Effects of dietary n-3 fatty acids on Toll-like receptor activation in primary leucocytes from Atlantic salmon (Salmo salar)

Functional foods lipids: unraveling their role in the immune response in obesity

Functional lipids are lipids that are found in food matrices and play an important role in influencing human health as their role goes beyond energy storage and structural components. Ongoing research into functional lipids has highlighted their potential to modulate immune responses and other mechanisms associated with obesity, along with its comorbidities. These lipids represent a new field that may offer new therapeutic and preventive strategies for these diseases by understanding their contribution to health. In this review, we discussed in-depth the potential food sources of functional lipids and their reported potential benefit of the major lipid classification: based on their composition such as simple, compound, and derived lipids, and based on their function such as storage and structural, by investigating the intricate mechanisms through which these lipids interact in the human body. We summarize the key insights into the bioaccessibility and bioavailability of the most studied functional lipids. Furthermore, we review the main immunomodulatory mechanisms reported in the literature in the past years. Finally, we discuss the perspectives and challenges faced in the food industry related to functional lipids.

Effects of eicosapentaneoic acid on innate immune responses in an Atlantic salmon kidney cell line in vitro

Studies of the interplay between metabolism and immunity, known as immunometabolism, is steadily transforming immunological research into new understandings of how environmental cues like diet are affecting innate and adaptive immune responses. The aim of this study was to explore antiviral transcriptomic responses under various levels of polyunsaturated fatty acid. Atlantic salmon kidney cells (ASK cell line) were incubated for one week in different levels of the unsaturated n-3 eicosapentaneoic acid (EPA) resulting in cellular levels ranging from 2-20% of total fatty acid. These cells were then stimulated with the viral mimic and interferon inducer poly I:C (30 ug/ml) for 24 hours before total RNA was isolated and sequenced for transcriptomic analyses. Up to 200 uM EPA had no detrimental effects on cell viability and induced very few transcriptional changes in these cells. However, in combination with poly I:C, our results shows that the level of EPA in the cellular membranes exert profound dose dependent effects of the transcriptional profiles induced by this treatment. Metabolic pathways like autophagy, apelin and VEGF signaling were attenuated by EPA whereas transcripts related to fatty acid metabolism, ferroptosis and the PPAR signaling pathways were upregulated. These results suggests that innate antiviral responses are heavily influenced by the fatty acid profile of salmonid cells and constitute another example of the strong linkage between general metabolic pathways and inflammatory responses.

Fads2b Plays a Dominant Role in ∆6/∆5 Desaturation Activities Compared with Fads2a in Common Carp (Cyprinus carpio)

Highly unsaturated fatty acids (HUFAs) are essential for mammalian health, development and growth. However, most mammals, including humans, are incapable of synthesizing n-6 and n-3 HUFAs. Fish can convert C18 unsaturated fatty acids into n-6 and n-3 HUFAs via fatty acid desaturase (Fads), in which Fads2 is a key enzyme in HUFA biosynthesis. The allo-tetraploid common carp theoretically encode two duplicated fads2 genes. The expression patterns and desaturase functions of these two homologous genes are still unknown. In this study, the full length of the fads2a and fads2b were identified in common carp (Cyprinus carpio). Expression analyses indicate that both genes were mainly expressed in the liver and the expression of fads2b is higher than fads2a at different developmental stages in carp embryos. Heterogenous expression and 3D docking analyses suggested that Fads2b demonstrated stronger ∆6 and ∆5 desaturase activities than Fads2a. The core promotor regions of fads2a and fads2b were characterized and found to have different potential transcriptional binding sites. These results revealed the same desaturase functions, but different activities of two homologues of fasd2 genes in common carp. The data showed that fads2b played a more important role in HUFA synthesis through both expression and functional analyses.

Nutritional immunomodulation of Atlantic salmon response to Renibacterium salmoninarum bacterin

