Alteration in mouse splenic phospholipid fatty acid composition and lymphoid cell populations by dietary fat

Fish oil supplementation benefits the murine host during the acute phase of a parasitic infection from Trypanosoma cruzi

Long-chain omega-3 polyunsaturated fatty acids (LC n-3 PUFA) are known to modulate a variety of immune cell functions. On occasion, this has led to diminished host resistance to certain viral and bacterial infections. Little is known about the impact of n-3 PUFA on host resistance to parasitic infection, however, based on results from a small study conducted more than two decades ago, we hypothesized that providing mice LC n-3 PUFA will diminish host resistance to Trypanosoma cruzi, the parasitic pathogen responsible for Chagas disease. To investigate this, C57BL/6 mice were supplemented by gavage (0.6% v/w) with phosphate-buffered saline, corn oil (CO), or menhaden fish oil (FO, a fat source rich in LC n-3 PUFA) for 15 days prior to T cruzi (Y strain) challenge and throughout the acute phase of infection. FO supplementation was associated with a transient 2-fold greater peak of blood parasitemia at 7 days postinfection (dpi), whereas subsequent cardiac parasitemia was ~60% lower at 12 dpi. FO treatment also ameliorated the leukopenia and thrombocytopenia observed in the early stages of a T cruzi infection. FO supplementation reduced circulating and cardiac nitric oxide at 7 and 12 dpi, respectively. FO supplementation altered ex vivo prostaglandin E₂ and cytokine and chemokine production by splenocytes isolated from uninfected and infected mice. Overall, our results suggest that oral administration of LC n-3 PUFA from FO can have beneficial effects on the host in the early course of a T cruzi infection.

Omega-3 polyunsaturated fatty acids enrichment alters performance and immune response in infectious bursal disease challenged broilers

BACKGROUND

Infectious bursal disease (IBD) results in economic loss due to mortality, reduction in production efficiency and increasing the usage of antibiotics. This study was carried out to investigate the modulatory roles of dietary n-3 polyunsaturated fatty acids (PUFA) enrichment in immune response and performance of IBD challenged broiler chickens.

METHODS

A total of 300 day old male broiler chicks were assigned to four dietary n-3 PUFA ascending levels as the treatment groups (T1: 0.5; T2: 8.0; T3: 11.5; T4: 16.5) using combinations of tuna oil and sunflower oil. All diets were isocaloric and isonitrogenous. On day 28, all birds were challenged with IBD virus. Antibody titer, cytokine production, bursa lesion pre and post-challenge and lymphoid organ weight were recorded.

RESULTS

On d 42 the highest body weight was observed in the T2 and T3 and the lowest in T4 chickens. Feed conversion ratio of the T2 broilers was significantly better than the other groups. Although productive parameters were not responded to the dietary n-3 PUFA in a dose-dependent manner, spleen weight, IBD and Newcastle disease antibody titers and IL-2 and IFN-γ concentrations were constantly elevated by n-3 PUFA enrichment.

CONCLUSIONS

Dietary n-3 PUFA enrichment may improve the immune response and IBD resistance, but the optimum performance does not coincide with the optimum immune response. It seems that dietary n-3 PUFA modulates the broiler chicken performance and immune response in a dose-dependent manner. Thus, a moderate level of dietary n-3 PUFA enrichment may help to put together the efficiency of performance and relative immune response enhancement in broiler chickens.

Important differences exist in the dose-response relationship between diet and immune cell fatty acids in humans and rodents

Omega-3 polyunsaturated fatty acids (n-3 PUFA) are noted for their ability to diminish inflammatory and immune responses in vitro and in a variety of animal-based models of autoimmunity and inflammation. Yet, recent systematic reviews suggest that the evidence for these fatty acids having beneficial effects on inflammation or autoimmunity in humans is equivocal. A possible explanation for these disappointing and somewhat paradoxical findings emerged from the analyses described in this review. The available data on the changes in immune cell fatty acid profiles in mice, rats and humans, fed various forms and amounts of n-3 PUFA are summarized and displayed graphically. The dose-response curves generated provide new insights into the relationship between dietary n-3 PUFA and immune cell fatty acid profiles. The author suggests that the poor predictive value of most in vitro as well as many animal trials may, in part, be a consequence of the frequent adoption of experimental conditions that create differences in immune cell fatty acid profiles that far exceed what is possible in free-living humans through dietary intervention. Recommendations for improving the preclinical value of future in vitro and animal-based studies with n-3 PUFA are provided.

