Development and validation of a high-throughput screening assay for human long-chain fatty acid transport proteins 4 and 5

SAH is a major metabolic sensor mediating worsening metabolic crosstalk in metabolic syndrome

In this study, we observed worsening metabolic crosstalk in mouse models with concomitant metabolic disorders such as hyperhomocysteinemia (HHcy), hyperlipidemia, and hyperglycemia and in human coronary artery disease by analyzing metabolic profiles. We found that HHcy worsening is most sensitive to other metabolic disorders. To identify metabolic genes and metabolites responsible for the worsening metabolic crosstalk, we examined mRNA levels of 324 metabolic genes in Hcy, glucose-related and lipid metabolic systems. We examined Hcy-metabolites (Hcy, SAH and SAM) by LS-ESI-MS/MS in 6 organs (heart, liver, brain, lung, spleen, and kidney) from C57BL/6J mice. Through linear regression analysis of Hcy-metabolites and metabolic gene mRNA levels, we discovered that SAH-responsive genes were responsible for most metabolic changes and all metabolic crosstalk mediated by Serine, Taurine, and G3P. SAH-responsive genes worsen glucose metabolism and cause upper glycolysis activation and lower glycolysis suppression, indicative of the accumulation of glucose/glycogen and G3P, Serine synthesis inhibition, and ATP depletion. Insufficient Serine due to negative correlation of PHGDH with SAH concentration may inhibit the folate cycle and transsulfurarion pathway and consequential reduced antioxidant power, including glutathione, taurine, NADPH, and NAD+. Additionally, we identified SAH-activated pathological TG loop as the consequence of increased fatty acid (FA) uptake, FA β-oxidation and Ac-CoA production along with lysosomal damage. We concluded that HHcy is most responsive to other metabolic changes in concomitant metabolic disorders and mediates worsening metabolic crosstalk mainly via SAH-responsive genes, that organ-specific Hcy metabolism determines organ-specific worsening metabolic reprogramming, and that SAH, acetyl-CoA, Serine and Taurine are critical metabolites mediating worsening metabolic crosstalk, redox disturbance, hypomethylation and hyperacetylation linking worsening metabolic reprogramming in metabolic syndrome.

Fatty acid transport proteins (FATPs) in cancer

Lipids play pivotal roles in cancer biology. Lipids have a wide range of biological roles, especially in cell membrane synthesis, serve as energetic molecules in regulating energy-demanding processes; and they play a significant role as signalling molecules and modulators of numerous cellular functions. Lipids may participate in the development of cancer through the fatty acid signalling pathway. Lipids consumed in the diet act as a key source of extracellular pools of fatty acids transported into the cellular system. Increased availability of lipids to cancer cells is due to increased uptake of fatty acids from adipose tissues. Lipids serve as a source of energy for rapidly dividing cancerous cells. Surviving requires the swift synthesis of biomass and membrane matrix to perform exclusive functions such as cell proliferation, growth, invasion, and angiogenesis. FATPs (fatty acid transport proteins) are a group of proteins involved in fatty acid uptake, mainly localized within cells and the cellular membrane, and have a key role in long-chain fatty acid transport. FATPs are composed of six isoforms that are tissue-specific and encoded by a specific gene. Previous studies have reported that FATPs can alter fatty acid metabolism, cell growth, and cell proliferation and are involved in the development of various cancers. They have shown increased expression in most cancers, such as melanoma, breast cancer, prostate cancer, renal cell carcinoma, hepatocellular carcinoma, bladder cancer, and lung cancer. This review introduces a variety of FATP isoforms and summarises their functions and their possible roles in the development of cancer.

Epigenetic association study uncovered H3K27 acetylation enhancers and dysregulated genes in high-fat-diet-induced nonalcoholic fatty liver disease in rats

Aim: To evaluate the regulatory landscape underlying the active enhancer marked by H3K27ac in high-fat diet (HFD)-induced nonalcoholic fatty liver disease (NAFLD) in rats. Materials & methods: H3K27ac chromatin immunoprecipitation and high-throughput RNA sequencing to construct regulatory profiles and transcriptome of liver from NAFLD rat model induced by HFD. De novo motif analysis for differential H3K27ac peaks. Functional enrichment, Kyoto Encyclopedia of Genes and Genomes pathway and protein-protein interaction network were examined for differential peak-genes. The mechanism was further verified by western blot, chromatin immunoprecipitation-quantitative PCR and real-time PCR. Results: A total of 1831 differential H3K27ac peaks were identified significantly correlating with transcription factors and target genes (CYP8B1, PLA2G12B, SLC27A5, CYP7A1 and APOC3) involved in lipid and energy homeostasis. Conclusion: Altered acetylation induced by HFD leads to the dysregulation of gene expression, further elucidating the epigenetic mechanism in the etiology of NAFLD.

