n-3 PUFAs enhance the frequency of murine B-cell subsets and restore the impairment of antibody production to a T-independent antigen in obesity

Lipid metabolism in B cell biology

In recent years, the field of immunometabolism has solidified its position as a prominent area of investigation within the realm of immunological research. An expanding body of scientific literature has unveiled the intricate interplay between energy homeostasis, signalling molecules, and metabolites in relation to fundamental aspects of our immune cells. It is now widely accepted that disruptions in metabolic equilibrium can give rise to a myriad of pathological conditions, ranging from autoimmune disorders to cancer. Emerging evidence, although sometimes fragmented and anecdotal, has highlighted the indispensable role of lipids in modulating the behaviour of immune cells, including B cells. In light of these findings, this review aims to provide a comprehensive overview of the current state of knowledge regarding lipid metabolism in the context of B cell biology.

Impact of cow, buffalo, goat or camel milk consumption on oxidative stress, inflammation and immune response post weaning time

Milk is a whitish liquid that is secreted from mammary glands; and considered as the primary source of nutrition for newborns since they are not able to digest solid food. However, it contains primary nutrients, as well as growth and immune factors. Early weaning is a critical issue that face women and their babies in developing countries. To avoid infant malnutrition, they tend to use other milk types instead of baby formula. Therefore, the present study aimed to evaluate the impact of cow, buffalo, goat or camel milk consumption on oxidative stress, inflammation and immune response in male and female Sprague Dawley rats post weaning time. The amino acids, fatty acids, minerals and vitamins in the tested milk types were evaluated. Animals were divided into 5 groups (control, cow, buffalo, goat and camel milk administrated groups) (10 rats/group); each animal was administrated by 3.4 ml/day. Rats were administered with milk for 6 weeks; at the end of the 5th week, five animals of each group were isolated and the remaining five animals were immunized with sheep red blood cells (SRBCs) and kept for another week to mount immune response. The effect of different milk types on rats' immune response towards SRBCs was evaluated through pro-inflammatory cytokines, antioxidants, ESR and CRP measurement; together, with the histopathological examination of spleen samples and hemagglutination assay. Camel milk consumption reduced oxidative stress and inflammation in spleen that resulted from SRBCs immunization; in addition to, B cell stimulation that was apparent from the high level of anti-SRBCs antibodies. Camel milk is recommended for newborn consumption, due to its high-water content, unsaturated fatty acids, and vitamin C, as well as low lactose and fat content.

Lipid metabolism in regulation of B cell development and autoimmunity

B cells play an important role in adaptive immunity and participate in the process of humoral immunity mainly by secreting antibodies. The entire development and differentiation process of B cells occurs in multiple microenvironments and is regulated by a variety of environmental factors and immune signals. Differentiation biases or disfunction of B cells participate in the process of many autoimmune diseases. Emerging studies report the impact of altered metabolism in B cell biology, including lipid metabolism. Here, we discuss how extracellular lipid environment and metabolites, membrane lipid-related components, and lipid synthesis and catabolism programs coordinate B cell biology and describe the crosstalk of lipid metabolic programs with signal transduction pathways and transcription factors. We conclude with a summary of therapeutic targets for B cell lipid metabolism and signaling in autoimmune diseases and discuss important future directions.

Does inclusion of bioactive n-3 PUFAs in parenteral nutrition benefit postoperative patients undergoing liver surgery? A systematic review and meta-analysis of randomised control trials

OBJECTIVES

This meta-analysis aims to evaluate the effect of n-3 polyunsaturated fatty acids (PUFAs) as a part of parenteral nutrition in patients undergoing liver surgery.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

PubMed, the Cochrane Central Register of Controlled Trials, Springer link, Web of Science, China National Knowledge Infrastructure and VIP Database.

ELIGIBILITY CRITERIA

We included randomised controlled trials (RCTs) and evaluated the outcomes of liver function, inflammatory reaction, the influence of certain markers of the immune system, and specific clinical indexes for patients undergoing liver surgery and receiving parenteral nutrition with n-3 PUFAs.

DATA EXTRACTION AND SYNTHESIS

The Cochrane Collaboration's tool was used to assess the risk of bias for each study. Findings were summarised in Grades of Recommendation, Assessment, Development and Evaluation evidence profiles and synthesised qualitatively.

RESULTS

Eight RCTs, including 748 patients (trial: 374; control: 374), were included in the meta-analysis. Compared with patients in the control group, the patients in the n-3 PUFA group who underwent liver surgery had significantly lower aspartate aminotransferase (mean difference, MD -42.72 (95% CI -71.91 to -13.52); p=0.004), alanine aminotransferase (MD -38.90 (95% CI -65.44 to -12.37); p=0.004), white cell count (MD -0.93 (95% CI -1.60 to -0.26); p=0.007) and IL-6 (MD -11.37 (95% CI -14.62 to -8.13); p<0.00001) levels and a higher albumin level (MD 0.42 (95% CI 0.26 to 0.57); p<0.00001). They also had fewer infection complications (OR 0.44 (95% CI 0.28 to 0.68); p=0.0003) and a shorter duration of hospital stay (MD -2.17 (95% CI -3.04 to -1.3); p<0.00001) than the controls. However, there were no significant differences in terms of total bilirubin, TNF-α, IL-2, IgA, IgG, IgM and CD3, biliary leakage and mortality between the two groups.

CONCLUSIONS

We found that n-3 PUFAs can benefit patients undergoing liver surgery by improving liver function and certain clinical indexes and decreasing related inflammation factors. However, there are limited RCTs on the application of n-3 PUFAs for patients undergoing liver surgery. Further evidence of the benefit of n-3 PUFAs in these patients warrants further exploration.

The function of omega-3 polyunsaturated fatty acids in response to cadmium exposure

Throughout history, pollution has become a part of our daily life with the improvement of life quality and the advancement of industry and heavy industry. In recent years, the adverse effects of heavy metals, such as cadmium (Cd), on human health have been widely discussed, particularly on the immune system. Here, this review summarizes the available evidence on how Cd exposure may affect health. By analyzing the general manifestations of inflammation caused by Cd exposure, we find that the role of omega-3 (n-3) polyunsaturated fatty acids (PUFAs) in vivo can counteract Cd-induced harm. Additionally, we elucidate the effects of n-3 PUFAs on the immune system, and analyze their prophylactic and therapeutic effects on Cd exposure. Overall, this review highlights the role of n-3 PUFAs in the pathological changes induced by Cd exposure. Although n-3 PUFAs remain to be verified whether they can be used as therapeutic agents, as rehabilitation therapy, supplementation with n-3 PUFAs is reliable and effective.

A Pilot Study to Examine If Dietary Habits Can Affect Symptomology in Mild Pre-Vaccination COVID-19 Cases

The heterogeneity of the severity of symptoms of COVID-19 experienced by the young and healthy individuals is poorly understood. The present study was undertaken to mainly examine whether the respective diets and the type of symptoms experienced by patients are predictive of having long COVID-19. Disease severity was assessed with a symptomatology questionnaire and used to group 55 participants in asymptomatic (AS), mild symptoms (S) and long COVID (LC). We found that experiencing a higher number of symptoms as well as fatigue were predictors of developing LC whereas those who experienced rhinorrhea were less likely to develop LC. Blood samples were also taken to measure vitamin D [25(OH)D] concentrations and duration of spike IgG antibodies. In this study, serum 25(OH)D was not significantly different between 3 symptom groups with median (IQR) ng/mL levels of 22.0 (12.3) in the AS, 22.3 (7.5) in S, and 24.9 (9.4) in the LC group (p ≥ 0.05). The duration of IgG antibody response was found to vary greatly, with some individuals showing raised IgG over a year after infection. To examine whether dietary factors can influence the severity of symptoms, diet was analysed using 4–7-day food diaries as well as a Food Frequency Questionnaire (FFQ). Some nutrients such as vitamin E, polyunsaturated fatty acids, fibre, and iron were associated with lower severity of COVID-19. Lower intake of vitamin E was associated with having LC with a median (IQR) intake of 6.2 mg (3.8) seen in LC vs. 8.6 mg (7.2) in the AS group (p = 0.047). This pilot study has highlighted a few differences in the number and type of symptoms experienced by the young non-hospitalised individuals with mild and long COVID-19 and identified a few dietary components for their potential protective role against long COVID-19, however, the findings need to be confirmed with further large scale studies.

