Dietary fenofibrate attenuated high-fat-diet-induced lipid accumulation and inflammation response partly through regulation of pparα and sirt1 in juvenile black seabream (Acanthopagrus schlegelii)

Dietary lipid sensing through fatty acid oxidation and chylomicron formation in the gastrointestinal tract of rainbow trout

In mammals, physiological processes related to lipid metabolism, such as chylomicron synthesis or fatty acid oxidation (FAO), modulate eating, highlighting the importance of energostatic mechanisms in feeding control. This study, using rainbow trout (Oncorhynchus mykiss) as model, aimed to characterize the role of FAO and chylomicron formation as peripheral lipid sensors potentially able to modulate feeding in fish. Fish fed with either a normal- (24%) or high- (32%) fat diet were intraperitoneally injected with water alone or containing etomoxir (inhibitor of FAO rate-limiting enzyme carnitine palmitoyl-transferase 1). First, feed intake levels were recorded. We observed an etomoxir-derived decrease in feeding at short times, but a significant increase at 48 h after treatment in fish fed normal-fat diet. Then, we evaluated putative etomoxir effects on the mRNA abundance of genes related to lipid metabolism, chylomicron synthesis and appetite-regulating peptides. Etomoxir treatment upregulated mRNA levels of genes related to chylomicron assembly in proximal intestine, while opposite effects occurred in distal intestine, indicating a clear regionalization in response. Etomoxir also modulated gastrointestinal hormone mRNAs in proximal intestine, upregulating ghrl in fish fed normal-fat diet and pyy and gcg in fish fed high-fat diet. These results provide evidence for an energostatic control of feeding related to FAO and chylomicron formation at the peripheral level in fish.

Proteomics and Its Combined Analysis with Transcriptomics: Liver Fat-Lowering Effect of Taurine in High-Fat Fed Grouper (Epinephelus coioides)

In order to understand the intervention effect of taurine on liver fat deposition induced by high fat intake in the orange-spotted grouper (Epinephelus coioides), we performed proteomic analysis and association analysis with previously obtained transcriptomic data. Three isoproteic (47% crude protein) diets were designed to contain two levels of fat and were named as the 10% fat diet (10F), 15% fat diet (15F), and 15% fat with 1% taurine (15FT). The 10F diet was used as the control diet. After 8 weeks of feeding, the 15F diet exhibited comparable weight gain, feed conversion ratio, and hepatosomatic index as the 10F diet, but the former increased liver fat content vs. the latter. Feeding with the 15FT diet resulted in an improvement in weight gain and a reduction in feed conversion ratio, hepatosomatic index, and liver fat content compared with feeding the 15F diet. When comparing liver proteomic data between the 15F and 15FT groups, a total of 133 differentially expressed proteins (DEPs) were identified, of which 51 were upregulated DEPs and 82 were downregulated DEPs. Among these DEPs, cholesterol 27-hydroxylase, phosphatidate phosphatase LPIN, phosphatidylinositol phospholipase C, and 6-phosphofructo-2-kinase were further screened out and were involved in primary bile acid biosynthesis, glycerolipid metabolism, the phosphatidylinositol signaling system, and the AMPK signaling pathway as key DEPs in terms of alleviating liver fat deposition of taurine in high-fat fed fish. With the association analysis of transcriptomic and proteomic data through KEGG, three differentially expressed genes (atp1a, arf1_2, and plcd) and four DEPs (CYP27α1, LPIN, PLCD, and PTK2B) were co-enriched into five pathways related to fat metabolism including primary bile acid synthesis, bile secretion, glycerolipid metabolism, phospholipid D signaling, or/and phosphatidylinositol signaling. The results showed that dietary taurine intervention could trigger activation of bile acid biosynthesis and inhibition of triglyceride biosynthesis, thereby mediating the liver fat-lowering effects in high-fat fed orange-spotted grouper. The present study contributes some novel insight into the liver fat-lowering effects of dietary taurine in high-fat fed groupers.

