Dietary l -carnitine supplementation increases lipid deposition in the liver and muscle of yellow catfish ( Pelteobagrus fulvidraco ) through changes in lipid metabolism

Evaluation of fatty acids and carnitine as biomarkers of PFOS exposure in biota (fish and dolphin) from Galveston Bay and the northwestern Gulf of Mexico

Perfluorooctane sulfonate (PFOS) is a ubiquitous pollutant that elicits a wide range of toxic effects in exposed biota. Coastal zones in highly urbanized or industrial areas are particularly vulnerable to PFOS pollution. At present, information is lacking on biomarkers to assess PFOS effects on aquatic wildlife. This study investigated the efficacy of l-carnitine (or carnitine) and fatty acids as biomarkers of PFOS exposure in aquatic biota. The levels of PFOS, total and free carnitine, and 24 fatty acids (measured as fatty acid methyl esters or FAMEs) were measured in the liver, and muscle or blubber, of fish and dolphins sampled from Galveston Bay and the northern Gulf of Mexico (nGoM). Overall, bottlenose dolphins (Tursiops truncatus) had the highest hepatic PFOS levels. Galveston Bay fish, gafftopsail catfish (Bagre marinus), red drum (Sciaenops ocellatus), and spotted seatrout (Cynoscion nebulosus), had hepatic PFOS levels ∼8-13× higher than nGoM pelagic fish species, red snapper (Lutjanus campechanus) and yellowfin tuna (Thunnus albacares). The multivariate analysis of PFOS liver body-burdens and biomarkers found carnitine to be a more modal biomarker of PFOS exposure than FAMEs. Significant positive correlation of hepatic PFOS levels with total carnitine was evident for biota from Galveston Bay (fish only), and a significant correlation between PFOS and total and free carnitine was evident for biota from the nGoM (fish and dolphins). Given the essential role of carnitine in mediating fatty acid β-oxidation, our results suggest carnitine to be a likely candidate biomarker of environmental PFOS exposure and indicative of potential dyslipidemia effects.

Influences of chronic copper exposure on intestinal histology, antioxidative and immune status, and transcriptomic response in freshwater grouper (Acrossocheilus fasciatus)

Copper (Cu) contamination is commonly found in both natural water environments and fish farms, and it can cause severe damage to different fish organs, but Cu-induced intestinal damage has been rarely studied. This study subjected three groups of freshwater grouper (Acrossocheilus fasciatus) (initial weight: 1.56 ± 0.10 g) to 0 mg/L, 0.01 mg/L, and 0.04 mg/L Cu2+ for 30 days, named Con, Cu0.01, and Cu0.04 groups, respectively. The histological observation indicated that the Cu0.04 group caused a significant decrease in villus length, lamina propria width, and muscular thickness compared to the Con group (P < 0.05). Additionally, the Cu0.04 group significantly increased intestinal superoxide dismutase (SOD), glutathione peroxidase (GPx), lysozyme (LZM) activities, as well as malondialdehyde (MDA) content than the Con group (P < 0.05). Meanwhile, the Cu0.01 and Cu0.04 groups showed significantly increased immunoglobulin M (IgM), complement 3 (C3), and glutathione (GSH) contents than the Con group (P < 0.05). Transcriptomic analysis revealed a total of 101 differentially expressed genes (DEGs), including 47 up-regulated and 54 down-regulated DEGs, were identified between the Cu0.04 and Con groups. Notably, the DEGs were mainly related to intestinal structure construction, immune functions, apoptosis, and resistance to DNA damage and pathogen infection. The findings suggest that chronic Cu exposure caused intestinal histological alterations, activated the antioxidative and immune systems, and induced systematic adaptation to cope with the physical barrier injury, DNA damage, and potential pathogen growth.

Effect of Adding L-carnitine to High-Fat/Low-Protein Diets of Common Carp (Cyprinus carpio) and the Mechanism of Regulation of Fat and Protein Metabolism

L-carnitine is a low molecular weight amino acid that plays an essential role in the oxidation of long-chain fatty acids. The regulatory effects and molecular mechanisms of L-carnitine on fat and protein metabolism in common carp (Cyprinus carpio) were investigated in this study. Common carp (n = 270) were randomly divided into three groups and fed either (1) common carp diet, (2) high-fat/low-protein diet, or (3) L-carnitine-high-fat/low-protein diet. Growth performance, plasma biochemistry, muscle composition, and ammonia excretion rate were all examined after 8 weeks. Additionally, each group's hepatopancreas was subjected to transcriptome analysis. The results showed that decreasing the feed protein/fat ratio resulted in a considerable increase in feed conversion ratio and a significant decrease in common carp-specific growth rate to 1.19 ± 0.02 (P < 0.05). Similarly, total plasma cholesterol sharply increased to 10.15 ± 2.07, while plasma urea nitrogen, muscle protein, and ammonia excretion levels dropped (P < 0.05). After adding L-carnitine to the high-fat/low-protein diet, it was found that the specific growth rate and protein content of the dorsal muscle increased significantly (P < 0.05). In contrast, the plasma total cholesterol and ammonia excretion rate decreased considerably at most time points after feeding (P < 0.05). The expression of genes in the hepatopancreas differed substantially between the different groups. Through GO analysis, it was demonstrated that L-carnitine increased the ability of fat decomposition by up-regulating the expression of cpt1 in the hepatopancreas and decreased the expression of fasn and elovl6 to reduce the production and extension of lipids. Simultaneously, mtor was more abundant in the hepatopancreas, implying that L-carnitine can increase protein synthesis. According to the findings, adding L-carnitine to high-fat/low-protein diets can stimulate growth by enhancing lipolysis and protein synthesis.