Obesity Dysregulates the Immune Response to Influenza Infection and Vaccination Through Metabolic and Inflammatory Mechanisms

The COVID-19 pandemic demonstrates that obesity alone, independent of comorbidities, is a significant risk factor for severe outcomes from infection. This susceptibility mirrors a similar pattern with influenza infection; that is, obesity is a unique risk factor for increased morbidity and mortality. Therefore, it is critical to understand how obesity contributes to a reduced ability to respond to respiratory viral infections. Herein, we discuss human and animal studies with influenza infection and vaccination that show obesity impairs immunity. We cover several key mechanisms for the dysfunction. These mechanisms include systemic and cellular level changes that dysregulate immune cell metabolism and function in addition to how obesity promotes deficiencies in metabolites that control the resolution of inflammation and infection. Finally, we discuss major gaps in knowledge, particularly as they pertain to diet and mechanisms, which will drive future efforts to improve outcomes in response to respiratory viral infections in an increasingly obese population.

The Impact of Resolution of Inflammation on Tumor Microenvironment: Exploring New Ways to Control Cancer Progression

Simple Summary

The evolution of cancer is strongly influenced by the context in which tumor cells develop and grow, known as the tumor microenvironment (TME). The TME is constituted of a set of cells with different natures, which can produce various factors or interact with cancer cells, thus favoring or inhibiting cancer growth. Specific factors with the ability to shape the TME, in order to create an unfavorable context for tumor cells, are the Specialized Pro-resolving Mediators (SPMs). SPMs are small lipid molecules derived from ω-3 and ω-6 fatty acids, exerting the physiologic role of dampening the inflammatory responses and helping tissues to regain their homeostasis after insults. Here, we present the knowledge relative to the action of SPMs on each component of the TME and its effects on tumor growth and progression. These summarized findings highlight novel potential strategies to manage cancer progression.

Abstract

Non-resolving inflammation is an enabling feature of cancer. A novel super-family of lipid mediators termed Specialized Pro-resolving Mediators (SPMs) have a role as bioactive molecules mediating the resolution of inflammation in cancer biology. SPMs are derived from ω-3 and ω-6 polyunsaturated fatty acids through the activity of lipoxygenases. SPMs have been described to directly modulate cancer progression by interfering with the epithelial to mesenchymal transition and invasion of cancer cells. SPMs have also been demonstrated to act on several components of the tumor microenvironment (TME). Consistently with their natural immunomodulatory and anti-inflammatory properties, SPMs are able to reprogram macrophages to favor phagocytosis of cell debris, which are an important source of pro-inflammatory and pro-angiogenic signals; sustain a direct cytotoxic immune response against cancer cells; stimulate neutrophils anti-tumor activities; and inhibit the development of regulatory T and B cells, thus indirectly leading to enhanced anti-tumor immunity. Furthermore, the resolution pathways exert crucial anti-angiogenic functions in lung, liver, and gastrointestinal cancers, and inhibit cancer-associated fibroblast differentiation and functions in hepatocellular carcinoma and pancreatic cancer. The present review will be focused on the potential protective effects of resolution pathways against cancer, exerted by modulating different components of the TME.

Specialized Pro-Resolving Mediators Derived from N-3 Polyunsaturated Fatty Acids: Role in Metabolic Syndrome and Related Complications

Significance: Metabolic syndrome (MetS) prevalence continues to grow and represents a serious public health issue worldwide. This multifactorial condition carries the risk of hastening the development of type 2 diabetes (T2D), non-alcoholic fatty liver disease (NAFLD), and cardiovascular diseases (CVD). Another troubling aspect of MetS is the requirement of poly-pharmacological therapy not devoid of side effects. Therefore, there is an urgent need for prospecting alternative nutraceuticals as effective therapeutic agents for MetS. Recent Advances: Currently, there is an increased interest in understanding the regulation of metabolic derangements by specialized pro-resolving lipid mediators (SPMs), especially those derived from the long chain n-3 polyunsaturated fatty acids. Critical Issues: The SPMs are recognized as efficient modulators that are capable of inhibiting the production of pro-inflammatory cytokines, blocking neutrophil activation/recruitment, and inducing non-phlogistic (anti-inflammatory) activation of macrophage engulfment and removal of apoptotic inflammatory cells and debris. The aim of the present review is precisely to first underline key concepts relative to SPM functions before focusing on their status and actions on MetS components (e.g., obesity, glucose dysmetabolism, hyperlipidemia, hypertension) and complications such as T2D, NAFLD, and CVD. Future Directions: Valuable data from preclinical and clinical investigations have emphasized the SPM functions and influence on oxidative stress- and inflammation-related MetS. Despite these promising findings obtained without compromising host defense, additional efforts are needed to evaluate their potential therapeutic applications and further develop practical tools to monitor their bioavailability to cope with cardiometabolic disorders. Antioxid. Redox Signal. 37, 54-83.

Modification of subcutaneous white adipose tissue inflammation by omega-3 fatty acids is limited in human obesity-a double blind, randomised clinical trial

Background

Obesity is associated with enhanced inflammation. However, investigation in human subcutaneous white adipose tissue (scWAT) is limited and the mechanisms by which inflammation occurs have not been well elucidated. Marine long chain omega-3 polyunsaturated fatty acids (LC n-3 PUFAs) have anti-inflammatory actions and may reduce scWAT inflammation.

Methods

Subcutaneous white adipose tissue (scWAT) biopsies were collected from individuals living with obesity (n=45) and normal weight individuals (n=39) prior to and following a 12-week intervention with either 3 g/day of a fish oil concentrate (providing 1.1 g eicosapentaenoic acid (EPA) + 0.8 g docosahexaenoic acid (DHA)) or 3 g/day of corn oil. ScWAT fatty acid, oxylipin, and transcriptome profiles were assessed by gas chromatography, ultra-pure liquid chromatography tandem mass spectrometry, RNA sequencing and qRT-PCR, respectively.

Findings

Obesity was associated with greater scWAT inflammation demonstrated by lower concentrations of specialised pro-resolving mediators (SPMs) and hydroxy-DHA metabolites and an altered transcriptome with differential expression of genes involved in LC n-3 PUFA activation, oxylipin synthesis, inflammation, and immune response. Intervention with LC n-3 PUFAs increased their respective metabolites including the SPM precursor 14-hydroxy-DHA in normal weight individuals and decreased arachidonic acid derived metabolites and expression of genes involved in immune and inflammatory response with a greater effect in normal weight individuals.

Interpretation

Downregulated expression of genes responsible for fatty acid activation and metabolism may contribute to an inflammatory oxylipin profile and limit the effects of LC n-3 PUFAs in obesity. There may be a need for personalised LC n-3 PUFA supplementation based on obesity status.

Funding

European Commission Seventh Framework Programme (Grant Number 244995) and Czech Academy of Sciences (Lumina quaeruntur LQ200111901).

