Dietary iron affects lipid deposition, nutritional element, and muscle quality in coho salmon (Oncorhynchus kisutch).

We investigated effect of dietary iron (Fe) on the lipid deposition, nutritional element, and muscle quality in coho salmon. Four level Fe diets at 23.7, 46.4, 77.3, and 127.7 mg/kg were fed to the post-larval coho salmon for 12 weeks. Our results showed that dietary Fe decreased the content of triglyceride and the activity of fatty acid synthetase, ATP-citrate lyase, and acetyl-CoA carboxylase. The content of Fe in muscle was increased with increasing dietary Fe levels, and dietary Fe affected the content of nutritional elements. In addition, dietary Fe levels affected the composition of fatty acids and the content of free amino acids, and increased muscle fiber size. The lower dietary Fe levels also affected the hardness, chewiness, resilience, springiness, cohesiveness, and gumminess of salmon muscle. In all, dietary Fe inhibited the lipid deposition and affected the content of nutritional element and muscle quality in coho salmon.

A novel phenolic formulation for treating hepatic and peripheral insulin resistance by regulating GLUT4-mediated glucose uptake.

Chronic insulin resistance suppresses muscle and liver response to insulin, which is partially due to impaired vesicle trafficking. We report here that a formula consisting of resveratrol, ferulic acid and epigallocatechin-3-O-gallate is more effective in ameliorating muscle and hepatic insulin resistance than the anti-diabetic drugs, metformin and AICAR. The formula enhanced glucose transporter-4 (GLUT4) translocation to the plasma membrane in the insulin-resistant muscle cells by regulating both insulin-independent (calcium and AMPK) and insulin-dependent (PI3K) signaling molecules. Particularly, it regulated the subcellular location of GLUT4 through endosomes to increase glucose uptake under insulin-resistant condition. Meanwhile, this phytochemicals combination increased glycogen synthesis and decreased glucose production in the insulin-resistant liver cells. On the other hand, this formula also showed anti-diabetic potential by the reduction of lipid content in the myotubes, hepatocytes, and adipocytes. This study demonstrated that the three phenolic compounds in the formula could work in distinct mechanisms and enhance both insulin-dependent and independent vesicles trafficking and glucose transport mechanisms to improve carbohydrate and lipid metabolism.

Lipid alterations in chronic liver disease and liver cancer.

Lipids are a complex and diverse group of molecules with crucial roles in many physiological processes, as well as in the onset, progression, and maintenance of cancers. Fatty acids and cholesterol are the building blocks of lipids, orchestrating these crucial metabolic processes. In the liver, lipid alterations are prevalent as a cause and consequence of chronic hepatitis B and C virus infections, alcoholic hepatitis, and non-alcoholic fatty liver disease and steatohepatitis. Recent developments in lipidomics have also revealed that dynamic changes in triacylglycerols, phospholipids, sphingolipids, ceramides, fatty acids, and cholesterol are involved in the development and progression of primary liver cancer. Accordingly, the transcriptional landscape of lipid metabolism suggests a carcinogenic role of increasing fatty acids and sterol synthesis. However, limited mechanistic insights into the complex nature of the hepatic lipidome have so far hindered the development of effective therapies.

Metabolic dysregulation and emerging therapeutical targets for hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is an aggressive human cancer with increasing incidence worldwide. Multiple efforts have been made to explore pharmaceutical therapies to treat HCC, such as targeted tyrosine kinase inhibitors, immune based therapies and combination of chemotherapy. However, limitations exist in current strategies including chemoresistance for instance. Tumor initiation and progression is driven by reprogramming of metabolism, in particular during HCC development. Recently, metabolic associated fatty liver disease (MAFLD), a reappraisal of new nomenclature for non-alcoholic fatty liver disease (NAFLD), indicates growing appreciation of metabolism in the pathogenesis of liver disease, including HCC, thereby suggesting new strategies by targeting abnormal metabolism for HCC treatment. In this review, we introduce directions by highlighting the metabolic targets in glucose, fatty acid, amino acid and glutamine metabolism, which are suitable for HCC pharmaceutical intervention. We also summarize and discuss current pharmaceutical agents and studies targeting deregulated metabolism during HCC treatment. Furthermore, opportunities and challenges in the discovery and development of HCC therapy targeting metabolism are discussed.

