Fatty Acid Composition and Fatty Acid Associated Gene-Expression in Gilthead Sea Bream (Sparus aurata) are Affected by Low-Fish Oil Diets, Dietary Resveratrol, and Holding Temperature

Resveratrol ameliorates intestinal lipid metabolism through the PPAR signaling pathway in high-fat diet-fed red tilapia (Oreochromis niloticus)

Feeding high-fat (HF) diets has been shown to cause hepatic and intestinal impairment in fish species, but the mode of action, especially the pathways involved in the intestine, has not been determined yet. In this study, the effects of resveratrol (RES) supplementation on the intestinal structure, microbial flora, and fat metabolism in red tilapia (Oreochromis niloticus) were determined. The results showed RES maintained the structural integrity of the intestine and significantly increased the number of goblet cells in the midgut. RES significantly induced interferon (IL)-1β, IL-6, IL-10, and tumor necrosis factor (TNF)-α, serumal and fecal trimetlylamine oxide (TMAO) and lipopolysaccharides (LPS), intestinal acetic acid levels. However, the concentrations of bound bile acids increased in HF-fed red tilapia. Atp5fa1 and Pafah1b3 significantly increased, Pmt and Acss2 significantly decreased, respectively, with RES supplementation, which was alleviated and retained at the same level in the selisistat (EX527) group. While for transcriptome and proteomics results, RES was found to promote fatty acid β-oxidation and arachidonic acid metabolism associated with the peroxisome proliferator-activated receptor (PPAR) signaling pathway. The next validation experiment showed some genes related to apoptosis and fatty acid metabolism pathways were altered by RES supplementation. Namely, sn6, loc100702698, new_14481, and prkaa1 were upregulated, while ffrs1, ap3s1, and loc100705861 were downregulated. RES significantly increased Planctomycetes and Verrucomicrobia while decreased Moonvirus, Citrobacter, and Pseudomonas. Akkermansia and Fusobacterium significantly increased and Aeromonas significantly decreased. Thus, unsaturated fatty acid biosynthesis significantly increased and carbohydrate/energy metabolism decreased. To conclude, RES enabled the body to complete fatty acid β-oxidation and arachidonic acid metabolism, whereas the addition of inhibitors increased the expression of the phagosome transcriptome and reduced fatty acid β-oxidative metabolism.

Welfare and performance of ballan wrasse (Labrus bergylta) reared at two different temperatures after a preparatory feeding trial with enhanced dietary eicosapentaenoic acid

Concerns have long been raised about the welfare of ballan wrasse (Labrus bergylta) used for the biological control of sea lice in Atlantic salmon (Salmo salar) aquaculture. This study assessed the effect of increased dietary eicosapentaenoic acid (EPA) levels and initial condition factor (CF) on the subsequent performance and welfare of ballan wrasse farmed in high and low water temperatures. Fish were fed a diet with either commercial or high EPA levels for 3 months at 15°C. Subsequently, fish were tagged with a passive integrated transponder, measured for their CF and divided into two groups consisting of fish from both treatments and reared for 4.5 months at either 15 or 6°C fed a commercial diet. Each fish was categorized as high (≥2.7) or low CF (<2.7) fish based on the calculated average CF of the population. Dietary composition influenced the fatty acid (FA) profile of the stored lipids without affecting the growth or welfare of ballan wrasse. Fish reared at 15°C showed higher growth, more fat and energy reserves and less ash content. Fish reared at 6°C lost weight, using up their body lipids at the end of the temperature trial. Gene expression analyses showed upregulation of the positive growth marker (GHrα) and two genes involved in the synthesis and oxidation of FAs (elovl5, cpt1) and downregulation of the negative growth marker (mstn) in fish reared at 15°C compared to those reared at 6°C. Fish reared at 6°C showed upregulated levels of il-6 compared to those reared at 15°C, suggesting an enhanced immune reaction in response to low temperature. Fish with high CF showed better survival, growth and performance compared to those with low CF. External welfare scoring showed higher prevalence and severity in emaciation, scale loss and the sum index score (of all measured welfare parameters) in fish reared at 6°C compared to those reared at 15°C and better welfare in fish with high CF compared to those with low CF. Histological examination of the skin showed that fish reared at 6°C had decreased epidermal thickness, a lower overall number of mucous cells in the inner and outer epidermis and a different organization of mucous cells compared to fish reared at 15°C, indicating stress in fish reared at 6°C. Overall, low water temperatures had profound effects on the performance and external and internal welfare parameters of ballan wrasse and can be considered a stressor likely affecting the delousing efficacy. These findings support the seasonal use of different cleaner fish species. High CF, but not increased dietary EPA levels, appeared to help fish cope better with low water temperatures and should thus be assessed and considered before deploying them in salmon cages.