Beneficial effects of eicosapentaenoic acid on the metabolic profile of obese female mice entails upregulation of HEPEs and increased abundance of enteric Akkermansia muciniphila

Eicosapentaenoic acid (EPA) ethyl esters are of interest given their clinical approval for lowering circulating triglycerides and cardiometabolic disease risk. EPA ethyl esters prevent metabolic complications driven by a high fat diet in male mice; however, their impact on female mice is less studied. Herein, we first investigated how EPA influences the metabolic profile of female C57BL/6J mice consuming a high fat diet. EPA lowered murine fat mass accumulation, potentially through increased biosynthesis of 8-hydroxyeicosapentaenoic acid (HEPE), as revealed by mass spectrometry and cell culture studies. EPA also reversed the effects of a high fat diet on circulating levels of insulin, glucose, and select inflammatory/metabolic markers. Next, we studied if the improved metabolic profile of obese mice consuming EPA was associated with a reduction in the abundance of key gut Gram-negative bacteria that contribute toward impaired glucose metabolism. Using fecal 16S-ribosomal RNA gene sequencing, we found EPA restructured the gut microbiota in a time-dependent manner but did not lower the levels of key Gram-negative bacteria. Interestingly, EPA robustly increased the abundance of the Gram-negative Akkermansia muciniphila, which controls glucose homeostasis. Finally, predictive functional profiling of microbial communities revealed EPA-mediated reversal of high fat diet-associated changes in a wide range of genes related to pathways such as Th-17 cell differentiation and PI3K-Akt signaling. Collectively, these results show that EPA ethyl esters prevent some of the deleterious effects of a high fat diet in female mice, which may be mediated mechanistically through 8-HEPE and the upregulation of intestinal Akkermansia muciniphila.

Specialized pro-resolving mediators as modulators of immune responses

Specialized pro-resolving mediators (SPMs) are endogenous small molecules produced mainly from dietary omega-3 polyunsaturated fatty acids by both structural cells and cells of the active and innate immune systems. Specialized pro-resolving mediators have been shown to both limit acute inflammation and promote resolution and return to homeostasis following infection or injury. There is growing evidence that chronic immune disorders are characterized by deficiencies in resolution and SPMs have significant potential as novel therapeutics to prevent and treat chronic inflammation and immune system disorders. This review focuses on important breakthroughs in understanding how SPMs are produced by, and act on, cells of the adaptive immune system, specifically macrophages, B cells and T cells. We also highlight recent evidence demonstrating the potential of SPMs as novel therapeutic agents in topics including immunization, autoimmune disease and transplantation.

Schizochytrium sp. Dietary supplementation modify Toll-like receptor 4 (TLR4) transcriptional regulation in monocytes and neutrophils of dairy goats

Animals protect themselves against pathogens or abiotic factors by innate or adaptive mechanisms. Long-chain polyunsaturated fatty acids (ω3) of microalgae modify both human and mice' immune systems resulting in a beneficial balance between pro-inflammatory and anti-inflammatory pathways. However, scarce information exists on their impact on lactating animals' immunity. The objective of this study was to investigate the impact of dietary inclusion of Schizochytrium sp. (rich in docosapentaenoic and docosahexaenoic acid), on the expression of several genes involved in the innate immunity of goats. Twenty-four dairy goats were divided into four homogeneous sub-groups (n = 6). All goats were fed individually with alfalfa hay and concentrate. The concentrate of the control group (CON) had no microalgae while those of the treated groups were supplemented daily with 20 (ALG20), 40 (ALG40), and 60 (ALG60) g Schizochytrium sp. Monocytes and neutrophils were isolated from goats' blood in the 20th, 40th^, and 60th days from the beginning of the experimental period. The relative transcript levels of TLR4, MYD88, MAPK, IRF3, IFNG, and pro-inflammatory cytokines (IL1B, IL2, IL8, TNF), and chemokines (CCL5 and CXCL16) were decreased in monocytes of microalgae treated goats compared to the CON. In contrast, MAPK and IL1B relative transcript levels were increased in neutrophils of ALG40 and ALG60 groups. In conclusion, the supplementation of goats' diet with 20 g Schizochytrium sp. resulted in a downregulation of the pro-inflammatory transcriptions, and following further research could be considered as a sustainable alternative strategy to improve immune function.

Dietary Supplementation With Eicosapentaenoic Acid Inhibits Plasma Cell Differentiation and Attenuates Lupus Autoimmunity

Accumulating evidence suggests that cholesterol accumulation in leukocytes is causally associated with the development of autoimmune diseases. However, the mechanism by which fatty acid composition influences autoimmune responses remains unclear. To determine whether the fatty acid composition of diet modulates leukocyte function and the development of systemic lupus erythematosus, we examined the effect of eicosapentaenoic acid (EPA) on the pathology of lupus in drug-induced and spontaneous mouse models. We found that dietary EPA supplementation ameliorated representative lupus manifestations, including autoantibody production and immunocomplex deposition in the kidneys. A combination of lipidomic and membrane dynamics analyses revealed that EPA remodels the lipid composition and fluidity of B cell membranes, thereby preventing B cell differentiation into autoantibody-producing plasma cells. These results highlight a previously unrecognized mechanism by which fatty acid composition affects B cell differentiation into autoantibody-producing plasma cells during autoimmunity, and imply that EPA supplementation may be beneficial for therapy of lupus.

The Influence of Nutritional Factors on Immunological Outcomes

Through food intake, humans obtain a variety of nutrients that are essential for growth, cellular function, tissue development, energy, and immune defense. A special interaction between nutrients and gut-associated lymphoid tissue occurs in the intestinal tract. Enterocytes of the intestinal barrier act as sensors for antigens from nutrients and the intestinal microbiota, which they deliver to the underlying immune system of the lamina propria, triggering an immune response. Studies investigating the mechanism of influence of nutrition on immunological outcomes have highlighted an important role of macronutrients (proteins, carbohydrates, fatty acids) and micronutrients (vitamins, minerals, phytochemicals, antioxidants, probiotics) in modulating immune homeostasis. Nutrients exert their role in innate immunity and inflammation by regulating the expression of TLRs, pro- and anti-inflammatory cytokines, thus interfering with immune cell crosstalk and signaling. Chemical substrates derived from nutrient metabolism may act as cofactors or blockers of enzymatic activity, influencing molecular pathways and chemical reactions associated with microbial killing, inflammation, and oxidative stress. Immune cell function appears to be influenced by certain nutrients that form parts of the cell membrane structure and are involved in energy production and prevention of cytotoxicity. Nutrients also contribute to the initiation and regulation of adaptive immune responses by modulating B and T lymphocyte differentiation, proliferation and activation, and antibody production. The purpose of this review is to present the available data from the field of nutritional immunology to elucidate the complex and dynamic relationship between nutrients and the immune system, the delineation of which will lead to optimized nutritional regimens for disease prevention and patient care.

Fatty acid-binding protein 3 regulates differentiation of IgM-producing plasma cells

Plasma cells (PCs), which aim to protect host health, produce various subsets of immunoglobulin (Ig) in response to extracellular pathogens. Blimp-1 (encoded by Prdm1)-a protein that is highly expressed by PCs-is important for PC functions, including the generation of Igs. Fatty acid-binding protein 3 (FABP3) is a carrier protein of polyunsaturated fatty acids (PUFAs) and participates in multiple cellular functions. Although the functions of FABP3 in neurons and cardiac myocytes are well-noted, their roles in immune cells remain to be fully elucidated. In this study, we demonstrate that FABP3 is expressed in activated B cells and that FABP3 promotes PC development and IgM secretion. Moreover, we provide the first evidence that FABP3 is necessary for Blimp-1 expression, by regulating the histone modification of its promoter region. Taken together, our findings reveal that FABP3 acts as a positive regulator of B-cell activation by controlling histone acetylation of the Blimp-1 gene, thereby playing a role in host defense against pathogens.

Hormonal Dysregulation and Unbalanced Specialized Pro-Resolving Mediator Biosynthesis Contribute toward Impaired B Cell Outcomes in Obesity

Diet-induced obesity is associated with impaired B-cell-driven humoral immunity, which coincides with chronic inflammation and has consequences for responses to infections and vaccinations. Key nutritional, cellular, and molecular mechanisms by which obesity may impair aspects of humoral immunity such as B cell development, class switch recombination, and formation of long-lived antibody secreting cells are reviewed. A key theme to emerge is the central role of white adipose tissue on the formation and function of pro-inflammatory B cell subsets that exacerbate insulin resistance. The underlying role of select hormones such as leptin is highlighted, which may be driving the formation of pro-inflammatory B cells in the absence of antigen stimulation. This review also extensively covers the regulatory role of lipid metabolites such as prostaglandins and specialized pro-resolving mediators (SPMs) that are synthesized from polyunsaturated fatty acids. Notably, SPM biosynthesis is impaired in obesity and contributes toward impaired antibody production. Future directions for research, including avenues for therapeutic intervention, are included.