Pparα activation stimulates autophagic flux through lipid catabolism-independent route

Autophagy is a cellular process that involves the fusion of autophagosomes and lysosomes to degrade damaged proteins or organelles. Triglycerides are hydrolyzed by autophagy, releasing fatty acids for energy through mitochondrial fatty acid oxidation (FAO). Inhibited mitochondrial FAO induces autophagy, establishing a crosstalk between lipid catabolism and autophagy. Peroxisome proliferator-activated receptor α (PPARα), a transcription factor, stimulates lipid catabolism genes, including fatty acid transport and mitochondrial FAO, while also inducing autophagy through transcriptional regulation of transcription factor EB (TFEB). Therefore, the study explores whether PPARα regulates autophagy through TFEB transcriptional control or mitochondrial FAO. In aquaculture, addressing liver lipid accumulation in fish is crucial. Investigating the link between lipid catabolism and autophagy is significant for devising lipid-lowering strategies and maintaining fish health. The present study investigated the impact of dietary fenofibrate and L-carnitine on autophagy by activating Pparα and enhancing FAO in Nile tilapia (Oreochromis niloticus), respectively. The dietary fenofibrate and L-carnitine reduced liver lipid content and enhanced ATP production, particularly fenofibrate. FAO enhancement by L-carnitine showed no changes in autophagic protein levels and autophagic flux. Moreover, fenofibrate-activated Pparα promoted the expression and nuclear translocation of Tfeb, upregulating autophagic initiation and lysosomal biogenesis genes. Pparα activation exhibited an increasing trend of LC3II protein at the basal autophagy and cumulative p62 protein trends after autophagy inhibition in zebrafish liver cells. These data show that Pparα activation-induced autophagic flux should be independent of lipid catabolism.

Regulatory effects of Astragalus membranaceus polysaccharides on lipid metabolism disorders induced by a high-fat diet in spotted sea bass (Lateolabrax maculatus)

This study evaluated the regulatory effects of Astragalus membranaceus polysaccharides (AMP) on lipid metabolism disorders induced by a high-fat diet (HFD) in spotted sea bass (Lateolabrax maculatus). Compared with the normal diets (10 % lipids), diets containing 15 % lipid levels were used as the high-fat diet (HFD). Three levels of the AMP (0.06 %, 0.08 %, 0.10 %) were added in the HFD and used as experimental diets. A total of 375 spotted sea bass (average weight 3.00 ± 0.01 g) were divided into 15 tanks and deemed as 5 groups, with each tank containing 25 fish. Fish in each group were fed with different diets for 56 days. After feeding, the HFD induced lipid metabolism disorders in fish, as evidenced by elevated serum lipids, malonaldehyde levels, and more severe liver damage. The AMP alleviated the HFD-induced liver damage, as evidenced by the reduced severity of liver histological lesions and malonaldehyde levels. The low-density lipoprotein cholesterol was reduced, and the expression of FAS and PPAR-α were down and up-regulated, respectively. However, the AMP had a limited ability to affect the serum lipids and abdominal fat percentage. These results reveal the potential of the AMP used in aquaculture to regulate lipid metabolism disorders induced by the HFD.

Effects of Dietary Bile Acids on Growth Performance, Lipid Deposition, and Intestinal Health of Rice Field Eel (Monopterus albus) Fed with High-Lipid Diets

