Red blood cell PUFAs reflect the phospholipid PUFA composition of major organs.

Numerous clinical trials examining the use of omega-3 long chain polyunsaturated fatty acids (n-3 LCPUFAs) on various health outcomes have been conducted, and fish oil remains one of the most widely used nutritional supplements. More recently, studies have begun to utilize the omega-3 index, defined as the sum of EPA+DHA in red blood cells (RBCs), as both a biomarker of n-3 LCPUFA exposure and a potential risk factor for coronary heart disease (CHD). Considerably less research evaluates whether RBC phospholipid fatty acids reflect the phospholipid fatty acid composition of other tissues across increasing intakes of n-3 LCPUFAs. We fed mice diets containing increasing amounts of EPA+DHA, equivalent to current recommendations by the American Heart Association on a percent of energy basis, and analyzed the phospholipid fatty acid composition of various tissues in relation to RBCs. We observed that RBCs, heart, muscle, spleen, lung, and adipose tissues all respond to dietary supplementation with EPA+DHA with increasing n-3 LCPUFA and decreasing n-6 LCPUFA levels. Furthermore, the n-3 LCPUFA profiles of all measured tissues had strong (r>0.7) and significant (p<0.001) correlations to RBCs. Interestingly, we also observed changes in saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) levels across various tissues in response to increased EPA+DHA intakes despite there being no change in dietary SFA and MUFA. Specifically, there were increases in RBC SFA and spleen MUFA and decreases in heart MUFA. These demonstrate that the RBC, including the omega-3 index, may serve as a marker for the relative levels of n-3 and n-6 LCPUFAs in phospholipids of certain tissues.

Marine fish oils are not equivalent with respect to B-cell membrane organization and activation.

We previously reported that docosahexaenoic-acid (DHA)-enriched fish oil (DFO) feeding altered B-cell membrane organization and enhanced B-cell function. The purpose of this study was to evaluate whether menhaden oil (MO) and eicosapentaenoic-acid (EPA)-enriched fish oil (EFO) alters B-cell function/phenotype similarly. Mice were fed control (CON), MO, EFO or DFO diets for 5weeks. We evaluated the fatty acid composition of B-cell phospholipids, membrane microdomain organization, ex vivo B-cell functionality and in vivo B-cell subsets. Red blood cells and B cells were found to be strongly (r>0.85) and significantly (P<.001) correlated for major n-3 and n-6 long-chain polyunsaturated fatty acids (LCPUFAs). Compared to CON, MO and DFO resulted in decreased clustering of membrane microdomains, whereas EFO increased clustering. All fish oil treatments had 1.12-1.60 times higher CD40 expression following stimulation; however, we observed 0.86 times lower major histocompatibility complex class II expression and 0.7 times lower interleukin (IL)-6 production from EFO, but 3.25 times higher interferon-γ from MO and 1.5 times higher IL-6 from DFO. By 90min of incubation, MO had 1.11 times higher antigen uptake compared to CON, whereas EFO was 0.86 times lower. All fish oil treatments resulted in decreasingly mature splenic and bone marrow B-cell subsets. We conclude that diets high in n-3 LCPUFAs may elicit similar B-cell phenotypes but different organizational and functional outcomes. More specifically, these data suggest that the EPA and DHA content of a diet influences immunological outcomes, highlighting the importance of understanding how specific n-3 LCPUFAs modulate B-cell development and function.

Is the omega-3 index a valid marker of intestinal membrane phospholipid EPA+DHA content?

Despite numerous studies investigating n-3 long chain polyunsaturated fatty acid (LCPUFA) supplementation and inflammatory bowel diseases (IBD), the extent to which dietary n-3 LCPUFAs incorporate in gastrointestinal (GI) tissues and correlate with red blood cell (RBC) n-3 LCPUFA content is unknown. In this study, mice were fed three diets with increasing percent of energy (%en) derived from eicosapentaenoic acid (EPA)+docosahexaenoic acid (DHA). Dietary levels reflected recommended intakes of fish/fish oil by the American Heart Association. We analyzed the FA composition of phospholipids extracted from RBCs, plasma, and GI tissues. We observed that the 0.1%en EPA+DHA diet was sufficient to significantly increase the omega-3 index (RBC EPA+DHA) after 5 week feeding. The baseline EPA levels were 0.2-0.6% across all tissues increasing to 1.6-4.3% in the highest EPA+DHA diet; these changes resulted in absolute increases of 1.4-3.9% EPA across tissues. The baseline DHA levels were 2.2-5.9% across all tissues increasing to 5.8-10.5% in the highest EPA+DHA diet; these changes resulted in absolute increases of 3.2-5.7% DHA across tissues. These increases in EPA and DHA across all tissues resulted in strong (r>0.91) and significant (P<0.001) linear correlations between the omega-3 index and plasma/GI tissue EPA+DHA content, suggesting that the omega-3 index reflects the relative amounts of EPA+DHA in GI tissues. These data demonstrate that the GI tissues are highly responsive to dietary LCPUFA supplementation and that the omega-3 index can serve as a valid biomarker for assessing dietary EPA+DHA incorporation into GI tissues.