Dietary isoleucine affects muscle fatty acid and amino acid profiles through regulating lipid metabolism and autophagy in hybrid catfish Pelteobagrus vachelli ♀ × Leiocassis longirostris ♂

The present study explored the impacts of Ile on muscle fatty acid and amino acid profiles, lipid metabolism, and autophagy in hybrid catfish. Seven isonitrogenous (387.8 g/kg protein) semi-purified diets were formulated to contain 5.0 (control), 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 g Ile/kg diet respectively. The fish (initial weight of 33.11 ± 0.09 g) were randomly assigned to 7 groups for a 56-day trial. Each group has 3 replicates with 30 fish per replicate, fed at 08:00 and 18:00 each day. Results showed that muscle protein and lipid, C14:0, C18:0, C22:0, C14:1, C18:1n-9, polyunsaturated fatty acid (PUFA), Arg, Ile, Ala, Cys, Gly, Tyr, essential amino acid (EAA), and total amino acid (TAA) contents and flavor amino acid (FAA)/TAA in muscle had positive linear and/or quadratic responses to dietary Ile levels (P < 0.05). Fatty acid synthase (FAS), stearoyl-CoA desaturase (SCD), acetyl-CoA carboxylase (ACC), and lipoprotein lipase (LPL) activities had positive linear and/or quadratic responses, but carnitine palmitoyl transferase 1 (CPT1) activity had a negative response with increasing dietary Ile levels (P < 0.05). The mRNA expressions of FAS, SCD, ACC, LPL, fatty acid binding protein 4 (FABP4), FATP1, sterol response element-binding protein 1c (SREBP-1c), sequestosome 1 (SQSTM1), and adenosine 5′-monophosphate-activated protein kinase (AMPK) had positive linear and/or quadratic responses to dietary Ile levels (P < 0.05). The mRNA expressions of hormone-sensitive lipase (HSL), CPT1, peroxisome proliferator-activated receptor α (PPARα), PPARγ, uncoordinated 51-like kinase 1 (ULK1), beclin1 (Becn1), autophagy-related protein 9α (Atg9α), Atg4b, Atg7, autophagy marker light chain 3 B (LC3B), and SQSTM1 in muscle had negative linear and/or quadratic responses to dietary Ile levels (P < 0.05). The p-AMPK and ULK1 protein levels, and p-AMPK/AMPK were decreased by 12.5 g Ile/kg in the diet (P < 0.05). Finally, SQSTM1 protein level had the opposite effect (P < 0.05). The above results indicate that dietary Ile improves fish muscle fatty acid and amino acid profiles potentially via respectively regulating lipid metabolism and autophagy. The Ile requirement of hybrid catfish (33 to 72 g) were estimated to be 12.63, 13.77, 13.75, 11.45, 10.50, 12.53 and 12.21 g/kg diet based on the regression analysis of protein, lipid, SFA, PUFA, FAA, EAA, and TAA muscle contents, respectively.

An NMR-Based Metabolomics Assessment of the Effect of Combinations of Natural Feed Items on Juvenile Red Drum, Sciaenops ocellatus

This study evaluated the effects of seven diets composed of natural feed components (chopped fish, shrimp, and squid) alone or in combination on the liver metabolite profile of juvenile red drum (Sciaenops ocellatus) cultured in a 24-tank recirculating aquaculture system over the course of 12 weeks using Nuclear Magnetic Resonance (NMR)-based metabolomics. Experimental diets included fish (F), shrimp (SH), squid (SQ), fish and shrimp (FSH), fish and squid (FSQ), shrimp and squid (SHSQ), fish, shrimp, and squid (FSHSQ). A commercial fishmeal-based pelleted diet was used as a control. Fish were fed isocalorically. Red drum liver samples were collected at five different time points: T0, before the start of the trial (n = 12), and subsequently every 3 weeks over the course of 12 weeks (T3, T6, T9, T12), with n = 9 fish/diet/time point. Polar liver extracts were analyzed by NMR-based metabolomics. Multivariate statistical analyses (PCA, PLS-DA) revealed that red drum fed the F diet had a distinct liver metabolite profile from fish fed the other diets, with those fed SH, SQ and the combination diets displaying greater similarities in their metabolome. Results show that 19 metabolites changed significantly among the different dietary treatments, including amino acids and amino acid derivatives, quaternary amines and methylamines, carbohydrates and phospholipids. Specifically, γ-butyrobetaine, N-formimino-L-glutamate (FIGLU), sarcosine and beta-alanine were among the most discriminating metabolites. Significant correlations were found between metabolites and six growth performance parameters (final body weight, total length, condition factor, liver weight, hepatosomatic index, and eviscerated weight). Metabolites identified in this study constitute potential candidates for supplementation in fish feeds for aquaculture and optimization of existing formulations. Additionally, we identified a quaternary amine, γ-butyrobetaine as a potential biomarker of shrimp consumption in red drum. These results warrant further investigation and biomarker validation and have the potential for broader applicability outside of the aquaculture field in future investigations in wild red drum populations and potentially other carnivorous marine fishes.

Artemisinin and l-carnitine combination therapy alters the erythrocytes redox status

Hematopoiesis is a sensitive target of artemisinin (ART) and its derivatives, and hemolysis is one of their commonly reported side effects. L-carnitine (LC), an amino acid derivative involved in lipid metabolism, is beneficial for hematological parameters. Sixty adult laboratory mice were randomly divided into six groups. Group I (control) received saline and corn oil; groups II and III received therapeutic (50 mg/kg) and toxic (250 mg/kg) doses of ART, respectively; groups IV and V received 370 mg/kg LC along with the 50 and 250 mg/kg ART, respectively; and group VI received 370 mg/kg LC. Drugs were administered orally for seven consecutive days. The erythrocyte glucose 6-phosphate dehydrogenase (G6PD), catalase (CAT), and peroxidase (POX) activity, and the reduced glutathione (GSH) level were assessed by colorimetric methods. ART reduced the G6PD activity both at therapeutic and toxic doses. The therapeutic dose of ART reduced the CAT activity and the GSH level, non-significantly. The toxic dose of ART reduced the CAT activity and increased the POX activity. LC reduced the G6PD, CAT, and POX activities and increased GSH level. The therapeutic dose of ART and LC showed synergy in reducing the G6PD activity. LC and ART combination reduced POX activity and increased GSH level without any significant effect on the CAT activity. Inhibition of G6PD may be a potentially new mechanism of ART action. Co-administration of LC with ART or following treatment with ART may have protective effects on erythrocytes. This article is protected by copyright. All rights reserved.