The purpose of this trial was to study the positive effects of bile acids (BAs) on growth performance and intestinal health of rice field eel fed with high-lipid diets (HLDs). Rice field eels (initial weight 17.00 ± 0.10 g) were divided into four groups, each group containing four repetitions and feeding with different isonitrogenous diet: control diet containing 7% lipid content, HLDs containing the lipid content increased to 13%, HLDs supplementing with 0.025% BAs and 0.05% BAs, respectively. After 8 weeks, compared control group, the fish fed HLDs had no significant effect on weight gain rate and specific growth rate (P > 0.05), but increased the lipid deposition in tissues and intestinal lipase activity, and damaged to intestinal oxidative stress, inflammatory response, physical barrier, and structural integrity (P < 0.05). Dietary BAs significantly increased weight gain rate and specific growth rate in fish fed with HL diets (P < 0.05) and reduced feed conversation rate (P < 0.05). Further, the eels fed with BAs reduced the total lipid content in liver, muscle, and whole body (P < 0.05). Dietary BAs decreased the activity of intestinal lipase (P < 0.05). Meanwhile, BAs supplemented in HLDs improved intestinal antioxidant capacity through increasing the activities of T-SOD (total superoxide dismutase), GSH-PX (glutathione peroxidase), CAT (catalase), T-AOC (total antioxidant capacity), whereas reducing MDA (malondialdehyde) content (P < 0.05). Moreover, dietary BAs regulated the mRNA expression related to inflammatory response, oxidative stress, and physical barrier in intestine, such as tnf-α, il-8, tlr-8, il-10, nrf2, keap1, claudin12, and claudin15 (P < 0.05). Dietary BAs supplementation also enhanced the intestinal structural integrity characterized by increased fold height and lamina propria width (P < 0.05). This study showed that dietary BAs supplemented in HLDs (13% lipid) could increase the growth performance of rice field eel, reduce lipid deposition in tissues and whole body, and enhance intestinal health.

High-fat-diet induced inflammation and apoptosis via activation of Ire1α in liver and hepatocytes of black seabream (Acanthopagrus schlegelii)

The present study aimed to reveal the role of inositol-requiring enzyme 1α (Ire1α) in mediating high-fat-diet (HFD) induced inflammation and apoptosis in fish and elucidate underling mechanisms of action. In experiment 1, black seabream juveniles were fed a control diet (Control, 12 % dietary lipid) or a high fat diet (HFD, 19 % dietary lipid) for eight weeks. In experiment 2, primary hepatocytes were isolated from black seabream juveniles and treated with oleic acid (OA, 200 μmol/L), OA + transfection with non-silencing control siRNA (negative control) (OA + NC), and OA + transfection with ire1α-small interfering RNA (OA + siire1α) for 48 h versus untreated (Control). Results indicated that fish fed HFD increased lipid deposition in the liver and caused hepatic steatosis. HFD group had significantly higher ire1α/Ire1α mRNA and phosphorylated protein expression and endoplasmic reticulum stress (ERS) related genes expression compared to the Control group, indicating that ERS was triggered. Meanwhile, feeding HFD induced inflammation and apoptosis by evaluated nuclear factor kappa B (nf-κb) mRNA and phosphorylated Nf-κb p65 protein expression, and c-Jun N-terminal kinase (jnk) mRNA and protein expression. However, knock down of ire1α (OA + siire1α) in primary hepatocytes alleviated OA-induced increased expression of ire1α/Ire1α mRNA and protein expression, nf-κb/Nf-κb p65 mRNA and phosphorylated protein expression, and jnk/Jnk mRNA and phosphorylated protein expression. These findings revealed the underling mechanism of action of HFD in fish, confirming that HFD increased ESR stress and Ire1α that, in turn, activated Nf-κb and Jnk pathways in hepatocytes and liver mediating HFD-induced inflammation and apoptosis.

Role of PPAR-Allopregnanolone Signaling in Behavioral and Inflammatory Gut-Brain Axis Communications