Fatty acid metabolism and acyl-CoA synthetases in the liver-gut axis

Fatty acids are energy substrates and cell components which participate in regulating signal transduction, transcription factor activity and secretion of bioactive lipid mediators. The acyl-CoA synthetases (ACSs) family containing 26 family members exhibits tissue-specific distribution, distinct fatty acid substrate preferences and diverse biological functions. Increasing evidence indicates that dysregulation of fatty acid metabolism in the liver-gut axis, designated as the bidirectional relationship between the gut, microbiome and liver, is closely associated with a range of human diseases including metabolic disorders, inflammatory disease and carcinoma in the gastrointestinal tract and liver. In this review, we depict the role of ACSs in fatty acid metabolism, possible molecular mechanisms through which they exert functions, and their involvement in hepatocellular and colorectal carcinoma, with particular attention paid to long-chain fatty acids and small-chain fatty acids. Additionally, the liver-gut communication and the liver and gut intersection with the microbiome as well as diseases related to microbiota imbalance in the liver-gut axis are addressed. Moreover, the development of potentially therapeutic small molecules, proteins and compounds targeting ACSs in cancer treatment is summarized.

An Overview of Cell-Based Assay Platforms for the Solute Carrier Family of Transporters

The solute carrier (SLC) superfamily represents the biggest family of transporters with important roles in health and disease. Despite being attractive and druggable targets, the majority of SLCs remains understudied. One major hurdle in research on SLCs is the lack of tools, such as cell-based assays to investigate their biological role and for drug discovery. Another challenge is the disperse and anecdotal information on assay strategies that are suitable for SLCs. This review provides a comprehensive overview of state-of-the-art cellular assay technologies for SLC research and discusses relevant SLC characteristics enabling the choice of an optimal assay technology. The Innovative Medicines Initiative consortium RESOLUTE intends to accelerate research on SLCs by providing the scientific community with high-quality reagents, assay technologies and data sets, and to ultimately unlock SLCs for drug discovery.

Bile acids mediated potential functional interaction between FXR and FATP5 in the regulation of Lipid Metabolism

Perturbation in lipid homeostasis is one of the major bottlenecks in metabolic diseases, especially Non-alcoholic Fatty Liver Disease (NAFLD), which has emerged as a leading global cause of chronic liver disease. The bile acids (BAs) and their derivatives exert a variety of metabolic effects through complex and intertwined pathways, thus becoming the attractive target for metabolic syndrome treatment. To modulate the lipid homeostasis, the role of BAs, turn out to be paramount as it is essential for the absorption, transport of dietary lipids, regulation of metabolic enzymes and transporters that are essential for lipid modulation, flux, and excretion. The synthesis and transport of BAs (conjugated and unconjugated) is chiefly controlled by nuclear receptors and the uptake of long-chain fatty acids (LCFA) and BA conjugation via transporters. Among them, from in-vivo studies, farnesoid X receptor (FXR) and liver-specific fatty acid transport protein 5 (FATP5) have shown convincing evidence for their key roles in lipid homeostasis and reversal of fatty liver disease substantially. BAs have a wider range of biological effects as they are identified as modulators for FXR and FATP5 both and therefore hold a significant promise for altering the lipid content in the treatment of a metabolic disorder. BAs also have received noteworthy interest in drug delivery research due to its peculiar physicochemical properties and biocompatibility. Here, we are highlighting the connecting possibility of BAs as an agonist for FXR and antagonist for FATP5, paving an avenue to target them for designing synthetic small molecules for lipid homeostasis.

