High dose eicosapentaenoic acid ethyl ester: effects on lipids and neutrophil leukotriene production in normal volunteers

Impact of expanded FDA indication for icosapent ethyl on enhanced cardiovascular residual risk reduction

Hypertriglyceridemia is associated with increased cardiovascular disease (CVD) risk. The Reduction of Cardiovascular Events with Icosapent Ethyl-Intervention Trial (REDUCE-IT) demonstrated that the purified, stable ethyl ester of eicosapentaenoic acid, icosapent ethyl (IPE), added to statins reduced CVD events by 25% (p < 0.001), leading to an expanded indication in the USA. IPE is now approved as an adjunct to maximally tolerated statins to reduce CVD event risk in adults with triglyceride (TG) levels ≥150 mg/dl and either established CVD or diabetes mellitus plus ≥2 additional CVD risk factors. The new indication allows co-administration of IPE for elevated TG levels with statin treatment, enabling effective residual risk reduction in a broader at-risk population beyond what can be achieved with intensive low-density lipoprotein cholesterol control alone.

Gut bacteria profiles of Mus musculus at the phylum and family levels are influenced by saturation of dietary fatty acids

BACKGROUND

Mammalian gut microbiota have been implicated in a variety of functions including the breakdown of ingested nutrients, the regulation of energy intake and storage, the control of immune system development and activity, and the synthesis of novel chemicals. Previous studies have shown that feeding mammalian hosts a high-fat diet shifts gut bacteria at the phylum level to reduce the ratio of Bacteroidetes-to-Firmicutes, while feeding hosts a fat-restricted diet increases this ratio. However, few studies have investigated the differential effects of fatty acid type on gut bacterial profile.

METHODS

Over a 14-week period, Mus musculus were fed a diet rich in omega-3 polyunsaturated fatty acids (n-3 PUFAs), omega-6 polyunsaturated fatty acids (n-6 PUFAs), or saturated fatty acids (SFAs). Fecal pellets were collected before and after the treatment period from 12 randomly selected mice (4 per treatment group). Bacterial DNA was extracted from the pellets and characterized by analysis of the hypervariable V3 region of the 16S rRNA. Nominal logistic regression models were used to assess shifts in microbial profile at the phylum and family levels in response to diet.

RESULTS

A significant decrease in the proportion of phylum Bacteroidetes species was observed for mice fed any of the three diets over time. However, the SFA-rich diet group showed a significantly greater decrease in Bacteroidetes proportion (-28%) than did either the n-3 PUFA group (-10%) or the n-6 PUFA group (-12%). At the family level, a significant decrease in proportion of Porphyromonadaceae was observed for mice fed the n-6 PUFA-rich diet, and a significant decrease in proportion of Lachnospiraceae was observed for mice fed the SFA-rich diet. There was no significant effect of diet type on body mass change.

CONCLUSION

Our results indicate that SFAs have stronger effects than PUFAs in shifting gut microbiota profiles toward those typical of obese individuals, and that dietary fatty acid saturation influences shifts in gut microbiota independently of changes in body mass.

ω-3 fatty acids attenuate mucosal inflammation in premature rat pups

BACKGROUND

Necrotizing enterocolitis (NEC) is a devastating intestinal disease of premature infants. Although ω-3 fatty acids are known to have antiinflammatory effects, their effect against NEC remains unclear.

METHODS

Mother rats fed a soybean-based, docosahexaenoic acid (DHA)- or eicosapentaenoic acid (EPA)-enriched diet from days 7 to 20 of gestation were examined. On day 20, the rat pups were delivered by abdominal incision, their intestines were removed, and messenger RNA was extracted. A rat NEC model was used to confirm the effects of ω-3 fatty acids on the inflamed intestine (n = 20-28). The expression of inflammatory molecules was analyzed by real-time polymerase chain reaction (n = 11-14).