Metabolic dysregulation and emerging therapeutical targets for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an aggressive human cancer with increasing incidence worldwide. Multiple efforts have been made to explore pharmaceutical therapies to treat HCC, such as targeted tyrosine kinase inhibitors, immune based therapies and combination of chemotherapy. However, limitations exist in current strategies including chemoresistance for instance. Tumor initiation and progression is driven by reprogramming of metabolism, in particular during HCC development. Recently, metabolic associated fatty liver disease (MAFLD), a reappraisal of new nomenclature for non-alcoholic fatty liver disease (NAFLD), indicates growing appreciation of metabolism in the pathogenesis of liver disease, including HCC, thereby suggesting new strategies by targeting abnormal metabolism for HCC treatment. In this review, we introduce directions by highlighting the metabolic targets in glucose, fatty acid, amino acid and glutamine metabolism, which are suitable for HCC pharmaceutical intervention. We also summarize and discuss current pharmaceutical agents and studies targeting deregulated metabolism during HCC treatment. Furthermore, opportunities and challenges in the discovery and development of HCC therapy targeting metabolism are discussed.

New targets for NAFLD.

Non-alcoholic fatty liver disease (NAFLD) is a growing cause of chronic liver disease worldwide. It is characterised by steatosis, liver inflammation, hepatocellular injury and progressive fibrosis. Several preclinical models (dietary and genetic animal models) of NAFLD have deepened our understanding of its aetiology and pathophysiology. Despite the progress made, there are currently no effective treatments for NAFLD. In this review, we will provide an update on the known molecular pathways involved in the pathophysiology of NAFLD and on ongoing studies of new therapeutic targets.

The presence of 3-hydroxypropionate and 1,3-propanediol suggests an alternative path for conversion of glycerol to Acetyl-CoA.

BACKGROUND: In our recent study using [U-13C3]glycerol, a small subset of hamsters showed an unusual profile of glycerol metabolism: negligible gluconeogenesis from glycerol plus conversion of glycerol to 1,3-propanediol (1,3PDO) and 3-hydroxypropionate (3HP) which were detected in the liver and blood. The purpose of the current study is to evaluate the association of these unusual glycerol products with other biochemical processes in the liver. METHODS: Fasted hamsters received acetaminophen (400 mg/kg; n = 16) or saline (n = 10) intraperitoneally. After waiting 2 h, all the animals received [U-13C3]glycerol intraperitoneally. Liver and blood were harvested 1 h after the glycerol injection for NMR analysis and gene expression assays. RESULTS: 1,3PDO and 3HP derived from [U-13C3]glycerol were detected in the liver and plasma of eight hamsters (two controls and six hamsters with acetaminophen treatment). Glycerol metabolism in the liver of these animals differed substantially from conventional metabolic pathways. [U-13C3]glycerol was metabolized to acetyl-CoA as evidenced with downstream products detected in glutamate and ß-hydroxybutyrate, yet 13C labeling in pyruvate and glucose was minimal (p < 0.001, 13C labeling difference in each metabolite). Expression of aldehyde dehydrogenases was enhanced in hamster livers with 1,3PDO and 3HP (p < 0.05). CONCLUSION: Detection of 1,3PDO and 3HP in the hamster liver was associated with unorthodox metabolism of glycerol characterized by conversion of 3HP to acetyl-CoA followed by ketogenesis and oxidative metabolism through the TCA cycle. Additional mechanistic studies are needed to determine the causes of unusual glycerol metabolism in a subset of these hamsters.