We investigated the immunomodulatory effect of varying levels of dietary ω6/ω3 fatty acids (FA) on Atlantic salmon (Salmo salar) antibacterial response. Two groups were fed either high-18:3ω3 or high-18:2ω6 FA diets for 8 weeks, and a third group was fed for 4 weeks on the high-18:2ω6 diet followed by 4 weeks on the high-18:3ω3 diet and termed “switched-diet”. Following the second 4 weeks of feeding (i.e., at 8 weeks), head kidney tissues from all groups were sampled for FA analysis. Fish were then intraperitoneally injected with either a formalin-killed Renibacterium salmoninarum bacterin (5 × 10⁷ cells mL⁻¹) or phosphate-buffered saline (PBS control), and head kidney tissues for gene expression analysis were sampled at 24 h post-injection. FA analysis showed that the head kidney profile reflected the dietary FA, especially for C₁₈ FAs. The qPCR analyses of twenty-three genes showed that both the high-ω6 and high-ω3 groups had significant bacterin-dependent induction of some transcripts involved in lipid metabolism (ch25ha and lipe), pathogen recognition (clec12b and tlr5), and immune effectors (znrf1 and cish). In contrast, these transcripts did not significantly respond to the bacterin in the “switched-diet” group. Concurrently, biomarkers encoding proteins with putative roles in biotic inflammatory response (tnfrsf6b) and dendritic cell maturation (ccl13) were upregulated, and a chemokine receptor (cxcr1) was downregulated with the bacterin injection regardless of the experimental diets. On the other hand, an inflammatory regulator biomarker, bcl3, was only significantly upregulated in the high-ω3 fed group, and a C-type lectin family member (clec3a) was only significantly downregulated in the switched-diet group with the bacterin injection (compared with diet-matched PBS-injected controls). Transcript fold-change (FC: bacterin/PBS) showed that tlr5 was significantly over 2-fold higher in the high-18:2ω6 diet group compared with other diet groups. FC and FA associations highlighted the role of DGLA (20:3ω6; anti-inflammatory) and/or EPA (20:5ω3; anti-inflammatory) vs. ARA (20:4ω6; pro-inflammatory) as representative of the anti-inflammatory/pro-inflammatory balance between eicosanoid precursors. Also, the correlations revealed associations of FA proportions (% total FA) and FA ratios with several eicosanoid and immune receptor biomarkers (e.g., DGLA/ARA significant positive correlation with pgds, 5loxa, 5loxb, tlr5, and cxcr1). In summary, dietary FA profiles and/or regimens modulated the expression of some immune-relevant genes in Atlantic salmon injected with R. salmoninarum bacterin. The modulation of Atlantic salmon responses to bacterial pathogens and their associated antigens using high-ω6/high-ω3 diets warrants further investigation.

A study of the potential effect of yellow mealworm (Tenebrio molitor) substitution for fish meal on growth, immune and antioxidant capacity in juvenile largemouth bass (Micropterus salmoides)

This study aimed to evaluate the effects of partial replacement of fish meal (FM) with yellow mealworm (Tenebrio molitor, TM) on the growth performance, food utilization and intestinal immune response of juvenile largemouth bass (Micropterus salmoides). Seven diets containing increasing levels of TM (FM substitution) were designed (approximately 0% (0%), 4% (11.1%), 8.1% (22.2%), 12.2% (33.3%), 16.3% (44.4%), 20.4% (55.5%), and 24.5% (66.6%), designated TM0, TM11, TM22, TM33, TM44, TM55, and TM66, respectively). 420 fish were randomly selected and placed in 21 cages (1 m*1 m*1 m, 7 treatments for triplicate, 20 fish per cage). Fish (initial weight 6.25 ± 0.03 g) were fed seven isonitrogenous (47%) and isocaloric (19 MJ kg^-1) diets to satiety twice daily for 8 weeks. Compared to the control group (TM0), TM11 showed no significant difference in the weight gain rate (WGR), specific growth rate (SGR) or feed conversion ratio (FCR), while all other TM inclusion groups presented different degrees of decline. There was no significant difference in the whole-body composition among all groups (P > 0.05). Plasma total protein (TP), triglyceride (TG) and albumin (ALB) contents were significantly decreased in TM55 and TM66 (P < 0.05). The highest plasma aspartate transaminase (AST) activity was observed in TM66 (P < 0.05). TM33, TM44 and TM55 showed the lowest activities of plasma alanine amiotransferase (ALT) and alkaline phosphatase (ALP) (P < 0.05). Moreover, increased mRNA levels of superoxide dismutase (SOD) and catalase (CAT) were measured in the TM11 to TM55 groups, while intestinal SOD activity peaked in TM11 (P < 0.05). With the exception of TM11, the other TM inclusion groups showed significant inhibition of the relative expression of RelA, C3 and TNF-α (P < 0.05). All experimental groups exhibited lower expression of IL-10 than TM0 (P < 0.05). The TM11 group showed significantly upregulated expression of IL-1β and TGF-β (P < 0.05). In addition, TLR2 expression was increased in TM11 and TM22 (P < 0.05). Considering enzyme activities and immune-related gene expression, TM supplementation levels should not exceed 4% (TM11).