RESULTS

The concentrations of DHA and EPA in the intestine were significantly increased in the DHA and EPA groups (P < .01). The expression of the antiinflammatory prostaglandin E2 receptor EP3 was increased in the DHA (P < .05) and EPA groups (P < .01). In the NEC model, the reduced incidence of colitis was confirmed in the DHA and EPA groups. The expression of peroxisome proliferator-activated receptor γ was increased (P < .05), and the inhibitor of nuclear factor-κB α/β decreased in both the DHA (P < .01) and EPA groups (P < .05).

CONCLUSION

Our findings indicate that ω-3 fatty acids are beneficial for protecting the premature intestine from inflammation by regulating eicosanoid- and nuclear factor-κB-related metabolite expression.

Dispelling the myths about omega-3 fatty acids

Although there is an enormous amount of information available on omega-3 fatty acids, it is sometimes misleading, contradictory, and unsupported by scientific fact. Consumers and medical professionals may be confused regarding the potential value of omega-3 fatty acid supplements, despite having either read or heard about fi sh oil consumption and/or omega-3 fatty acid benefits and risks. The availability of a prescription formulation of omega-3-acid ethyl esters (P-OM3) has provided important new information that helps to dispel the myths and alleviate concerns surrounding the use of omega-3 fatty acids in clinical practice. The safety and efficacy of P-OM3, but not dietary-supplement omega-3 fatty acids, are documented in placebo-controlled trials. In general, studies using Food and Drug Administration-approved dosages of P-OM3 have not substantiated various myths surrounding the negative effects of omega-3 fatty acids. Thus, there are now evidence-based clinical guidelines for the use of omega-3 fatty acids in clinical practice.

The independent effects of eicosapentaenoic acid and docosahexaenoic acid on cardiovascular risk factors in humans

PURPOSE OF REVIEW

This review details the independent effects of purified eicosapentaenoic acid and docosahexaenoic acid on cardiovascular risk factors in humans. We report data from the recent literature and our own controlled clinical trials which compared the independent effects of these fatty acids in individuals at increased risk of cardiovascular disease, namely overweight hyperlipidaemic men and treated-hypertensive, type 2 diabetic men and women. We discuss the biological effects of these fatty acids and the potential mechanisms through which they may affect cardiovascular disease risk factors.

RECENT FINDINGS

A cardioprotective effect for omega3 fatty acids is supported by prospective studies demonstrating an inverse association between fish intake and coronary heart disease mortality. Data from secondary prevention trials support a reduction in ventricular fibrillation as a primary mechanism for the decreased incidence of myocardial infarction. Clinical trials and experimental studies have shown that omega3 fatty acids have many other potentially important antiatherogenic and antithrombotic effects. Omega-3 fatty acids lower blood pressure and heart rate, improve dyslipidaemia, reduce inflammation, and improve vascular and platelet function. These favourable effects have until recently been primarily attributed to the omega3 fatty acid eicosapentaenoic acid, which is present in large amounts in fish oil. Controlled studies in humans now demonstrate that docosahexaenoic acid, although often present in lower quantities, has equally important anti-arrhythmic, anti-thrombotic and anti-atherogenic effects.

SUMMARY

Available evidence strongly suggests that eicosapentaenoic acid and docosahexaenoic acid have differing haemodynamic and anti-atherogenic properties. The effects of the two fatty acids may also differ depending on the target population.

A double-blind, randomized, placebo-controlled trial of essential fatty acid supplementation in the maintenance of remission of ulcerative colitis

BACKGROUND

Essential fatty acid supplementation has been found to ameliorate certain chronic inflammatory diseases. This effect is thought to be mediated through the modulation of eicosanoid synthesis. Pro-inflammatory eicosanoids have been implicated in ulcerative colitis.

AIM

To investigate the possible therapeutic benefit of essential fatty acids in quiescent ulcerative colitis to reduce the frequency of disease relapse.

METHODS

A randomized, double-blind, placebo-controlled study was performed with a treatment duration of 12 months. Patients with quiescent disease received either trial medication (gamma-linolenic acid, 1.6 g, eicosapentaenoic acid, 270 mg, and docosahexaenoic acid, 45 mg, per day) or placebo (sunflower oil, 500 mg/day). The primary end-point was disease activity, assessed by a previously validated clinical index, sigmoidoscopic appearance and histology.