Effect of rare earth element lanthanum on lipid deposition and Wnt10b signaling in the liver of male zebrafish

This paper investigates the effect of lanthanum (La) on lipid deposition and Wnt10b signaling in the liver of male zebrafish with exposure of 0, 10, 20, and 30 μmol/L La. It suggests that La can be accumulated in liver, and its treatments decrease the activities and gene expression of enzymes related to fatty acid synthesis. The levels of total cholesterol (TC), triglyceride (TG), and nonesterified fatty acids (NEFA) as well as the size of lipid droplets are decreased by La treatments. Moreover, La treatments affect the composition of fatty acids and the content of nutrient elements. Meanwhile, they also induce the gene expression of wnt10b, β-catenin, pparα, and pparγ, but inhibit gsk-3β gene expression in liver. Further study on the result of wnt10b gene interference shows that Wnt10b/β-catenin signaling plays a crucial role in the regulatory process of hepatic lipid deposition. Taken together, our observations suggest that La accumulation affects lipid deposition in the liver of male zebrafish, and Wnt10b signaling pathway may be involved in this process.

Nutrient-related metabolite profiles explain differences in body composition and size in Nile tilapia (Oreochromis niloticus) from different lakes

This study investigated how metabolite analysis can explain differences in tissue composition and size in fish from different habitats. We, therefore, studied Nile tilapia (Oreochromis niloticus) from three Ethiopian lakes (Gilgel Gibe, Ziway, and Langano) using dried bloodspot (DBS) analysis of carnitine esters and free amino acids. A total of sixty (N = 60) Nile tilapia samples were collected comprising twenty (n = 20) fish from each lake. The proximate composition of the targeted tissues (muscle, skin, gill, gut, and liver) were analyzed. The DBS samples were analyzed for acylcarnitine and free amino acid profiles using quantitative electrospray tandem mass spectrometry. Metabolite ratios were calculated from relevant biochemical pathways that could identify relative changes in nutrient metabolism. The mean weight of Nile tilapia sampled from each lake showed weight variation among the lakes, fish from Lake Ziway were largest (178 g), followed by Gilgel Gibe reservoir (134 g) and Lake Langano (118 g). Fish from Gilgel Gibe showed significantly higher fat composition in all tissues (P < 0.05) except the liver in which no significant variation was observed. The source of fish affected the tissue fat composition. Marked differences were observed in Nile tilapia metabolic activity between the lakes. For instance, the lower body weight and condition of the fish in Lake Langano coincided with several metabolite ratios pointing to a low flow of glucogenic substrate to the citric acid cycle. The low propionyl to acetylcarnitine ratio (C3:C2) in Gilgel Gibe fish is indicating that more of the available acetyl CoA is not led into the citric acid cycle, but instead will be used for fat synthesis. The metabolic markers for lipogenesis and metabolic rate could explain the high-fat concentration in several parts of the body composition of fish from Gilgel Gibe. Our results show that nutrition-related blood metabolite ratios are useful to understand the underlying metabolic events leading to the habitat-dependent differences in the growth of Nile tilapia, and by extension, other species.

Nutrition and Functions of Amino Acids in Fish

Aquaculture is increasingly important for providing humans with high-quality animal protein to improve growth, development and health. Farm-raised fish and shellfish now exceed captured fisheries for foods. More than 70% of the production cost is dependent on the supply of compound feeds. A public debate or concern over aquaculture is its environmental sustainability as many fish species have high requirements for dietary protein and fishmeal. Protein or amino acids (AAs), which are the major component of tissue growth, are generally the most expensive nutrients in animal production and, therefore, are crucial for aquatic feed development. There is compelling evidence that an adequate supply of both traditionally classified nutritionally essential amino acids (EAAs) and non-essential amino acids (NEAAs) in diets improve the growth, development and production performance of aquatic animals (e.g., larval metamorphosis). The processes for the utilization of dietary AAs or protein utilization by animals include digestion, absorption and metabolism. The digestibility and bioavailability of AAs should be carefully evaluated because feed production processes and AA degradation in the gut affect the amounts of dietary AAs that enter the blood circulation. Absorbed AAs are utilized for the syntheses of protein, peptides, AAs, and other metabolites (including nucleotides); biological oxidation and ATP production; gluconeogenesis and lipogenesis; and the regulation of acid-base balance, anti-oxidative reactions, and immune responses. Fish producers usually focus on the content or digestibility of dietary crude protein without considering the supply of AAs in the diet. In experiments involving dietary supplementation with AAs, inappropriate AAs (e.g., glycine and glutamate) are often used as the isonitrogenous control. At present, limited knowledge is available about either the cell- and tissue-specific metabolism of AAs or the effects of feed processing methods on the digestion and utilization of AAs in different fish species. These issues should be addressed to develop environment-friendly aquafeeds and reduce feed costs to sustain the global aquaculture.