The gut microbiome regulates emotional behavior, stress responses, and inflammatory processes by communicating with the brain. How and which neurobiological mediators underlie this communication remain poorly understood. PPAR-α (peroxisome proliferator-activated receptor α), a transcription factor susceptible to epigenetic modifications, regulates pathophysiological functions, including metabolic syndrome, inflammation, and behavior. Mood disorders, inflammatory processes, and obesity are intertwined phenomena that are associated with low blood concentrations of the anti-inflammatory and "endogenous tranquilizer" neurosteroid allopregnanolone and poor PPAR-α function. Stress and consumption of obesogenic diets repress PPAR function in brain, enterocytes, lipocytes, and immune modulatory cells favoring inflammation, lipogenesis, and mood instability. Conversely, micronutrients and modulators of PPAR-α function improve microbiome composition, dampen systemic inflammation and lipogenesis, and improve anxiety and depression. In rodent stress models of anxiety and depression, PPAR activation normalizes both PPAR-α expression downregulation and decreased allopregnanolone content and ameliorates depressive-like behavior and fear responses. PPAR-α is known to regulate metabolic and inflammatory processes activated by short-chain fatty acids; endocannabinoids and congeners, such as N-palmitoylethanolamide, drugs that treat dyslipidemias; and micronutrients, including polyunsaturated fatty acids. Both PPAR-α and allopregnanolone are abundantly expressed in the colon, and they exert potent anti-inflammatory actions by blocking the toll-like receptor-4-nuclear factor-κB pathway in peripheral immune cells, neurons, and glia. The perspective that PPAR-α regulation in the colon by gut microbiota or metabolites influences central allopregnanolone content after trafficking to the brain, thereby serving as a mediator of gut-brain axis communications, is examined in this review.

Lycium barbarum polysaccharides improve lipid metabolism disorders of spotted sea bass Lateolabrax maculatus induced by high lipid diet

This experiment explored the effects of Lycium barbarum polysaccharides (LBP) on lipid metabolism of spotted sea bass Lateolabrax maculatus. Blank and experimental control diets with 100 and 150 g/kg lipid were designed, respectively, and three dosages of LBP (0.75, 1.00, 1.25 g/kg) were supplemented in the experimental control diet. A total 375 of spotted sea bass (19.33 ± 0.15) g were divided into 5 groups, and were given experimental diets for 56 days, respectively. Results showed fish were induced to lipid metabolism disorders with dietary 150 g/kg lipid intake, which manifested in reduced feeding, oxidative stress, elevated serum lipid, and more severe hepatic damage. Dietary LBP improved the lipid metabolism disorders of fish, as indicated by significant enhancements in weight gain, digestion, superoxide dismutase activity, and decreases in malonaldehyde content, and activity of alanine aminotransferase and aspartate aminotransferase. Accordingly, an improvement in the hepatic morphological and expression of lipid metabolism related genes, including FAS, PPAR-α, CPT1 and ATGL, was observed. Nevertheless, no significant variation in serum triglyceride and total cholesterol was observed. Overall, dietary LBP can improve the growth, digestion, antioxidant capacity, and liver health of spotted sea bass, thereby improving the lipid metabolism disorders induced by 150 g/kg dietary lipid intake.

Targeting PPARs for therapy of atherosclerosis: A review

Atherosclerosis, a chief pathogenic factor of cardiovascular disease, is associated with many factors including inflammation, dyslipidemia, and oxidative stress. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors and are widely expressed with tissue- and cell-specificity. They control multiple genes that are involved in lipid metabolism, inflammatory response, and redox homeostasis. Given the diverse biological functions of PPARs, they have been extensively studied since their discovery in 1990s. Although controversies exist, accumulating evidence have demonstrated that PPAR activation attenuates atherosclerosis. Recent advances are valuable for understanding the mechanisms of action of PPAR activation. This article reviews the recent findings, mainly from the year of 2018 to present, including endogenous molecules in regulation of PPARs, roles of PPARs in atherosclerosis by focusing on lipid metabolism, inflammation, and oxidative stress, and synthesized PPAR modulators. This article provides information valuable for researchers in the field of basic cardiovascular research, for pharmacologists that are interested in developing novel PPAR agonists and antagonists with lower side effects as well as for clinicians.

