Modulation of exercise-induced immunosuppression by dietary polyunsaturated fatty acids in mice

The possible interaction between intense exercise, known to suppress the immune response, and nutritive factors, such as polyunsaturated fatty acids (PUFA), was examined in inbred female C57Bl/6 mice. The animals received for 8 wk either a natural ingredient diet or a diet supplemented with 10 g/100 g linseed oil containing over 50% of 18:3 (n-3) alpha-linoleic acid. Other groups received PUFA containing only traces of 18:3 (n-3) fatty acid; beef tallow, containing mostly 18:1 (n-9) saturated fat, safflower oil, an 18:2 (n-6) PUFA, and fish oil, containing longer chain (n-3) PUFA. Each dietary group was divided into two subgroups: sedentary diet controls and exercised animals. Exercise consisted of continuous swimming at high intensity until exhaustion. It was shown in three separate experiments that (1) the primary humoral response to sheep red blood cells, determined by the plaque-forming cell (PFC) assay, was affected by PUFA diet in sedentary animals in the order beef tallow > control diet > safflower oil > fish oil > linseed oil, and (2) the PFC response was suppressed by the exhaustive exercise, as compared to sedentary controls, except for animals fed 18:3 (n-3) linseed oil, where the normal response was noted. Phagocytosis of fluorescent microspheres by peritoneal macrophages, determined by flow cytometry, was significantly lower in exercised animals receiving the linseed oil diet, whereas other diets either increased or did not significantly change the macrophage phagocytic activity, compared to the sedentary diet controls. Spleen lymphocyte subsets were unchanged in exercised animals except for a marked shift from the lymphoid peak toward the erythroid peak. Generally, our data showed a marked immunomodulatory effect of 18-3 (n-3) alpha-linoleic acid on the exhaustive exercise-related immunosuppression, as compared to the effects of other selected PUFA.     

Long-chain polyunsaturated fatty acids

Long-chain polyunsaturated fatty acids (LC-PUFA) are essential for normal development. Fetal accretion of LC-PUFA occurs during the last trimester of gestation; therefore, premature infants are born with minimal LC-PUFA reserves. Recent studies indicate that the newborn can synthesize LC-PUFA from essential fatty acid precursors; however, the extent of de novo synthesis remains to be established. Postnatally, human milk provides LC-PUFA to the newborn. Maternal LC-PUFA reserves depend upon diet and can be improved by supplementation of docosahexaenoic acid and arachidonic acid during pregnancy and lactation. This in turn affects fetal LC-PUFA accretion and postnatal provision through mother's milk. Supplementation of formula-fed preterm or full-term infants with docosahexaenoic acid and arachidonic acid leads to plasma and red blood cell LC-PUFA levels similar to those of breast-fed infants. The higher blood and presumably tissue levels of LC-PUFA following supplementation lead, however, to only temporary functional benefits.     

Peroxisomal beta-oxidation of polyunsaturated fatty acids

Peroxisomes have been shown to play an important role in the oxidative degradation of (poly)unsaturated fatty acids, and contain the enzyme activities needed for the metabolism of double bonds of unsaturated fatty acids in connection with this physiological function. Our understanding of the metabolic pathways and enzyme activities involved in the degradation of unsaturated acyl-CoAs has undergone a re-evaluation recently, and though many open questions still remain significant progress has been made, especially concerning the reactions metabolizing double bonds. The enzyme activities to be discussed here are 2,4-dienoyl-CoA reductase; 3/2-enoyl-CoA isomerase; 2-enoyl-CoA hydratase 2; 5-enoyl-CoA reductase and 3,5/2,4-dienoyl-CoA isomerase. Some of these activities are integral parts of the multifunctional proteins of beta-oxidation systems, which must also be taken into account in this context.     

Regulation of tumour cell fatty acid oxidation by n-6 polyunsaturated fatty acids

