Effects of dietary glucose and dextrin on activity and gene expression of glucokinase and fructose-1,6-bisphosphatase in liver of turbot Scophthalmus maximus

Taurine alleviates endoplasmic reticulum stress, inflammatory cytokine expression and mitochondrial oxidative stress induced by high glucose in the muscle cells of olive flounder (Paralichthysolivaceus)

The aim of the present study was to evaluate the effects of taurine on endoplasmic reticulum stress, inflammatory cytokine expression and mitochondrial oxidative stress induced by high glucose in primary cultured muscle cells of olive flounder (Paralichthys olivaceus). Three experimental groups were designed as follows: muscle cells of olive flounder incubated with three kinds of medium containing 5 mM glucose (control), 33 mM glucose (HG) or 33 mM glucose + 10 mM taurine (HG + T), respectively. Results showed that taurine addition significantly alleviated the decreased activity of superoxide dismutase (SOD) and the ratio of reduced to oxidized glutathione (GSH/GSSG) induced by high glucose. The increase of cellular reactive oxygen species (ROS), malondialdehyde content and cell apoptosis induced by high glucose were alleviated by taurine. Besides, gene expression of glucose-regulated protein 78, PKR-like ER kinase, tumor necrosis factor-α, interleukin-6, interleukin-1β, interleukin-8, muscle atrophy F-box protein and muscle RING-finger protein 1 were significantly up-regulated in the HG group, and taurine addition decreased the expression of these genes. High glucose led to the swelling of the endoplasmic reticulum (ER). Meanwhile, the nuclear translocation of nuclear factor κB (NF-κB) and the release of cytochrome C from mitochondria induced by high glucose were suppressed by taurine addition. These results demonstrated that taurine alleviated ERS, inflammation and mitochondrial oxidative stress induced by high glucose in olive flounder muscle cells. The ROS production, NF-κB signaling pathway and mitochondria function were the main targets of the biological effects of taurine under high glucose condition.

Dietary carbohydrates influence muscle texture of olive flounder Paralichthys olivaceus through impacting mitochondria function and metabolism of glycogen and protein

The present study was conducted to estimate the effects of dietary carbohydrates on muscle quality and the underlying mechanisms. Six isonitrogenous and isolipidic diets were formulated to contain graded levels of carbohydrates (0%, 8%, 12%, 16%, 20% and 24%, respectively). These diets were named as C0, C8, C12, C16, C20 and C24, respectively. After a 10-week feeding trial, results showed that the muscle pH, liquid holding capacity (LHC) and hardness were significantly decreased by the increasing dietary carbohydrate levels. Dietary carbohydrates significantly decreased the muscle fibre diameter, and the highest value was found in the C0 group. Accumulated glycogen and degenerated mitochondrial cristae were observed in the C24 group. Significantly higher contents of protein carbonyls were observed in the C20 group and C24 group (P < 0.05). There was a significant decrease of mtDNA copy number in the C24 group compared with that in the C0 and C8 groups. The AMP/ATP ratio in muscle decreased first and then increased with the increasing dietary carbohydrate levels. The dietary incorporation of carbohydrate significantly reduced the expression of opa1, pygm and genes involved in myogenesis (myf5 and myog). Meanwhile, proteolysis-related genes (murf-1, mafbx, capn2 and ctsl), pro-inflammatory cytokines (il-6 and tnf-α) and mstn were significantly up-regulated. In the C24 group, significant increase of phosphorylation of AMPK (Thr172), up-regulation of PGC-1α and GLUT4 were observed, while the phosphorylation level of S6 (Ser235/236) was significantly decreased. It was concluded that excessive dietary carbohydrate level (24%) had negative impacts on mitochondria function and promoted glycogen accumulation, and thereafter influenced the muscle quality of olive flounder. The activation of AMPK as well as the upregulation of PGC-1α and GLUT4 was the key mechanism.

Comparatively study on the insulin-regulated glucose homeostasis through brain-gut peptides in Japanese flounder Paralichthys olivaceus after intraperitoneal and oral administration of glucose

The present study comparatively analyzed the blood glucose and insulin concentration, the temporal and spatial expression of brain-gut peptides and the key enzymes of glycolysis and gluconeogenesis in Japanese flounder by intraperitoneal injection (IP) and oral administration (OR) of glucose. Samples were collected at 0, 1, 3, 5, 7, 9, 12, 24 and 48 h after IP and OR glucose, respectively. Results showed that the hyperglycemia lasted for about 10 h and 21 h in OR and IP group, respectively. The serum insulin concentration significantly decreased at 3 h (1.58 ± 0.21 mIU/L) after IP glucose. However, it significantly increased at 3 h (3.37 ± 0.341 mIU/L) after OR glucose. The gene expressions of prosomatostatin, neuropeptide Y, cholecystokinin precursor and orexin precursor in the brain showed different profiles between the OR and IP group. The OR not IP administration of glucose had significant effects on the gene expressions of preprovasoactive intestinal peptide, pituitary adenylate cyclase activating polypeptide and gastrin in intestine. In conclusion, brain-gut peptides were confirmed in the present study. And the serum insulin and the brain-gut peptides have different responses between the IP and OR administration of glucose. The OR could stimulate the brain-gut peptide expressions, which have effects on the insulin secretion and then regulate the blood glucose levels. However, in IP group, there is little chance to stimulate brain-gut peptide expression to influence the insulin secretion, which leads to a longer hyperglycemia.