Kinetics of transcriptional response against poly (I:C) and infectious salmon anemia virus (ISAV) in Atlantic salmon kidney (ASK) cell line

Vaccine adjuvants induce host innate immune responses improving long-lasting adaptive immunity against vaccine antigens. In vitro models can be used to compare these responses between adjuvants and the infection targeted by the vaccine. We utilized transcriptomic profiling of an Atlantic salmon cell line to compare innate immune responses against ISAV and an experimental viral vaccine adjuvant: poly (I:C). Induction of interferon and interferon induced genes were observed after both treatments, but often with different amplitude and kinetics. Using KEGG ortholog database and available software from Bioconductor we could specify a complete bioinformatic pipeline for analysis of transcriptomic data from Atlantic salmon, a feature not previously available. We have identified important differences in the transcriptional profile of Atlantic salmon cells exposed to viral infection and a viral vaccine adjuvant candidate, poly (I:C). This report increases our knowledge of viral host-pathogen interaction in salmon and to which extent these can be mimicked by adjuvant compounds.

Interaction between dietary fatty acids and genotype on immune response in Atlantic salmon (Salmo salar) after vaccination: A transcriptome study

A pivotal matter to aquaculture is the sourcing of sustainable resources as ingredients to aquafeeds. Levels of plant delivered oils as source of fatty acids (FA) in aquafeeds have reached around 70% resulting in reduced levels of long-chain omega-3 polyunsaturated fatty acids (LC n-3 PUFA), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), in salmon fillet composition. EPA and DHA can modulate inflammation and immune response, so it is crucial to understand how fish immune response is affected by low LC n-3 PUFA diet and if this diet can have a detrimental effect on vaccine response. Atlantic salmon (Salmo salar) can produce EPA/DHA from α-linolenic acid (ALA) and this endogenous capacity can be explored to develop families with higher tolerance to low LC n-3 PUFA diets. Here we analyze innate and adaptive immune response in Atlantic salmon to a commercial vaccine after being fed low levels of EPA and DHA, and we also compare three strains of salmon selected by their endogenous capacity of synthesizing LC- n-3 PUFA. A total of 2,890 differentially expressed genes (DEGs) were identified (p-value adjusted < 0.1) when comparing vaccinated fish against control non-vaccinated. Gene ontology (GO) and KEGG analysis with 442 up/downregulated genes revealed that most DEGs were both related to immune response as well as part of important immune related pathways, as "Toll-like receptor" and "Cytokine-Cytokine interaction". Adaptive response was also addressed by measuring antigen specific IgM, and titers were significantly higher than in the pre-immune fish at 62 days post-immunization. However, diet and strain had no/little effect on vaccine-specific IgM or innate immune responses. Atlantic salmon therefore display robustness in its response to vaccination even when feed low levels of LC n-3 PUFA.

Environmentally-realistic concentration of cadmium combined with polyunsaturated fatty acids enriched diets modulated non-specific immunity in rainbow trout

Nutrition is crucial to grow healthy fish particularly in a context of pollution, overcrowding and pathogen risks. Nowadays, the search for food components able to improve fish health is increasingly developing. Here, the influence of four dietary polyunsaturated fatty acids (PUFAs) that are alpha-linolenic acid (ALA, 18:3n-3), linoleic acid (LA, 18:2n-6), eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) on the sensitivity of rainbow trout (Oncorhynchus mykiss) juveniles to environmentally realistic cadmium (Cd, 0.3 μg/L) concentration was investigated. Fish diets were designed to ensure the specific abundance of one of these individual PUFAs, and were given for a 4-week pre-conditioning period followed by a 6-week Cd exposure period. Focus was put on growth performance and immune responses following a short (24 h) and a long-term (6 weeks) Cd exposure. For each experimental condition, some fish were submitted to a bacterial challenge (24 h) with Aeromonas salmonicida achromogenes at the end of Cd conditioning period. DHA-enriched diet improved growth performances as compared to LA-enriched diet, but also increased ROS production (after short-term exposure to Cd) that could lead to a higher inflammation status, and some immunity-related genes (at short and long-term exposure). We notably highlighted the fact that even a low, environmentally-realistic concentration, Cd can strongly impact the immune system of rainbow trout, and that specific dietary PUFA enrichment strategies can improve growth performance (DHA-enriched diet), provide protection against oxidative stress (ALA- and EPA-enriched diet) and stimulate non-specific immunity.