Dietary berberine regulates lipid metabolism in muscle and liver of black sea bream (Acanthopagrus schlegelii) fed normal or high-lipid diets

The present study investigated the influence of berberine (BBR) supplementation in normal and high-lipid (HL) diets on lipid metabolism and accumulation in black sea bream (Acanthopagrus schlegelii). BBR was supplemented at 50 mg/kg to control (Con, 11·1 % crude lipid) and high-lipid (HL, 20·2 % crude lipid) diets and named as ConB and HLB, respectively. After the 8-week feeding trial, fish body length and specific growth rate were significantly reduced by HL diets (P < 0·05). Muscle and whole-body crude lipid contents were significantly influenced by both BBR supplementation and dietary lipid level. Fish fed the HLB diet had significantly lower serum TAG, LDL-cholesterol contents and alanine aminotransferase activity compared with the HL group. The HL group presented vast lipid accumulation in the liver, and hypertrophied hepatocytes along with large lipid droplets, and translocation of nuclear to the cell periphery. These abnormalities in black sea bream were alleviated in the HLB group. BBR supplementation in the HL diet significantly down-regulated the hepatic expression levels of acetyl-CoA carboxylase α, sterol regulatory element-binding protein-1, 6-phosphogluconate dehydrogenase, glucose 6-phosphate dehydrogenase and pparγ, whereas the lipoprotein lipase, hormone-sensitive lipase and carnitine palmitoyltransferase 1a expression levels were significantly up-regulated. However, the expression levels of these genes showed opposite trends in muscle (except for pparγ). In conclusion, dietary BBR supplementation in the HL diet reduced hepatic lipid accumulation by down-regulating lipogenesis gene expression and up-regulating lipolysis gene expression, and it increased muscle lipid contents with opposite trends of the mechanism observed in the liver.

Effects of Dietary Carbohydrate to Lipid Ratios on Growth Performance, Muscle Fatty Acid Composition, and Intermediary Metabolism in Juvenile Black Seabream (Acanthopagrus schlegelii)

An 8-week feeding trial was conducted to evaluate the effects of dietary carbohydrate to lipid (CHO:L) ratios on growth performance, muscle fatty acid composition, and intermediary metabolism in juvenile black seabream (Acanthopagrus schlegelii). Five isonitrogenous and isoenergetic diets (48.0% crude protein and 18.0 MJ kg-1 gross energy) were formulated to contain different CHO:L ratios ranging from 0.33 to 3.75. Triplicate groups of 20 fish averaging 0.51 ± 0.01 g were fed with experimental diets twice daily to apparent satiation. The results indicated that final body weight (FBW), percentage weight gain (PWG), specific growth rate (SGR), and protein efficiency ratio (PER) were significantly influenced by the dietary CHO:L ratios (p < 0.05). The highest FBW, PWG, and SGR were observed in fish fed the diet with a CHO:L ratio of 1.36 (p < 0.05). A two-slope broken-line regression analysis based on PWG indicated that the optimal dietary CHO:L is 1.08. Lipid content in the whole body decreased, and glycogen concentration in the liver increased with the increase of dietary CHO:L ratios from 0.33 to 3.75 (p < 0.05). Moreover, there was a positive correlation between muscle fatty acid composition and dietary fatty acid composition. The relative expression levels of genes involved in glucose metabolism, such as gk, pepck, and glut2 were upregulated by increasing the dietary CHO:L ratio. Also, the mRNA expression level of genes related to lipid synthesis, such as fas and accα were significantly upregulated with dietary CHO:L ratios increasing from 0.33 to 3.75. The highest expression of genes involved in fatty acid β-oxidation, such as cpt1 and acox1, were observed in fish fed the 1.36 CHO:L ratio diet. The gene expression of Δ6 fatty acyl desaturase (fads2) in the liver significantly increased with increase of dietary CHO:L ratios from 0.33 to 3.75. Fish fed the diet with CHO:L ratios of 2.26 and 3.75 had lower expression levels of elovl5 than those fed the other diets. These results demonstrate that dietary optimal CHO:L ratios could improve PWG and SGR but also influence expression of genes involved in glucose and lipid metabolism. Based on the overall results, the optimal dietary CHO:L ratio is 1.08 for black seabream.

Effects of Chromium and Carnitine Co-supplementation on Body Weight and Metabolic Profiles in Overweight and Obese Women with Polycystic Ovary Syndrome: a Randomized, Double-Blind, Placebo-Controlled Trial

The primary aim of our study was to determine the influence of taking chromium plus carnitine on insulin resistance, with a secondary objective of evaluating the influences on lipid profiles and weight loss in overweight subjects with polycystic ovary syndrome (PCOS). In a 12-week randomized, double-blind, placebo-controlled clinical trial, 54 overweight women were randomly assigned to receive either supplements (200 μg/day chromium picolinate plus 1000 mg/day carnitine) or placebo (27/each group). Chromium and carnitine co-supplementation decreased weight (- 3.6 ± 1.8 vs. - 1.0 ± 0.7 kg, P < 0.001), BMI (- 1.3 ± 0.7 vs. - 0.3 ± 0.3 kg/m², P < 0.001), fasting plasma glucose (FPG) (- 5.1 ± 6.0 vs. - 1.1 ± 4.9 mg/dL, P = 0.01), insulin (- 2.0 ± 1.4 vs. - 0.2 ± 1.2 μIU/mL, P < 0.001), insulin resistance (- 0.5 ± 0.4 vs. - 0.04 ± 0.3, P < 0.001), triglycerides (- 18.0 ± 25.2 vs. + 5.5 ± 14.4 mg/dL, P < 0.001), total (- 17.0 ± 20.3 vs. + 3.6 ± 12.0 mg/dL, P < 0.001), and LDL cholesterol (- 13.3 ± 19.2 vs. + 1.4 ± 13.3 mg/dL, P = 0.002), and elevated insulin sensitivity (+ 0.007 ± 0.005 vs. + 0.002 ± 0.005, P < 0.001). In addition, co-supplementation upregulated peroxisome proliferator-activated receptor gamma (P = 0.02) and low-density lipoprotein receptor expression (P = 0.02). Overall, chromium and carnitine co-supplementation for 12 weeks to overweight women with PCOS had beneficial effects on body weight, glycemic control, lipid profiles except HDL cholesterol levels, and gene expression of PPAR-γ and LDLR. Clinical trial registration number: http://www.irct.ir: IRCT20170513033941N38.