Resveratrol Modulates the Redox Response and Bile Acid Metabolism to Maintain the Cholesterol Homeostasis in Fish Megalobrama amblycephala Offered a High-Carbohydrate Diet

This study aimed to characterize the effects of resveratrol on the redox balance, cholesterol homeostasis and bile acid metabolism of Megalobrama amblycephala offered a high-carbohydrate diet. Fish (35.0 ± 0.15 g) were fed four diets including one control diet (32% nitrogen-free extract), one high-carbohydrate diet (45% nitrogen-free extract, HC), and the HC diet supplemented with different levels (0.04%, HCR1; 0.08%, HCR2) of resveratrol for 12 weeks. The HC diet-induced redox imbalance is characterized by increased MDA content and decreased T-SOD and CAT activities in the liver. Resveratrol attenuated this by up-regulating the transcription of Cu/Zn-sod, and increasing the activities of T-SOD, CAT, and GPX. The HC diet enhanced the cholesterol synthesis, but decreased the bile acid synthesis via up-regulating both hmgcr and acat2, and down-regulating cyp7a1, thus resulting in excessive cholesterol accumulation. Resveratrol supplement decreased cholesterol synthesis, and increased cholesterol uptake in the liver by down-regulating both hmgcr and acat2, and up-regulating ldlr. It also increased bile acid synthesis and biliary excretion by up-regulating cyp7a1, and down-regulating mrp2, oatp1, and oatp4 in the hindgut, thereby decreasing cholesterol accumulation. In conclusion, resveratrol improves the cholesterol homeostasis of Megalobrama amblycephala fed a high-carbohydrate diet by modulating the redox response and bile acid metabolism.

Sex-Dependent Effects of Eicosapentaenoic Acid on Hepatic Steatosis in UCP1 Knockout Mice

Visceral obesity may be a driving factor in nonalcoholic fatty liver disease (NAFLD) development. Previous studies have shown that the omega-3 polyunsaturated fatty acid, eicosapentaenoic acid (EPA), ameliorates obesity in high-fat (HF) fed male, C57Bl/6 mice at thermoneutral conditions, independent of uncoupling protein 1 (UCP1). Our goals herein were to investigate sex-dependent mechanisms of EPA in the livers of wild type (WT) and UCP1 knockout (KO) male and female mice fed a HF diet (45% kcal fat; WT-HF, KO-HF) with or without supplementation of 36 g/kg EPA (WT-EPA, KO-EPA). KO significantly increased body weight in males, with no significant reductions with EPA in the WT or KO groups. In females, there were no significant differences in body weight among KO groups and no effects of EPA. In males, liver TGs were significantly higher in the KO-HF group and reduced with EPA, which was not observed in females. Accordingly, gene and protein markers of mitochondrial oxidation, peroxisomal biogenesis and oxidation, as well as metabolic futile cycles were sex-dependently impacted by KO and EPA supplementation. These findings suggest a genotypic difference in response to dietary EPA supplementation on the livers of male and female mice with diet-induced obesity and housed at thermoneutrality.