The aim of this study was to evaluate acute effects of ethyl tert-butyl ether (ETBE) in man after short-term exposure. ETBE may in the future replace methyl tert-butyl ether, a widely used oxygenate in unleaded gasoline. Eight healthy male volunteers were exposed to ETBE vapor for 2 h at four levels (0, 5, 25, and 50 ppm) during light physical exercise. The subjects rated irritative symptoms, discomfort, and central nervous system effects in a questionnaire. Ocular (eye redness, tear film break-up time, conjunctival epithelial damage, and blinking frequency), nasal (acoustic rhinometry and analysis of inflammatory markers and cells in nasal lavage fluid), and pulmonary (peak expiratory flow, forced expiratory volume in 1 s, forced vital capacity, vital capacity, and transfer factor) measurements were performed. Significantly increased ratings of solvent smell (p = 0.001, repeated-measures ANOVA) were seen during exposures and correlated to exposure levels. Furthermore, significantly elevated ratings of discomfort in throat and airways were seen during and after 50 ppm compared to the control exposure (p = 0.02). Increased nasal swelling (p = 0.001) and blinking frequency (p = 0.01) were noted at all exposure levels, but their magnitudes were not related to exposure levels. A slightly impaired pulmonary function was seen at 25 and 50 ppm, since forced vital capacity (p = 0.02) and vital capacity (p = 0.04) differed significantly from the clean air exposure. Although the impairments seemed to fall within normal inter- and intraindividual variation and have no clinical relevance as such, it cannot be excluded that other individuals may react more severely than eight healthy male volunteers in this study.     

Modulation of breast cancer cell adhesion by unsaturated fatty acids

Triglycerides, which are major constituents of dietary fat, contain a mixture of saturated and unsaturated fatty acids. One newly recognized function of unsaturated fatty acids is modulation of cell adhesion to components of the extracellular matrix. Alterations in cell adhesiveness or cell adhesion molecule expression accompany the onset of a number of diseases including arthritis, atherosclerosis, and cancer. Cell adhesion is necessary for the metastatic spread of cancer cells to new organs. Circulating cancer cells adhere to endothelial cells and the underlying subendothelial basement membrane as an initial step in the process of invading target organs during metastasis. Several recent studies have provided convincing evidence that unsaturated fatty acids and their metabolites influence adhesion of cultured human cancer cells to individual components of the basement membrane. These unsaturated fatty acid effects appear to be dependent in some instances on the expression of specific cell surface adhesion molecules. Unsaturated fatty acids influence the development of metastases in animal tumor models by largely unexplored mechanisms; the possibility that cell adhesion is involved in this process has not been thoroughly investigated. Future studies of unsaturated fatty acid effects on cell adhesion molecule expression in breast cancer patients should reveal the clinical relevance of the studies reviewed here.     

The benefits and risks of n-3 polyunsaturated fatty acids

There is a growing number of animal models and clinical trials of n-3 polyunsaturated fatty acid (PUFAs) supplementation in disease. Epidemiologic and biochemical studies have suggested beneficial effects of n-3 PUFAs. But also, the use of n-3 PUFAs has some potential toxicological risks that can be circumvented by careless processing, storing, and preserving the PUFAs. The use of n-3 PUFAs is safe if appropriate preparations and dosages are selected. Much research is needed to clarify their use under different disease conditions. The newly established clinical and nutritional facts on n-3 PUFAs will induce industry to develop food products based on this knowledge.     

Incorporation of n-3 polyunsaturated fatty acids into processed foods

The aim of dose reduction of chemotherapeutic agents following weight loss is to avoid excessive toxicity while maintaining an equivalent therapeutic effect. Several methods of calculating this dose reduction are currently in use, including dose reduction in proportion to the reduction in body surface area (BSA) or the amount of weight lost and no dose reduction unless significant toxicity occurs. Each of these methods results in the administration of a different dose and therefore different drug exposure, as measured by the area under the time versus concentration curve (AUC). We have used pharmacokinetic modeling software and normative data on the pharmacokinetics of high-dose methotrexate to determine the change in AUC resulting from dose reduction by each of the methods cited for patients with weight loss. Dose reduction in proportion to the reduction in weight results in the same AUC and therefore equivalent drug exposure as before weight loss. In contrast, the more common practice of dose reduction in proportion to the decrease in BSA (as determined by recalculating BSA) results in a higher AUC than before weight loss. This results in increased drug exposure and potentially increased toxicity, which may be avoided if dose reduction is carried out in proportion to the decrease in weight rather than in BSA. The same principles are applicable to other drugs, particularly those associated with dose-dependent toxicity.     

The effects of n-6 polyunsaturated fatty acids on the expression of nm-23 in human cancer cells

Over an interval of approximately six months beginning in October 1993, most haemophilia A patients in Canada were switched from a plasma-derived intermediate-purity factor VIII concentrate (i.p. VIII) to a recombinant factor VIII (rVIII). In order to determine the consequence of this change in therapy on progression of HIV infection, we gathered surveillance data on clinical status and CD4 and CD8 cell counts in those patients who were HIV seropositive at the time of switching concentrates. Data were recorded at the time of switchover, annually for 2 years thereafter, and retrospectively at a point 1 year prior to the switch. CD4 cells fell significantly over the study period. Multiple direct comparisons revealed that this decline was restricted to the time intervals which included the final year in which patients received intermediate-purity factor VIII concentrate (i.p. VIII). In the 2 year interval in which rVIII was used exclusively, there was a nonsignificant fall in CD4 cells. Changes in CD4 cells did not correlate with the intensity of exposure to either i.p.VIII or rVIII. CD8 cells did not fall significantly over the study period. There was no obvious reduction in the incidence of death or clinical progression over the 2 years in which rVIII was used. However, we are hopeful that the stabilizing trend in CD4 cell counts which followed the introduction of rVIII will be predictive of corresponding clinical stabilization over the coming years.     