Molecular targeting of FATP4 transporter for oral delivery of therapeutic peptide

Low oral bioavailability of peptide drugs has limited their application to parenteral administration, which suffers from poor patient compliance. Here, we show that molecular targeting of the FATP4 transporter is an effective approach to specifically transport long-chain fatty acid (LCFA)-conjugated peptides across the enterocytic membrane and, thus, enables oral delivery of drug peptides. We packaged LCFA-conjugated exendin-4 (LCFA-Ex4) into liposomes and coated with chitosan nanoparticles to form an orally deliverable Ex4 (OraEx4). OraEx4 protected LCFA-Ex4 from damage by the gastric fluid and released LCFA-Ex4 in the intestinal cavity, where LCFA-Ex4 was transported across the enterocyte membrane by the FAPT4 transporter. OraEx4 had a high bioavailability of 24.8% with respect to subcutaneous injection and exhibited a substantial hypoglycemic effect in murine models of diabetes mellitus. Thus, molecular targeting of the FATP4 transporter enhances oral absorption of therapeutic peptides and provides a platform for oral peptide drug development.

Intestinal Saturated Long-Chain Fatty Acid, Glucose and Fructose Transporters and Their Inhibition by Natural Plant Extracts in Caco-2 Cells

The intestinal absorption of fatty acids, glucose and fructose is part of the basic requirements for the provision of energy in the body. High access of saturated long-chain fatty acids (LCFA), glucose and fructose can facilitate the development of metabolic diseases, particularly the metabolic syndrome and type-2 diabetes mellitus (T2DM). Research has been done to find substances which decelerate or inhibit intestinal resorption of these specific food components. Promising targets are the inhibition of intestinal long-chain fatty acid (FATP2, FATP4), glucose (SGLT1, GLUT2) and fructose (GLUT2, GLUT5) transporters by plant extracts and by pure substances. The largest part of active components in plant extracts belongs to the group of polyphenols. This review summarizes the knowledge about binding sites of named transporters and lists the plant extracts which were tested in Caco-2 cells regarding uptake inhibition.

Computational Discovery and Experimental Validation of Inhibitors of the Human Intestinal Transporter OATP2B1

Human organic anion transporters (OATPs) are vital for the uptake and efflux of drugs and endogenous compounds. Current identification of inhibitors of these transporters is based on experimental screening. Virtual screening remains a challenge due to a lack of experimental three-dimensional protein structures. Here, we describe a workflow to identify inhibitors of the OATP2B1 transporter in the DrugBank library of over 5,000 drugs and druglike molecules. OATP member 2B1 transporter is highly expressed in the intestine, where it participates in oral absorption of drugs. Predictions from a Random forest classifier, prioritized by docking against multiple comparative protein structure models of OATP2B1, indicated that 33 of the 5,000 compounds were putative inhibitors of OATP2B1. Ten predicted inhibitors that are prescription drugs were tested experimentally in cells overexpressing the OATP2B1 transporter. Three of these ten were validated as potent inhibitors of estrone-3-sulfate uptake (defined as more than 50% inhibition at 20 μM) and tested in multiple concentrations to determine exact IC₅₀. The IC₅₀ values of bicalutamide, ticagrelor, and meloxicam suggest that they might inhibit intestinal OATP2B1 at clinically relevant concentrations and therefore modulate the absorption of other concomitantly administered drugs.

The Concise Guide to PHARMACOLOGY 2013/14: transporters

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. Transporters are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

SLC27 fatty acid transport proteins

The uptake and metabolism of long chain fatty acids (LCFA) are critical to many physiological and cellular processes. Aberrant accumulation or depletion of LCFA underlie the pathology of numerous metabolic diseases. Protein-mediated transport of LCFA has been proposed as the major mode of LCFA uptake and activation. Several proteins have been identified to be involved in LCFA uptake. This review focuses on the SLC27 family of fatty acid transport proteins, also known as FATPs, with an emphasis on the gain- and loss-of-function animal models that elucidate the functions of FATPs in vivo and how these transport proteins play a role in physiological and pathological situations.

Specific bile acids inhibit hepatic fatty acid uptake in mice

Bile acids are known to play important roles as detergents in the absorption of hydrophobic nutrients and as signaling molecules in the regulation of metabolism. We tested the novel hypothesis that naturally occurring bile acids interfere with protein-mediated hepatic long chain free fatty acid (LCFA) uptake. To this end, stable cell lines expressing fatty acid transporters as well as primary hepatocytes from mouse and human livers were incubated with primary and secondary bile acids to determine their effects on LCFA uptake rates. We identified ursodeoxycholic acid (UDCA) and deoxycholic acid (DCA) as the two most potent inhibitors of the liver-specific fatty acid transport protein 5 (FATP5). Both UDCA and DCA were able to inhibit LCFA uptake by primary hepatocytes in a FATP5-dependent manner. Subsequently, mice were treated with these secondary bile acids in vivo to assess their ability to inhibit diet-induced hepatic triglyceride accumulation. Administration of DCA in vivo via injection or as part of a high-fat diet significantly inhibited hepatic fatty acid uptake and reduced liver triglycerides by more than 50%.