RESULTS

Sixty-three patients were randomized, 31 to receive essential fatty acid treatment and 32 to receive placebo. Disease relapse rates were similar at 12 months (placebo, 38%; essential fatty acids, 55%), as were changes in sigmoidoscopic grade from baseline.

CONCLUSIONS

The supplementation of the diet with this combination of essential fatty acids does not prolong the period of disease remission of ulcerative colitis.

In vivo effects of highly purified docosahexaenoic acid on rectal insulin absorption

The purpose of this study was to evaluate the effectiveness and the toxicity of polyunsaturated fatty acid, such as oleic acid, eicosapentaenoic acid (DHA), as potential absorption enhancer for rectal delivery of insulin, using a water-in-oil-in water (W/O/W) multiple emulsion. In a single administration study, rectal insulin absorption was enhanced markedly, and marked hypoglycemia was induced by the emulsion incorporating various fatty acids in an insulin dose-related fashion. The pharmacological availability of the emulsion incorporating 2% oleic acid, EPA and DHA was approximately 7.7, 11.0 and 25.4%, respectively. The insulin absorption enhancement effect was not increased in proportion to the amount of DHA in the emulsion, the mean T(max) value of the serum glucose-time curve could be extended to twice that of the emulsion without PF 127. In a multiple administration study, the mean AUC(glucose) values of the emulsion incorporating DHA showed almost the same value on the first and the tenth day. From the morphological appearance of the mucosal surface, the emulsion incorporating DHA induced no or little mucosal damage. Our findings demonstrated that DHA has a strong insulin permeability enhancement effect and little toxicity. Thus, DHA is an attractive candidate as an absorption enhancer for intestinal delivery of insulin.

Reducing cell membrane n-6 fatty acids attenuate mucosal damage in food-sensitive enteropathy in mice

Mucosal damage is commonly observed in food-sensitive enteropathy in infants, and the generation of leukotrienes is involved in the pathogenesis of this enteropathy. Because supplementing n-3 fatty acids is known to modify the production of leukotrienes, we investigated whether a change of dietary fatty acid composition affects leukotriene synthesis and food hypersensitivity reactions in the intestine by using a mouse model of food-sensitive enteropathy. The model was prepared by feeding ovalbumin to BALB/c mice after intraperitoneal injection of cyclophosphamide. Diets were prepared from soybean oil (control), perilla oil, lard, corn oil, and 0.125 volume of corn oil (low fat diet) and given to mice for 4 wk. Villous heights, crypt depths, leukotriene B4 and C4 production in the intestine were measured. Crypt hyperplasia and villous atrophy were severer in the corn oil-fed group than those of control group, whereas mucosal damage in the perilla oil and low fat diet groups was minimal. In the corn oil-fed group, red blood cell membrane levels of n-3 fatty acids were lower than the control, and the synthesis of leukotrienes was highest among all groups. In the perilla oil and low fat diet groups, n-6 fatty acids were lower than those of control group and leukotriene production was significantly suppressed. These results indicate that reducing cell membrane levels of n-6 fatty acids by feeding less n-6 fatty acids or supplementing n-3 fatty acids, is important to suppress leukotriene biosynthesis for prevention from mucosal damage in food-sensitive enteropathy.

Eicosapentaenoic acid is primarily responsible for hypotriglyceridemic effect of fish oil in humans