Hyperoside attenuates non-alcoholic fatty liver disease in rats via cholesterol metabolism and bile acid metabolism.

Introduction: Non-alcoholic fatty liver disease (NAFLD) results from increased hepatic total cholesterol (TC) and total triglyceride (TG) accumulation. In our previous study, we found that rats treated with hyperoside became resistant to hepatic lipid accumulation. Objectives: The present study aims to investigate the possible mechanisms responsible for the inhibitory effects of hyperoside on the lipid accumulation in the liver tissues of the NAFLD rats. Methods: Label-free proteomics and metabolomics targeting at bile acid (BA) metabolism were applied to disclose the mechanisms for hyperoside reducing hepatic lipid accumulation among the NAFLD rats. Results: In response to hyperoside treatment, several proteins related to the fatty acid degradation pathway, cholesterol metabolism pathway, and bile secretion pathway were altered, including ECI1, Acnat2, ApoE, and BSEP, etc. The expression of nuclear receptors (NRs), including farnesoid X receptor (FXR) and liver X receptor α (LXRα), were increased in hyperoside-treated rats' liver tissue, accompanied by decreased protein expression of catalyzing enzymes in the hepatic de novo lipogenesis and increased protein level of enzymes in the classical and alternative BA synthetic pathway. Liver conjugated BAs were less toxic and more hydrophilic than unconjugated BAs. The BA-targeted metabolomics suggest that hyperoside could decrease the levels of liver unconjugated BAs and increase the levels of liver conjugated BAs. Conclusions: Taken together, the results suggest that hyperoside could improve the condition of NAFLD by regulating the cholesterol metabolism as well as BAs metabolism and excretion. These findings contribute to understanding the mechanisms by which hyperoside lowers the cholesterol and triglyceride in NAFLD rats.

Combined alcoholic and non-alcoholic steatohepatitis.

While metabolic syndrome and alcohol consumption are the two main causes of chronic liver disease, one of the two conditions is often predominant, with the other acting as a cofactor of morbimortality. It has been shown that obesity and alcohol act synergistically to increase the risk of fibrosis progression, hepatic carcinogenesis and mortality, while genetic polymorphisms can strongly influence disease progression. Based on common pathogenic pathways, there are several potential targets that could be used to treat both diseases; based on the prevalence and incidence of these diseases, new therapies and clinical trials are needed urgently.

Platelet Acetyl-CoA Carboxylase Phosphorylation: A Risk Stratification Marker That Reveals Platelet-Lipid Interplay in Coronary Artery Disease Patients.

Adenosine monophosphate-activated protein kinase (AMPK) acetyl-CoA carboxylase (ACC) signaling is activated in platelets by atherogenic lipids, particularly by oxidized low-density lipoproteins, through a CD36-dependent pathway. More interestingly, increased platelet AMPK-induced ACC phosphorylation is associated with the severity of coronary artery calcification as well as acute coronary events in coronary artery disease patients. Therefore, AMPK-induced ACC phosphorylation is a potential marker for risk stratification in suspected coronary artery disease patients. The inhibition of ACC resulting from its phosphorylation impacts platelet lipid content by down-regulating triglycerides, which in turn may affect platelet function.

Matrine attenuates oxidative stress and cardiomyocyte apoptosis in doxorubicin-induced cardiotoxicity via maintaining AMPKα/UCP2 pathway.

