Feed-to-Fillet Transfer of Selenite and Selenomethionine Additives to Plant-Based Feeds to Farmed Atlantic Salmon Fillet

HSF1-SELENOS pathway mediated dietary inorganic Se-induced lipogenesis via the up-regulation of PPARγ expression in yellow catfish

At present, studies involved in the effects of dietary Se sources on lipid metabolism were very scarce and the underlying mechanism remains unknown. Previous studies reported that dietary Se sources differentially affected selenoprotein S (SELENOS) expression and SELENOS affected lipid metabolism via the inositol-requiring enzyme 1α (IRE1α)- spliced X-box binding protein 1 (XBP1s) pathway. Thus, we used yellow catfish as an experimental model to explore whether dietary selenium sources affected the hepatic lipid metabolism, and further determined the role of SELENOS-IRE1α-XBP1s pathway in dietary selenium sources affecting hepatic lipid metabolism. Compared with the selenomethionine (S-M) group, sodium selenite (SS) group possessed higher liver triglycerides (TGs) (34.7%), lipogenic enzyme activities (57.9-70.6%), and lower antioxidant enzyme activities (23.3-35.5%), increased protein levels of heat shock transcription factor 1 (HSF1) and SELENOS (1.17-fold and 47.4%, respectively), and XBP1s- peroxisome proliferators-activated receptor γ (PPARγ) pathway. Blocking SELENOS and PPARγ by RNA interference demonstrated that the SELENOS/XBP1s/PPARγ axis was critical for S-S-induced lipid accumulation. Moreover, S-S-induced upregulation of SELENOS was via the increased DNA binding capacity of HSF1 to SELENOS promoter, which activated the XBP1s/PPARγ pathway and promoted lipogenesis and lipid accumulation. XBP1s is required for S-S-induced upregulation of PPARγ expression. Our finding elucidated the mechanism of dietary Se sources affecting the lipid metabolism in the liver of yellow catfish and demonstrated novel function of SELENOS in metabolic regulation. Our study also suggested that seleno-methionine was a better Se source than selenite against abnormal lipid deposition in the liver of yellow catfish.

Long-term effect of parental selenium supplementation on the one-carbon metabolism in rainbow trout (Oncorhynchus mykiss) fry exposed to hypoxic stress

This study evaluated how different forms of selenium (Se) supplementation into rainbow trout broodstock diets modified the one-carbon metabolism of the progeny after the beginning of exogenous feeding and followed by hypoxia challenge. The progeny of three groups of rainbow trout broodstock fed either a control diet (Se level: 0·3 µg/g) or a diet supplemented with inorganic sodium selenite (Se level: 0·6 µg/g) or organic hydroxy-selenomethionine (Se level: 0·6 µg/g) was cross-fed with diets of similar Se composition for 11 weeks. Offspring were sampled either before or after being subjected to an acute hypoxic stress (1·7 mg/l dissolved oxygen) for 30 min. In normoxic fry, parental Se supplementation allowed higher glutathione levels compared with fry originating from parents fed the control diet. Parental hydroxy-selenomethionine treatment also increased cysteine and cysteinyl-glycine concentrations in fry. Dietary Se supplementation decreased glutamate-cysteine ligase (cgl) mRNA levels. Hydroxy-selenomethionine feeding also lowered the levels of some essential free amino acids in muscle tissue. Supplementation of organic Se to parents and fry reduced betaine-homocysteine S-methyltransferase (bhmt) expression in fry. The hypoxic stress decreased whole-body homocysteine, cysteine, cysteinyl-glycine and glutathione levels. Together with the higher mRNA levels of cystathionine beta-synthase (cbs), a transsulphuration enzyme, this suggests that under hypoxia, glutathione synthesis through transsulphuration might have been impaired by depletion of a glutathione precursor. In stressed fry, S-adenosylmethionine levels were significantly decreased, but S-adenosylhomocysteine remained stable. Decreased bhmt and adenosylmethionine decarboxylase 1a (amd1a) mRNA levels in stressed fry suggest a nutritional programming by parental Se also on methionine metabolism of rainbow trout.