Dietary (n-3) Polyunsaturated Fatty Acids Do Not Affect the In Vivo Development and Function of Listeria-Specific CD4+ and CD8+ Effector and Memory/Effector T Cells in Mice

We previously reported that in a mouse model, a diet high in (n-3) PUFA diminishes host survival following an infection from Listeria monocytogenes, a gram-positive bacterial pathogen. In this study we investigated the impact of (n-3) PUFA on the adaptive immune response to L. monocytogenes. BALB/c mice were fed experimental diets either devoid of or rich in (n-3) PUFA from fish oil for 4 wk and then infected with 10(6) actA-deficient L. monocytogenes. At 7 and 35 d postchallenge, effector and memory/effector T cells in the spleen were enumerated by flow cytometry. Surprisingly, the number of Listeria-specific CD4(+) and CD8(+) effector and memory/effector T cells in the spleen was not affected by (n-3) PUFA. Also, the effector cells derived from mice fed either diet were equally capable of conferring protective immunity upon adoptive transfer to naive recipients. Despite our previous data, which demonstrated that (n-3) PUFA profoundly impaired host resistance to L. monocytogenes, pathogen-specific T cell responses were not substantially affected by dietary (n-3) PUFA.

Fatty acids, the immune response, and autoimmunity: a question of n-6 essentiality and the balance between n-6 and n-3

The essentiality of n-6 polyunsaturated fatty acids (PUFA) is described in relation to a thymus/thymocyte accretion of arachidonic acid (20:4n-6, AA) in early development, and the high requirement of lymphoid and other cells of the immune system for AA and linoleic acid (1 8:2n-6, LA) for membrane phospholipids. Low n-6 PUFA intakes enhance whereas high intakes decrease certain immune functions. Evidence from in vitro and in vivo studies for a role of AA metabolites in immune cell development and functions shows that they can limit or regulate cellular immune reactions and can induce deviation toward a T helper (Th)2-like immune response. In contrast to the effects of the oxidative metabolites of AA, the longer-chain n-6 PUFA produced by gamma-linolenic acid (18:3n-6, GLA) feeding decreases the Th2 cytokine and immunoglobulin (Ig)G1 antibody response. The n-6 PUFA, GLA, dihomo-gamma-linolenic acid (20:3n-6, DHLA) and AA, and certain oxidative metabolites of AA can also induce T-regulatory cell activity, e.g., transforming growth factor (TGF)-beta-producing T cells; GLA feeding studies also demonstrate reduced proinflammatory interleukin (IL)-1 and tumor necrosis factor (TNF)-alpha production. Low intakes of long-chain n-3 fatty acids (fish oils) enhance certain immune functions, whereas high intakes are inhibitory on a wide range of functions, e.g., antigen presentation, adhesion molecule expression, Th1 and Th2 responses, proinflammatory cytokine and eicosanoid production, and they induce lymphocyte apoptosis. Vitamin E has a demonstrable critical role in long-chain n-3 PUFA interactions with immune functions, often reversing the effects of fish oil. The effect of dietary fatty acids on animal autoimmune disease models depends on both the autoimmune model and the amount and type of fatty acids fed. Diets low in fat, essential fatty acid deficient (EFAD), or high in long-chain n-3 PUFA from fish oils increase survival and reduce disease severity in spontaneous autoantibody-mediated disease, whereas high-fat LA-rich diets increase disease severity. In experimentally induced T cell-mediated autoimmune disease, EFAD diets or diets supplemented with long-chain n-3 PUFA augment disease, whereas n-6 PUFA prevent or reduce the severity. In contrast, in both T cell- and antibody-mediated autoimmune disease, the desaturated/elongated metabolites of LA are protective. PUFA of both the n-6 and n-3 families are clinically useful in human autoimmune-inflammatory disorders, but the precise mechanisms by which these fatty acids exert their clinical effects are not well understood. Finally, the view that all n-6 PUFA are proinflammatory requires revision, in part, and their essential regulatory and developmental role in the immune system warrants appreciation.

