulation was measured. The [(3)H]AA/[(14)C]AA ratios of LTs were markedly different from the ratios in TG, thus providing further evidence that AA pools in TG are not a major source of AA for LT generation.

NADPH-oxidase activity and lipid peroxidation in neutrophils from rats fed fat-rich diets

In order to investigate the effect of fat-rich diets on neutrophil functions, 21 day-aged rats were fed for 6 weeks with a control diet consisting of a regular laboratory rodent chow (4 per cent final fat content), a control diet supplied with soybean oil (15 per cent final fat content), or a control diet supplied with coconut oil (15 per cent final fat content). Glycogen-elicited peritoneal neutrophils from rats fed soybean and coconut oil-enriched diets presented a reduction in spontaneous and PMA-stimulated H2O2 generation relative to neutrophils from rats fed the control diet. The activity of superoxide dismutase, glutathione peroxidase and catalase did not change in animals fed fat-rich diets. In addition, the capacity to generate O2-, spontaneously or in response to PMA, did not change in neutrophils from animals fed fat-rich diets. Values attained matched those observed in animals fed the control diet, regardless of the method used to measure O2-, the superoxide dismutase-inhibitable reduction of cytochrome c or the lucigenin-dependent chemiluminescence. However, the initial rate of O2- generation both in resting neutrophils and in PMA-stimulated cells was significantly reduced when animals were fed with coconut or soybean oil-enriched diets due, at least in part, to a reduction in the activity of glucose-6-phosphate dehydrogenase. The concentration of thiobarbituric acid reactive substances, an index of lipid peroxidation, was increased in animals fed both fat-rich diets. This was accompanied by an increase in arachidonic acid content in these cells. Results presented suggest that lipid peroxidation in neutrophils from animals fed fat-rich diets may be associated with a consumption of H2O2 yielding more reactive oxygen-derived species such as the hydroxyl radical.

Increased production of TNF-alpha and decreased levels of dienoic eicosanoids, IL-6 and IL-10 in mice fed menhaden oil and juniper oil diets in response to an intraperitoneal lethal dose of LPS

Eicosapentaenoic acid (EPA) and the non-methylene interrupted fatty acids (NMIFA) displace arachidonic acid (AA: 20:4omega6 -5,8,11,14) in the membrane phospholipids. Unlike EPA (20:5omega3 -5,8,11,14,17), the NMIFA (20:3omega6 -5,11,14 and 20:4omega3 -5,11,14,17) lacking the delta-8 double bond are not substrates for the formation of eicosanoids. For 20 days, the mice were fed diets containing 5wt% dietary fats from various sources. The magnitudes in the production of eicosanoids and cytokines produced in response to an intraperitoneal injection of endotoxin in mice fed menhaden fish oil (MO) diets enriched with EPA were compared with those maintained on juniper oil (JO) containing NMIFA or on safflower oil (SO), a major source of the AA precursor, linoleic acid. The levels of PGE2, 6-keto-PGF1alpha and TXB2 were markedly lower (P < 0.01) in animals fed either MO or JO diets compared to the controls. The plasma levels of tumor necrosis factor (TNF)-alpha were significantly higher (P < 0.05) with a concomitant decrease of interleukin (IL)-6 and of IL-10 in mice fed MO or JO diets (P < 0.01) compared to those fed SO diet. These data suggest that the effects of consuming NMIFA of JO despite their inability to form eicosanoids are similar to those of feeding EPA which forms biologically active alternate metabolites.

Dietary alpha-linolenic acid increases TNF-alpha, and decreases IL-6, IL-10 in response to LPS: effects of sesamin on the delta-5 desaturation of omega6 and omega3 fatty acids in mice

Sesamin (a non-fat portion of sesame seed oil) inhibits delta-5 desaturase activity resulting in an accumulation of dihomo-gamma-linolenic acid (DGLA) which can displace arachidonic acid (AA) and decrease the formation of pro-inflammatory mediators. We investigated the effects of consumption of diets containing 0.25wt% sesamin and 15 wt% safflower oil (SO) (providing 12% of the added fat as linoleic acid) or a 15 wt% 2:1 mixture of linseed oil and SO (LOSO) (providing 6% alpha-linolenic acid and 6% linoleic acid) for 3 weeks on the liver membrane fatty acid composition and on the production of prostaglandin (PG) E2, TNF-alpha, IL-6 and IL10 in mice. Consumption of sesamin-supplemented SO and LOSO diets resulted in a significant increase in the levels of 20:3omega6 (DGLA), suggesting that sesamin inhibited delta-5 desaturation of omega6 fatty acids. In animals fed LOSO diets, the levels of alpha-linolenic acid, eicosapentaenoic acid (EPA) and of docosahexaenoic acid (DHA) were elevated with a concomitant decrease of arachidonic acid (AA) in the liver membrane phospholipids. Further, in animals fed LOSO diets with or without sesamin, an increase in the circulating levels of TNF-alpha was associated with a concomitant decrease in PGE2. Despite a lack of differences in the levels of AA, the PGE2 levels were significantly lower in mice fed sesamin-supplemented SO compared to those fed SO alone. Thus, these data suggest that irrespective of the availability of a specific fatty acid as a substrate, through regulating the PGE2 synthesis, the production of TNF-alpha could be modulated.