CONCLUSION

The data demonstrate a novel role for specific bile acids, and the secondary bile acid DCA in particular, in the regulation of hepatic LCFA uptake. The results illuminate a previously unappreciated means by which specific bile acids, such as UDCA and DCA, can impact hepatic triglyceride metabolism and may lead to novel approaches to combat obesity-associated fatty liver disease.

Caffeine dose-dependently induces thermogenesis but restores ATP in HepG2 cells in culture

Caffeine has been hypothesised as a thermogenic agent that might help to maintain a healthy body weight. Since very little is known about its actions on cellular energy metabolism, we investigated the effect of caffeine on mitochondrial oxidative phosphorylation, cellular energy supply and thermogenesis in HepG2 cells, and studied its action on fatty acid uptake and lipid accumulation in 3T3-L1 adipocytes at concentrations ranging from 30-1500 μM. In HepG2 cells, caffeine induced a depolarisation of the inner mitochondrial membrane, a feature of mitochondrial thermogenesis, both directly and after 24 h incubation. Increased concentrations of uncoupling protein-2 (UCP-2) also indicated a thermogenic activity of caffeine. Energy generating pathways, such as mitochondrial respiration, fatty acid oxidation and anaerobic lactate production, were attenuated by caffeine treatment. Nevertheless, HepG2 cells demonstrated a higher energy charge potential after exposure to caffeine that might result from energy restoration through attenuation of energy consuming pathways, as typically found in hibernating animals. In 3T3-L1 cells, in contrast, caffeine increased fatty acid uptake, but did not affect lipid accumulation. We provide evidence that caffeine stimulates thermogenesis but concomitantly causes energy restoration that may compensate enhanced energy expenditure.

Ontogenic expression pattern and genetic polymorphisms of the fatty acid transport protein 4 (FATP4) gene in Chinese chicken populations

In the current research, the polymorphism of FATP4 gene was analyzed in Erlang Mountainous chickens. A total of nine genetic variants were identified by FATP4 gene sequencing analysis across the chicken samples. Significant associations (p < 0.05) were observed for two SNPs (g.5608778C>T and g.5608814G>A in exon 6) with certain carcass traits (such as live weight, carcass weight, eviscerated weight) in S01 and S05 populations, respectively. Meanwhile, in S05 population, haplotype 3 (T-G) and haplotype 2 (C-A) were associated with higher and lower partial carcass traits such as live weight, carcass weight, eviscerated weight and semi-eviscerated weight, respectively. Moreover, we investigated the expression profile of this gene during ontogenesis in Mountainous black-boned chicken. Quantitative real-time PCR analysis showed that FATP4 mRNA had the highest expression level in small intestine tissue over all other tissues examined. The FATP4 mRNA levels presented remarkable developmental changes with age in the various tissues. These results suggested that the FATP4 gene might play an important role in controlling chicken carcass traits.

Structure-based discovery of anti-influenza virus A compounds among medicines

BACKGROUND

Influenza A virus (IAV) infection is nowadays a major public health concern, in particular since the 2009 H1N1 flu pandemic. The outbreak of IAV strains resistant to currently available drugs, such as oseltamivir or zanamivir targeting the neuraminidase, is a real threat for humans as well as for animals. Thus the development of anti-IAV drugs with a novel action mechanism may be an urgent theme.

METHODS

We performed a docking simulation targeting the interface of PA interacting with PB1 using a drug database including ~4000 compounds. We then conducted cell viability assay and plaque assay using IAV/WSN/33. Finally we examined their anti-IAV mechanism by surface plasmon resonance and IAV replicon assay.

RESULTS

We found that benzbromarone, diclazuril, and trenbolone acetate had strong anti-IAV activities. We confirmed that benzbromarone and diclazuril bound with PA subunit, and decreased the transcriptional activity of the viral RNA polymerase.

CONCLUSIONS

Benzbromarone and diclazuril had strong anti-IAV activities with novel action mechanism, i.e. inhibition of viral RNA polymerase.

GENERAL SIGNIFICANCE

Since benzbromarone and diclazuril are already used in public as medicines, these could be the candidates for alternatives in case of an outbreak of IAV which is resistant to pre-existing anti-IAV drugs.