More Than an Antioxidant: Role of Dietary Astaxanthin on Lipid and Glucose Metabolism in the Liver of Rainbow Trout (Oncorhynchus mykiss).

This study investigated the influence of dietary astaxanthin (AX) on glucose and lipid metabolism in rainbow trout liver. Two iso-nitrogenous and iso-lipidic diets were tested for 12 weeks in rainbow trout with an initial mean weight of 309 g. The S-ASTA diet was supplemented with 100 mg of synthetic AX per kg of feed, whereas the control diet (CTRL) had no AX. Fish fed the S-ASTA diet displayed lower neutral and higher polar lipids in the liver, associated with smaller hepatocytes and lower cytoplasm vacuolization. Dietary AX upregulated adipose triglyceride lipase (atgl), hormone-sensitive lipase (hsl2) and 1,2-diacylglycerol choline phosphotransferase (chpt), and downregulated diacylglycerol acyltransferase (dgat2), suggesting the AX's role in triacylglycerol (TAG) turnover and phospholipid (PL) synthesis. Dietary AX may also affect beta-oxidation with the upregulation of carnitine palmitoyltransferase 1 (cpt1α2). Although hepatic cholesterol levels were not affected, dietary AX increased gene expression of sterol regulatory element-binding protein 2 (srebp2). Dietary AX upregulated the expression of 6-phosphogluconate dehydrogenase (6pgdh) and downregulated pyruvate kinase (pkl). Overall, results suggest that dietary AX modulates the oxidative phase of the pentose phosphate pathway and the last step of glycolysis, affecting TAG turnover, ß-oxidation, PL and cholesterol synthesis in rainbow trout liver.

Gill Oxidative Stress Protection through the Use of Phytogenics and Galactomannan Oligosaccharides as Functional Additives in Practical Diets for European Sea Bass (Dicentrarchus labrax) Juveniles.

The aim of the present study is to evaluate the potential of two functional additives as gill endogenous antioxidant capacity boosters in European sea-bass juveniles fed low-FM/FO diets when challenged against physical and biological stressors. For that purpose, two isoenergetic and isonitrogenous diets with low FM (10%) and FO (6%) contents were supplemented with 5000 ppm plant-derived galactomannan-oligosaccharides (GMOS) or 200 ppm of a mixture of garlic and labiate plant essential oils (PHYTO). A control diet was void from supplementation. Fish were fed the experimental diet for nine weeks and subjected to a confinement stress challenge (C challenge) or a confinement stress challenge combined with an exposure to the pathogen Vibrio anguillarum (CI challenge). Both GMOS and PHYTO diets attenuated fish stress response, inducing lower circulating plasma cortisol and down-regulating nfκß2 and gr relative gene-expression levels in the gill. This attenuated stress response was associated with a minor energetic metabolism response in relation to the down-regulation of nd5 and coxi gene expression.

Influence of Dietary Astaxanthin on the Hepatic Oxidative Stress Response Caused by Episodic Hyperoxia in Rainbow Trout.

A 13-week feeding trial was carried out with juvenile rainbow trout to test two diets: a control diet without astaxanthin (AX) supplementation (CTRL diet), and a diet supplemented with 100 mg/kg of synthetic AX (ASTA diet). During the last week of the feeding trial, fish were exposed to episodic hyperoxia challenge for 8 consecutive hours per day. Episodic hyperoxia induced physiological stress responses characterized by a significant increase in plasma cortisol and hepatic glycogen and a decrease in plasma glucose levels. The decrease of plasma glucose and the increase of hepatic glycogen content due to episodic hyperoxia were emphasized with the ASTA diet. Hyperoxia led to an increase in thiobarbituric acid-reactive substances in the muscle, diminished by dietary AX supplementation in both liver and muscle. Muscle and liver AX were increased and decreased respectively after 7-day episodic hyperoxia, leading to an increase in flesh redness. This augment of muscle AX could not be attributed to AX mobilization, since plasma AX was not affected by hyperoxia. Moreover, hyperoxia decreased most of antioxidant enzyme activities in liver, whereas dietary AX supplementation specifically increased glutathione reductase activity. A higher mRNA level of hepatic glutathione reductase, thioredoxin reductase, and glutamate-cysteine ligase in trout fed the ASTA diet suggests the role of AX in glutathione and thioredoxin recycling and in de novo glutathione synthesis. Indeed, dietary AX supplementation improved the ratio between reduced and oxidized glutathione (GSH/GSSG) in liver. In addition, the ASTA diet up-regulated glucokinase and glucose-6-phosphate dehydrogenase mRNA level in the liver, signaling that dietary AX supplementation may also stimulate the oxidative phase of the pentose phosphate pathway that produces NADPH, which provides reducing power that counteracts oxidative stress. The present results provide a broader understanding of the mechanisms by which dietary AX is involved in the reduction of oxidative status.