Obesity-Driven Deficiencies of Specialized Pro-resolving Mediators May Drive Adverse Outcomes During SARS-CoV-2 Infection

Obesity is a major independent risk factor for increased morbidity and mortality upon infection with Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2), which is responsible for the current coronavirus disease pandemic (COVID-19). Therefore, there is a critical need to identify underlying metabolic factors associated with obesity that could be contributing toward increased susceptibility to SARS-CoV-2 in this vulnerable population. Here, we focus on the critical role of potent endogenous lipid metabolites known as specialized pro-resolving mediators (SPMs) that are synthesized from polyunsaturated fatty acids. SPMs are generated during the transition of inflammation to resolution and have a vital role in directing damaged tissues to homeostasis; furthermore, SPMs display anti-viral activity in the context of influenza infection without being immunosuppressive. We cover evidence from rodent and human studies to show that obesity, and its co-morbidities, induce a signature of SPM deficiency across immunometabolic tissues. We further discuss how the effects of obesity upon SARS-CoV-2 infection are likely exacerbated with environmental exposures that promote chronic pulmonary inflammation and augment SPM deficits. Finally, we highlight potential approaches to overcome the loss of SPMs using dietary and pharmacological interventions. Collectively, this mini-review underscores the need for mechanistic studies on how SPM deficiencies driven by obesity and environmental exposures may exacerbate the response to SARS-CoV-2.

Spleen Oxylipin and Polyunsaturated Fatty Acid Profiles are Altered by Dietary Source of Polyunsaturated Fatty Acid and by Sex

As the largest secondary lymphoid organ, the spleen plays an important role in immune responses. The role of arachidonic acid (ARA) and its 20-carbon eicosanoids in modulating immune function has long been of interest. However, recent advances have enabled the identification of numerous other n-6 and n-3 polyunsaturated fatty acid (PUFA)-derived oxylipins. Here, we investigate the effects of diet and sex on the spleen nonesterified oxylipin profiles and phospholipid and neutral lipid PUFA composition in Sprague-Dawley rats supplemented with oils rich in α-linolenic acid (ALA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), or linoleic acid. Dietary ALA, EPA, and DHA resulted in lower levels of ARA and ARA oxylipins. Oxylipins derived from other n-6 PUFA were also reduced despite no or opposite effect on their PUFA levels. Each diet also resulted in higher levels of oxylipins almost exclusively derived from the supplemented PUFA, despite PUFA in the same biosynthetic pathway also often being increased. Further, while oxylipin differences often reflected changes to phospholipid PUFA, there were instances where they corresponded more closely to changes in neutral lipid PUFA. With respect to sex effects, >50% of lipoxygenase ARA-derived oxylipins were higher in males in at least one diet group, while multiple DHA oxylipins were lower in males only in rats provided the DHA diet. This fundamental description of oxylipin composition in the spleen, including the influence of diet and sex and the relationship to PUFA composition, will help inform future studies examining the functions of these oxylipins under physiological and pathological conditions.

The Influence of Dietary Fatty Acids on Immune Responses

Diet-derived fatty acids (FAs) are essential sources of energy and fundamental structural components of cells. They also play important roles in the modulation of immune responses in health and disease. Saturated and unsaturated FAs influence the effector and regulatory functions of innate and adaptive immune cells by changing membrane composition and fluidity and by acting through specific receptors. Impaired balance of saturated/unsaturated FAs, as well as n-6/n-3 polyunsaturated FAs has significant consequences on immune system homeostasis, contributing to the development of many allergic, autoimmune, and metabolic diseases. In this paper, we discuss up-to-date knowledge and the clinical relevance of the influence of dietary FAs on the biology, homeostasis, and functions of epithelial cells, macrophages, dendritic cells, neutrophils, innate lymphoid cells, T cells and B cells. Additionally, we review the effects of dietary FAs on the pathogenesis of many diseases, including asthma, allergic rhinitis, food allergy, atopic dermatitis, rheumatoid arthritis, multiple sclerosis as well as type 1 and 2 diabetes.

Effects of Omega-3 Fatty Acids on Immune Cells

Alterations on the immune system caused by omega-3 fatty acids have been described for 30 years. This family of polyunsaturated fatty acids exerts major alterations on the activation of cells from both the innate and the adaptive immune system, although the mechanisms for such regulation are diverse. First, as a constitutive part of the cellular membrane, omega-3 fatty acids can regulate cellular membrane properties, such as membrane fluidity or complex assembly in lipid rafts. In recent years, however, a new role for omega-3 fatty acids and their derivatives as signaling molecules has emerged. In this review, we describe the latest findings describing the effects of omega-3 fatty acids on different cells from the immune system and their possible molecular mechanisms.

Frontline Science: A reduction in DHA-derived mediators in male obesity contributes toward defects in select B cell subsets and circulating antibody

Obesity dysregulates B cell populations, which contributes toward poor immunological outcomes. We previously reported that differing B cell subsets are lowered in the bone marrow of obese male mice. Here, we focused on how lipid metabolites synthesized from docosahexaenoic acid (DHA) known as specialized pro-resolving lipid mediators (SPMs) influence specific B cell populations in obese male mice. Metabololipidomics revealed that splenic SPM precursors 14-hydroxydocosahexaenoic acid (14-HDHA), 17-hydroxydocosahexaenoic acid (17-HDHA), and downstream protectin DX (PDX) were decreased in obese male C57BL/6J mice. Simultaneous administration of these mediators to obese mice rescued major decrements in bone marrow B cells, modest impairments in the spleen, and circulating IgG2c, which is pro-inflammatory in obesity. In vitro studies with B cells, flow cytometry experiments with ALOX5^-/- mice, and lipidomic analyses revealed the lowering of 14-HDHA/17-HDHA/PDX and dysregulation of B cell populations in obesity was driven indirectly via B cell extrinsic mechanisms. Notably, the lowering of lipid mediators was associated with an increase in the abundance of n-6 polyunsaturated fatty acids, which have a high affinity for SPM-generating enzymes. Subsequent experiments revealed female obese mice generally maintained the levels of SPM precursors, B cell subsets, and antibody levels. Finally, obese human females had increased circulating plasma cells accompanied by ex vivo B cell TNFα and IL-10 secretion. Collectively, the data demonstrate that DHA-derived mediators of the SPM pathway control the number of B cell subsets and pro-inflammatory antibody levels in obese male but not female mice through a defect that is extrinsic to B cells.

Key roles for lipid mediators in the adaptive immune response

Chronic inflammation is an underlying feature of many diseases, including chronic obstructive pulmonary disease, rheumatoid arthritis, asthma, and multiple sclerosis. There is an increasing appreciation of the dysregulation of adaptive immunity in chronic inflammatory and allergic diseases. The discovery of specialized pro-resolving lipid mediators (SPMs) that actively promote the resolution of inflammation has opened new avenues for the treatment of chronic inflammatory diseases. Much work has been done focusing on the impact of SPMs on innate immune cells. However, much less is known about the influence of SPMs on the development of antigen-specific adaptive immune responses. This Review highlights the important breakthroughs concerning the effects of SPMs on the key cell types involved in the development of adaptive immunity, namely dendritic cells, T cells, and B cells.