Functional differences between l- and d-carnitine in metabolic regulation evaluated using a low-carnitine Nile tilapia model

l-Carnitine is essential for mitochondrial β-oxidation and has been used as a lipid-lowering feed additive in humans and farmed animals. d-Carnitine is an optical isomer of l-carnitine and dl-carnitine has been widely used in animal feeds. However, the functional differences between l- and d-carnitine are difficult to study because of the endogenous l-carnitine background. In the present study, we developed a low-carnitine Nile tilapia model by treating fish with a carnitine synthesis inhibitor, and used this model to investigate the functional differences between l- and d-carnitine in nutrient metabolism in fish. l- or d-carnitine (0·4 g/kg diet) was fed to the low-carnitine tilapia for 6 weeks. l-Carnitine feeding increased the acyl-carnitine concentration from 3522 to 10 822 ng/g and alleviated the lipid deposition from 15·89 to 11·97 % in the liver of low-carnitine tilapia. However, as compared with l-carnitine group, d-carnitine feeding reduced the acyl-carnitine concentration from 10 822 to 5482 ng/g, and increased lipid deposition from 11·97 to 20·21 % and the mRNA expression of the genes involved in β-oxidation and detoxification in the liver. d-Carnitine feeding also induced hepatic inflammation, oxidative stress and apoptosis. A metabolomic investigation further showed that d-carnitine feeding increased glycolysis, protein metabolism and activity of the tricarboxylic acid cycle and oxidative phosphorylation. Thus, l-carnitine can be physiologically utilised in fish, whereas d-carnitine is metabolised as a xenobiotic and induces lipotoxicity. d-Carnitine-fed fish demonstrates increases in peroxisomal β-oxidation, glycolysis and amino acid degradation to maintain energy homeostasis. Therefore, d-carnitine is not recommended for use in farmed animals.

Pancreastatin inhibitor activates AMPK pathway via GRP78 and ameliorates dexamethasone induced fatty liver disease in C57BL/6 mice

AIMS

To investigate the role of pancreastatin inhibitor (PSTi8) in lipid homeostasis and insulin sensitivity in dexamethasone induced fatty liver disease associated type 2 diabetes.

MAIN METHODS

Glucose releases assay, lipid O staining and ATP/AMP ratio were performed in HepG2 cells. Twenty four mice were randomly divided into 4 groups: Control group (saline), DEX (1 mg/kg, im) for 17 days, DEX+PSTi8 (acute 5 mg/kg and chronic 2 mg/kg, ip) for 10 days. The glucose, insulin and pyruvate tolerance tests (GTT, ITT and PTT), biochemical parameters and Oxymax-CLAMS were performed. Further to elucidate the action mechanisms of PSTi8, we performed genes expression and western blotting of biological samples.

KEY FINDINGS

We found that PSTi8 suppresses hepatic glucose release, lipid deposition, oxidative stress induced by DEX, stimulates the cellular energy level in hepatocytes and enhances GRP78 activity. It reduces lipogensis and enhances fatty acid oxidation to improve insulin sensitivity and glucose tolerance in DEX induced diabetic mice. The above cellular effects are the result of activated AMPK signalling pathway in liver, which increases Srebp1c and ACC phosphorylation. The increased ACC phosphorylation suppresses protein kinase C activity and enhances insulin sensitivity. The increased expression of UCP3 in liver elicits fatty acid oxidation and energy expenditure, which suppress oxidative stress.

SIGNIFICANCE

Thus the activation of AMPK signalling through GRP78, improves lipid homeostasis, enhances insulin sensitivity via inhibition of PKC activity. PSTi8 suppresses inflammation associated with incomplete fatty acid oxidation. Hence, PSTi8 may be a potential therapeutic agent to treat glucocorticoid-induced fatty liver associated type 2 diabetes.

Dietary Radix Bupleuri extracts improves hepatic lipid accumulation and immune response of hybrid grouper (Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀)

In this study, two experiments were performed to explore the effect of Radix Bupleuri extracts (RBE) on growth, lipid deposition and metabolism and immune response of hybrid grouper (Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀) using in vitro and in vivo models. In vitro, we used 2 ml/L 20% lipid emulsion (LE)-induced steatosis in hybrid grouper primary hepatocytes, then RBE (200, 400 and 800 μg/ml) was added to the hepatocytes after (post-treatment) the incubation with 20% LE (2 ml/L) in the culture medium. We found that RBE markedly increased cell viability, which were consistent with hepatocytes morphological structure examination and lipid metabolism and immune related genes study. The above result suggested that RBE has a protective effect on this model of hepatocytes damage. In vivo, five graded levels of RBE at 0, 200, 400, 800 and 1600 mg/kg diet were supplemented to a basal diet with 15% lipid levels (high lipid), and fed to a total of 300 hybrid grouper with an average initial weight of 25.58 ± 0.05 g for 8 weeks. Growth performance, liver histology, plasma biochemical parameters, and expression of genes involved in lipid metabolism and immune-related were measured. The study indicated that dietary RBE significantly improved growth performance and feed utilization and reduced hepatosomatic index. Dietary supplementation with 200-800 mg/kg RBE diets effectively decreased serum ALP, ALT, AST and LDH contents in fish. Furthermore, adipogenesis relative mRNA levels of DGAT2, G6PD, ME1 and DGKα in fish fed 200-400 mg/kg RBE diets were lower (P < 0.05) than in those fed RBE0 diets, while dietary supplementation with 200-800 mg/kg RBE diets up-regulated lipolysis-related genes (CPT1, LPL and PPARα) expression in the liver of hybrid grouper. Moreover, dietary RBE down-regulated the expression of apoptosis-related genes (caspase-9), up-regulated the expression of antioxidant genes (CAT) and immune-related genes (MHC2, IKKα and TGF-β1). Thus, our data suggest that RBE suppressed lipid accumulation and enhanced immune capability in hybrid grouper both in vitro and in vivo. These results offer new insight into RBE as a hepatoprotective in fish.

