| In recent years, the aquaculture develop rapidly. However, fat metabolism disorders of fish often happen due to intensive and high density farming, the shorten production cycle, satiation feeding, deterioration of water and so on. Fatty liver is the most prone to aquaculture, and fish with fatty liver often grow slowly and attenuate the resistance to disease. In order to prevent fat metabolism disorder, it is important to investigate the formation mechanism of fatty liver. In this study, the lipid metabolism between normal and steatotic blunt snout bream have been compared in order to research the mechanism of excessive lipid deposition in liver. The main results are as follows:1 Establishment of nutritional fatty liver model induced by high-fat diets in blunt snout bream Megalobrama amblycephalaThis study examined effects of high-fat diets on alterations of liver histology and blood biochemistry in blunt snout bream Megalobrama amblycephala. Fish were fed with three diets containing 5%,10% and 15% fat, respectively, for 6 weeks. Liver histology and blood biochemistry were examined. The livers of fish fed 5% fat diet showed normal structure, whereas those of the fish fed higher fat diets presented nucleus polarization and lipid vacuolization. Under the transmission electron microscopy, there were lots of ultrastructural alterations of hepatocyte in fish fed 15% fat diet, with alterations involving mitochondrion, nucleus and endoplasmic reticulum (ER). The alterations of blood biochemistry were evaluated to correlate the changes with histological alterations of liver in order to assess the suitable of the investigated blood parameters as rapid indicators of liver condition. In fish fed 15% fat diet, significantly higher aspartate aminotransferase (AST), alanine aminotransferase (ALT) activities and triglycerides and cholesterol presented. On the whole, the present results clearly showed that high fat intake resulted in fat accumulation and the ultrastructure of mitochondrion, nucleus and ER impaired; the blood sample measurements (AST, ALT, triglycerides and cholesterol) could be used as quick diagnosis for liver status of blunt snout bream.2 The immune, oxidative stress and hepatocyte apoptosis in blunt snout bream(Megalobrama amblycephala) fed a high-fat dietThe goal of this study was therefore to investigate possible adverse effects and how they develop. Blunt snout bream(Megalobrama amblycephala) juveniles (initial weight 17.70 ± 0.10 g) were fed with two diets (5% or 15% fat). After the 8-week feeding, fish fed the 15% fat diet showed a high rate of mortality and poor growth. The histological results clearly showed that the high fat intake resulted in fat and glycogen accumulation and structural alterations of the hepatocye, mitochondrion and nucleus. The mitochondria swelled and lost the cristae and matrices in the high-fat group, showing the impairments of mitochondria. Fish fed the 15% fat diet exhibited low succinate dehydrogenase and Na+-K+-ATPase activities and cytochrome c release from mitochondria. The genes expressions of complex Ⅰ and Ⅲ subunits of mitochondrial respiratory chain in fish fed the high-fat diet were down-regulated. The increase of malondialdehyde level and the ratio of oxidized and reduced glutathione (GSSG/GSH) suggested oxidative stress in liver of fish fed the high-fat diet. Moreover, the lower leucocyte count, lysozyme and alternative complement activities and globulin level indicated the suppressive immune responses in the high-fat group. On the whole, the intake of excessive fat impaired mitochondrial bioenergetics and physiological functions. The dysfunction of mitochondria subsequently mediated oxidative stress and hepatocyte apoptosis. Then reductions of the efficacy of the immune system occurred as a consequence of these disorders.3 Hepatic triacylglycerol secretion, lipid transport and tissue lipid uptake in blunt snout bream(Megalobrama amblycephala) fed a high-fat dietThe goal of the study was therefore to investigate effects of fat-rich diet on mechanisms involved in fat deposition in liver. Three hundred blunt snout bream (Megalobrama amblycephala) juveniles (initial weight 18.00±0.05 g) were fed with two diets (5% or 15% fat) for 8 weeks. Histological and biochemical parameters were determined. The hepatic triacylglycerol (TG) secretion rate was measured by intraperitoneal injection with poloxamer 407 (a lipoprotein lipase inhibitor). Lipid transport was studied by determining components of lipoproteins. We also examined lipid uptake by assaying lipoprotein lipase (LPL) activities and mRNA expressions in tissues. Our results showed that ultrastructural lesions of organelles in hepatocytes occurred after intake high-fat