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The present study aimed at investigating interactive effects between dietary lipids and both short- and long-term exposures to a low, environmentally realistic, cadmium (Cd) concentration. Juvenile rainbow trout were fed four isolipidic diets (31.7 g/kg) enriched in either linoleic acid (LA, 18:2n-6), alpha-linolenic acid (ALA, 18:3n-3), eicosapentaenoic acid (EPA, 20:5n-3) or docosahexaenoic acid (DHA, 22:6n-3). From the 4th week of this 10-week experiment, the lipid level of the diet was increased (120.0 g/kg) and half of the fish fed each diet were aqueously exposed to Cd (0.3 μg/L) while the other half were not exposed to Cd (control). Fish were sampled and their liver was harvested for fatty acid profile, hepatic Cd and calcium concentrations, total glutathione level and gene expression assessment, either (i) after 4 weeks of feeding and 24 h of Cd contamination (day 29) (short-term Cd exposure) or (ii) after 10 weeks of feeding and 6 weeks of Cd contamination (day 70) (long-term Cd exposure). We found that both dietary lipids and Cd exposure influenced fatty acid homeostasis and metabolism. The hepatic fatty acid profile mostly reflected that of the diet (e.g. n-3/n-6 ratio) with some differences, including selective retention of specific long chain polyunsaturated fatty acids (LC-PUFAs) like DHA and active biotransformation of dietary LA and ALA into LC-PUFAs. Cd effects on hepatic fatty acid profiles were influenced by the duration of the exposure and the nutritional status of the fish. The effects of diet and Cd exposure on the fatty acid profiles were only sparsely explained by variation of the expression pattern of genes involved in fatty acid metabolism. The biological responses to Cd were also influenced by dietary lipids. Fish fed the ALA-enriched diet seemed to be the least affected by the Cd exposure, as they showed a higher detoxifying ability against Cd with an early upregulation of protective metallothionein a (MTa) and apoptosis regulator BCL2-Like1 (BCLx) genes, an increased long-term phospholipid synthesis and turnover and fatty acid bioconversion efficiency, as well as a lower long-term accumulation of Cd in their liver. In contrast, fish fed the EPA-enriched diet seemed to be the most sensitive to a long-term Cd exposure, with an impaired growth performance and a decreased antioxidant capacity (lower glutathione level). Our results highlight that low, environmentally realistic aqueous concentrations of Cd can affect biological response in fish and that these effects are influenced by the dietary fatty acid composition., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Polyunsaturated fatty acids (PUFAs) have key biological roles in fish cells. We recently showed that the phospholipid composition of rainbow trout liver cells (RTL-W1 cell line) modulates their tolerance to an acute cadmium (Cd) challenge. Here, we investigated (i) the extent to which PUFAs and Cd impact fatty acid homeostasis and metabolism in these cells and (ii) possible mechanisms by which specific PUFAs may confer cytoprotection against Cd. First, RTL-W1 cells were cultivated for one week in growth media spiked with 50 μmol L -1 of either alpha-linolenic acid (ALA, 18:3n-3), eicosapentaenoic acid (EPA, 20:5n-3), linoleic acid (LA, 18:2n-6) or arachidonic acid (AA, 20:4n-6) in order to modulate their fatty acid profile. Then, the cells were challenged with Cd (0, 50 or 100 μmol L -1 ) for 24 h prior to assaying viability, fatty acid profile, intracellular Cd content, proteomic landscape and expression levels of genes involved in fatty acid metabolism, synthesis of PUFA-derived signalling molecules and stress response. We observed that the fatty acid supply and, to a lesser extent, the exposure to Cd influenced cellular fatty acid homeostasis and metabolism. The cellular fatty acid composition of fish liver cells modulated their tolerance to an acute Cd challenge. Enrichments in ALA, EPA, and, to a lesser extent, AA conferred cytoprotection while enrichment in LA had no impact on cell viability. The present study ruled out the possibility that cytoprotection reflects a decreased Cd burden. Our results rather suggest that the PUFA-derived cytoprotection against Cd occurs through a reduction of the oxidative stress induced by Cd and a differential induction of the eicosanoid cascade, with a possible role of peroxiredoxin and glutaredoxin (antioxidant enzymes) as well as cytosolic phospholipase A2 (enzyme initiating the eicosanoid cascade)., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The polyunsaturated fatty acid (PUFA) composition of fish tissues, which generally reflects that of the diet, affects various cellular properties such as membrane structure and fluidity, energy metabolism and susceptibility to oxidative stress. Since these cellular parameters can play an important role in the cellular response to organic and inorganic pollutants, a variation of the PUFA supply might modify the toxicity induced by such xenobiotics. In this work, we investigated whether the cellular fatty acid profile has an impact on the in vitro cell sensitivity to two environmental pollutants: methylmercury and cadmium. Firstly, the fatty acid composition of the rainbow trout liver cell line RTL-W1 was modified by enriching the growth medium with either alpha-linolenic acid (ALA, 18:3n-3), eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3), linoleic acid (LA, 18:2n-6), arachidonic acid (AA, 20:4n-6) or docosapentaenoic acid (DPA, 22:5n-6). These modified cells and their control (no PUFA enrichment) were then challenged for 24h with increasing concentrations of methylmercury or cadmium. We observed that (i) the phospholipid composition of the RTL-W1 cells was profoundly modulated by changing the PUFA content of the growth medium: major modifications were a high incorporation of the supplemented PUFA in the cellular phospholipids, the appearance of direct elongation and desaturation metabolites in the cellular phospholipids as well as a change in the gross phospholipid composition (PUFA and monounsaturated fatty acid (MUFA) levels and n-3/n-6 ratio); (ii) ALA, EPA and DPA enrichment significantly protected the RTL-W1 cells against both methylmercury and cadmium; (iv) DHA enrichment significantly protected the cells against cadmium but not methylmercury; (v) AA and LA enrichment had no impact on the cell tolerance to both methylmercury and cadmium; (vi) the abundance of 20:3n-6, a metabolite of the n-6 biotransformation pathway, in phospholipids was negatively correlated to the cell tolerance to both methylmercury and cadmium. Overall, our results highlighted the importance of the fatty acid supply on the tolerance of fish liver cells to methylmercury and cadmium., (Copyright © 2016 Elsevier B.V. All rights reserved.)