The mechanism of action of a fat regulator: Glycyrrhetinic acid (GA) stimulating fatty acid transmembrane and intracellular transport in blunt snout bream (Megalobrama amblycephala)

High-fat diets are associated with fatty liver and aberrant hepatic lipid metabolism, and glycyrrhetinic acid (GA) has been shown to exert a beneficial effect on lipolysis and fat deposition in fish. In the present study, we evaluated the effect of GA on the growth performance and expression of hepatic lipid transport related genes in blunt snout bream (Megalobrama amblycephala) fed a high fat diet. Two hundred and sixteen fish (average body weight: 45.57 g ± 0.98 g) were fed three experimental diets (6% fat/L6 group, control, 11% fat/L11 group, and 11% fat with 0.3 mg kg^-1 GA/L11GA group) for 8 weeks. Compared to the control group, the weight gain and specific growth rate of high-fat fed group at the end of the trialwere significantly improved (P < .05).However, GA showed no effect on animals' growth performance(P > .05). Dietary supplementation with 0.3 mg kg^-1 GA significantly decreased the hepatosomatic index, viscera/body ratio, and intraperitoneal fat ratio (P < .05), and up-regulated the expression levels of fatty acids transport protein (FATP), fatty acids binding protein (FABP), fatty acid translocase (CD36), carnitine palmitoyl transferase I (CPT1) and peroxisome proliferators-activated receptors α (PPARα) compared to both the L6 group and L11 group (P < .05). However, no significant difference was observed in fatty acid synthetase (FAS), acetyl-CoA carboxylase α (ACCα), or lipoprotein lipase (LPL) between groups (P > .05). In conclusion, GA significantly rescued high-fat diet induced hepatic lipid accumulation and metabolism dysfunction in M. amblycephalaby stimulating hepatic fatty acid transport and β-oxidation. Dietary GA may be used as a promising supplement to alleviate high-fat diet induced side effects on M. amblycephala.

Ameliorative effect of Sedum sarmentosum Bunge extract on Tilapia fatty liver via the PPAR and P53 signaling pathway

Fatty liver disease is a growing problem in fish aquaculture and there is an urgent need to identify causes and possible remedies. In the present study, the effects of treating fatty liver disease in the Nile tilapia (Oreochromis niloticus Linnaeus, 1758) with an extract derived from a herb, Sedum sarmentosum Bunge (SSB), was investigated. We found that the SSB extract could restore the changes to feed coefficient, immune capacity, and pathological index caused by fatty liver disease, and also prevent apoptosis in hepatocytes. An RNA-seq analysis showed that treatment with SSB extract altered expression of genes in the lipid metabolic process, metabolic process, and oxidation-reduction process. Our results suggest that disorders of the PPAR and p53 signaling pathways may be involved in steatohepatitis development and in the therapeutic mechanism of the SSB extract treatment; these observations shed new light on possible treatment of steatohepatitis.

Growth performance, fatty-acid composition, lipid deposition and hepatic-lipid metabolism-related gene expression in juvenile pond loach Misgurnus anguillicaudatus fed diets with different dietary soybean oil levels

A 10 week feeding trial was conducted to evaluate the effects of different dietary soybean oil (SO) levels on growth performance, fatty-acid composition and lipid deposition in viscera, histology and histochemistry of liver, intestine and hepatic-lipid metabolism-related gene expressions in pond loach Misgurnus anguillicaudatus juveniles. Misgurnus anguillicaudatus (mean ± s.d. mass 0·40 ± 0·01 g) were fed five experimental diets containing SO at different concentrations: 0, 20, 32, 56 and 100% SO and a diet containing 100% fish oil (100% FO). The mass gains and specific growth rates of M. anguillicaudatus fed 20% SO and 100% FO diets were significantly higher than those of the other groups (P < 0·05). The lipid content of viscera and the amount of cytoplasmic vacuolation in the liver increased with incremental dietary SO level. Meanwhile, increasing dietary SO levels up-regulated the messenger (m)RNA levels of lipogenic genes (such as Δ6fad, scd, pparγ, fas and srebp-1) and down-regulated the mRNA levels of the lipolytic genes (such as pparα, cpt1, atgl and hsl) in the liver. The percentage of 20:4n-6 significantly (P < 0·05) increased with increasing dietary SO level, which might be correlated with the up-regulation of the mRNA level of Δ6fad. The highest levels of dietary SO, however, had a negative effect on growth performance, lipid deposition of viscera and histology and histochemstry of liver and intestine. The increased lipid accumulation induced by incremental dietary SO level probably occurred through different strategies for lipid metabolism as a result of competition between lipolysis and lipogenesis and between export and import of lipids in this species.

Nicotinamide prevents sweet beverage-induced hepatic steatosis in rats by regulating the G6PD, NADPH/NADP+ and GSH/GSSG ratios and reducing oxidative and inflammatory stress

