Effects of polyunsaturated fatty acids on inflammation and lipid metabolism, using zebrafish as a model

Steatosis and obesity are defined by a fat accumulation that induces chronic inflammation. Chronic inflammation can be the cause of many metabolic disorders such as type 2 diabetes, cardiovascular diseases, cancers. A possible way to prevent or fix those diseases is through a diet enriched with polyunsaturated fatty acids (PUFAs). PUFAs include two main groups, the n-6, pro-inflammatory PUFAs and n-3 PUFAs, anti-inflammatory PUFAs. Western diets are characterized by excessive amounts of n-6 PUFA and high n-6/n-3 ratios, which promote chronic inflammation and associated pathologies. On the other hand, increased levels of omega-3 PUFA with low n-6/n-3 ratio exert the opposite effect. More recently, another kind of PUFA (n-5 PUFA) has shown promising potential to reduce inflammation and overcome those disorders: the conjugated linolenic acids (CLnA), which include punicic acid (PunA), mostly found in pomegranate seed oil (Pom). The objectives of this Master’s thesis were to investigate the effects of specific PUFAs integrated into different diets on inflammation and on lipid metabolism using zebrafish (ZF) as a model. To do this, four diets enriched each with a specific oil were created. The first diet was enriched with sunflower oil for its content in linoleic acid (LA) (n-6 PUFA); the second with linseed oil, rich in α-linolenic acid (ALA) (n-3 PUFA); the third diet was enriched with fish oil for its eicosapentaenoic acid (EPA) (n-3 PUFA) and docosahexaenoic acid (DHA) (n-3 PUFA) content; and the last diet was enriched in Pom rich in PunA (n-5 PUFA). Those four diets were given to four groups of ZF for 1 week of acclimation and 7 weeks of experiment. Then, ZF were sampled for measurements of fatty acid incorporation and relative gene expression (RGE) was measured. For inflammation, three pro-inflammatory cytokines (TNF-α, IL1β, and IL6) and three anti-inflammatory cytokines (IL4, IL10, and IL13) were analysed and for lipid metabolism, three enzymes involved in the n-3 and n-6 pathways (FADS2, ELOVL5, and ELOVL2) were analysed as well as three enzymes (RetSat, Ptgr, and CYP4F3) potentially responsible of the transformation of PunA into rumenic acid (RumA). Overall, there does not appear to be a dietary effect on the gene expression of any of the targets we were interested in. However, as expected, the pro-inflammatory cytokines tend to be more expressed following the diet rich in n-6 and less expressed following the diets rich in n-3 and n-5 PUFAs. For the anti-inflammatory cytokines, no trend was evident. For lipid metabolism, our results indicated that ZF are not efficient at biotransforming n-3 and n-6 PUFAs into longer and more unsaturated metabolites. Unexpectedly we did not detect high levels of expression for genes responsible for the transformation of PunA, even though significant levels of RumA were detected in fish tissues.