diet. The hepatic TG secretion rate and plasma very low density lipoprotein (VLDL) amount of fish fed high-fat diet were significantly lower compared to those of fish fed control diet. Concomitantly, variations of components of lipoproteins were also apparent. In liver, muscle and mesenteric fat tissue, the percentage of polyunsaturated fatty acid (PUFA) was significantly increased, while both saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) percentages decreased in high-fat group. Both activities and mRNA expressions of LPL were also increased in these tissues. On the whole, a low level of lipid transport out of liver, alterations of lipid transport and elevated lipid uptake contributed to fatty liver of blunt snout bream fed high-fat diet.4 Hepatic fatty acid β-oxidation in blunt snout bream Megalobrama amblycephala fed a high fat dietThis study investigated the effects of a fat-rich diet on the mechanisms of fat deposition in the liver. Three-hundred blunt snout bream (Megalobrama amblycephala) juveniles (initial mass 18.00±0.05 g) were fed with one of two diets (5% or 15% fat) for 8 weeks. β-Oxidation capacity and regulation of rate-limiting enzymes were assessed. Large fat droplets were present in hepatocytes of fish fed the high-fat diet. This observation is thought to be largely owing to the reduced capacity for mitochondrial and peroxisomal β-oxidation in the livers of fish fed the high-fat diet, as well as the decreased activities of camitine palmitoyltransferase (CPT) I and acyl-CoA oxidase (ACO), which are enzymes involved in fatty-acid metabolism. Study of CPT I kinetics showed that CPT I had a low affinity for its substrates and a low catalytic efficiency in fish fed the high-fat diet. Expression of both CPT I and ACO was significantly down-regulated in fish fed the high-fat diet. Moreover, the fatty-acid composition of the mitochondrial membrane varied between the two groups. In conclusion, the attenuated P-oxidation capacity observed in fish fed a high-fat diet is proposed to be owing to decreased activity and/or catalytic efficiency of the rate-limiting enzymes CPT I and ACO, via both genetic and non-genetic mechanisms.5 Molecular characterization and tissues distribution of carnitine palmitoyltransferase I in blunt snout bream Megalobrama amblycephalaCarnitine palmitoyltransferase I (CPT I) of blunt snout bream(Megalobrama amblycephala) was cloned and sequenced using a RACE assays. The effect of starvation on tissue CPT I and PPARs mRNA expressions was also investigated. The obtained full-length nucleotide sequence covered 2499 bp with an open reading frame of 2181 bp, translating 726 amino acids. The CPT I protein encoded had a calculated molecular weight of 82950.8 and a PI of 8.99. Three trans-membrane domains were also identified. Sequence analysis revealed a typical conserved domain of CPT I gene. Moreover, CPT I mRNAs were detected in different tissues of blunt snout bream including adipose tissue, gill, heart, liver, spleen, kidney, white muscle, intestine, brain and eye. In blunt snout bream, the expression of CPT I in white muscle and heart was highest followed by liver and brain, and it was lowest in eye. Blunt snout bream CPT I mRNA expression progressively decreases in heart, liver and muscle up to 12 h after last feeding, but returns to initial, non-fasted levels after 12-24 h. CPT I mRNA expression is highly correlated with the expression of peroxisomal proliferator-activated receptor a (PPARa)。6 Effects of berberine on lipid metabolism in blunt snout bream Megalobrama amblycephala fed the high fat dietThe purpose of this study was to determine whether berberine has a protective effect against fatty liver induced by a high-fat diet and to elucidate its underlying molecular mechanisms in blunt snout bream Megalobrama amblycephala. Fish were fed a normal diet (5% fat), high-fat diet (HFD,15% fat), or berberine-supplemented diets (BSD,15% fat with 50 or 100 ppm berberine) for 8 weeks. Histological, molecular and biochemical parameters were determined. The result showed that supplementation of HFD with berberine could reverse the HFD-induced liver lipid deposition along with plasma, oxidative injury and apoptosis in blunt snout bream. The activities of complex I, II, III in mitochondrial respiratory chain elevated in berberine-supplemented diets. Ultrastructural damage of mitochondria and endoplasmic reticulum could be alleviate by berberine. The expression of genes relating to fatty acid oxidation and lipoprotein secretion, such as CPT I and Apo B were up-regulated, whereas the expressions of genes relating to fatty acid uptake and synthesis was down-regulated in the liver of BSD-fed fish compared to HFD-fed fish. |
PDF Full Text Request