Immunomodulation by dietary long chain omega-3 fatty acids and the potential for adverse health outcomes.

Recommendations to consume fish for prevention of cardiovascular disease (CVD), along with the U.S. Food and Drug Administration-approved generally recognized as safe (GRAS) status for long chain omega-3 fatty acids, may have had the unanticipated consequence of encouraging long-chain omega-3 (ω-3) fatty acid [(eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] supplementation and fortification practices. While there is evidence supporting a protective role for EPA/DHA supplementation in reducing sudden cardiac events, the safety and efficacy of supplementation with LCω-3PUFA in the context of other disease outcomes is unclear. Recent studies of bacterial, viral, and fungal infections in animal models of infectious disease demonstrate that LCω-3PUFA intake dampens immunity and alters pathogen clearance and can result in reduced survival. The same physiological properties of EPA/DHA that are responsible for the amelioration of inflammation associated with chronic cardiovascular pathology or autoimmune states, may impair pathogen clearance during acute infections by decreasing host resistance or interfere with tumor surveillance resulting in adverse health outcomes. Recent observations that high serum LCω-3PUFA levels are associated with higher risk of prostate cancer and atrial fibrillation raise concern for adverse outcomes. Given the widespread use of supplements and fortification of common food items with LCω-3PUFA, this review focuses on the immunomodulatory effects of the dietary LCω-3PUFAs, EPA and DHA, the mechanistic basis for potential negative health outcomes, and calls for biomarker development and validation as rational first steps towards setting recommended dietary intake levels.

DHA-enriched fish oil targets B cell lipid microdomains and enhances ex vivo and in vivo B cell function.

DHA is a n-3 LCPUFA in fish oil that generally suppresses T lymphocyte function. However, the effect of fish oil on B cell function remains relatively understudied. Given the important role of B cells in gut immunity and increasing human fish oil supplementation, we sought to determine whether DFO leads to enhanced B cell activation in the SMAD-/- colitis-prone mouse model, similar to that observed with C57BL/6 mice. This study tested the hypothesis that DHA from fish oil is incorporated into the B cell membrane to alter lipid microdomain clustering and enhance B cell function. Purified, splenic B cells from DFO-fed mice displayed increased DHA levels and diminished GM1 microdomain clustering. DFO enhanced LPS-induced B cell secretion of IL-6 and TNF-α and increased CD40 expression ex vivo compared with CON. Despite increased MHCII expression in the unstimulated ex vivo B cells from DFO-fed mice, we observed no difference in ex vivo OVA-FITC uptake in B cells from DFO or CON mice. In vivo, DFO increased lymphoid tissue B cell populations and surface markers of activation compared with CON. Finally, we investigated whether these ex vivo and in vivo observations were consistent with systemic changes. Indeed, DFO-fed mice had significantly higher plasma IL-5, IL-13, and IL-9 (Th2-biasing cytokines) and cecal IgA compared with CON. These results support the hypothesis and an emerging concept that fish oil enhances B cell function in vivo.

Supplementation with galacto-oligosaccharides increases the percentage of NK cells and reduces colitis severity in Smad3-deficient mice.

The gut microbiota plays an essential role in intestinal immunity. Prebiotics, including galacto-oligosaccharides (GOS), are fermentable fibers that beneficially affect the host by stimulating the growth of specific microbial populations. We investigated the effect of GOS on colitis development and on immune variables in Smad3-deficient mice treated with the pathogen Helicobacter hepaticus. Mice were supplemented daily with 5000 mg GOS/kg body weight 2 wk prior to infection and 4 wk postinfection, a time period during which colitis severity peaks in this model. Mice (n = 4-8/treatment at each time) were killed preinfection (0 d) and at 3, 7, and 28 d postinfection to evaluate immune variables in the spleen and in mesenteric lymph nodes (MsLN) by flow cytometry. Colon and cecum samples were collected for histopathologic analysis. Fecal pellets (n = 8-9/treatment) were collected prior to infection to measure relative changes in Bifidobacterium ssp. and Lactobacillum ssp. by real-time PCR. GOS significantly reduced colitis severity in response to H. hepaticus (P < 0.0001). This was associated with a significant increase in the percentage of NK cells in the spleen (P < 0.001) and in MsLN (P < 0.001) at 3 d postinfection and a 1.5-fold increase in fecal Bifidobacterium ssp. (P = 0.003). GOS stimulated NK expression of CCR9, a chemokine receptor involved in lymphocyte trafficking to the gut preinfection (0 d) in the blood (P = 0.02), spleen (P = 0.033), and MsLN (P = 0.017). In addition, GOS stimulated colonic IL-15 production 3 d postinfection (P < 0.001). These data suggest that GOS reduces colitis by modulating the function and trafficking of NK cells and may provide a novel therapeutic strategy for individuals with inflammatory bowel disease.