Abstract
Arachidonic acid (ARA, 20:4n-6) and dihomo-γ-linolenic acid (DGLA, 20:3n-6) are omega-6 long-chain polyunsaturated fatty acids (LC-PUFA), which are key precursors for lipid mediators of the immune system and inflammatory response. The microalga Lobosphaera incisa (WT) and its Δ5-desaturase mutant P127 (MUT) are unique photosynthetic sources for ARA and DGLA, respectively. This study explores the effect of dietary supplementation with L. incisa and P127 biomass on tissue fatty acid composition, immune function, and disease resistance in zebrafish (Danio rerio). The broken microalgal biomass was added to commercial fish feed at 7.5 and 15% (w/w), providing 21.8 mg/g feed ARA for the WT-supplemented group and 13.6 mg/g feed DGLA for the MUT-supplemented group at the 15% inclusion levels. An unsupplemented group was used as the control. After 1 month of feeding, fish were challenged with Streptococcus iniae. Fish were sampled before the challenge and 1 week after the challenge for various analyses. Tissue ARA and DGLA levels significantly increased in the liver, corresponding to microalgal supplementation levels. The elevated expression of specific immune-related genes was evident in the kidneys in all treatment groups after 1 month of feeding, including genes related to eicosanoid synthesis, lysozyme, and NF-κB. In the liver, microalgal supplementation led to the upregulation of genes related to immune function and antioxidant defense while the expression of examined genes involved in ARA metabolism was downregulated. Importantly, fish fed with 15% of both WT- and MUT-supplemented feed showed significantly (p < 0.05) higher survival percentages (78 and 68%, respectively, as compared to only 46% in the control group). The elevated expression of genes related to inflammatory and immune responses was evident post-challenge. Collectively, the results of the current study demonstrate the potential of microalgae-derived dietary ARA and DGLA in improving immune competence and resistance to bacterial infection in zebrafish as a model organism.
Highlights
Alterations in the dietary composition and proportion of omega3 and omega-6 long-chain polyunsaturated fatty acids (LCPUFA) groups are known to affect a wide range of physiological processes [1, 2]
Enrichment with the biomass of both microalgae reduced the relative percentage of the n-3 fatty acids, eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), in the experimental diets by up to 42% as compared to the control
Studies have established the role of Arachidonic acid (ARA) as a pro-inflammatory long-chain polyunsaturated fatty acids (LC-PUFA), while DGLA has been associated with relieving inflammation [6, 19]
Summary
Alterations in the dietary composition and proportion of omega and omega-6 long-chain polyunsaturated fatty acids (LCPUFA) groups are known to affect a wide range of physiological processes [1, 2] In addition to their structural and metabolic functions, omega-6 (n-6) LC-PUFA are precursor molecules for numerous bioactive lipid mediators. There are no reports of studies on DGLA dietary supplementation in fish, largely due to limitations in the availability of this rare LC-PUFA In this context, the microalga Lobosphaera incisa wild type (WT) and its 5-desaturase mutant P127 (MUT) are unique photosynthetic sources for ARA and DGLA, respectively [22, 23], whose potential in aquaculture nutrition is yet to be explored. While the majority of research efforts have addressed n-3 LC-PUFA supplementation, known for their health-promoting benefits, in our research, we focus on the n-6 LC-PUFAaccumulating microalga L. incisa
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