Docosahexaenoic acid regulates the formation of lipid rafts: A unified view from experiment and simulation

Docosahexaenoic acid (DHA, 22:6) is an n-3 polyunsaturated fatty acid (n-3 PUFA) that influences immunological, metabolic, and neurological responses through complex mechanisms. One structural mechanism by which DHA exerts its biological effects is through its ability to modify the physical organization of plasma membrane signaling assemblies known as sphingomyelin/cholesterol (SM/chol)-enriched lipid rafts. Here we studied how DHA acyl chains esterified in the sn-2 position of phosphatidylcholine (PC) regulate the formation of raft and non-raft domains in mixtures with SM and chol on differing size scales. Coarse grained molecular dynamics simulations showed that 1-palmitoyl-2-docosahexaenoylphosphatylcholine (PDPC) enhances segregation into domains more than the monounsaturated control, 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC). Solid state ²H NMR and neutron scattering experiments provided direct experimental evidence that substituting PDPC for POPC increases the size of raft-like domains on the nanoscale. Confocal imaging of giant unilamellar vesicles with a non-raft fluorescent probe revealed that POPC had no influence on phase separation in the presence of SM/chol whereas PDPC drove strong domain segregation. Finally, monolayer compression studies suggest that PDPC increases lipid-lipid immiscibility in the presence of SM/chol compared to POPC. Collectively, the data across model systems provide compelling support for the emerging model that DHA acyl chains of PC lipids tune the size of lipid rafts, which has potential implications for signaling networks that rely on the compartmentalization of proteins within and outside of rafts.

Interrelation of Diet, Gut Microbiome, and Autoantibody Production

B cells possess a predominant role in adaptive immune responses via antibody-dependent and -independent functions. The microbiome of the gastrointestinal tract is currently being intensively investigated due to its profound impact on various immune responses, including B cell maturation, activation, and IgA antibody responses. Recent findings have demonstrated the interplay between dietary components, gut microbiome, and autoantibody production. "Western" dietary patterns, such as high fat and high salt diets, can induce alterations in the gut microbiome that in turn affects IgA responses and the production of autoantibodies. This could contribute to multiple pathologies including autoimmune and inflammatory diseases. Here, we summarize current knowledge on the influence of various dietary components on B cell function and (auto)antibody production in relation to the gut microbiota, with a particular focus on the gut-brain axis in the pathogenesis of multiple sclerosis.

How does high DHA fish oil affect health? A systematic review of evidence

The health benefits of fish oil, and its omega-3 long chain polyunsaturated fatty acid content, have attracted much scientific attention in the last four decades. Fish oils that contain higher amounts of eicosapentaenoic acid (EPA; 20:5n-3) than docosahexaenoic acid (DHA; 22:6n-3), in a distinctive ratio of 18/12, are typically the most abundantly available and are commonly studied. Although the two fatty acids have traditionally been considered together, as though they were one entity, different physiological effects of EPA and DHA have recently been reported. New oils containing a higher quantity of DHA compared with EPA, such as fractionated and concentrated fish oil, tuna oil, calamari oil and microalgae oil, are increasingly becoming available on the market, and other oils, including those extracted from genetically modified oilseed crops, soon to come. This systematic review focuses on the effects of high DHA fish oils on various human health conditions, such as the heart and cardiovascular system, the brain and visual function, inflammation and immune function and growth/Body Mass Index. Although inconclusive results were reported in several instances, and inconsistent outcomes observed in others, current data provides substantiated evidence in support of DHA being a beneficial bioactive compound for heart, cardiovascular and brain function, with different, and at times complementary, effects compared with EPA. DHA has also been reported to be effective in slowing the rate of cognitive decline, while its possible effects on depression disorders are still unclear. Interestingly, gender- and age- specific divergent roles for DHA have also been reported. This review provides a comprehensive collection of evidence and a critical summary of the documented physiological effects of high DHA fish oils for human health.

Effects of fish oils on ex vivo B-cell responses of obese subjects upon BCR/TLR stimulation: a pilot study

The long-chain n-3 polyunsaturated fatty acids (LC-PUFAs) eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) in fish oil have immunomodulatory properties. B cells are a poorly studied target of EPA/DHA in humans. Therefore, in this pilot study, we tested how n-3 LC-PUFAs influence B-cell responses of obese humans. Obese men and women were assigned to consume four 1-g capsules per day of olive oil (OO, n=12), fish oil (FO, n=12) concentrate or high-DHA-FO concentrate (n=10) for 12 weeks in a parallel design. Relative to baseline, FO (n=9) lowered the percentage of circulating memory and plasma B cells, whereas the other supplements had no effect. There were no postintervention differences between the three supplements. Next, ex vivo B-cell cytokines were assayed after stimulation of Toll-like receptors (TLRs) and/or the B-cell receptor (BCR) to determine if the effects of n-3 LC-PUFAs were pathway-dependent. B-cell IL-10 and TNFα secretion was respectively increased with high DHA-FO (n=10), relative to baseline, with respective TLR9 and TLR9+BCR stimulation. OO (n=12) and FO (n=12) had no influence on B-cell cytokines compared to baseline, and there were no differences in postintervention cytokine levels between treatment groups. Finally, ex vivo antibody levels were assayed with FO (n=7) after TLR9+BCR stimulation. Compared to baseline, FO lowered IgM but not IgG levels accompanied by select modifications to the plasma lipidome. Altogether, the results suggest that n-3 LC-PUFAs could modulate B-cell activity in humans, which will require further testing in a larger cohort.

Emerging role of chemoprotective agents in the dynamic shaping of plasma membrane organization

In the context of an organism, epithelial cells by nature are designed to be the defining barrier between self and the outside world. This is especially true for the epithelial cells that form the lining of the digestive tract, which absorb nutrients and serve as a barrier against harmful substances. These cells are constantly bathed by a complex mixture of endogenous (bile acids, mucus, microbial metabolites) and exogenous (food, nutrients, drugs) bioactive compounds. From a cell biology perspective, this type of exposure would directly impact the plasma membrane, which consists of a myriad of complex lipids and proteins. The plasma membrane not only functions as a barrier but also as the medium in which cellular signaling complexes form and function. This property is mediated by the organization of the plasma membrane, which is exquisitely temporally (nanoseconds to minutes) and spatially (nanometers to micrometers) regulated. Since numerous bioactive compounds found in the intestinal lumen can directly interact with lipid membranes, we hypothesize that the dynamic reshaping of plasma membrane organization underlies the chemoprotective effect of select membrane targeted dietary bioactives (MTDBs). This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

B Cell Activity Is Impaired in Human and Mouse Obesity and Is Responsive to an Essential Fatty Acid upon Murine Influenza Infection

Obesity is associated with increased risk for infections and poor responses to vaccinations, which may be due to compromised B cell function. However, there is limited information about the influence of obesity on B cell function and underlying factors that modulate B cell responses. Therefore, we studied B cell cytokine secretion and/or Ab production across obesity models. In obese humans, B cell IL-6 secretion was lowered and IgM levels were elevated upon ex vivo anti-BCR/TLR9 stimulation. In murine obesity induced by a high fat diet, ex vivo IgM and IgG were elevated with unstimulated B cells. Furthermore, the high fat diet lowered bone marrow B cell frequency accompanied by diminished transcripts of early lymphoid commitment markers. Murine B cell responses were subsequently investigated upon influenza A/Puerto Rico/8/34 infection using a Western diet model in the absence or presence of docosahexaenoic acid (DHA). DHA, an essential fatty acid with immunomodulatory properties, was tested because its plasma levels are lowered in obesity. Relative to controls, mice consuming the Western diet had diminished Ab titers whereas the Western diet plus DHA improved titers. Mechanistically, DHA did not directly target B cells to elevate Ab levels. Instead, DHA increased the concentration of the downstream specialized proresolving lipid mediators (SPMs) 14-hydroxydocosahexaenoic acid, 17-hydroxydocosahexaenoic acid, and protectin DX. All three SPMs were found to be effective in elevating murine Ab levels upon influenza infection. Collectively, the results demonstrate that B cell responses are impaired across human and mouse obesity models and show that essential fatty acid status is a factor influencing humoral immunity, potentially through an SPM-mediated mechanism.