Dietary supplementation with gamma-linolenic acid alters fatty acid content and eicosanoid production in healthy humans

To understand the in vivo metabolism of dietary gamma-linolenic acid (GLA), we supplemented the diets of 29 volunteers with GLA in doses of 1.5-6.0 g/d. Twenty-four subjects ate controlled eucaloric diets consisting of 25% fat; the remaining subjects maintained their typical Western diets. GLA and dihomo-gamma-linolenic acid (DGLA) increased in serum lipids of subjects supplemented with 3.0 and 6.0 g/d; serum arachidonic acid increased in all subjects. GLA supplementation with 3.0 and 6.0 g/d also resulted in an enrichment of DGLA in neutrophil phospholipids but no change in GLA or AA levels. Before supplementation, DGLA was associated primarily with phosphatidylethanolamine (PE) of neutrophil glycerolipids, and DGLA increased significantly in PE and neutral lipids after GLA supplementation. Extending the supplementation to 12 wk did not consistently change the magnitude of increase in either serum or neutrophil lipids in subjects receiving 3.0 g/d. After GLA supplementation, A23187-stimulated neutrophils released significantly more DGLA, but AA release did not change. Neutrophils obtained from subjects after 3 wk of supplementation with 3.0 g/d GLA synthesized less leukotriene B4 (P < 0.05) and platelet-activating factor. Together, these data reveal that DGLA, the elongase product of GLA, but not AA accumulates in neutrophil glycerolipids after GLA supplementation. The increase in DGLA relative to AA within inflammatory cells such as the neutrophil may attenuate the biosynthesis of AA metabolites and may represent a mechanism by which dietary GLA exerts an anti-inflammatory effect.

Alteration of n-3 fatty acid composition in lung tissue after short-term infusion of fish oil emulsion attenuates inflammatory vascular reaction

OBJECTIVES

To investigate whether modulation of the fatty acid profile can be achieved by the short-term infusion of a fish oil emulsion which may attenuate the pulmonary response to inflammatory stimulation. Changes of fatty acid pattern in-lung tissue and perfusate were analyzed and correlated with physiologic data after a 3-hr infusion of fish oil in comparison with a soybean oil preparation.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Experimental laboratory in a university teaching hospital.

SUBJECTS

Forty standard breed rabbits of either gender.

INTERVENTIONS

Isolated lungs from anesthetized rabbits were ventilated and recirculation-perfused (200 mL/min) with 200 mL of cell-free buffer solution to which either 2 mL of saline (control, n = 6), 2 mL of a 10% soybean oil preparation (n = 6), or 2 mL of a 10% fish oil emulsion (n = 6) were added. Samples of perfusate and lung tissue were collected for analysis of fatty acid composition. Tissue and perfusate fatty acid composition were analyzed by capillary gas chromatography. To study metabolic alterations in states of inflammatory stimulation, lungs of each group were stimulated with small doses of the calcium ionophore, A23187 (10(-8) M), during the 180-min lipid perfusion period and again after washing out the lipids by exchanging the perfusion fluid. Pulmonary arterial pressure and lung weight gain were monitored, and eicosanoids were analyzed in the perfusate.

MEASUREMENTS AND MAIN RESULTS

Free eicosapentaenoic acids increased several-fold in lung tissue and perfusate during a 3-hr infusion with fish oil. The intravenously administered n-3 fatty acids were rapidly hydrolyzed, as indicated by the appearance of substantial quantities of eicosapentaenoic acid in the perfusate free fatty acid fraction. This increase of perfusion levels of eicosapentaenoic acid was paralleled by an attenuated pressure increase and edema formation due to calcium ionophore challenge and an altered eicosanoid spectrum determined in the perfusate compared with soybean oil-treated lungs.

CONCLUSION

Short-term n-3 lipid application (fish oil emulsion) exerts anti-inflammatory effects on lung vasculature, which may be due to the metabolism of eicosapentaenoic acid resulting in the generation of less potent inflammatory eicosanoids.