The aim of this study was to determine whether eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA), or both, were responsible for the triglyceride (TG)-lowering effects of fish oil. EPA (91% pure) and DHA (83% pure), a fish oil concentrate (FOC; 41% EPA and 23% DHA) and an olive oil (OO) placebo (all ethyl esters) were tested. A total of 49 normolipidemic subjects participated. Each subject was given placebo for 2-3 wk and one of the n-3 supplements for 3 wk in randomized, blinded trials. The target n-3 fatty acid (FA) intake was 3 g/day in all studies. Blood samples were drawn twice at the end of each supplementation phase and analyzed for lipids, lipoproteins, and phospholipid FA composition. In all groups, the phospholipid FA composition changed to reflect the n-3 FA given. On DHA supplementation, EPA levels increased to a small but significant extent, suggesting that some retroconversion may have occurred. EPA supplementation did not raise DHA levels, however. FOC and EPA produced significant decreases in both TG and very low density lipoprotein (VLDL) cholesterol (C) levels (P < 0.01) and increases in low density lipoprotein (LDL) cholesterol levels (P < 0.05). DHA supplementation did not affect cholesterol, triglyceride, VLDL, LDL, or high density lipoprotein (HDL) levels, but it did cause a significant increase in the HDL2/HDL3 cholesterol ratio. We conclude that EPA appears to be primarily responsible for TG-lowering (and LDL-C raising) effects of fish oil.

Impact of polyunsaturated fatty acids on human colonic bacterial metabolism: an in vitro and in vivo study

Dietary polyunsaturated fatty acids (PUFA) reduce colonic proliferation and exert a mild laxative effect. We have studied the effect of the highly unsaturated eicosapentaenoic acid ethyl ester (EPA-EE) on the growth and metabolism of colonic bacteria in vitro, and in vivo. For the in vitro study, growth was assessed by viable counts. Bacteroides thetaiotaomicron was significantly inhibited in anaerobic media containing EPA-EE at concentrations > 7 milligrams. Escherichia coli was apparently resistant even at 100 milligrams. For the in vivo study, ten healthy volunteers ingested 18 g EPA-EE/d for 7 d. Stool frequency, 24 h stool weight and whole-gut transit time were assessed together with breath H2 and 14CO2 excretion following oral ingestion of 15 g lactitol labelled with 0.18 MBq [14C]lactitol. The area under the breath-H2-time curve was significantly reduced by EPA-EE, from a control value of 690.3 (SE 94.2) ppm.h to 449.5 (SE 91.7) ppm.h. Percentage dose of 14CO2 excreted, total stool weight and whole-gut transit time were unaltered, being respectively 24 (SE 2)%, 281 (SE 66) g and 45 (SE 4) h with EPA-EE v. control values of 27 (SE 1)%, 300 (SE 89) g and 42 (SE 5) h. It is concluded that dietary supplementation with EPA-EE reduces breath H2 excretion without apparently impairing overall colonic carbohydrate fermentation. The observed reduction may reflect utilization of H2 to hydrogenate the five double bonds of EPA-EE.

Eicosapentaenoic acid modulates arachidonic acid metabolism in rat alveolar macrophages

Eicosapentaenoic acid (EPA) is an unsaturated fatty acid contained in fish oils. In order to clarify the mechanism of its anti-inflammatory effects on the lung, we studied arachidonic acid (AA) metabolism by in vitro exposure of rat alveolar macrophages to EPA. EPA was found to inhibit the endogenous production of leukotriene B4 (LTB4) from AA. At a low concentration of EPA, generation of LTB5 was increased, while at a high concentration it was decreased. These results suggest that at a lower concentration EPA may be competitive with AA as a substrate, and that at a higher concentration it may directly inhibit AA metabolism via inhibition of 5-lipoxygenase or phospholipase A2.

Metabolism of omega-3 fatty acids in patients with autosomal dominant retinitis pigmentosa

Abnormalities in lipid metabolism have been reported in numerous patients with retinitis pigmentosa. As an initial step in evaluating these anomalies, two trials of fatty acid intervention were conducted with autosomal dominant retinitis pigmentosa (adRP) patients and controls. The first trial addressed absorption and incorporation of omega 3 long-chain fatty acids from a fish-oil concentrate into red blood cell (RBC) lipids. The utilization of omega 3 long-chain fatty acids by adRP patients was found to be equivalent to that of controls. The second trial addressed the conversion of precursor, eicosapentaenoic acid (EPA, 20:5 omega 3), to end-product, docosahexaenoic acid (DHA, 22:6 omega 3), following oral supplementation of EPA ethyl ester. Although the levels of EPA and the intermediate, docosapentaenoic acid (22:5 omega 3), were both elevated by EPA supplementation in RBCs of adRP patients with rhodopsin gene mutations and controls, DHA production was elevated only in controls. Based on these results, we suggest the presence of a metabolic defect in the final stages of DHA biosynthesis.