Diet-Induced Obesity Does Not Alter Tigecycline Treatment Efficacy in Murine Lyme Disease

Obese individuals more frequently suffer from infections, as a result of increased susceptibility to a number of bacterial pathogens. Furthermore, obesity can alter antibiotic treatment efficacy due to changes in drug pharmacokinetics which can result in under-dosing. However, studies on the treatment of bacterial infections in the context of obesity are scarce. To address this research gap, we assessed efficacy of antibiotic treatment in diet-induced obese mice infected with the Lyme disease pathogen, Borrelia burgdorferi. Diet-induced obese C3H/HeN mice and normal-weight controls were infected with B. burgdorferi, and treated during the acute phase of infection with two doses of tigecycline, adjusted to the weights of diet-induced obese and normal-weight mice. Antibiotic treatment efficacy was assessed 1 month after the treatment by cultivating bacteria from tissues, measuring severity of Lyme carditis, and quantifying bacterial DNA clearance in ten tissues. In addition, B. burgdorferi-specific IgG production was monitored throughout the experiment. Tigecycline treatment was ineffective in reducing B. burgdorferi DNA copies in brain. However, diet-induced obesity did not affect antibiotic-dependent bacterial DNA clearance in any tissues, regardless of the tigecycline dose used for treatment. Production of B. burgdorferi-specific IgGs was delayed and attenuated in mock-treated diet-induced obese mice compared to mock-treated normal-weight animals, but did not differ among experimental groups following antibiotic treatment. No carditis or cultivatable B. burgdorferi were detected in any antibiotic-treated group. In conclusion, obesity was associated with attenuated and delayed humoral immune responses to B. burgdorferi, but did not affect efficacy of antibiotic treatment.

Epigenetic Mechanisms of Integrative Medicine

Since time immemorial humans have utilized natural products and therapies for their healing properties. Even now, in the age of genomics and on the cusp of regenerative medicine, the use of complementary and alternative medicine (CAM) approaches represents a popular branch of health care. Furthermore, there is a trend towards a unified medical philosophy referred to as Integrative Medicine (IM) that represents the convergence of CAM and conventional medicine. The IM model not only considers the holistic perspective of the physiological components of the individual, but also includes psychological and mind-body aspects. Justification for and validation of such a whole-systems approach is in part dependent upon identification of the functional pathways governing healing, and new data is revealing relationships between therapies and biochemical effects that have long defied explanation. We review this data and propose a unifying theme: IM's ability to affect healing is due at least in part to epigenetic mechanisms. This hypothesis is based on a mounting body of evidence that demonstrates a correlation between the physical and mental effects of IM and modulation of gene expression and epigenetic state. Emphasis on mapping, deciphering, and optimizing these effects will facilitate therapeutic delivery and create further benefits.

Splenic Immune Response Is Down-Regulated in C57BL/6J Mice Fed Eicosapentaenoic Acid and Docosahexaenoic Acid Enriched High Fat Diet

Dietary n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are associated with reduction of inflammation, although the mechanisms are poorly understood, especially how the spleen, as a secondary lymphoid organ, is involved. To investigate the effects of EPA and DHA on spleen gene expression, male C57BL/6J mice were fed high fat diets (HFD) differing in fatty acid composition, either based on corn oil (HFD-CO), or CO enriched with 2 g/100 g EPA and DHA (HFD-ED), for eight weeks. Spleen tissue was analyzed using transcriptomics and for fatty acids profiling. Biological processes (BPs) related to the immune response, including T-cell receptor signaling pathway, T-cell differentiation and co-stimulation, myeloid dendritic cell differentiation, antigen presentation and processing, and the toll like receptor pathway were downregulated by HFD-ED compared with control and HFD-CO. These findings were supported by the down-regulation of NF-κB in HFD-ED compared with HFD-CO fed mice. Lower phospholipid arachidonic acid levels in HFD-ED compared with HFD-CO, and control mice suggest attenuation of pathways via prostaglandins and leukotrienes. The HFD-ED also upregulated BPs related to erythropoiesis and hematopoiesis compared with control and HFD-CO fed mice. Our findings suggest that EPA and DHA down-regulate the splenic immune response induced by HFD-CO, supporting earlier work that the spleen is a target organ for the anti-inflammatory effects of these n-3 fatty acids.

Mucosal Interactions between Genetics, Diet, and Microbiome in Inflammatory Bowel Disease

Numerous reviews have discussed gut microbiota composition changes during inflammatory bowel diseases (IBD), particularly Crohn’s disease (CD). However, most studies address the observed effects by focusing on studying the univariate connection between disease and dietary-induced alterations to gut microbiota composition. The possibility that these effects may reflect a number of other interconnected (i.e., pantropic) mechanisms, activated in parallel, particularly concerning various bacterial metabolites, is in the process of being elucidated. Progress seems, however, hampered by various difficult-to-study factors interacting at the mucosal level. Here, we highlight some of such factors that merit consideration, namely: (1) the contribution of host genetics and diet in altering gut microbiome, and in turn, the crosstalk among secondary metabolic pathways; (2) the interdependence between the amount of dietary fat, the fatty acid composition, the effects of timing and route of administration on gut microbiota community, and the impact of microbiota-derived fatty acids; (3) the effect of diet on bile acid composition, and the modulator role of bile acids on the gut microbiota; (4) the impact of endogenous and exogenous intestinal micronutrients and metabolites; and (5) the need to consider food associated toxins and chemicals, which can introduce confounding immune modulating elements (e.g., antioxidant and phytochemicals in oils and proteins). These concepts, which are not mutually exclusive, are herein illustrated paying special emphasis on physiologically inter-related processes.

Concentration and ratio of essential fatty acids influences the inflammatory response in lipopolysaccharide challenged mice

The goal of this study was to evaluate the role of both the % of dietary, 18-carbon PUFA (2.5%, 5% and 10%) and the n-6:n-3 ratio (1:1, 10:1 and 20:1) on the acute inflammatory response. Mice were fed diets for 8 weeks and injected intraperitoneally with LPS to induce acute inflammation. After 24h mice were sacrificed and plasma cytokines measured. Diets significantly affected the erythrocyte PUFA composition and the effect of PUFA ratio was more prominent than of PUFA concentration. The % dietary PUFA affected feed efficiency (p<0.05) and there was a PUFA×ratio interaction with body fat (p<0.01). In mice fed high %kcal from PUFA, those given a low n-6:n-3 ratio had more body fat than those fed a high ratio. Of the twelve cytokines measured, eleven were significantly affected by the % PUFA (p<0.05), whereas five were affected by the ratio (p<0.05). For seven cytokines, there was a significant PUFA×ratio interaction according to a two way ANOVA (p<0.05). These data indicate that dietary polyunsaturated fatty acids can affect LPS induced-inflammation.

Membrane Disordering by Eicosapentaenoic Acid in B Lymphomas Is Reduced by Elongation to Docosapentaenoic Acid as Revealed with Solid-State Nuclear Magnetic Resonance Spectroscopy of Model Membranes

BACKGROUND

Plasma membrane organization is a mechanistic target of n-3 (ω-3) polyunsaturated fatty acids. Previous studies show that eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) differentially disrupt plasma membrane molecular order to enhance the frequency and function of B lymphocytes. However, it is not known whether EPA and DHA affect the plasma membrane organization of B lymphomas differently to influence their function.

OBJECTIVE

We tested whether EPA and DHA had different effects on membrane order in B lymphomas and liposomes and studied their effects on B-lymphoma growth.

METHODS

B lymphomas were treated with 25 μmol EPA, DHA, or serum albumin control/L for 24 h. Membrane order was measured with fluorescence polarization, and cellular fatty acids (FAs) were analyzed with GC. Growth was quantified with a viability assay. (2)H nuclear magnetic resonance (NMR) studies were conducted on deuterated phospholipid bilayers.