Oxidative stress and cardiomyocyte apoptosis are involved in the pathogenesis of doxorubicin (DOX)-induced cardiotoxicity. Matrine is well-known for its powerful anti-oxidant and anti-apoptotic capacities. Our present study aimed to investigate the effect of matrine on DOX-induced cardiotoxicity and try to unearth the underlying mechanisms. Mice were exposed with DOX to generate DOX-induced cardiotoxicity or normal saline as control. H9C2 cells were used to verify the effect of matrine in vitro. DOX injection triggered increased generation of reactive oxygen species (ROS) and excessive cardiomyocyte apoptosis, which were significantly mitigated by matrine. Mechanistically, we found that matrine ameliorated DOX-induced uncoupling protein 2 (UCP2) downregulation, and UCP2 inhibition by genipin could blunt the protective effect of matrine on DOX-induced oxidative stress and cardiomyocyte apoptosis. Besides, 5'-AMP-activated protein kinase α2 (Ampkα2) deficiency inhibited matrine-mediated UCP2 preservation and abolished the beneficial effect of matrine in mice. Besides, we observed that matrine incubation alleviated DOX-induced H9C2 cells apoptosis and oxidative stress level via activating AMPKα/UCP2, which were blunted by either AMPKα or UCP2 inhibition with genetic or pharmacological methods. Matrine attenuated oxidative stress and cardiomyocyte apoptosis in DOX-induced cardiotoxicity via maintaining AMPKα/UCP2 pathway, and it might be a promising therapeutic agent for the treatment of DOX-induced cardiotoxicity.

Matrine attenuates oxidative stress and cardiomyocyte apoptosis in doxorubicin-induced cardiotoxicity maintaining AMPK/UCP2 pathway

Oxidative stress and cardiomyocyte apoptosis are involved in the pathogenesis of doxorubicin (DOX)-induced cardiotoxicity. Matrine is well-known for its powerful anti-oxidant and anti-apoptotic capacities. Our present study aimed to investigate the effect of matrine on DOX-induced cardiotoxicity and try to unearth the underlying mechanisms. Mice were exposed with DOX to generate DOX-induced cardiotoxicity or normal saline as control. H9C2 cells were used to verify the effect of matrine . DOX injection triggered increased generation of reactive oxygen species (ROS) and excessive cardiomyocyte apoptosis, which were significantly mitigated by matrine. Mechanistically, we found that matrine ameliorated DOX-induced uncoupling protein 2 (UCP2) downregulation, and UCP2 inhibition by genipin could blunt the protective effect of matrine on DOX-induced oxidative stress and cardiomyocyte apoptosis. Besides, 5'-AMP-activated protein kinase 2 () deficiency inhibited matrine-mediated UCP2 preservation and abolished the beneficial effect of matrine in mice. Besides, we observed that matrine incubation alleviated DOX-induced H9C2 cells apoptosis and oxidative stress level activating AMPK/UCP2, which were blunted by either AMPK or UCP2 inhibition with genetic or pharmacological methods. Matrine attenuated oxidative stress and cardiomyocyte apoptosis in DOX-induced cardiotoxicity maintaining AMPK/UCP2 pathway, and it might be a promising therapeutic agent for the treatment of DOX-induced cardiotoxicity.

Cissus quadrangularis extract (CQR-300) inhibits lipid accumulation by downregulating adipogenesis and lipogenesis in 3T3-L1 cells.

The objective of this study was to evaluate the anti-obesity activity and the action mechanism of Cissus quadrangularis extracts (CQR-300) in 3T3-L1 adipocytes. Cissus quadrangularis was extracted with hot water, resulting in CQR-300. The anti-obesity activity of CQR-300 in 3T3-L1 adipocytes was examined by Oil-red O staining. Possible mechanisms of CQR-300 in 3T3-L1 adipocytes were determined by real-time PCR and western blot. Treatment with CQR-300 inhibited lipid accumulation without showing cytotoxicity to 3T3-L1 adipocytes. Furthermore, CQR-300 decreased adipogenesis/lipogenesis-related mRNA expression levels of fatty acid binding protein (aP2), fatty acid synthase (FAS), lipoprotein lipase (LPL), stearoyl-CoA desaturase-1 (SCD-1), and acetyl-CoA carboxylase (ACC). CQR-300 also down-regulated expression levels of adipogenesis/lipogenesis-associated proteins, including peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding protein α (C/EBPα), sterol regulatory element binding protein-1c (SREBP-1c), and FAS. It's also up-regulated the expression level of phosphorylated-AMPK (p-AMPK). Collectively, these results suggested that CQR-300 might have an anti-obesity effect by its ability to decrease expression levels of adipogenesis/lipogenesis-related genes and proteins.