Effects of Genistein on Lipid Metabolism, Antioxidant Activity, and Immunity of Common Carp (Cyprinus carpio L.) Fed with High-Carbohydrate and High-Fat Diets

A 56-day feeding trial was conducted to investigate the effects of genistein on growth, lipid metabolism, antioxidant capacity, and immunity of common carp fed with high-carbohydrate or high-fat diets. Five diets were used to feed fish: control diet (5% fat; CO), high-fat diet (11% fat; HF), high-carbohydrate diet (45% carbohydrate; HC), and HF or HC diet with 500 mg/kg genistein (FG or CG). Results showed that final body weight (FW) and specific growth rate (SGR) were significantly reduced, but the supplementation with genistein resulted in higher values of FW and SGR than the HF or HC group. Both high carbohydrate and high fat belong to high-energy diets, which may promote lipid deposition. Genistein obviously decreased liver triglyceride (TG) content and alleviated hepatic fat vacuolation in the HF and HC groups. The expression of lipid metabolism genes (cpt-1 and atgl) was markedly higher in the FG group than in the HF group. The lipid synthesis-related genes (fas, acc, and pparγ) were elevated in high-energy diets but recovered to the control level or reduced after genistein treatments. With respect to fatty acid transporter genes, fatp increased in the FG group, and cd36 increased in the CG group. Furthermore, the antioxidant and immune indexes, such as total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-PX), superoxide dismutase (SOD), acid phosphatase (ACP), and lysozyme (LZM) activities, were decreased, while malonate aldehyde (MDA) content, activities of alanine aminotransferase (ALT), and aspartate aminotransferase (AST) were enhanced in the HF and HC groups. The antioxidant and immunity values could be ameliorated by treatment with genistein. Moreover, the transcript levels of antioxidant-related genes (cat, gr, and nrf2) in the liver and anti-inflammatory factors (tgf-β and il-10) and lyz in the head kidney tissue were promoted, although the expression levels of proinflammatory factors (tnf-α and il-6) declined in the genistein supplementation group, which confirmed the antioxidant and immune-enhancing effects of genistein. Therefore, 500 mg/kg genistein could ameliorate the negative effects of high-energy diets on immunity.

The Benefit of Optimal Dietary Lipid Level for Black Seabream Acanthopagrus schlegelii Juveniles under Low-Salinity Environment

The present study was aimed at evaluating the regulatory effects of dietary lipid levels on growth performance, osmoregulation, fatty acid composition, lipid metabolism, and physiological response in Acanthopagrus schlegelii under low salinity (5 psu). An 8-week feeding trial was conducted in juvenile A. schlegelii with an initial weight of 2.27 ± 0.05 g, and six isonitrogenous experimental diets were formulated with graded levels of lipid: 68.7 g/kg (D1), 111.7 g/kg (D2), 143.5 g/kg (D3), 188.9 g/kg (D4), 239.3 g/kg (D5), and 269.4 g/kg (D6), respectively. Results indicated that fish fed with diet containing 188.9 g/kg lipid significantly improved growth performance. Dietary D4 improved ion reabsorption and osmoregulation by increasing the concentrations of Na⁺, K⁺, and cortisol in serum and activities of Na⁺/K⁺-ATPase as well as expression levels of osmoregulation related to gene expression levels in the gill and intestine. The expression levels of long chain polyunsaturated fatty acid biosynthesis-related genes were dramatically upregulated when dietary lipid levels increased from 68.7 g/kg to 189.9 g/kg with levels of docosahexaenoic (DHA), eicosapentaenoic (EPA), and DHA/EPA ratio being highest in the D4 group. When fish fed dietary lipid levels from 68.7 g/kg to 188.9 g/kg, lipid homeostasis could be maintained by upregulating sirt1 and pparα expression levels, whereas lipid accumulation was observed in dietary lipid levels of 239.3 g/kg and over. Fish fed with high dietary lipid levels resulted in physiological stress related to oxidative stress and endoplasmic reticulum stress. In conclusion, based on weight gain, the optimal dietary lipid requirement of juvenile A. schlegelii reared at low-salinity water is 196.0 g/kg. These findings indicate that the optimal dietary lipid level can improve growth performance, n-3 LC-PUFA accumulation, and osmoregulatory ability and maintain lipid homeostasis and normal physiological functions of juvenile A. schlegelii.

