Dietary Supplementation with Omega-6 LC-PUFA-Rich Microalgae Regulates Mucosal Immune Response and Promotes Microbial Diversity in the Zebrafish Gut

Abstract

The effect of dietary omega-6 long-chain polyunsaturated fatty acid (LC-PUFA) on host microbiome and gut associated immune function in fish is unexplored. The effect of dietary supplementation with the omega-6 LC-PUFA-rich microalga Lobosphaera incisa wild type (WT) and its delta-5 desaturase mutant (MUT), rich in arachidonic-acid and dihomo-gamma-linolenic acid (DGLA), respectively, on intestinal gene expression and microbial diversity was analyzed in zebrafish. For 1 month, fish were fed diets supplemented with broken biomass at 7.5% and 15% (w/w) of the two L. incisa strains and a control nonsupplemented commercial diet. Dietary supplementation resulted in elevated expression of genes related to arachidonic acid metabolism-cyclooxygenase 2 (cox-2), lipoxygenase 1(lox-1), anti-inflammatory cytokine-interleukin 10 (il-10), immune defense-lysozyme (lys), intestinal alkaline phosphatase (iap), complement (c3b), and antioxidants-catalase (cat), glutathione peroxidase (gpx). Microbiome analysis of the gut showed higher diversity indices for microbial communities in fish that were fed the supplemented diets compared to controls. Different treatment groups shared 237 operational taxonomic units (OTUs) that corresponded to the core microbiome, and unique OTUs were evident in different dietary groups. Overall, the zebrafish gut microbiome was dominated by the phylum Fusobacteria and Proteobacteria (averaging 38.4% and 34.6%, respectively), followed by Bacteroidetes (12.9%), Tenericutes, Planctomycetes, and Actinobacteria (at 3.1–1.3%). Significant interaction between some of the immune-related genes and microbial community was demonstrated.

DGLA from the Microalga Lobosphaera Incsa P127 Modulates Inflammatory Response, Inhibits iNOS Expression and Alleviates NO Secretion in RAW264.7 Murine Macrophages

“…Here, we demonstrated that DGLA administration in several forms modulated the immune response in RAW264.7 macrophages. While this work was confined to a cell model, the results further support the anti-inflammatory and immunomodulatory potential of the L. incisa -derived DGLA, previously demonstrated in zebrafish feeding trials [ 23 , 63 ]. Additional studies are required to translate these findings to the use of DGLA as feed and health-promoting food supplements for conditions and pathologies that are caused by imbalance in the immune system.…”

Arachidonic acid matters

“…22 In a zebrafish study, it was also found that dietary supplementation of n-6 LC-PUFA-rich microalga resulted in elevated expression of anti-inflammatory cytokine interleukin 10 (il-10). 184 In addition, an in vitro study with head kidney leukocytes isolated from Atlantic cod revealed that a high level of ARA + EPA upregulated the gene expression of il-10 and downregulated that of the proinflammatory cytokine il-1β (Table 4). 185 However, in Japanese flounder, a concurrent increase in ARA level and inflammation symptom was observed after hemorrhagic septicemia virus infection, 186 as similarly observed in some mammal studies.…”

“…207 However, on the opposite, in zebrafish gut, dietary supplementation of n-6 LC-PUFA-rich microalga led to higher diversity indices for microbial communities. 184 Another study with winter flounder (Pseudopleuronectes americanus)…”

“…In European sea bass, ARA deficiency upregulated the expression of pro‐inflammatory genes in the distal intestine, altogether pointing to a long‐term compromised physical barrier integrity and immune functionality of the distal intestine 22 . In a zebrafish study, it was also found that dietary supplementation of n‐6 LC‐PUFA‐rich microalga resulted in elevated expression of anti‐inflammatory cytokine interleukin 10 ( il‐10 ) 184 . In addition, an in vitro study with head kidney leukocytes isolated from Atlantic cod revealed that a high level of ARA + EPA upregulated the gene expression of il‐10 and downregulated that of the pro‐inflammatory cytokine il‐1β (Table 4).…”

Microbiota composition and intestinal integrity remain unaltered after the inclusion of hydrolysed Nannochloropsis gaditana in Sparus aurata diet

“…In the present study, the tendency of more homogeneous data (less values of variance) and medium values of diversity index between the anterior and posterior sections have been observed when the fish are fed with the FH diet. Reference 41 concluded that changes in diversity are due to an adaptation of the microbiota to digest and assimilate the ingredients added, such as cell walls, polysaccharides and lipids, which affect or modify colonization by minority groups. Avoiding loss of diversity is considered as a positive aspect that protects intestinal mucose and gives protection against diseases 42 .…”