A time-course study of the effects of a high-carbohydrate diet on the growth performance, glycolipid metabolism and mitochondrial biogenesis and function of blunt snout bream (Megalobrama amblycephala)

This study investigated the dynamic effects of feeding a high-carbohydrate diet on the growth performance, glycolipid metabolism and mitochondrial biogenesis and function of Megalobrama amblycephala. Fish were fed diets containing two dietary carbohydrate levels (30% and 43%) for 16 weeks, and were sampled at 2, 4, 8 and 16 weeks. The results showed that weight gain, protein efficiency, tissue glycogen and lipid contents, plasma levels of glucose, TC, TG and AGES, hepatic contents of AMP, ATP and AMPK protein, mitochondrial Na+-K+-ATPase and CS activities, as well as the transcriptions of GLUT2, GK, PK, GS, G6PDH, FAS, SREBP1 and ACCα all increased significantly with increasing sampling times. However, the opposite was true for nitrogen and energy retention, hepatic PGC-1β protein content, the AMP/ATP and the p-AMPK/t-AMPK ratios, as well as mitochondrial respiratory chain complex II, III and IV activities. In terms of diets, tissue glycogen and lipid contents, plasma levels of glucose, TG, TC and AGES, hepatic AMPK content as well as the transcriptions of GLUT2, GK, PK, GS, G6PDH, SREBP1, FAS and ACCα all increased significantly with increasing dietary carbohydrate levels, while the opposite was true for the contents of cytochrome C, PGC-1β and NRF-1, the p-AMPK/t-AMPK ratio, the activities of Na+-K+-ATPase, SDH, CS and complex II, III and IV, as well as the transcriptions of FBPase, CPT1 and ACO. Furthermore, the glycolipid metabolism and mitochondrial biogenesis and function were also significantly affected by the interaction between sampling times and diets. In conclusion, feeding a high-carbohydrate diet for more than 8 weeks could enhance the glucose transport, glycogenesis and lipogenesis of blunt snout bream, but down-regulate gluconeogenesis and fatty acid β-oxidation coupled with the impaired mitochondrial biogenesis and function.