Hydroxytyrosol-rich extract from olive juice as an additive in gilthead sea bream juveniles fed a high-fat diet: Regulation of somatic growth

The dietary inclusion of plant-based products in fish feeds formulation is required for the sustainable development of aquaculture. Moreover, considering functional diets, hydroxytyrosol, one of the major phenolic compounds found in olives (Olea europaea), has been identified as a potential candidate to be used in the aquafeeds industry due to its health promoting abilities. The aim of this study was to evaluate the effects of the inclusion of an olive juice extract rich in hydroxytyrosol as an additive (0.52 g HT/kg feed) in a high-fat (24% lipids) diet in gilthead sea bream (Sparus aurata) juveniles. Moreover, the experimental diets, with or without the extract, were administered daily at a standard (3% of total biomass in the tank) or restricted ration (40% reduction) for 8–9 weeks. Growth and biometric parameters, insulin-like growth factor 1 (IGF-1) plasma levels and growth hormone/IGF axis-, myogenic- and osteogenic-related genes expression in liver, white muscle and/or bone were analyzed. Moreover, in vitro cultures of vertebra bone-derived cells from fish fed the diets at a standard ration were performed at weeks 3 and 9 to explore the effects of hydroxytyrosol on osteoblasts development. Although neither body weight or any other biometric parameter were affected by diet composition after 4 or 8 weeks, the addition of the hydroxytyrosol-rich extract to the diet increased IGF-1 plasma levels, regardless of the ration regime, suggesting an anabolic condition. In muscle, the higher mRNA levels of the binding protein igfbp-5b and the myoblast fusion marker dock5 in fish fed with the hydroxytyrosol-rich diet suggested that this compound may have a role in muscle, inducing development and a better muscular condition. Furthermore in bone, increased osteogenic potential while delayed matrix mineralization after addition to the diet of the olive juice extract was supported by the upregulated expression of igf-1 and bmp4 and reduced transcript levels of osteopontin. Overall, this study provides new insights into the beneficial use of hydroxytyrosol as a dietary additive in gilthead sea bream functional diets to improve muscle-skeletal condition and, the aquaculture industry.

Lipid metabolic disorders and physiological stress caused by a high-fat diet have lipid source-dependent effects in juvenile black seabream Acanthopagrus schlegelii

This study was conducted to evaluate the effects of different dietary lipid sources on growth performance, lipid metabolism, and physiological stress responses including oxidative stress (OS) and endoplasmic reticulum stress (ERS) of juvenile Acanthopagrus schlegelii (initial weight 0.88 ± 0.01 g) fed a high-fat diet (HFD). Four isonitrogenous and isolipidic experimental diets containing different lipid sources were formulated: fish oil (FO), palm oil (PO), linseed oil (LO), and soybean oil (SO), respectively. Results indicated that fish fed HFD supplemented with FO significantly improved growth than SO treatment. The high concentrations of aspartate aminotransferase and alanine transaminase were found in HFD supplemented with SO. Fish fed dietary LO supplementation showed significantly lower serum cholesterol, triglyceride, low-density lipoprotein, and high-density lipoprotein contents than those in SO group. Likewise, hepatic paraffin section analysis indicated that HFD with PO or SO supplementation increased fat drop. The expression levels of peroxisome proliferators-activated receptor alpha (pparα) and silent regulator 1 (sirt1) were significantly elevated by HFD with FO or LO supplementation. Additionally, the key marker of OS malonaldehyde was significantly increased in FO and SO groups. ERS-related genes were activated in dietary PO or SO supplementation and, hence, triggering inflammation and apoptosis by promoting the expression levels of nuclear factor kappa B (nf-κb) and c-Jun N-terminal kinase (jnk). Overall, the present study reveals that lipid metabolic disorders and physiological stress caused by a HFD have significant lipid source-dependent effects, which have important guiding significance for the use of HFD in marine fish.