RESULTS

Treating Raji, Ramos, and RPMI lymphomas for 24 h with 25 μmol EPA or DHA/L lowered plasma membrane order by 10-40% relative to the control. There were no differences between EPA and DHA on membrane order for the 3 cell lines. FA analyses revealed complex changes in response to EPA or DHA treatment and a large fraction of EPA was converted to docosapentaenoic acid (DPA; 22:5n-3). NMR studies, which were used to understand why EPA and DHA had similiar membrane effects, showed that phospholipids containing DPA, similar to DHA, were more ordered than those containing EPA. Finally, treating B lymphomas with 25 μmol EPA or DHA/L did not increase the frequency of B lymphomas compared with controls.

CONCLUSIONS

The results establish that 25 μmol EPA and DHA/L equally disrupt membrane order and do not promote B lymphoma growth. The data open a new area of investigation, which is how EPA's conversion to DPA substantially moderates its influence on membrane properties.

Short-term consumption of n-3 PUFAs increases murine IL-5 levels, but IL-5 is not the mechanistic link between n-3 fatty acids and changes in B-cell populations

N-3 polyunsaturated fatty acids (PUFAs) exert immunomodulatory effects on B cells. We previously demonstrated that n-3 PUFAs enhanced the relative percentage and/or frequency of select B2 cell subsets. The objectives here were to determine if n-3 PUFAs (a) could boost cytokines that target B-cell frequency, (b) enhance the frequency of the B1 population and (c) to identify the mechanism by which n-3 PUFAs modify the proportion of B cells. Administration of n-3 PUFAs as fish oil to C57BL/6 mice enhanced secretion of the Th2 cytokine IL-5 but not IL-9 or IL-13. N-3 PUFAs had no influence on the percentage or frequency of peritoneal B1 or B2 cells. Subsequent experiments with IL-5(-/-) knockout mice showed n-3 PUFAs decreased the percentage of bone marrow B220(lo)IgM(hi) cells and increased the proportion and number of splenic IgM(+)IgD(lo)CD21(lo) cells compared to the control. These results, when compared with our previous findings with wild-type mice, suggested IL-5 had no role in mediating the effect of n-3 PUFAs on B-cell populations. To confirm this conclusion, we assayed IL-5 secretion in a diet-induced obesity model in which n-3 PUFAs enhanced the frequency of select B-cell subsets. N-3 PUFA supplementation as ethyl esters to obesogenic diets did not alter circulating IL-5 levels. Altogether, the data establish that n-3 PUFAs as fish oil can increase circulating IL-5 in lean mice, which has implications for several disease end points, but this increase in IL-5 is not the mechanistic link between n-3 PUFAs and changes in B-cell populations.

Omega-3 Polyunsaturated Fatty Acids: The Way Forward in Times of Mixed Evidence

Almost forty years ago, it was first hypothesized that an increased dietary intake of omega-3 polyunsaturated fatty acids (PUFA) from fish fat could exert protective effects against several pathologies. Decades of intense preclinical investigation have supported this hypothesis in a variety of model systems. Several clinical cardiovascular studies demonstrated the beneficial health effects of omega-3 PUFA, leading medical institutions worldwide to publish recommendations for their increased intake. However, particularly in recent years, contradictory results have been obtained in human studies focusing on cardiovascular disease and the clinical evidence in other diseases, particularly chronic inflammatory and neoplastic diseases, was never established to a degree that led to clear approval of treatment with omega-3 PUFA. Recent data not in line with the previous findings have sparked a debate on the health efficacy of omega-3 PUFA and the usefulness of increasing their intake for the prevention of a number of pathologies. In this review, we aim to examine the controversies on the possible use of these fatty acids as preventive/curative tools against the development of cardiovascular, metabolic, and inflammatory diseases, as well as several kinds of cancer.

High levels of fish oil enhance neutrophil development and activation and influence colon mucus barrier function in a genetically susceptible mouse model

Dietary fatty acids influence immunologic homeostasis, but their effect on initiation of colitis, an immune-mediated disease, is not well established. Previously, our laboratory demonstrated that high doses of dietary fish oil (FO) increased colon inflammation and dysplasia in a model of infection-induced colitis. In the current study, we assessed the effects of high-dose dietary FO, 6% by weight, on colon inflammation, neutrophil recruitment and function, and mucus layer integrity in a genetically susceptible, colitis-prone mouse model in the absence of infection. FO-fed SMAD3(-/-) mice had increased colon inflammation evidenced by increased numbers of systemic and local neutrophils and increased neutrophil chemoattractant and inflammatory cytokine gene expression in the colon. Mucus layer thickness in the cecum and goblet cell numbers in the cecum and colon in FO-fed mice were reduced compared to control. FO consumption affected colitis in male and female mice differently. Compared to female control mice, neutrophils from FO-fed female mice had reduced reactive oxygen species (ROS) upon ex vivo stimulation with phorbol myristate acetate while FO-fed male mice produced increased ROS compared to control-fed male mice. In summary, dietary FO impaired mucus layer integrity and was associated with colon inflammation characterized by increased neutrophil numbers and altered neutrophil function. High-dose FO may have detrimental effects in populations genetically susceptible for inflammatory bowel disease and these effects may differ between males and females.

Are obesity-related insulin resistance and type 2 diabetes autoimmune diseases?

Obesity and associated insulin resistance predispose individuals to develop chronic metabolic diseases, such as type 2 diabetes and cardiovascular disease. Although these disorders affect a significant proportion of the global population, the underlying mechanisms of disease remain poorly understood. The discovery of elevated tumor necrosis factor-α in adipose tissue as an inducer of obesity-associated insulin resistance marked a new era of understanding that a subclinical inflammatory process underlies the insulin resistance and metabolic dysfunction that precedes type 2 diabetes. Advances in the field identified components of both the innate and adaptive immune response as key players in regulating such inflammatory processes. As antigen specificity is a hallmark of an adaptive immune response, its role in modulating the chronic inflammation that accompanies obesity and type 2 diabetes begs the question of whether insulin resistance and type 2 diabetes can have autoimmune components. In this Perspective, we summarize current data that pertain to the activation and perpetuation of adaptive immune responses during obesity and discuss key missing links and potential mechanisms for obesity-related insulin resistance and type 2 diabetes to be considered as potential autoimmune diseases.

N-3 polyunsaturated fatty acids modulate B cell activity in pre-clinical models: Implications for the immune response to infections

B cell antigen presentation, cytokine production, and antibody production are targets of pharmacological intervention in inflammatory and infectious diseases. Here we review recent pre-clinical evidence demonstrating that pharmacologically relevant levels of n-3 polyunsaturated fatty acids (PUFA) derived from marine fish oils influence key aspects of B cell function through multiple mechanisms. N-3 PUFAs modestly diminish B cell mediated stimulation of classically defined naïve CD4(+) Th1 cells through the major histocompatibility complex (MHC) class II pathway. This is consistent with existing data showing that n-3 PUFAs suppress the activation of Th1/Th17 cells through direct effects on helper T cells and indirect effects on antigen presenting cells. Mechanistically, n-3 PUFAs lower antigen presentation and T cell signaling by disrupting the formation of lipid microdomains within the immunological synapse. We then review data to show that n-3 PUFAs boost B cell activation and antibody production in the absence and presence of antigen stimulation. This has potential benefits for several clinical populations such as the aged and obese that have poor humoral immunity. The mode of action by which n-3 PUFA boost B cell activation and antibody production remains unclear, but may involve Th2 cytokines, enhanced production of specialized proresolving lipid mediators, and targeting of protein lateral organization in lipid microdomains. Finally, we highlight evidence to show that different n-3 PUFAs are not biologically equivalent, which has implications for the development of future interventions to target B cell activity.