Fatty Acid Profile of Neutral and Polar Lipid Fraction of Wild Eggs and Hatchlings from Wild and Captive Reared Broodstock of Octopus vulgaris.

The culture of Octopus vulgaris is constrained by unsolved problems in paralarvae rearing, mainly associated to the unknown nutritional requirements of this species in early stages. In this article we studied the fatty acid profile (total, neutral, and polar lipid fractions) in wild eggs and wild hatchlings, collected in Gran Canaria (SW) (Spain) with artificial dens, in comparison to hatchlings obtained in captivity from broodstock fed on trash fish species. Total lipids were 11.5-13.5% dw, with the polar fraction representing a 70.6-75.5% of total lipid, with lower values in wild hatchling in comparison with captive ones. Docosahexaenoic acid (DHA) was the main component in neutral and polar fatty acid profile in all samples, underlying its importance in this species. Decreasing levels of saturates and arachidonic acid (ARA) from wild eggs to hatchlings, mainly associated to the polar fraction, suggest their use during embryonic development. In hatchlings, increasing levels of oleic acid in the neutral fraction and eicosapentaenoic acid (EPA) in the polar fraction, suggests their importance in hatchlings quality. Wild hatchlings showed in the polar fraction higher oleic acid and ARA, and lower DHA/ARA and EPA/ARA ratios in comparison with captive hatchlings, suggesting a difference in paralarvae nutritional status. These results suggest the importance of n-3 highly unsaturated fatty acids (HUFA), oleic acid, and ARA, presented in the adequate lipid fraction, in the diet of broodstock and paralarvae of O. vulgaris.

Increased Mauthner cell activity and escaping behaviour in seabream fed long-chain PUFA.

There is limited information on the specific effects of long-chain PUFA (LCPUFA) on neuron development and functioning. Deficiency of those essential fatty acids impairs escape and avoidance behaviour in fish, where Mauthner cells (M-cells) play a particularly important role in initiating this response. Gilthead seabream larvae fed two different LCPUFA profiles were challenged with a sonorous stimulus. Feeding n-3 LCPUFA increased the content of these fatty acids in fish tissues and caused a higher number of larvae to react to the stimulus with a faster burst swimming speed response. This faster startle response in fish fed n-3 LCPUFA was also associated with an increased immune-positive neural response, particularly in M-cells, denoting a higher production of acetylcholine. The present study shows the first evidence of the effect of n-3 LCPUFA on the functioning of particular neurons in fish, the M-cells and the behaviour response that they modulate to escape from a sound stimulus.

Chronic copper exposure and fatty acid composition of the amphipod Dikerogammarus villosus: results from a field study.

Field study allows assessment of long-term effects on fatty acid (FA) composition of organisms under chronic exposure to metals. One expected effect of copper is peroxidation of lipids and essentially polyunsaturated fatty acids (PUFA). FA analysis was established for the amphipod Dikerogammarus villosus subjected to different degrees of copper exposure (4-40 microg Cu L(-1)). A previous study in our team showed that this species regulates its body Cu concentration (106-135 mg Cu kg(-1) dry weight). Despite the high capacity of bioaccumulation, the absence of a correlation between copper concentration in D. villosus and water prevents its use as bioindicator of copper pollution. Both sexes from the most polluted site showed the lowest total FA content, but the highest PUFA percent, mainly of the long-chained variety (C20-C22). Mechanisms leading to the prevention of lipid peroxidation in this species were discussed (metallothioneins and intracellular granules) and proposed with support from literature data.

Fatty acid composition of the amphipod Dikerogammarus villosus: feeding strategies and trophic links.

Fatty acid (FA) compositions were determined for the invader amphipod Dikerogammarus villosus collected from July to September 2002, in an overheated, high-conductivity dammed reservoir in north-eastern France. Predominant fatty acids were the polyunsaturated fatty acids (PUFA): eicosapentaenoic acid (EPA), linoleic acid (LA), arachidonic acid (ARA), linolenic acid (LNA) together with the monounsaturated fatty acid 18:1omega9 and the saturated fatty acid 16:0. FA markers indicated that available food was constituted of incompletely degraded phytodetritus and terrestrial inputs, as well as animal remains. PUFA contents depended on the diet and the capacity of animals to desaturate and elongate LNA and LA in long chain PUFA as EPA and ARA respectively. Based on their FA compositions, we showed that gammarids represent naturally-occurring freshwater sources of essential PUFA, and could play a fundamental role in pelagic-benthic coupling and energy recycling in the ecosystem. The complexity of the feeding strategies of D. villosus--detritivorous, omnivorous, carnivorous--makes this species efficient at exploiting different components of the available food and may be a key factor in its high invasive success.