Hepatic Transcriptome Analysis Provides New Insight into the Lipid-Reducing Effect of Dietary Taurine in High–Fat Fed Groupers (Epinephelus coioides)

A transcriptome analysis was conducted to provide the first detailed overview of dietary taurine intervention on liver lipid accumulation caused by high–fat in groupers. After an eight-week feeding, the fish fed 15% fat diet (High–fat diet) had higher liver lipid contents vs. fish fed 10% fat diet (Control diet). 15% fat diet with 1% taurine (Taurine diet) improved weight gain and feed utilization, and decreased hepatosomatic index and liver lipid contents vs. the High–fat diet. In the comparison of the Control vs. High–fat groups, a total of 160 differentially expressed genes (DEGs) were identified, of which up- and down-regulated genes were 72 and 88, respectively. There were 49 identified DEGs with 26 and 23 of up- and down-regulated in the comparison to High–fat vs. Taurine. Several key genes, such as cysteine dioxygenase (CDO1), ADP–ribosylation factor 1/2 (ARF1_2), sodium/potassium–transporting ATPase subunit alpha (ATP1A), carnitine/acylcarnitine translocase (CACT), and calcium/calmodulin–dependent protein kinase II (CAMK) were obtained by enrichment for the above DEGs. These genes were enriched in taurine and hypotaurine metabolism, bile secretion, insulin secretion, phospholipase D signaling pathway, and thermogenesis pathways, respectively. The present study will also provide a new insight into the nutritional physiological function of taurine in farmed fish.

A New Insight Into the Underlying Adaptive Strategies of Euryhaline Marine Fish to Low Salinity Environment Through Cholesterol Nutrition to Regulate Physiological Responses

Salinity is an important environmental factor that can affect the metabolism of aquatic organisms, while cholesterol can influence cellular membrane fluidity which are vital in adaption to salinity changes. Hence, a 4-week feeding trial was conducted to evaluate the effects of water salinity (normal 23 psu and low 5 psu) and three dietary cholesterol levels (CH0.16, 0.16%, CH1.0, 1.0% and CH1.6, 1.6%) on osmoregulation, cholesterol metabolism, fatty acid composition, long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis, oxidative stress (OS), and endoplasmic reticulum stress (ERS) of the euryhaline fish black seabream (Acanthopagrus schlegelii). The results indicated that in low salinity, fish fed with the CH1.0 diet improved ion reabsorption and osmoregulation by increased Na+ concentration in serum as well as expression levels of osmoregulation-related gene expression levels in gills. Both dietary cholesterol level and water salinity significantly affected most cholesterol metabolic parameters in the serum and tissues, and the results showed that low salinity promoted cholesterol synthesis but inhibited cholesterol catabolism. Besides, in low salinity, hepatic expression levels of LC-PUFA biosynthesis genes were upregulated by fed dietary cholesterol supplementation with contents of LC-PUFAs, including EPA and DHA being increased. Malondialdehyde (MDA) was significantly increased in low-salinity environment, whereas MDA content was decreased in fish fed with dietary CH1.0 by activating related antioxidant enzyme activity and gene expression levels. A similar pattern was recorded for ERS, which stimulated the expression of nuclear factor kappa B (nf-κb), triggering inflammation. Nevertheless, fish reared in low salinity and fed with dietary CH1.0 had markedly alleviated ERS and downregulated gene expression levels of pro-inflammatory cytokines. Overall, these findings demonstrate that cholesterol, as an important nutrient, plays vital roles in the process of adaptation to low salinity of A. schlegelii, and provides a new insight into underlying adaptive strategies of euryhaline marine fish reared in low salinity.