Mechanisms of prostanoid synthesis in human synovial cells: cytokine-peptide synergism

Bradykinin (BK)2 and interleukin-1 (IL-1) interact synergistically to stimulate prostaglandin synthesis in human synovial fibroblast-like cells. The effect of BK is rapid and correlates with its capacity to elevate cytosolic levels of calcium ([Ca2+]i), while IL-1's effect is slow and s dependent upon de novo protein synthesis. The mechanism of this synergistic interaction was investigated. In the basal state, high levels of arachidonic acid (AA) were spontaneously released from synovial cells but near absent levels of cyclooxygenase activity prevented metabolism of AA to prostanoid. BK was a potent stimulus for elevating AA, but not prostaglandins, above basal levels. IL-1, in contrast, increased prostaglandins but not AA, above basal levels. IL-1 treatment was not associated with a loss or redistribution of AA among phospholipid classes. These results are consistent with high basal phospholipase activity in synovial cells and demonstrate the ability of BK, presumably via its ability to raise [Ca2+]i, to further elevate this activity(ies). Metabolism of AA to prostanoid is minimal in resting and BK-stimulated synovial cells, however, without the concomitant induction of cyclooxygenase activity by IL-1. These studies clarify the different, but synergistic, mechanisms of action of a peptide and cytokine in stimulating prostanoid synthesis in synovial cells. In addition, these data extend the results of previous investigations in demonstrating that basal phospholipase activity provides sufficient AA substrate for IL-1 induced prostanoid synthesis without invoking the concomitant induction of phospholipase activity by IL-1.

Migration of human inflammatory cells into the lung results in the remodeling of arachidonic acid into a triglyceride pool

Increasing evidence suggests that the metabolism of arachidonic acid (AA) may be different in inflammatory cells isolated from blood or migrating into tissues. To explore the possibility that changes in AA metabolism between blood and tissue inflammatory cells could be due in part to a different content or distribution of AA in glycerolipid classes, we studied these parameters in six human inflammatory cells isolated from blood (eosinophils, monocytes, neutrophils, and platelets) or from the lung tissue (mast cells and macrophages). Lung cells generally had a higher total cellular content of AA than that found in the blood cells. In addition, both mast cells and macrophages had a large endogenous pool of AA associated with triglycerides (TG), containing 45 and 22% of their total cellular AA, respectively. To address the hypothesis that cells migrating into the lung had a higher cellular level of AA and a larger AA pool in TG, we studied neutrophils isolated from the bronchoalveolar lavage (BAL) of patients with adult respiratory distress syndrome. BAL neutrophils had a fourfold increase in cellular AA as compared with blood neutrophils and contained 25% of their AA in TG versus 3% in blood neutrophils. BAL neutrophils also had a higher number of cytoplasmic lipid bodies (8 +/- 3/cell) relative to blood neutrophils (2 +/- 1/cell). High concentrations of free AA were also found in the cell-free BAL fluid of adult respiratory distress syndrome patients. To explore whether changes in BAL neutrophils may be due to the exposure of the cells to high concentrations of exogenous AA found in BAL, we incubated blood neutrophils in culture with AA (10-100 microM) for 24 h. Neutrophils supplemented with AA had a 10-fold increase in the amount of AA associated with TG and a sixfold increase in the number of lipid bodies. In addition, supplementation with AA induced a dose-dependent formation of hypodense cells. Taken together, these data indicate that human inflammatory cells undergo a fundamental and consistent remodeling of AA pools as they mature or enter the lung from the blood. These biochemical and morphological changes can be mimicked in vitro by exposing the cells to high levels of AA. This mechanism may be responsible for the changes in AA mobilization and eicosanoid metabolism observed in tissue inflammatory cells.

Regulation of arachidonic acid, eicosanoid, and phospholipase A2 levels in murine mast cells by recombinant stem cell factor