Low dose aspirin: selective inhibition of rectal dialysis thromboxane B2 in healthy volunteers

AIM

To investigate the degree and selectivity of rectal thromboxane inhibition by low dose aspirin and there by investigate the contribution of platelet thromboxane to rectal thromboxane.

METHODS

The study was a randomized double-blind placebo controlled crossover study. Twelve healthy volunteers were studied, each over four separate study periods with two weeks wash-out between each period. Changes in levels of thromboxane (TX) B2, prostaglandin (PG) E2 and leukotriene (LT) B4 in rectal dialysates were measured in response to 5 days oral low dose aspirin therapy in one of three once-daily formulations (plain 75 mg, plain 300 mg or enteric coated 300 mg), and compared to placebo. For each study period, rectal dialysates (4 h duration) were obtained at baseline and twice more after 5 days of aspirin or placebo therapy. Dialysate levels of thromboxane B2, leukotriene B4, prostaglandin E2, and serum thromboxane B2 were measured by radioimmunoassay.

RESULTS

Dialysate thromboxane B2 levels were consistently inhibited by low dose aspirin (overall results of all formulations, 75 to 300 mg daily) from 1.06 ng/ml (geometric mean, 95% CI: 0.79-1.43 ng/ml) on placebo, by 29% (95% CI: 11-40%) to 0.75 ng/ml (0.56-1.01 ng/ml) (P = 0.046) on aspirin. In the absence of aspirin the level of prostaglandin E2 was 1.47 ng/ml (0.97-2.23 ng/ml) and in the presence of aspirin was not significantly changed. The dialysate level of leukotriene B4 was 0.45 ng/ml (0.34-0.61 ng/ml) in the absence of aspirin and there was no significant change on low dose aspirin. Serum thromboxane was inhibited by 80% to 20% of placebo values by plain aspirin 75 mg, by 95% by plain aspirin 300 mg, and by 82% by enteric coated aspirin 300 mg, respectively (P < 0.01). These results show that 29% of the rectal thromboxane, but none of the rectal prostaglandin E2 or leukotriene B4 is inhibited by low dose aspirin. We infer that 34% of the rectal thromboxane B2 is platelet-derived in our volunteers.

CONCLUSION

Low dose aspirin will selectively inhibit a proportion of rectal thromboxane and may have prophylactic therapeutic potential in inflammatory bowel disease.

Interobserver variation in assessment of gastroduodenal lesions associated with non-steroidal anti-inflammatory drugs

Video endoscopic images were used to investigate whether gastroenterologists could agree on the definition of lesions within the stomach seen at endoscopy, with particular reference to those seen in patients taking non-steroidal anti-inflammatory drugs. Seven experienced endoscopists, unaware of the patients' clinical history or drug consumption, recorded their classification for 93 randomised video images of gastric lesions. There was complete agreement in the diagnosis of ulceration for nine images from patients who were not taking non-steroidal anti-inflammatory drugs; eight of nine were classified as deep ulcers, with 86% agreement for this subclassification. By contrast, the overall agreement for lesions in patients taking non-steroidal anti-inflammatory drugs was only 55%. Only nine of 44 ulcers were subclassified as deep, and there was considerable cross classification of non-haemorrhagic erosions and ulcers. In conclusion, ulcers that occur in patients taking non-steroidal anti-inflammatory drugs differ from those in patients who are not taking these drugs in that they are often more superficial and difficult to distinguish from erosions. The prognostic importance of these lesions is, therefore, uncertain.