Target Deconvolution of Fenofibrate in Nonalcoholic Fatty Liver Disease Using Bioinformatics Analysis

Background

Nonalcoholic fatty liver disease (NAFLD) is a prevalent form of liver damage, affecting ~25% of the global population. NAFLD comprises a spectrum of liver pathologies, from hepatic steatosis to nonalcoholic steatohepatitis (NASH), and may progress to liver fibrosis and cirrhosis. The presence of NAFLD correlates with metabolic disorders such as hyperlipidemia, obesity, blood hypertension, cardiovascular, and insulin resistance. Fenofibrate is an agonist drug for peroxisome proliferator-activated receptor alpha (PPARα), used principally for treatment of hyperlipidemia. However, fenofibrate has recently been investigated in clinical trials for treatment of other metabolic disorders such as diabetes, cardiovascular disease, and NAFLD. The evidence to date indicates that fenofibrate could improve NAFLD. While PPARα is considered to be the main target of fenofibrate, fenofibrate may exert its effect through impact on other genes and pathways thereby alleviating, and possibly reversing, NAFLD. In this study, using bioinformatics tools and gene-drug, gene-diseases databases, we sought to explore possible targets, interactions, and pathways involved in fenofibrate and NAFLD.

Methods

We first determined significant protein interactions with fenofibrate in the STITCH database with high confidence (0.7). Next, we investigated the identified proteins on curated targets in two databases, including the DisGeNET and DISEASES databases, to determine their association with NAFLD. We finally constructed a Venn diagram for these two collections (curated genes-NAFLD and fenofibrate-STITCH) to uncover possible primary targets of fenofibrate. Then, Gene Ontology (GO) and KEGG were analyzed to detect the significantly involved targets in molecular function, biological process, cellular component, and biological pathways. A P value < 0.01 was considered the cut-off criterion. We also estimated the specificity of targets with NAFLD by investigating them in disease-gene associations (STRING) and EnrichR (DisGeNET). Finally, we verified our findings in the scientific literature.

Results

We constructed two collections, one with 80 protein-drug interactions and the other with 95 genes associated with NAFLD. Using the Venn diagram, we identified 11 significant targets including LEP, SIRT1, ADIPOQ, PPARA, SREBF1, LDLR, GSTP1, VLDLR, SCARB1, MMP1, and APOC3 and then evaluated their biological pathways. Based on Gene Ontology, most of the targets are involved in lipid metabolism, and KEGG enrichment pathways showed the PPAR signaling pathway, AMPK signaling pathway, and NAFLD as the most significant pathways. The interrogation of those targets on authentic disease databases showed they were more specific to both steatosis and steatohepatitis liver injury than to any other diseases in these databases. Finally, we identified three significant genes, APOC3, PPARA, and SREBF1, that showed robust drug interaction with fenofibrate.

Conclusion

Fenofibrate may exert its effect directly or indirectly, via modulation of several key targets and pathways, in the treatment of NAFLD.

Hepatic Glucose Metabolism and Its Disorders in Fish

Carbohydrate, which is the most abundant nutrient in plant-sourced feedstuffs, is an economically indispensable component in commercial compound feeds for fish. This nutrient can enhance the physical quality of diets and allow for pellet expansion during extrusion. There is compelling evidence that an excess dietary intake of starch causes hepatic disorders, thereby further reducing the overall food consumption and growth performance of fish species. Among the severe metabolic disturbances are glycogenic hepatopathy (hepatomegaly caused by the excessive accumulation of glycogen in hepatocytes) and hepatic steatosis (the accumulation of large vacuoles of triacylglycerols in hepatocytes). The development of those disorders is mainly due to the limited ability of fish to oxidize glucose and control blood glucose concentration. The prolonged elevations of blood glucose increase glucose intake by the liver, and excess glucose is stored either as glycogen through glycogenesis in hepatocytes or as triglycerides via lipogenesis in tissues, depending on the species. In some fish species (e.g., largemouth bass), the liver has a low ability to regulate glycolysis, gluconeogenesis, and glycogen breakdown in response to high starch intake. For most species of fish, the liver size increases with lipid or glycogen accumulation when they have a high starch intake. It is a challenge to develop the same set of diagnostic criteria for all fish species as their physiology or metabolic patterns differ. Although glycogenic hepatopathy appears to be a common disease in carnivorous fish, it has been under-recognized in many studies. As a result, understanding these diseases and their pathogeneses in different fish species is crucial for manufacturing cost-effective pellet diets to promote the health, growth, survival, and feed efficiency of fish in future.