Effects of dietary supplementation with fish oil on in vivo production of inflammatory mediators in clinically normal dogs

Casey J. LeBlanc, University of Tennessee, Knoxville
David W. Horohov
John E. Bauer
Giselle Hosgood
Glenna E. Mauldin

Abstract

Objective—To evaluate the effect of diets enriched with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on in vivo production of interleukin (IL)-1, IL-6, tumor necrosis factor (TNF)-α, prostaglandin E₂ (PGE₂), and platelet-activating factor (PAF) in dogs.

Animals—15 young healthy dogs.

Procedures—Dogs were randomly allocated to receive an isocaloric ration supplemented with sunflower oil (n = 5), fish oil (5), or fish oil plus vitamin E (5) for 12 weeks. At week 12, in vivo production of inflammatory mediators was evaluated in serum at multiple time points for 6 hours following stimulation with IV administration of lipopolysaccharide (LPS).

Results—Serum activity or concentration (area under the curve) of IL-1, IL-6, and PGE₂ significantly increased after LPS injection in all groups but to a lesser extent in dogs receiving the fish oil diet, compared with results for dogs receiving the sunflower oil diet. Serum activity of TNF-α and PAF concentration also increased significantly after LPS injection in all groups but did not differ significantly among groups.

Conclusions and Clinical Relevance—A fish oil–enriched diet consisting of 1.75 g of EPA/kg of diet and 2.2 g of DHA/kg of diet (dry-matter basis) with an n-6:n-3 fatty acid ratio of 3.4:1 was associated with significant reductions in serum PGE₂ concentrations and IL-1 and IL-6 activities. Results supported the use of EPA- and DHA-enriched diets as part of antiinflammatory treatments for dogs with chronic inflammatory diseases. Additional studies in affected dogs are warranted to further evaluate beneficial anti-inflammatory effects of EPA- and DHA-enriched diets.

Cytokines are multifunctional peptides that are produced predominantly by activated lymphocytes and macrophages during immune and inflammatory reactions. Tumor necrosis factor-α, IL-1β, and IL-6 are among the most important cytokines produced by macrophages. Enhanced release of TNF-α, IL-1, and IL-6 is considered a hallmark of sepsis and hemorrhagic shock. These cytokines promote a multitude of changes, including fever; increased production of acute-phase proteins; hypotension; activation and infiltration of neutrophils; increased synthesis of cytokines by lymphocytes; and increased synthesis of lipid mediators, such as prostaglandins, leukotrienes, and PAF. These effects are crucial during the acute response against pathogens and injuries; however, overproduction of these cytokines can be severely detrimental to the host. Inappropriate or prolonged production has been associated with cartilage breakdown, organ dysfunction, anorexia and cachexia, and nonregenerative anemia.

Cytokines are not the only important mediators of immunity and inflammation. Activation of cellular phospholipases leads to the synthesis of prostaglandins, leukotrienes, and PAF. Prostaglandin E₂ is an arachidonic acid metabolite produced predominantly by macrophages that is important in local acute inflammatory responses, such as swelling and erythema, and systemic inflammatory effects, especially fever. Platelet-activating factor is actually a family of structurally similar bioactive phospholipid-derived mediators. It is known that PAF has many proinflammatory effects on blood vessels, small airways, and leukocytes, including increases in vascular permeability, bronchoconstriction, and adhesion and chemotaxis of neutrophils and eosinophils. Platelet-activating factor can enhance the synthesis of TNF-α and IL-1 by stimulated macrophages.

Finding ways to inhibit the synthesis or block the biological effects of these inflammatory mediators is an active area of research. The ability to control these mediators offers the potential to minimize the negative impact of many chronic inflammatory diseases. However, commercially available anti-inflammatory medications can be expensive, and many have important toxic effects in humans and other animals, especially with long-term use. Dietary supplementation with n-3 fatty acids obtained from fish or fish oils has been suggested as a method to modulate the immune response while avoiding some of these toxic effects, and it appears to provide beneficial anti-inflammatory effects.

The principle n-3 fatty acids in fish or fish oils are EPA and DHA. Analysis of data suggests that dietary supplementation with these nutrients can influence the production of inflammatory mediators, which potentially could reduce the severity of some diseases. However, evaluations of the effects of dietary supplementation with n-3 fatty acids on these mediators in dogs are scarce and contradict results in other species. In 1 study conducted by our laboratory group, we reported the effect of a diet enriched by the addition of EPA and DHA, with and without supplemental vitamin E, on selected hematologic and serum biochemical variables, serum concentrations of vitamin E, and lipid peroxidation in healthy young crossbred-hound dogs. In another study conducted by our laboratory group, lymphocyte proliferation of those same crossbred-hound dogs was significantly decreased in a group fed the same EPA- and DHA-enriched diet. The objective of the study reported here was to evaluate the effect of these same diets supplemented with EPA and DHA on in vivo production of IL-1, IL-6, TNF-α, PGE2, and PAF in similar healthy dogs.