Effects of dietary omega-3 and omega-6 lipids and vitamin E on serum cytokines, lipid mediators and anti-DNA antibodies in a mouse model for rheumatoid arthritis

OBJECTIVE

Omega-3 (omega-3) fatty acid rich-fish oil (FO) and vitamin E (vit-E) may delay the progress of certain autoimmune diseases. The present study examined the mechanism of action of omega-3 and omega-6 lipids and vit-E on the serum cytokines and lipid mediators in autoimmune-prone MRL/lpr mice (a model for rheumatoid arthritis, RA). The lpr (lymphoproliferative) gene is overexpressed in these mice causing extensive lymphoproliferation, lupus-like symptoms and accelerated aging.

METHODS

Weanling female MRL/lpr and congenic control MRL/++ mice were fed 10% corn oil (CO, omega6) or FO-based semipurified diets containing two levels of vitamin E (vit-E-75, I.U. and vit-E-500 I.U./Kg diet) for four months. At the end of the experiment, serum anti-DNA antibodies, cytokines and lipid mediators levels were determined.

RESULTS

The appearance of enlarged lymph nodes was delayed in the mice fed FO, and the FO-500 IU vit-E diet offered further protection against enlargement of lymph nodes. The MRL/lpr mice exhibited significantly higher levels of serum anti-dsDNA antibodies. The FO-fed mice had significantly lower serum IL-6, IL-10, IL-12, TNF-alpha, PGE2, TXB2 and LTB4 levels compared with CO-fed mice. In mice fed 500 IU vit-E diets, the serum IL-6, IL-10, IL-12 and TNF-alpha levels were significantly lower and serum IL-1beta was significantly higher compared to 75 IU-vit-E-fed mice in CO/FO or both. The levels of anti-DNA antibodies, IL-4, IL-6, TNF-alpha, IL-10 and IL-12 were higher in the sera of MRL/lpr mice. The FO diet lowered the levels of these cytokines (except IL-4) and lipid mediators. Adding 500 IU of vit-E to the FO diet further lowered the levels of IL-6, IL-10, IL-12, and TNF-alpha.

CONCLUSION

It is clear from our observations that the beneficial effects of FO can be enhanced by the addition of 500 IU of vit-E in the diet. The FO diet containing 500 IU of vit-E may specifically modulate the levels of IL-6, IL-10, IL-12 and TNF-alpha and thereby may delay the onset of autoimmunity in the MRL/lpr mouse model. The observations from this study may form a basis for selective nutrition intervention based on specific fatty acids and antioxidants in delaying the progress of RA.

Dietary fat and prostate cancer: current status

Efforts to elucidate the causes of prostate cancer have met with little success to date. All that is known with certainty is that the incidence increases exponentially with age, varies by geography and by race or ethnicity, and is higher among men whose father or brother had the disease. Because the incidence changes in migrants and their offspring, exogenous factors certainly contribute to the risk of prostate cancer. Early epidemiologic studies implicated dietary fat as a likely causal factor for this cancer. However, scientific support for such an association has diminished in recent years as more epidemiologic evidence has accrued. Accordingly, we reviewed the relevant English language literature on this topic, including epidemiologic and animal studies, as well as current concepts regarding the involvement of fat in carcinogenesis to re-examine the fat-prostate cancer hypothesis. We conclude that dietary fat may indeed be related to prostate cancer risk, although the specific fat components that are responsible are not yet clear. Given the diverse effects of fatty acids on cellular biology and chemistry, it seems likely that the relationship is complex, involving the interplay of fat with other dietary factors, such as antioxidant vitamins and minerals, or with genetic factors that influence susceptibility. Some suggestions for further research are offered.

Linoleic and alpha-linolenic acids differently modify the effects of elaidic acid on polyunsaturated fatty acid metabolism and some immune indices in rats

To explore whether the metabolic responses to trans, compared with cis, fatty acids depend on the source of dietary polyunsaturated fatty acids (PUFA), male Sprague-Dawley rats, 5 weeks old, were fed on diets containing 30 g oleic (cis) or elaidic (trans) acids/kg in combination with either 70 g perilla oil (alpha-linolenic acid) or safflowerseed oil (linoleic acid)/kg for 3 weeks in separate experiments. The dietary fats were adjusted to have the same level of total PUFA. The dietary manipulation did not influence the growth indices, but spleen weight was greater when the dietary PUFA source was perilla oil. The incorporation of trans fatty acid into liver phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and phosphatidylserine and adipose tissue lipids, particularly phospholipids, was significantly higher when rats were fed on safflowerseed oil compared with perilla oil. However, only limited differences were observed in the effects of cis and trans fatty acids on the proportions of PUFA in liver phospholipids. Splenic production of prostaglandin E2 was reduced by trans fatty acid when safflowerseed oil was the PUFA source, but no trans effect was observed on leukotriene C4 production. Dietary PUFA significantly influenced the concentration of plasma immunoglobulins (Ig) but the effect of geometry was only seen in IgG which was increased by trans acid. Dietary trans fatty acid increased the CD4+:CD8+ T-lymphocyte ratio in the spleen, reflecting a decreasing trend of the proportion of CD8+, when combined with perilla oil. These observations indicate that the type of PUFA simultaneously ingested specifically influences the effect that trans acid exerts on PUFA metabolism, eicosanoid production and some immune indices.