Immunoregulatory and anti-inflammatory effects of n-3 polyunsaturated fatty acids

1. Fish oils are rich in the long-chain n-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) acids. Linseed oil and green plant tissues are rich in the precursor fatty acid, alpha-linolenic acid (18:3n-3). Most vegetable oils are rich in the n-6 PUFA linoleic acid (18:2n-6), the precursor of arachidonic acid (20:4n-6). 2. Arachidonic acid-derived eicosanoids such as prostaglandin E2 are pro-inflammatory and regulate the functions of cells of the immune system. Consumption of fish oils leads to replacement of arachidonic acid in cell membranes by eicosapentaenoic acid. This changes the amount and alters the balance of eicosanoids produced. 3. Consumption of fish oils diminishes lymphocyte proliferation, T-cell-mediated cytotoxicity, natural killer cell activity, macrophage-mediated cytotoxicity, monocyte and neutrophil chemotaxis, major histocompatibility class II expression and antigen presentation, production of pro-inflammatory cytokines (interleukins 1 and 6, tumour necrosis factor) and adhesion molecule expression. 4. Feeding laboratory animals fish oil reduces acute and chronic inflammatory responses, improves survival to endotoxin and in models of autoimmunity and prolongs the survival of grafted organs. 5. Feeding fish oil reduces cell-mediated immune responses. 6. Fish oil supplementation may be clinically useful in acute and chronic inflammatory conditions and following transplantation. 7. n-3 PUFAs may exert their effects by modulating signal transduction and/or gene expression within inflammatory and immune cells.     

Prevention of ischemia-induced cardiac sudden death by n-3 polyunsaturated fatty acids in dogs

The objective of this study was to obtain functional information associated with the prevention by n-3 polyunsaturated fatty acids (PUFA) of ischemia-induced fatal cardiac ventricular arrhythmias in the intact, conscious, exercising dog. Thirteen dogs susceptible to ischemia-induced ventricular fibrillation were prepared surgically by ligation of their anterior descending left coronary artery and placement of an inflatable cuff around their left circumflex artery. After 4 wk of recovery, exercise-plus-ischemia tests were performed without and then with an intravenous infusion of an emulsion of free n-3 PUFA just prior to occluding the left circumflex artery while the animals were running on a treadmill. One week later the exercise-plus-ischemia test was repeated but with a control infusion replacing the emulsion of n-3 PUFA. The infusion of the free n-3 PUFA in quantities of 1.0 to 10 g prevented ventricular fibrillation in 10 of the 13 dogs tested (P < 0.005), apparently without esterification of the PUFA into membrane phospholipids. The antiarrhythmic effect of the n-3 PUFA was associated with slowing of the heart rate, shortening of the QT-interval (electrical action potential duration), reduction of left ventricular systolic pressure, and prolongation of the electrocardiographic atrial-ventricular conduction time (P-R interval). These effects are comparable with those we have reported in studies with cultured neonatal rat cardiac myocytes.     

Do long-chain polyunsaturated fatty acids influence infant cognitive behaviour?

OBJECTIVE: To determine: (i) the proportion of vesicoureteric reflux (VUR) associated with congenital renal damage and whether it can be severe enough to cause renal impairment from birth: (ii) to evaluate the distribution of males and females affected; and (iii) to describe the course of congenital damage in the first years of life. PATIENTS AND METHODS: A total of 108 children (76 male and 32 female, M:F 2.3:1), whose VUR was diagnosed before any infection, were followed from birth for a mean (range) of 4.3 (1-10) years. Renal damage was defined by serum creatinine concentration, creatinine clearance and renal imaging (ultrasonography and renal scintigraphy) performed within the first month of life and periodically thereafter. RESULTS: Of the 108 children, 58 had bilateral and 50 unilateral reflux (total number of refluxing units, 166). High-grade VUR (grade > or = 4) was found in 96 (58%) refluxing renal units (RRUs). Males had a prevalence of bilateral severe (> or = grade 4) reflux (M:F 5.2:1), while in those wit unilateral VUR, the M:F ration was 1.5:1. At birth, mild to moderate damage was present in 56 (36%) RRUs and only associated with VUR of grade > or = 3. Bilateral reflux of grade > or = 4 was associated with congenital moderate/severe renal failure in nine neonates (seven males). In infants with grade > or = 4 VUR who underwent surgical correction, VUR resolved in 92% of cases. In infants with VUR of grade > or = 4 followed medically, the reflux spontaneously resolved in 42% and ameliorated in 16% after 18 months. Serial renal scans during the follow-up showed no progression of renal damage. CONCLUSIONS: VUR diagnosed at birth on prenatal ultrasonography is associated with congenital damage, with males affected more often than females. The damage involves both kidneys in a consistent proportion and is an important cause of chronic renal impairment from birth. It does not progress in the first years of life if infections are prevented. It is suggested that males with this condition may constitute a major group at risk of developing chronic renal failure in later life.     