Acetyl-CoA carboxylase from Escherichia coli exhibits a pronounced hysteresis when inhibited by palmitoyl-acyl carrier protein.

Acetyl-CoA carboxylase (ACC) in bacteria is composed of three components: biotin carboxylase, biotin carboxyl carrier protein, and carboxyltransferase. ACC catalyzes the first committed step in fatty acid synthesis: the carboxylation of acetyl-CoA to form malonyl-CoA via a two-step reaction. In the first half-reaction, biotin carboxylase catalyzes the ATP-dependent carboxylation of the vitamin biotin covalently linked to biotin carboxyl carrier protein. In the second half-reaction, the carboxyl group is transferred from biotin to acetyl-CoA by the enzyme carboxyltransferase, to form malonyl-CoA. In most Gram-negative and Gram-positive bacteria, the three components of ACC form a complex that requires communication for catalysis, and is subject to feedback inhibition by acylated-acyl carrier proteins. This study investigated the mechanism of inhibition of palmitoyl-acyl carrier protein (PACP) on ACC. Unexpectedly, ACC was found to exhibit a significant hysteresis, meaning ACC was subject to inhibition by PACP in a time dependent manner. Pull-down assays demonstrated PACP does not prevent formation of the multiprotein complex, while steady-state kinetic analyses showed PACP inhibited ACC activity allosterically. Structure-activity analyses revealed that the pantothenic acid moiety of PACP is responsible for the inhibition of ACC. This study provides the first evidence of the hysteretic nature of ACC.

Maternal conjugated linoleic acid modulates TAG metabolism in adult rat offspring.

Conjugated linoleic acid (CLA) might regulate the lipid depots in liver and adipose tissue. As there is an association between maternal nutrition, fat depots and risk of offspring chronic disease, the aim was to investigate the effect of maternal CLA consumption on TAG regulation and some inflammatory parameters in adult male rat offspring receiving or not receiving CLA. Female Wistar rats were fed control (C) or CLA-supplemented (1 %, w/w) diets during 4 weeks before and throughout pregnancy and lactation. After weaning, male offspring of CLA rats were fed C or CLA diets (CLA/C and CLA/CLA groups, respectively), whereas C male rat offspring were fed a C diet (C/C group) for 9 weeks. Serum TAG levels were increased in the CLA/CLA and CLA/C groups, associated with a reduction of lipoprotein lipase activity and weights of adipose tissue. The liver TAG levels were decreased in the CLA/CLA group, related to a significant reduction of fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC) and glucose-6-phosphate dehydrogenase enzyme activities, as well as to the mRNA levels of FAS, ACC, stearoyl-CoA desaturase-1 and sterol regulatory element-binding protein-1c. Even though normal TAG levels were found in the liver of CLA/C rats, a reduction of lipogenesis was also observed. Thus, these results demonstrated a programming effect of CLA on the lipid metabolic pathways leading to a preventive effect on the TAG accretion in adipose tissue and the liver of male rat offspring. This knowledge could be important to develop some dietary strategies leading to a reduced incidence of obesity and fatty acid liver disease in humans.

Perinatal maternal high-fat diet induces early obesity and sex-specific alterations of the endocannabinoid system in white and brown adipose tissue of weanling rat offspring.