Dietary marine lipids suppress continuous expression of interleukin-1 beta gene transcription

n-3 Polyunsaturated fatty acids abundant in marine lipids suppress certain inflammatory and immune reactions, and dietary marine lipid supplements have antiinflammatory effects in experimental and human autoimmune disease. Previous work by other investigators demonstrated that dietary marine lipid supplements suppressed production of cytokines from stimulated human peripheral blood mononuclear cells ex vivo. The present study further documents the ability of n-3 fatty acids to inhibit cytokine formation, and in part defines the mechanism of the inhibition of production of interleukin-1 beta (IL-1 beta) by dietary n-3 fatty acid. Female BALB/c mice were each fed a fat-free balanced diet to which was added either a refined fish oil (FO) preparation as a source of n-3 fatty acid, or beef tallow (BT), which consisted primarily of saturated and monoenoic fatty acids. After ingesting the experimental diets for periods ranging from 3 to 12 wk. spleen cell preparations were stimulated ex vivo with either lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA), and proIL-1 beta mRNA (IL-1 beta mRNA) was measured by northern analysis. Levels of IL-1 beta mRNA in both LPS- and PMA-stimulated cells from BT-fed mice were elevated to a greater extent than in cells from FO-fed mice, at most concentrations of LPS and PMA. Stability of LPS-stimulated mRNA levels after actinomycin D was similar for BT and FO groups, indicating that lower levels of IL-1 mRNA with FO groups was related to suppressed IL-1 gene transcription and not due to accelerated transcript degradation. Nuclear run-on transcription assays revealed a more transient expression of the IL-1 beta gene in LPS-stimulated spleen cells from FO-fed mice compared to cells from BT-fed mice. We conclude that dietary marine lipids reduce transient expression of the IL-1 beta gene in stimulated splenic monocytic cells. Preliminary results from nuclear run-on transcription assays indicate that n-3 fatty acids may not change the initial rate of gene transcription but may promote more rapid shutting down of transcription of this gene after induction than do alternative lipids.

Effects of continuous tube feeding of dietary fat emulsions on eicosanoid production and on fatty acid composition during an acute septic shock in rats

The effects of a short-term (5 days) continuous intragastric tube feeding of diets containing n - 6 polyunsaturated fatty acids (PUFA) from safflower oil (SO) or n - 3 PUFA from menhaden oil (MO) on the production of proinflammatory mediators, and on the number of animals surviving after an intravenous injection of lipopolysaccharide (LPS) were investigated in rats. The phospholipid fatty acid composition of cell membranes from several organs and of plasma were also analyzed. No marked differences in the number of animals surviving or in the production of tumor necrosis factor-alpha were observed between the 2 groups of animals. However, 90 min after LPS exposure the plasma levels of prostaglandin (PG) E2 and 6-keto-PGF1 alpha decreased significantly (40% and 60%, respectively) for the group of rats fed MO diet compared to those fed SO diet (P < 0.05). Following continuous infusion of liquid MO diet, the amount of arachidonic acid (AA) detected was significantly lower in plasma (23%), spleen (43%), lungs (41%), and liver (38%), but was unchanged in the heart tissues. The percent of eicosapentaenoic acid (EPA) incorporated into phospholipids of plasma, spleen, lungs, liver, and heart were 7.6, 4.4, 2.1, 7.2, and 1.1%, respectively. These data indicate that after continuous MO feeding, a significant decrease in the production of proinflammatory eicosanoids was associated with a marked reduction in AA content. Further, these data suggest that nutritional intervention may have a therapeutic potential to ameliorate clinical symptoms due to excessive productions of eicosanoids during acute septic complications.