The disruption of redox state homeostasis, the overexpression of lipogenic transcription factors and enzymes, and the increase in lipogenic precursors induced by sweetened beverages are determinants of the development of nonalcoholic fatty liver disease. This study evaluated the action of nicotinamide (NAM) on the expression of glucose-6-phosphate dehydrogenase (G6PD) and redox, oxidative, and inflammatory states in a model of nonalcoholic hepatic steatosis induced by high and chronic consumption of carbohydrates. Male rats were provided drinking water with 30% glucose or fructose ad libitum for 12 weeks. Additionally, 30 days after the beginning of carbohydrate administration, some rats were simultaneously provided water with 0.06% or 0.12% NAM for 5h daily over the next 8 weeks. Biochemical profiles and expression levels of G6PD, tumor necrosis factor α (TNFα), and NADPH oxidase 4 (NOX4) were evaluated together with glutathione/glutathione disulfide (GSH/GSSG) and reduced nicotinamide adenine dinucleotide (phosphate)/nicotinamide adenine dinucleotide (phosphate) [NAD(P)H/NAD(P)] ratios and thiobarbituric acid reactive substances (TBARS). The results showed that hepatic steatosis induced by the chronic consumption of glucose or fructose was associated with body weight gain and increased levels of serum glucose, insulin, triacylglycerols, free fatty acids, transaminases, and TBARS. In the liver, the expression and activity of G6PD increased along with the GSSG, TBARS, and TG concentrations. These alterations were reduced by NAM treatment through the attenuation of increases in G6PD expression and activity and in the NADPH/NADP⁺ ratio, thereby slowing liver steatosis. NAM prevents redox, oxidative, and inflammatory alterations induced by high carbohydrate consumption.

Dietary zinc addition influenced zinc and lipid deposition in the fore- and mid-intestine of juvenile yellow catfishPelteobagrus fulvidraco

The present study explored the mechanisms of dietary Zn influencing Zn and lipid deposition in the fore- and mid- intestine in yellow catfishPelteobagrus fulvidraco, and investigated whether the mechanism was intestinal-region dependent. For this purpose, yellow catfish were fed three diets containing Zn levels of 8·83, 19·20 and 146·65 mg Zn/kg, respectively. Growth performance, intestinal TAG and Zn contents as well as activities and mRNA expression of enzymes and genes involved in Zn transport and lipid metabolism in the fore- and mid-intestine were analysed. Dietary Zn increased Zn accumulation as well as activities of Cu-, Zn-superoxide dismutase and ATPase in the fore- and mid-intestine. In the fore-intestine, dietary Zn up-regulated mRNA levels of ZnT1, ZnT5, ZnT7, metallothionein (MT) and metal response element-binding transcription factor-1 (MTF-1), but down-regulated mRNA levels of ZIP4 and ZIP5. In the mid-intestine, dietary Zn up-regulated mRNA levels of ZnT1, ZnT5, ZnT7, MT and MTF-1, but down-regulated mRNA levels of ZIP4 and ZIP5. Dietary Zn reduced TAG content, down-regulated activities of 6-phosphogluconate dehydrogenase (6PGD), glucose-6-phosphate dehydrogenase (G6PD), malic enzyme (ME) and fatty acid synthase (FAS) activities, and reduced mRNA levels of 6PGD, G6PD, FAS, PPARγand sterol-regulator element-binding protein (SREBP-1), but up-regulated mRNA levels of carnitine palmitoyltransferase IA, hormone-sensitive lipase (HSLa), adipose TAG lipase (ATGL) and PPARαin the fore-intestine. In the mid-intestine, dietary Zn reduced TAG content, activities of G6PD, ME, isocitrate dehydrogenase and FAS, down-regulated mRNA levels of 6PGD, G6PD, FAS, acetyl-CoA carboxylase a, PPARγand SREBP-1, but up-regulated mRNA expression of HSLa, ATGL and PPARγ. The reduction in TAG content following Zn addition was attributable to reduced lipogenesis and increased lipolysis, and similar regulatory mechanisms were observed between the fore- and mid-intestine.

Evaluation of the effects of L-carnitine on medaka (Oryzias latipes) fatty liver

Lifestyle-related diseases have become a major issue in recent years. The increasing incidence of fatty liver underlines the urgency with which the issues of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) need to be addressed. L-carnitine is a compound known to transport fatty acids into the mitochondria to enhance β-oxidation-mediated metabolism of fats. In this study, the effects of L-carnitine administration on fatty liver of medaka (Oryzias latipes) were analysed, to check for disease improvement and metabolic changes. Additionally, the effects of the concomitant administration of L-carnitine and eicosapentaenoic acid (20:5n-3) (EPA) were investigated. Findings indicated reduced lipid deposition, increase in metabolites associated with β-oxidation, and significant reduction in fatty acid levels in the liver, implying improvement in fatty liver condition. Concomitant administration of L-carnitine and EPA resulted in further benefits, via changes in fatty acid composition in the medaka fatty liver model.

Dietary DHA/EPA ratio affected tissue fatty acid profiles, antioxidant capacity, hematological characteristics and expression of lipid-related genes but not growth in juvenile black seabream (Acanthopagrus schlegelii)

An 8-week feeding trial was conducted to investigate the effects of dietary docosahexaenoic to eicosapentaenoic acid ratio (DHA/EPA) on growth performance, fatty acid profiles, antioxidant capacity, hematological characteristics and expression of some lipid metabolism related genes of juvenile black seabream (Acanthopagrus schlegelii) of initial weight 9.47 ± 0.03 g. Five isonitrogenous and isolipidic diets (45% crude protein and 14% crude lipid) were formulated to contain graded DHA/EPA ratios of 0.65, 1.16, 1.60, 2.03 and 2.67. There were no differences in growth performance and feed utilization among treatments. Fish fed higher DHA/EPA ratios had higher malondialdehyde (MDA) contents in serum than lower ratios. Serum triacylglycerol (TAG) content was significantly higher in fish fed the lowest DHA/EPA ratio. Tissue fatty acid profiles reflected the diets despite down-regulation of LC-PUFA biosynthesis genes, fatty acyl desaturase 2 (fads2) and elongase of very long-chain fatty acids 5 (elovl5), by high DHA/EPA ratios. Expression of acetyl-CoA carboxylase alpha (accα) and carnitine palmitoyl transferase 1A (cpt1a) were up-regulated by high DHA/EPA ratio, whereas sterol regulatory element-binding protein-1 (srebp-1) and hormone-sensitive lipase (hsl) were down-regulated. Fatty acid synthase (fas), 6-phosphogluconate dehydrogenase (6pgd) and peroxisome proliferator-activated receptor alpha (pparα) showed highest expression in fish fed intermediate (1.16) DHA/EPA ratio. Overall, this study indicated that dietary DHA/EPA ratio affected fatty acid profiles and significantly influenced lipid metabolism including LC-PUFA biosynthesis and other anabolic and catabolic pathways, and also had impacts on antioxidant capacity and hematological characteristics.