Parental LC-PUFA biosynthesis capacity and nutritional intervention with alpha-linolenic acid affect performance of Sparus aurata progeny

Environmental factors such as nutritional interventions during early developmental stages affect and establish long-term metabolic changes in all animals. Diet during the spawning period has a nutritional programming effect in offspring of gilthead seabream and affects long-term metabolism. Studies showed modulation of genes such as fads2, which is considered to be a rate-limiting step in the synthesis of n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA). However, it is still unknown whether this adaptation is related to the presence of precursors or to limitations in the pre-formed products, n-3 LC-PUFA, contained in the diets used during nutritional programming. This study investigated the combined effects of nutritional programming on Sparus aurata through broodstock diets during the spawning period and in broodfish showing higher or lower fads2 expression levels in the blood after 1 month of feeding with a diet containing high levels of plant protein sources and vegetable oils (VM/VO). Broodfish showing high fads2 expression had a noticeable improvement in spawning quality parameters as well as in the growth of 6 month old offspring when challenged with a high VM/VO diet. Further, nutritional conditioning with 18:3n-3-rich diets had an adverse effect in comparison to progeny obtained from fish fed high fish meal and fish oil (FM/FO) diets, with a reduction in growth of juveniles. Improved growth of progeny from the high fads2 broodstock combined with similar muscle fatty acid profiles is also an excellent option for tailoring and increasing the flesh n-3 LC-PUFA levels to meet the recommended dietary allowances for human consumption.

Intestinal phospholipase A2 from Sparidae species: Functional properties and cytotoxic potential evaluation

Marine species have gained significant attention as potential source for a broad spectrum of bioactive proteins. Fish phospholipases A₂ (PLA₂) have attracted renewed interest due to their excellent properties in lipid digestion. Herein, we report for the first time the catalytic properties of two intestinal secreted PLA₂ (sPLA₂) identified from Diplodus sargus (IDsPLA₂) and Sparus aurata (ISaPLA₂). The highest sequence identity was obtained with recently isolated Sparidae digestive PLA₂ (45%) and Human pancreatic PLA₂ (42%). IDsPLA₂ and ISaPLA₂ were overexpressed in E. coli as inclusion bodies, refolded and purified. Both enzymes have improved thermostability compared to mammalian pancreatic sPLA₂ since they are active and stable at 55 °C, with specific activities of 320 and 190 U mg^-1 measured on phosphatidylcholine, respectively. Interestingly, IDsPLA₂, but not ISaPLA₂, revealed weak toxicity towards macrophages and suggests its involvement in cell membrane degradation. ISaPLA₂ was found to be more active than IDsPLA₂ when using the monolayer technique at 20 mN m^-1. Structural models of both enzymes revealed their differences. In silico docking of phospholipids with both models allowed proposing key amino-acids in substrate binding and selectivity. Overall, these results provide insight into the enzymatic and structural properties of two novel sPLA₂ with potential for future applications.

Combined effects of nutritional, biochemical and environmental stimuli on growth performance and fatty acid composition of gilthead sea bream (Sparus aurata)

The reliance of the aquafeed industry on marine resources has to be reduced by innovative approaches in fish nutrition. Thus, a three-factorial approach (fish oil reduced diet, phytochemical genistein, and temperature reduction) was chosen to investigate the interaction of effects on growth performance and tissue omega-3 long chain polyunsaturated fatty acid (LC-PUFA) levels in juvenile sea bream (Sparus aurata, 12.5 ± 2.2 g). Genistein is a phytoestrogen with estrogen-like activity and thus LC-PUFA increasing potential. A decrease in the rearing temperature was chosen based on the positive effects of low temperature on fish lipid quality. The experimental diets were reduced in marine ingredients and had a fish oil content of either 6% dry matter (DM; F6: positive control) or 2% DM (F2: negative control) and were administered in the plain variant or with inclusion of 0.15% DM genistein (F6 + G and F2 + G). The feeding trial was performed simultaneously at 23°C and 19°C. The results indicated that solely temperature had a significant effect on growth performance and whole body nutrient composition of sea bream. Nevertheless, the interaction of all three factors significantly affected the fatty acid compositions of liver and fillet tissue. Most importantly, they led to a significant increase by 4.3% of fillet LC-PUFA content in sea bream fed with the diet F6 + G in comparison to control fish fed diet F6, when both groups were held at 19°C. It is hypothesized that genistein can act via estrogen-like as well as other mechanisms and that the dietary LC-PUFA content may impact its mode of action. Temperature most likely exhibited its effects indirectly via altered growth rates and metabolism. Although effects of all three factors and of genistein in particular were only marginal, they highlight a possibility to utilize the genetic capacity of sea bream to improve tissue lipid quality.