Perinatal maternal high-fat (HF) diet programmes offspring obesity. Obesity is associated with overactivation of the endocannabinoid system (ECS) in adult subjects, but the role of the ECS in the developmental origins of obesity is mostly unknown. The ECS consists of endocannabinoids, cannabinoid receptors (cannabinoid type-1 receptor (CB1) and cannabinoid type-2 receptor (CB2)) and metabolising enzymes. We hypothesised that perinatal maternal HF diet would alter the ECS in a sex-dependent manner in white and brown adipose tissue of rat offspring at weaning in parallel to obesity development. Female rats received standard diet (9 % energy content from fat) or HF diet (29 % energy content from fat) before mating, during pregnancy and lactation. At weaning, male and female offspring were killed for tissue harvest. Maternal HF diet induced early obesity, white adipocyte hypertrophy and increased lipid accumulation in brown adipose tissue associated with sex-specific changes of the ECS's components in weanling rats. In male pups, maternal HF diet decreased CB1 and CB2 protein in subcutaneous adipose tissue. In female pups, maternal HF diet increased visceral and decreased subcutaneous CB1. In brown adipose tissue, maternal HF diet increased CB1 regardless of pup sex. In addition, maternal HF diet differentially changed oestrogen receptor across the adipose depots in male and female pups. The ECS and oestrogen signalling play an important role in lipogenesis, adipogenesis and thermogenesis, and we observed early changes in their targets in adipose depots of the offspring. The present findings provide insights into the involvement of the ECS in the developmental origins of metabolic disease induced by inadequate maternal nutrition in early life.

Maternal resveratrol intake during lactation attenuates hepatic triglyceride and fatty acid synthesis in adult male rat offspring.

Resveratrol (3,5,4-trihydroxystilbene) is a natural polyphenolic compound found in grapes and red wine and has been shown to exert protective effects on the liver preventing lipid accumulation induced by a high-fat diet. However, no studies have shown that the nutritional resveratrol intake by the parental generation has modified lipogenesis in an adult offspring. The aim of this study was to investigate whether maternal resveratrol intake during lactation affects lipogenesis in adult male rat offspring, and if it does, what is the molecular mechanistic basis. Six male pups born from mothers given a control diets during lactation (CC group) and six male pups born from mothers given a control diet as well as resveratrol during lactation (CR group) were fed a standard diet until sacrifice at 36 weeks. Adult male offspring from mothers given resveratrol during lactation (CR group) had lower body weight from the fourth week of lactation until adulthood, but no significant change was observed in the relative food intake. Low levels of plasma triacylglycerol were found in the CR group compared to the CC group. Histopathological analysis of the livers of adult male rat offspring revealed lipid accumulation in hepatocytes in the CC group, whereas lipid droplets were rare in the CR group. Hepatic protein levels of AMPK-phosphorylated at ser403, Sirt1, and Nampt in the CR group were upregulated significantly compared to the CC group. These results indicated the maternal resveratrol intake during lactation-induced activation of AMPK through Sirt1 upregulation. In this study, significant upregulation of the levels of precursor of sterol regulatory element binding protein-1c (SREBP-1c) and downregulation of the ratio of active-SREBP-1c/precusor-SREBP-1c were observed in the CR group compared to the CC group. These results suggested that proteolytic processing of SREBP-1c was suppressed by AMPK in the livers of the CR group. It is well known that SREBP-1c regulates the lipogenic pathway by activating genes involved in triglyceride and fatty acid synthesis. The present study showed significant downregulation of hepatic fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC) levels in the CR group. These results indicated that maternal resveratrol intake during lactation suppressed SREBP-1c cleavage and nuclear translocation and repressed SREBP-1c target gene expression such as FAS and ACC in the livers of adult male offspring. These changes attenuate hepatic triacylglycerol and fatty acid synthesis in adult male offspring.

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

The present study explored the mechanisms of dietary Zn influencing Zn and lipid deposition in the fore- and mid- intestine in yellow catfish Pelteobagrus 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, PPARγ and 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 PPARα in 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, PPARγ and 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.

FGF21 does not require adipocyte AMP-activated protein kinase (AMPK) or the phosphorylation of acetyl-CoA carboxylase (ACC) to mediate improvements in whole-body glucose homeostasis.