N-3 Polyunsaturated Fatty Acids, Lipid Microclusters, and Vitamin E

Increased consumption of long-chain marine n-3 polyunsaturated fatty acids (PUFA) has potential health benefits for the general population and for select clinical populations. However, several key limitations remain in making adequate dietary recommendations on n-3 PUFAs in addition to translating the fatty acids into clinical trials for select diseases. One major constraint is an incomplete understanding of the underlying mechanisms of action of n-3 PUFAs. In this review, we highlight studies to show n-3 PUFA acyl chains reorganize the molecular architecture of plasma membrane sphingolipid-cholesterol-enriched lipid rafts and potentially sphingolipid-rich cholesterol-free domains and cardiolipin-protein scaffolds in the inner mitochondrial membrane. We also discuss the possibility that the effects of n-3 PUFAs on membrane organization could be regulated by the presence of vitamin E (α-tocopherol), which is necessary to protect highly unsaturated acyl chains from oxidation. Finally, we propose the integrated hypothesis, based predominately on studies in lymphocytes, cancer cells, and model membranes, that the mechanism by which n-3 PUFAs disrupt signaling microclusters is highly dependent on the type of lipid species that incorporate n-3 PUFA acyl chains. The current evidence suggests that n-3 PUFA acyl chains disrupt lipid raft formation by incorporating primarily into phosphatidylethanolamines but can also incorporate into other lipid species of the lipidome.

Obesity Increases Mortality and Modulates the Lung Metabolome during Pandemic H1N1 Influenza Virus Infection in Mice

Obese individuals are at greater risk for hospitalization and death from infection with the 2009 pandemic H1N1 influenza virus (pH1N1). In this study, diet-induced and genetic-induced obese mouse models were used to uncover potential mechanisms by which obesity increases pH1N1 severity. High-fat diet-induced and genetic-induced obese mice exhibited greater pH1N1 mortality, lung inflammatory responses, and excess lung damage despite similar levels of viral burden compared with lean control mice. Furthermore, obese mice had fewer bronchoalveolar macrophages and regulatory T cells during infection. Obesity is inherently a metabolic disease, and metabolic profiling has found widespread usage in metabolic and infectious disease models for identifying biomarkers and enhancing understanding of complex mechanisms of disease. To further characterize the consequences of obesity on pH1N1 infection responses, we performed global liquid chromatography-mass spectrometry metabolic profiling of lung tissue and urine. A number of metabolites were perturbed by obesity both prior to and during infection. Uncovered metabolic signatures were used to identify changes in metabolic pathways that were differentially altered in the lungs of obese mice such as fatty acid, phospholipid, and nucleotide metabolism. Taken together, obesity induces distinct alterations in the lung metabolome, perhaps contributing to aberrant pH1N1 immune responses.

Docosahexaenoic acid promotes micron scale liquid-ordered domains. A comparison study of docosahexaenoic versus oleic acid containing phosphatidylcholine in raft-like mixtures

The understanding of the functional role of the lipid diversity in biological membranes is a major challenge. Lipid models have been developed to address this issue by using lipid mixtures generating liquid-ordered (Lo)/liquid-disordered (Ld) immiscibility. The present study examined mixtures comprising Egg sphingomyelin (SM), cholesterol (chol) and phosphatidylcholine (PC) either containing docosahexaenoic (PDPC) or oleic acid (POPC). The mixtures were examined in terms of their capability to induce phase separation at the micron- and nano-scales. Fluorescence microscopy, electron spin resonance (ESR), X-ray diffraction (XRD) and calorimetry methods were used to analyze the lateral organization of the mixtures. Fluorescence microscopy of giant vesicles could show that the temperature of the micron-scale Lo/Ld miscibility is higher for PDPC than for POPC ternary mixtures. At 37°C, no micron-scale Lo/Ld phase separation could be identified in the POPC containing mixtures while it was evident for PDPC. In contrast, a phase separation was distinguished for both PC mixtures by ESR and XRD, indicative that PDPC and POPC mixtures differed in micron vs nano domain organization. Compared to POPC, the higher line tension of the Lo domains observed in PDPC mixtures is assumed to result from the higher difference in Lo/Ld order parameter rather than hydrophobic mismatch.

The effects of diet-induced obesity on B cell function

B-1 and B-2 B cell subsets carry out a diverse array of functions that range broadly from responding to innate stimuli, antigen presentation, cytokine secretion and antibody production. In this review, we first cover the functional roles of the major murine B cell subsets. We then highlight emerging evidence, primarily in preclinical rodent studies, to show that select B cell subsets are a therapeutic target in obesity and its associated co-morbidities. High fat diets promote accumulation of select murine B cell phenotypes in visceral adipose tissue. As a consequence, B cells exacerbate inflammation and thereby insulin sensitivity through the production of autoantibodies and via cross-talk with select adipose resident macrophages, CD4(+) and CD8(+) T cells. In contrast, interleukin (IL)-10-secreting regulatory B cells counteract the proinflammatory profile and improve glucose sensitivity. We subsequently review data from rodent studies that show pharmacological supplementation of obesogenic diets with long chain n-3 polyunsaturated fatty acids or specialized pro-resolving lipid mediators synthesized from endogenous n-3 polyunsaturated fatty acids boost B cell activation and antibody production. This may have potential benefits for improving inflammation in addition to combating the increased risk of viral infection that is an associated complication of obesity and type II diabetes. Finally, we propose potential underlying mechanisms throughout the review by which B cell activity could be differentially regulated in response to high fat diets.

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.

Eicosapentaenoic and docosahexaenoic acid ethyl esters differentially enhance B-cell activity in murine obesity

EPA and DHA are not biologically equivalent; however, their individual activity on B cells is unknown. We previously reported fish oil enhanced murine B-cell activity in obesity. To distinguish between the effects of EPA and DHA, we studied the ethyl esters of EPA and DHA on murine B-cell function as a function of time. We first demonstrate that EPA and DHA maintained the obese phenotype, with no improvements in fat mass, adipose inflammatory cytokines, fasting insulin, or glucose clearance. We then tested the hypothesis that EPA and DHA would increase the frequency of splenic B cells. EPA and DHA differentially enhanced the frequency and/or percentage of select B-cell subsets, correlating with increased natural serum IgM and cecal IgA. We next determined the activities of EPA and DHA on ex vivo production of cytokines upon lipopolysaccharide stimulation of B cells. EPA and DHA, in a time-dependent manner, enhanced B-cell cytokines with DHA notably increasing IL-10. At the molecular level, EPA and DHA differentially enhanced the formation of ordered microdomains but had no effect on Toll-like receptor 4 mobility. Overall, the results establish differential effects of EPA and DHA in a time-dependent manner on B-cell activity in obesity, which has implications for future clinical studies.

How polyunsaturated fatty acids modify molecular organization in membranes: insight from NMR studies of model systems

Marine long chain n-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), are bioactive molecules with clinical applications for the treatment of several diseases. In order to effectively translate these molecules into clinical trials, it is essential to establish the underlying mechanisms for n-3 PUFA. This review focuses on efforts to understand how EPA and DHA, upon incorporation into plasma membrane phospholipids, remodel the molecular organization of cholesterol-enriched lipid microdomains. We first give an overview of results from studies on cells. Paradoxical data generated from mouse studies indicate that EPA and DHA incorporate into lipid microdomains, yet in spite of their high disorder increase molecular order within the domain. We then spotlight the utility of solid state (2)H NMR spectroscopy of model bilayers as a tool for elucidating underlying mechanisms by which n-3 PUFA-containing phospholipids can regulate molecular organization of lipid microdomains. Evidence is presented demonstrating that n-3 PUFA exert differential structural effects when incorporated into phosphatidylethanolamines (PE) compared to phosphatidylcholines (PC), which explains some of the conflicting results observed in vivo. Recent studies that reveal differences between the interactions of EPA and DHA with lipid microdomains, potentially reflecting a differential in bioactivity, are finally described. Overall, we highlight the notion that NMR experiments on model membranes suggest a complex model by which n-3 PUFA reorganize lipid microdomains in vivo.