Healing and prevention of NSAID-induced peptic ulcers

Non-steroidal anti-inflammatory drug (NSAID) ingestion is associated with erosions, petechiae, type C gastritis, ulceration, interference with ulcer healing, ulcer complications and injury to the small and large intestines. In the UK, NSAIDs can probably be linked to approximately 1200 deaths per year, mainly in the elderly. Inhibition of prostaglandin synthesis plays a major part in NSAID-induced gastric mucosal injury, whilst inhibition of thromboxane synthesis by platelets and impaired platelet aggregation may contribute to ulcer bleeding. There is evidence to show that the impairment of healing of gastric and duodenal ulcer that is associated with concomitant NSAID therapy can be overcome by the use of omeprazole. Acid inhibition has been shown to be effective in prophylaxis of NSAID-induced duodenal lesions. Studies on the prevention of NSAID-associated gastric lesions have indicated that ranitidine is less effective than misoprostol, but that treatment with the latter is associated with a number of side effects, principally in the gastrointestinal tract (e.g. diarrhoea). Whether omeprazole will prevent gastric and duodenal ulceration due to NSAID ingestion is the subject of ongoing research, but studies of acute ulceration have shown efficacy against erosions and microbleeding.

Neuropsychiatric development: two case reports about the use of dietary fish oils and/or choline supplementation in children

Choline supplementation has been used with moderate success in subgroups of adult patients with neuropsychiatric and medical problems. The dietary fish oils have also been used in adults with hypercholesterolemia. We report on two young children with multiple neurodevelopmental delays, one who responded to choline and eicosapentaenoic acid, and the other to choline alone. A brief discussion about choline's metabolic pathways and benefits is included.

The enteral bioavailability of eicosapentaenoic acid and docosahexaenoic acid is as good from ethyl esters as from glyceryl esters in spite of lower hydrolytic rates by pancreatic lipase in vitro

Enteral absorption by healthy male volunteers of cis-5,8,11,14,17-eicosapentaenoic acid (20:5(n-3), EPA) and cis-4,7,10,13,16,19-docosahexaenoic acid (22:6(n-3), DHA) from an ethyl ester enriched in EPA and DHA (K85) and from natural fish oil (TG30) was found to be similar after intake of equivalent doses. Thus, after administration twice daily for 14 days, the amounts of EPA and DHA in total serum lipids and in serum phospholipids were essentially identical for the two ester forms of the n-3 fatty acids. A dose-dependent relationship between intake and total phospholipid serum levels was observed for EPA, which increased 6.5-12-fold and 4.8-9-fold, respectively, but DHA reached a plateau at 2-2.5-fold over the control after supplementation. Arachidonic acid (AA) did not change significantly in total serum lipids, but fell 10-20% in serum phospholipids. The supplementation resulted in a 6.3-11-fold increase in the EPA/AA ratio. A significant and dose-dependent 25-45% reduction in linoleic acid (18:2(n-6), LA) was found in serum phospholipids, while a smaller decrease was observed in total serum lipids. 20:3(n-6), 20:3(n-9) and 22:5(n-6) also decreased significantly in serum phospholipids. Saturated fatty acids remained essentially unchanged. Some 35-47% decrease in serum triacylglycerols and approx. 10% decrease in cholesterol levels were also observed. In spite of the similar serum levels of EPA and DHA obtained in vivo, in vitro hydrolysis by porcine pancreatic lipase of K85 was 3-fold slower than hydrolysis of a glyceryl ester (TG85) similarly enriched in EPA and DHA, and 15-fold slower than the hydrolysis of the 3-fold less enriched TG30 with EPA and DHA predominantly in the 2-position. Under similar conditions release of AA from glyceryl ester and ethyl ester was essentially similar and approx. 1.5-fold faster than release of EPA and DHA from ethyl esters. In vitro hydrolysis of olive oil was 1.8-fold faster than hydrolysis of a natural fish oil (TG30) under similar conditions. Thus, the order of the rates of hydrolyses was olive oil > TG30 > TG85 > triarachidonin > LA ethyl ester > AA ethyl ester > ethyl ester K85. Our results show that in spite of differences in the rate of hydrolysis by lipase in vitro, the enteral absorption of EPA and DHA is as least as good from a synthetic ethyl ester highly enriched in EPA and DHA as it is from a natural triacylglycerol containing equivalent amounts of these fatty acids.