The current study evaluates the capacity of recombinant rat stem cell factor (rrSCF) to regulate enzymes that control AA release and eicosanoid generation in mouse bone marrow-derived mast cells (BMMCs). Initial studies indicated that rrSCF provided for 24 h inhibited the release of AA into supernatant fluids of antigen- and ionophore A23187-stimulated BMMCs. Agonist-induced increases in cellular levels of AA were also inhibited, albeit to a lesser degree by rrSCF. To determine the inhibitory mechanism, several steps (e.g., mobilization of cytosolic calcium, release of BMMC granules, and regulation of phospholipase A2 [PLA2] activity) that could influence AA release were measured in rrSCF-treated cells. rrSCF did not alter the capacity of BMMCs to mobilize cytosolic calcium or release histamine in response to antigen and ionophore. BMMCs released large amounts of PLA2 with characteristics of the group II family in response to antigen and ionophore A23187. rrSCF treatment of BMMCs reduced the secretion of this PLA2 activity by BMMCs. Partial purification of acid-extractable PLA2 from rrSCF-treated and untreated BMMCs suggested that rrSCF decreased the quantity of acid-stable PLA2 within the cells. In contrast to group II PLA2, the quantity of cPLA2 (as determined by Western blot analysis) increased in response to rrSCF. To assess the ramifications of rrSCF-induced reductions in AA and group II PLA2, eicosanoid formation was measured in antigen- and ionophore-stimulated BMMCs, rrSCF-inhibited (100 ng/ml, 24 h) prostaglandin D2 (PGD2), thromboxane B2, and leukotriene B4 by 48.4 +/- 7.7%, 61.1 +/- 10.0% AND 38.1 +/- 3.6%, respectively, in antigen-stimulated cells. Similar patterns of inhibition were observed in ionophore-stimulated BMMCs. The addition of a group I PLA2 or exogenous AA to BMMCs reversed the inhibition of eicosanoid generation induced by rrSCF. Together, these data indicate that rrSCF differentially regulates group II and cytosolic PLA2 activities in BMMCs. The resultant reductions in eicosanoid generation suggest that group II PLA2 provides a portion of AA that is used for eicosanoid biosynthesis by BMMCs.

Eicosanoids, fatty acids and neutrophils: their relevance to the pathophysiology of disease

PUFA and their eicosanoid metabolites are potent biological modifiers. They have beneficial effects in a number of diseases, which may result in part from their direct actions on neutrophils as well as from their ability to modulate eicosanoid biosynthesis. A consideration of their interactions with other cell types, e.g. lymphocytes and macrophages, is beyond the scope of this review. Small alterations in structure can result in large changes in the neutrophil response. This will have important implications for the further development and use of fatty acids for therapeutic purposes.

Modulation of the endogenous leukotriene production by fish oil and vitamin E

We investigated the effects of fish oil and vitamin E on the endogenous leukotriene production. 10 healthy volunteers were supplemented for 1 week with fish oil (containing 40 mg/kg body weight per day of eicosapentaenoic and docosahexaenoic acid), vitamin E (540 mg, i.e., 800 IU of D-alpha-tocopherol per day), or with both agents. Treatment resulted in a significant increase in the eicosapentaenoate concentration in red blood cell membranes and/or in the vitamin E concentration in serum. In addition, nine obese patients were investigated who were on a hypocaloric diet including 10 mg vitamin E/day for 8 weeks. This diet was associated with a significant decrease in serum vitamin E concentration. The urinary concentration of leukotriene E4 plus N-acetylleukotriene E4 served as a measure for the endogenous leukotriene production. Fish oil reduced leukotriene production in eight of the 10 healthy individuals. After vitamin E supplementation, urinary leukotrienes were significantly reduced in all of the healthy volunteers. The combination of vitamin E plus fish oil had no synergistic effect on leukotriene production in the individuals tested. The decrease in serum vitamin E concentration during the hypocaloric, 10 mg vitamin E/day diet was associated with an increase in urinary leukotrienes in 8 of the 9 obese patients. Urinary prostaglandin metabolites, determined as tetranorprostanedioic acid, increased or decreased in parallel with urinary leukotrienes in most individuals; however, changes were less pronounced than those observed with leukotrienes. We conclude that the endogenous leukotriene production can be reduced effectively by high doses of fish oil or vitamin E, whereas vitamin E depletion is associated with an increase in leukotriene generation.

Regulation of neutrophil activation by oleic acid

Physiological concentrations of oleic acid inhibited C5a-induced myeloperoxidase release from neutrophils. The inhibition occurred promptly following the addition of oleic acid, was dose-dependent and saturable, and was greater at low concentrations of C5a. Kinetic analysis of the curve for 1/myeloperoxidase release against 1/[C5a] in the presence of oleic acid, was compatible with a cooperative pattern of interaction. The inhibitory effect persisted after repeated washings of cells preincubated with oleic acid. The effect of oleic acid was not specific for C5a-induced neutrophil activation; oleic acid also inhibited myeloperoxidase release induced by the Ca2+ ionophore A-23187, as well as zymosan activated serum-induced chemotaxis. In experiments designed to localize the site of action of oleic acid on neutrophil activation, an intracellular oleic acid-binding protein M(r) = 13,000) was isolated. The results suggest that acute changes in plasma fatty acid levels may have significant effects on neutrophil function under physiological conditions.