Omega-3 polyunsaturated fatty acids in rodent models of breast cancer

Quantitative increases in certain dietary fats promote mammary tumor growth, but the experimental data indicate that this tumor promoting capability is not equally expressed by all fatty acid families. There is a large body of evidence from experiments using either carcinogen-induced or transplanted animal mammary tumor models, as well as in vitro studies, which demonstrates that the omega-6 polyunsaturated fatty acids (PUFA) promote mammary tumor development more effectively than omega-3 PUFA. These data indicate that increases in the dietary levels of omega-6 PUFA enhance tumor development, while equivalent increases in dietary levels of omega-3 PUFA often delay or reduce tumor development. Several theoretical mechanisms have been proposed for these contrasting results, but as yet, no definitive explanation has been universally accepted.     

n-3 versus n-6 polyunsaturated fatty acids in critical illness

The aim of this study was to evaluate bone mineral density changes in patients with juvenile chronic arthritis (JCA) and to determine the most likely causes of osteoporosis in these patients. Eighteen (11 male, 7 female) patients suffering from JCA and 14 healthy controls (10 male, four female) were included in this study. The mean age of the patients and control groups were 11.0 +/- 3.2 and 10.9 +/- 2.9 years respectively. Disease activity was determined by clinical and laboratory evaluation and 'Articular Disease Severity Score' (ADSS). Bone mineral density (BMD) of the femoral neck and lumbar spine was measured by dual photon absorptiometry. BMD of the patients at the lumbar spine was significantly lower than the control group (p < 0.05). This difference was more marked in patients treated with steroids. Femoral neck BMD was also lower in the patient group but this difference was not statistically significant. There was a negative correlation between ADSS and BMD at the spine. In conclusion, trabecular bone loss is characteristic for osteoporosis in JCA. Our results indicate that steroid treatment and disease severity are important factors in the development of osteoporosis in JCA.     

N-3 polyunsaturated fatty acids modulate the expression of functionally associated molecules on human monocytes and inhibit antigen-presentation in vitro

N-3 polyunsaturated fatty acid (PUFA)-rich diets are associated with suppression of cell-mediated immune responses, but the mechanisms are unclear. Specific immune responses are initiated by antigen-presenting cells (APC). We have previously shown in vitro that the n-3 PUFA, eicosapentaenoic acid (EPA), inhibits the expression of HLA-DR, an MHC class II molecule required for normal APC function on human blood monocytes. In contrast, docosahexaenoic acid (DHA) enhanced the expression of this molecule on unstimulated monocytes, but both n-3 PUFA suppressed its expression on interferon-gamma (IFN-gamma)-activated monocytes. In the present study we show that when EPA and DHA were combined at the same ratio as is commonly found in fish oil supplement capsules (3:2) there was no significant effect in vitro on the expression of HLA-DR on unstimulated monocytes, but the expression on IFN-gamma-activated monocytes remained significantly inhibited. In the same in vitro system a significant reduction in the ability of IFN-gamma-activated monocytes to present tetanus toxoid antigen to autologous lymphocytes was observed following culture with the combined n-3 PUFA. These findings support previous animal studies which suggest that n-3 PUFA can inhibit the antigen-presenting function of mononuclear phagocytes.     

Inclusion of chufa in the human diet as a source of polyunsaturated fatty acids

In 2 experiments lasting 30 days each with participation of 6 volunteers the possibility of daily consumption in the diet of chufa in an amount allowing for minimal requirement of the organism in polyunsaturated fatty acids was studied. The experimental food ration accorded with individual requirements in its basic components. None of the participating volunteers demonstrated any untoward deviations of objective and subjective nature in their health status. For a month chufa was introduced daily at the rate of 1.7 g per kg of body weight.