OBJECTIVE: Fibroblast growth factor 21 (FGF21) shows great potential for the treatment of obesity and type 2 diabetes, as its long-acting analogue reduces body weight and improves lipid profiles of participants in clinical studies; however, the intracellular mechanisms mediating these effects are poorly understood. AMP-activated protein kinase (AMPK) is an important energy sensor of the cell and a molecular target for anti-diabetic medications. This work examined the role of AMPK in mediating the glucose and lipid-lowering effects of FGF21. METHODS: Inducible adipocyte AMPK ß1ß2 knockout mice (iß1ß2AKO) and littermate controls were fed a high fat diet (HFD) and treated with native FGF21 or saline for two weeks. Additionally, HFD-fed mice with knock-in mutations on the AMPK phosphorylation sites of acetyl-CoA carboxylase (ACC)1 and ACC2 (DKI mice) along with wild-type (WT) controls received long-acting FGF21 for two weeks. RESULTS: Consistent with previous studies, FGF21 treatment significantly reduced body weight, adiposity, and liver lipids in HFD fed mice. To add, FGF21 improved circulating lipids, glycemic control, and insulin sensitivity. These effects were independent of adipocyte AMPK and were not associated with changes in browning of white (WAT) and brown adipose tissue (BAT). Lastly, we assessed whether FGF21 exerted its effects through the AMPK/ACC axis, which is critical in the therapeutic benefits of the anti-diabetic medication metformin. ACC DKI mice had improved glucose and insulin tolerance and a reduction in body weight, body fat and hepatic steatosis similar to WT mice in response to FGF21 administration. CONCLUSIONS: These data illustrate that the metabolic improvements upon FGF21 administration are independent of adipocyte AMPK, and do not require the inhibitory action of AMPK on ACC. This is in contrast to the anti-diabetic medication metformin and suggests that the treatment of obesity and diabetes with the combination of FGF21 and AMPK activators merits consideration.

Knockdown of ATP citrate lyase in pancreatic beta cells does not inhibit insulin secretion or glucose flux and implicates the acetoacetate pathway in insulin secretion.

OBJECTIVE: Glucose-stimulated insulin secretion in pancreatic beta cells requires metabolic signals including the generation of glucose-derived short chain acyl-CoAs in the cytosol from mitochondrially-derived metabolites. One concept of insulin secretion is that ATP citrate lyase generates short chain acyl-CoAs in the cytosol from mitochondrially-derived citrate. Of these, malonyl-CoA, is believed to be an important signal in insulin secretion. Malonyl-CoA is also a precursor for lipids. Our recent evidence suggested that, in the mitochondria of beta cells, glucose-derived pyruvate can be metabolized to acetoacetate that is exported to the cytosol and metabolized to the same short chain acyl-CoAs and fatty acids that can be derived from citrate. We tested for redundancy of the citrate pathway. METHODS: We inhibited ATP citrate lyase activity using hydroxycitrate as well as studying a stable cell line generated with shRNA knockdown of ATP citrate lyase in the pancreatic beta cell line INS-1 832/13. RESULTS: In both instances glucose-stimulated insulin release was not inhibited. Mass spectrometry analysis showed that the flux of carbon from [U-(13)C]glucose and/or [U-(13)C]α-ketoisocaproic acid (KIC) into short chain acyl-CoAs in cells with hydroxycitrate-inhibited ATP citrate lyase or in the cell line with stable severe (>90%) shRNA knockdown of ATP citrate lyase was similar to the controls. Both (13)C-glucose and (13)C-KIC introduced substantial (13)C labeling into acetyl-CoA, malonyl-CoA, and HMG-CoA under both conditions. Glucose flux into fatty acids was not affected by ATP citrate lyase knockdown. CONCLUSION: The results establish the involvement of the acetoacetate pathway in insulin secretion in pancreatic beta cells.