The Protective Effect of Taurine on Oxidized Fish-Oil-Induced Liver Oxidative Stress and Intestinal Barrier-Function Impairment in Juvenile Ictalurus punctatus

Abstract

Dietary lipids provide energy for growth and development and provide fatty acids necessary for normal structure and biological function. However, oxidized lipids cause oxidative stress and intestinal damage. An 8-week feeding trial with fresh fish oil (FFO, control group), oxidized fish oil (OFO), and taurine-supplemented diets (OFOT, OFO + 0.2% of taurine) was conducted to evaluate the protective effect of taurine on oxidized fish-oil-induced liver oxidative stress and intestine impairment in juvenile Ictaluruspunctatus. The results showed that (1) Growth performance was significantly lower in fish fed OFO than in those fed other diets, whereas the opposite occurred in the hepatosomatic index. (2) OFO-feeding significantly increased lipid deposition compared with the FFO group. The addition of taurine ameliorated the OFO-induced increase in lipid vacuolization in the liver, significantly upregulated lpl mRNA expression, and downregulated fas and srebp1 mRNA expression. (3) OFO-feeding significantly reduced oxidative damage of liver. Compared with the OFO group, the OFOT group remarkably upregulated antioxidant enzyme mRNA expression through the Nrf2-Keap1 signaling pathway based on the transcriptional expression. (4) OFO diets induced intestinal physical and immune barrier damage. Compared with the OFO group, OFOT diets remarkably downregulated il-1β, il-6, tnf-α, and il-8 mRNA expression and upregulated tgf-β mRNA expression through the NF-κB signaling pathway. Besides, the addition of taurine to OFO diets significantly upregulated zo-2 and zo-1 mRNA expression, and downregulated claudin-15 and claudin-12 mRNA expression. In conclusion, oxidized-fish-oil diets can cause negative physiological health effects in Ictaluruspunctatus, while adding taurine can increase growth and antioxidant ability, reduce lipid deposition, and improve intestinal health.

Keywords: channel catfish; immune response; intestinal health; oxidative damage; signaling pathway.

Figure 1

Serum biochemical indices and lipid-metabolism-related gene expression of the liver in channel catfish (Ictalurus punctatus) fed the diets. (A) Triacylglycerol, TG; (B) total cholesterol, TC; and (C–E) lipid-metabolism-related genes (fas, acc, and srebp1). Data indicate the mean values of three replicate cages per treatment (three fish per replicate breeding barrel). Significance was evaluated by one-way ANOVA (p < 0.05) followed by Duncan’s multiple range tests. Values marked with different letters are significantly different between the treatment groups.

Figure 2

Histological characteristics of the liver in channel catfish (Ictalurus punctatus) fed the diets (H&E stain, magnification 400×). (A) Fresh fish oil (FFO) group; (B) oxidized fish oil (OFO) group; and (C) OFO diet with 0.2% taurine (OFOT) group.

Figure 3

Liver antioxidant indices of channel catfish (Ictalurus punctatus) subject to different treatment. (A) Malondialdehyde, MDA; (B) Superoxide dismutase, SOD; (C) Glutathione peroxidase, GPx; (D) Glutathione reductase, GR; (E) Glutathione, GSH; (F) Total antioxidant capacity, T-AOC. Data indicate the mean values of three replicate cages per treatment (three fish per replicate breeding barrel). Significance was evaluated by one-way ANOVA (p < 0.05) followed by Duncan’s multiple range tests. Values marked with different letters are significantly different between the treatment groups.

Figure 4

Effects of dietary taurine on liver antioxidant-related genes expression of channel catfish (Ictalurus punctatus) fed oxidized-fish-oil diets. (A) sod; (B) gpx1; (C) gpx8; (D) gr; (E) keap1; (F) nrf2. Data indicate the mean values of three replicate cages per treatment (three fish per replicate breeding barrel). Significance was evaluated by one-way ANOVA (p < 0.05) followed by Duncan’s multiple range tests. Values marked with different letters are significantly different between the treatment groups.

Figure 5

Effects of dietary taurine on intestinal morphology of channel catfish (Ictalurus punctatus) fed oxidized-fish-oil diets (magnification 40×). (A) Villi length; (B) muscular thickness; (C) goblet cell quantity; (D) FFO group; (E) OFO group; and (F) OFOT group. The red arrow indicates the villi length and the blue arrow indicates the muscular thickness, respectively. Significance was evaluated by one-way ANOVA (p < 0.05) followed by Duncan’s multiple range tests. * p < 0.05.

Figure 6

Effects of dietary taurine on intestinal physical-barrier-related genes expression of channel catfish (Ictalurus punctatus) fed oxidized-fish-oil diets. (A) zo-1; (B) zo-2; (C) occludin; (D) claudin-12; (E) claudin-15. Data indicate the mean values of three replicate cages per treatment (three fish per replicate breeding barrel). Significance was evaluated by one-way ANOVA (p < 0.05) followed by Duncan’s multiple range tests. Values marked with different letters are significantly different between the treatment groups.

Figure 7

Effects of dietary taurine on intestinal immune-barrier-related genes expression of channel catfish (Ictalurus punctatus) fed oxidized-fish-oil diets. (A) tnf-α; (B) il-1β; (C) il-6; (D) il-8; (E) nf-κb; (F) il-10; (G) tgf-β1; (H) tgf-β2; (I) tgf-β3. Data indicate the mean values of three replicate cages per treatment (three fish per replicate breeding barrel). Significance was evaluated by one-way ANOVA (p < 0.05) followed by Duncan’s multiple range tests. Values marked with different letters are significantly different between the treatment groups.

Figure 8

Correlative analysis of intestinal immune-barrier-related gene expression was performed using the R Programming Language. * p < 0.05, ** p < 0.01.