Dietary omega-3 polyunsaturated fatty acids inhibit phosphoinositide formation and chemotaxis in neutrophils

Earlier studies demonstrated that dietary omega-3 polyunsaturated fatty acid (PUFA) supplementation attenuates the chemotactic response of neutrophils and the generation of leukotriene (LT) B4 by neutrophils stimulated with calcium ionophore; however, the mechanisms and relationship of these effects were not examined. Neutrophils and monocytes from eight healthy individuals were examined before and after 3 and 10 wk of dietary supplementation with 20 g SuperEPA daily, which provides 9.4 g eicosapentaenoic acid (EPA) and 5 g docosahexaenoic acid. The maximal neutrophil chemotactic response to LTB4, assessed in Boyden microchambers, decreased by 69% after 3 wk and by 93% after 10 wk from prediet values. The formation of [3H]inositol tris-phosphate (IP3) by [3H]inositol-labeled neutrophils stimulated by LTB4 decreased by 71% after 3 wk (0.033 +/- 0.013% [3H] release, mean +/- SEM) and by 90% after 10 wk (0.011 +/- 0.011%) from predict values (0.114 +/- 0.030%) as quantitated by beta-scintillation counting after resolution on HPLC. LTB4-stimulated neutrophil chemotaxis and IP3 formation correlated significantly (P < 0.0001); each response correlated closely and negatively with the EPA content of the neutrophil phosphatidylinositol (PI) pool (P = 0.0003 and P = 0.0005, respectively). Neither the affinities and densities of the high and low affinity LTB4 receptors on neutrophils nor LTB4-mediated diglyceride formation changed appreciably during the study. Similar results were observed in neutrophils activated with platelet-activating factor (PAF). The summed formation of LTB4 plus LTB5 was selectively inhibited in calcium ionophore-stimulated neutrophils and was also inhibited in zymosan-stimulated neutrophils. The inhibition of the summed formation of LTB4 plus LTB5 in calcium ionophore-stimulated neutrophils and in zymosan-stimulated neutrophils did not correlate significantly with the EPA content of the PI pool. The data indicate that dietary omega-3 PUFA supplementation inhibits the autoamplification of the neutrophil inflammatory response by decreasing LTB4 formation through the inactivation of the LTA epoxide hydrolase and independently by inhibiting LTB4- (and PAF) stimulated chemotaxis by attenuating the formation of IP3 by the PI-selective phospholipase C. This is the initial demonstration that dietary omega-3 PUFA supplementation can suppress signal transduction at the level of the PI-specific phospholipase C in humans.

Therapeutic interventions in gastrointestinal disease based on an understanding of inflammatory mediators

Whatever initiates inflammation, the final message mediating cellular invasion is chemical. This consideration allows rational development of anti-inflammatory treatments. Two main classes of chemotactic mediator are recognised. Water-soluble peptides, e.g. cytokines derived from macrophages and other cells, play an important integrating part in the early recruitment of neutrophils and mononuclear cells, and in the amplification of immune responses. Lipid-soluble mediators, of which leukotriene B4 is the most highly chemotactic for neutrophils, are important in secondary amplification. In inflammatory bowel disease, we have shown evidence of increased synthesis of cytokines interleukin 1, 6 and 8. These are associated with activation of circulating monocytes in active Crohn's disease, of lamina propria macrophages in relapse of both ulcerative colitis and Crohn's disease, and development of adhesion molecules on vascular endothelium. Our studies show that interleukin 6 is selectively increased in Crohn's disease, whilst preliminary findings suggest that enhanced synthesis of interleukin 8 is particularly characteristic of ulcerative colitis. Patterns of cytokine synthesis may, therefore, be of diagnostic value. They also offer the potential for therapeutic strategies since cytokine antagonists are becoming available. We have also demonstrated increased synthesis of leukotrienes in active inflammatory bowel disease. Since leukotriene B4 is quantitatively the main chemotactic signal in the mucosa in inflammatory bowel disease during relapse, we investigated the therapeutic effect of suppressing leukotriene B4 synthesis by treating patients with fish oil (as Hi-EPA), giving 4.5 g daily of eicosapentaenoic acid. This competes for the 5-lipoxygenase enzymes, inhibiting leukotriene B4 and promoting synthesis of the less chemotactic product, LTB5.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of ulcerative colitis with fish oil supplementation: a prospective 12 month randomised controlled trial