Systemic regulation of L-carnitine in nutritional metabolism in zebrafish, Danio rerio

Excess fat accumulation has been observed widely in farmed fish; therefore, efficient lipid-lowering factors have obtained high attention in the current fish nutrition studies. Dietary L-carnitine can increase fatty acid β-oxidation in mammals, but has produced contradictory results in different fish species. To date, the mechanisms of metabolic regulation of L-carnitine in fish have not been fully determined. The present study used zebrafish to investigate the systemic regulation of nutrient metabolism by dietary L-carnitine supplementation. L-carnitine significantly decreased the lipid content in liver and muscle, accompanied by increased concentrations of total and free carnitine in tissues. Meanwhile, L-carnitine enhanced mitochondrial β-oxidation activities and the expression of carnitine palmitoyltransferase 1 mRNA significantly, whereas it depressed the mRNA expression of adipogenesis-related genes. In addition, L-carnitine caused higher glycogen deposition in the fasting state, and increased and decreased the mRNA expressions of gluconeogenesis-related and glycolysis-related genes, respectively. L-carnitine also increased the hepatic expression of mTOR in the feeding state. Taken together, dietary L-carnitine supplementation decreased lipid deposition by increasing mitochondrial fatty acid β-oxidation, and is likely to promote protein synthesis. However, the L-carnitine-enhanced lipid catabolism would cause a decrease in glucose utilization. Therefore, L-carnitine has comprehensive effects on nutrient metabolism in fish.

Regulation of glucose and lipid metabolism by dietary carbohydrate levels and lipid sources in gilthead sea bream juveniles

The long-term effects on growth performance, body composition, plasma metabolites, liver and intestine glucose and lipid metabolism were assessed in gilthead sea bream juveniles fed diets without carbohydrates (CH–) or carbohydrate-enriched (20 % gelatinised starch, CH+) combined with two lipid sources (fish oil; or vegetable oil (VO)). No differences in growth performance among treatments were observed. Carbohydrate intake was associated with increased hepatic transcripts of glucokinase but not of 6-phosphofructokinase. Expression of phosphoenolpyruvate carboxykinase was down-regulated by carbohydrate intake, whereas, unexpectedly, glucose 6-phosphatase was up-regulated. Lipogenic enzyme activities (glucose-6-phosphate dehydrogenase, malic enzyme, fatty acid synthase) and ∆6 fatty acyl desaturase (FADS2) transcripts were increased in liver of fish fed CH+ diets, supporting an enhanced potential for lipogenesis and long-chain PUFA (LC-PUFA) biosynthesis. Despite the lower hepatic cholesterol content in CH+ groups, no influence on the expression of genes related to cholesterol efflux (ATP-binding cassette G5) and biosynthesis (lanosterol 14α-demethylase, cytochrome P450 51 cytochrome P450 51 (CYP51A1); 7-dehydrocholesterol reductase) was recorded at the hepatic level. At the intestinal level, however, induction of CYP51A1 transcripts by carbohydrate intake was recorded. Dietary VO led to decreased plasma phospholipid and cholesterol concentrations but not on the transcripts of proteins involved in phospholipid biosynthesis (glycerol-3-phosphate acyltransferase) and cholesterol metabolism at intestinal and hepatic levels. Hepatic and muscular fatty acid profiles reflected that of diets, despite the up-regulation ofFADS2transcripts. Overall, this study demonstrated that dietary carbohydrates mainly affected carbohydrate metabolism, lipogenesis and LC-PUFA biosynthesis, whereas effects of dietary lipid source were mostly related with tissue fatty acid composition, plasma phospholipid and cholesterol concentrations, and LC-PUFA biosynthesis regulation. Interactions between dietary macronutrients induced modifications in tissue lipid and glycogen content.

Differential effects of dietary copper deficiency and excess on lipid metabolism in yellow catfish Pelteobagrus fulvidraco

The present study was conducted to investigate the effects and mechanism of dietary Cu deficiency and excess on lipid metabolism in the liver, muscle and VAT of juvenile Pelteobagrus fulvidraco. To this end, yellow catfish were fed 0.76 (Cu deficiency), 4.18 (adequate Cu) and 92.45 (Cu excess) mg Cu kg(-1) diet, respectively, for 8 weeks. WG and SGR in the adequate Cu group were significantly higher than those in Cu deficiency and excess groups. In liver, Cu deficiency showed no significant effect on Cu and lipid contents, the activities of 6PGD, G6PD and FAS, and the mRNA levels of many tested genes, including 6PGD, G6PD, FAS, ACCα, PPARγ, LXR, HSL, PPARα and ATGL. Cu excess induced Cu accumulation, reduced the lipid content, FAS activity as well as the mRNA levels of 6PGD, G6PD, FAS, ACCα, PPARγ, HSL and ATGL. In muscle, dietary Cu levels showed no significant effects on lipid content, the activities of lipogenic enzymes and the mRNA levels of the most tested genes, including of 6PGD, G6PD, FAS, SREBP-1, PPARγ, HSL and LPL. In VAT, Cu and lipid contents, FAS activity, and the mRNA levels of 6PGD, G6PD, FAS, SREBP-1, LXR, PPARα and LPL were not significantly influenced by dietary Cu levels. Thus, the change of lipid contents among tissues could be related to the enzymatic activities and gene expression related to lipid metabolism. Different response patterns of enzymatic activities and gene expression in various tissues following dietary Cu levels indicated the tissue-specific regulatory effect by Cu.