Effects of dietary ARA, DHA, and carbohydrates levels on gilthead sea bream liver and intestine oxidative stress, tissue histomorphology, and gut microbiota

The present study aims evaluate the oxidative status, histomorphology of liver and intestine, and intestinal microbiota modulation of gilthead sea bream juveniles (initial body weight = 47.5 g) fed four isoproteic and isolipidic diets (47% protein; 18% lipids) with high or low gelatinized starch levels (20% or 5%; diets HS or LS, respectively) and different dietary ARA or DHA content (2.3/0.3 or 0/2.6, diets ARA or DHA, respectively). ARA-rich diets reduced liver and intestine lipid peroxidation (LPO) circa 12 and 66%, respectively. Dietary ARA also increased liver glutathione redox status (total, reduced (GSH) and oxidized glutathione (GSSG)) circa of 35% but only in the HS diets. Independently of dietary starch level, dietary ARA also reduced GSSG content (80 and 63 nmol g⁻¹ tissue) and oxidative stress index (OSI) (8.7 and 7%) in the intestine. Fish fed DHA diets had increased hepatic superoxide dismutase (SOD) (749.1 and 489.1 U mg protein⁻¹) and glutathione reductase (GR) (3.7 to 1.9 mU mg protein⁻¹) activities. In the intestine, dietary ARA or DHA did not induce alterations in the activity of the antioxidant enzymes. Dietary starch improved liver OSI (1.5%), increased intestinal GSSG (80 and 128 nmol g⁻¹ tissue), and decreased intestinal LPO values (104 nmol MDA g⁻¹ tissue) in fish fed the DHA diets. Fish fed the HS diets had increased hepatic glucose-6-phosphate dehydrogenase (G6PDH) (171.4 and 166 mU mg protein⁻¹), GR (2 and 3.71 mU mg protein⁻¹), and glutathione peroxidase (GPX, only in DHA diets) (63.8 mU mg protein⁻¹) activities, but decreased GR (27.2 and 27.6 mU mg protein⁻¹) and SOD (2089.7 and 2158.8 U mg protein⁻¹) activities in the intestine. Diet composition did not induce major histomorphological alterations in the distal intestine. Nevertheless, the HS diets, especially when combined with DHA, promoted hepatocyte hypertrophy and alterations in nuclei position. Compared to the DHA diets, in fish fed the ARA diets, mucosa bacterial profile had a reduced number of operational taxonomic units (10.3 and 12.0), richness (0.6 and 0.7), and diversity (2.2 and 2.3), and higher similarity between bacterial communities (85.0 and 80.4%). In conclusion, fish fed high dietary ARA presented lower hepatic and intestinal LPO and fewer hepatocyte morphological alterations than fish fed high DHA diets. Furthermore, interactive effects between dietary starch and DHA on liver and intestine GSH metabolism, antioxidant enzymes, LPO susceptibility, and liver histomorphology may be attenuated by a balanced ARA/DHA dietary ratio.