The effect of fish oil on the course of ulcerative colitis was investigated in a randomised blinded controlled study. Eighty seven patients received supplements of 20 ml HiEPA fish oil as triglyceride (4.5 g of eicosapentaenoic acid) or olive oil placebo daily for one year. The oils were given in addition to standard drug therapy and trial entry was stratified for disease activity. Fish oil significantly increased the eicosapentaenoic acid content of rectal mucosa to 3.2% of total fatty acids at six months, compared with 0.63% for patients on olive oil. This was associated with increased synthesis of leukotriene B5, and 53% suppression of leukotriene B4 synthesis by ionophore--stimulated neutrophils. Leukotriene B4 suppression persisted for at least two months after treatment was stopped. Treatment with fish oil resulted in measurable, but only limited clinical benefit. For patients entering the trial in relapse (n = 53), there was a significant reduction in corticosteroid requirement after one and two months treatment. There was a trend towards achieving remission (off corticosteroids) faster in the patients on fish oil, although differences were not significant. For patients in remission at trial entry or during the trial (n = 69), there was no significant difference in the rate of relapse by log rank analysis. We conclude that fish oil supplementation produces a modest corticosteroid sparing effect in active disease, but there is no benefit in maintenance therapy.

Immunosuppressive effects of fish oil in normal human volunteers: correlation with the in vitro effects of eicosapentanoic acid on human lymphocytes

We have studied the effects of dietary supplementation with fish oil on immunological parameters in a group of six normal volunteers, four of whom received a fish oil extract (total EPA dose of 2.4 g/day, which is on the lower range of clinically effective doses) for 6 weeks and two of which received a placebo (olive oil) for an identical period of time. Each volunteer was followed up for a period of 23 weeks after the dietary intervention was ended. All volunteers were boosted with tetanus toxoid (TT) at the onset of the trial. Several immune parameters were followed longitudinally, including NBT reduction and lysozyme release to test neutrophil function; lymphocyte subpopulations; mitogenic responses to phytohemagglutinin (PHA), concanavalin A (Con A) and anti-CD3; IL-2 release after PHA and pokeweed mitogen (PWM) stimulation; immunoglobulin and anti-TT antibody (ATT) synthesis by stimulated lymphocytes; and serum levels of immunoglobulins and of ATT. No consistent changes were observed in neutrophil function tests, mitogenic responses to PHA and Con A, and lymphocyte subsets. The mitogenic response to anti-CD3 and the release of IL-2 after stimulation with PHA and PWM appeared reduced as a consequence of fish oil ingestion, and levels of serum immunoglobulins decreased in three of the volunteers receiving fish oil supplementation. The systemic humoral response after the TT booster appeared not to be influenced by the ingestion of fish oil. However, in those subjects who were given fish oil supplementation, the specific in vitro response of their peripheral blood lymphocytes to TT appeared to be compromised at Week 3. This could reflect the need for progressive accumulation of EPA in lymphocyte membranes for the suppressive effect to be detectable, but it could also reflect a differential sensitivity to the effects of fish oil of circulating B lymphocytes vs. bone marrow B lymphocytes. All the parameters apparently affected by fish oil ingestion were also affected by the incubation of normal lymphocytes with EPA in vitro. In conclusion, low doses of fish oil may have a mild immunosuppressive effect affecting both T and B cell functions. These observations stress the need for more extensive trials designed to determine whether immunosuppressive effects can be consistently elicited and for studies aimed at determining the mechanisms by which omega-3 fatty acids affect the immune system.