The synthetic liver X receptor agonist GW3965 reduces tissue factor production and inflammatory responses in human islets in vitro

Characterization of an Antibacterial Agent Targeting Ferrous Iron Transport Protein FeoB against Staphylococcus aureus and Gram-Positive Bacteria

The emergence of multidrug-resistant Staphylococcus aureus strains has become a serious clinical problem. Iron is absolutely required for the bacterial growth, virulence associated with colonization, and survival from the host immune system. The FeoB protein is a major iron permease in bacterial ferrous iron transport systems (Feo) that has been shown to play a crucial role in virulence of some pathogenic bacteria. However, FeoB is still uncharacterized in Gram-positive pathogens, and its effects on S. aureus pathogenesis are unknown. In this study, we identified a novel inhibitor, GW3965·HCl, that targets FeoB in S. aureus. The molecule effectively inhibited FeoB in vitro enzyme activity, bacterial growth, and virulence factor expression. Genome-editing and metabolomic analyses revealed that GW3965·HCl inhibited FeoB function and affected the associated mechanisms with reduced iron availability in S. aureus. Gentamicin resistance and Caenorhabditis elegans infection assays further demonstrated the power of GW3965·HCl as a safe and efficient antibacterial agent. In addition to S. aureus, GW3965·HCl also presented its effectiveness on inhibition of the FeoB activity and growth of Gram-positive bacteria. This novel inhibitor will provide new insight for developing a next-generation antibacterial therapy.

Approved LXR agonists exert unspecific effects on pancreatic β-cell function

Novel agonists of the nuclear liver-X-receptor (LXR) are designed to treat metabolic disorders or cancer. The rationale to develop these new drugs is based on promising results with established LXR agonist like T0901317 and GW3965. LXRα and LXRβ are expressed in β-cells, and expression is increased by T0901317. The aim of the present study was to evaluate whether effects of these drugs on β-cell function are specific and reliably linked to LXR activation. T0901317 and GW3965, widely used as specific LXR agonists, show rapid, non-genomic effects on stimulus-secretion coupling of mouse pancreatic β-cells at low µM concentrations. T0901317 lowered the cytosolic Ca²⁺ concentration, reduced or completely inhibited action potentials, and decreased insulin secretion. GW3965 exerted similar effects on insulin secretion. T0901317 affected the production of reactive oxygen species and ATP. The involvement of the classical nuclear LXRs in T0901317- and GW3965-mediated effects in β-cells could be ruled out using LXRα, LXRβ and double knockout mice. Our results strongly suggest that LXR agonists, that are considered to be specific for this receptor, interfere with mitochondrial metabolism and metabolism-independent processes in β-cells. Thus, it is indispensable to test novel LXR agonists accompanying to ongoing clinical trials for acute and chronic effects on cell function in cellular systems and/or animal models lacking classical LXRs.

Glucolipotoxicity Alters Insulin Secretion via Epigenetic Changes in Human Islets

Type 2 diabetes (T2D) is characterized by insufficient insulin secretion and elevated glucose levels, often in combination with high levels of circulating fatty acids. Long-term exposure to high levels of glucose or fatty acids impair insulin secretion in pancreatic islets, which could partly be due to epigenetic alterations. We studied the effects of high concentrations of glucose and palmitate combined for 48 h (glucolipotoxicity) on the transcriptome, the epigenome, and cell function in human islets. Glucolipotoxicity impaired insulin secretion, increased apoptosis, and significantly (false discovery rate <5%) altered the expression of 1,855 genes, including 35 genes previously implicated in T2D by genome-wide association studies (e.g., TCF7L2 and CDKN2B). Additionally, metabolic pathways were enriched for downregulated genes. Of the differentially expressed genes, 1,469 also exhibited altered DNA methylation (e.g., CDK1, FICD, TPX2, and TYMS). A luciferase assay showed that increased methylation of CDK1 directly reduces its transcription in pancreatic β-cells, supporting the idea that DNA methylation underlies altered expression after glucolipotoxicity. Follow-up experiments in clonal β-cells showed that knockdown of FICD and TPX2 alters insulin secretion. Together, our novel data demonstrate that glucolipotoxicity changes the epigenome in human islets, thereby altering gene expression and possibly exacerbating the secretory defect in T2D.

The effects of high glucose exposure on global gene expression and DNA methylation in human pancreatic islets

BACKGROUND

Type 2 diabetes (T2D) is a complex disease characterised by chronic hyperglycaemia. The effects of elevated glucose on global gene expression in combination with DNA methylation patterns have not yet been studied in human pancreatic islets. Our aim was to study the impact of 48 h exposure to high (19 mM) versus control (5.6 mM) glucose levels on glucose-stimulated insulin secretion, gene expression and DNA methylation in human pancreatic islets.

RESULTS

While islets kept at 5.6 mM glucose secreted significantly more insulin in response to short term glucose-stimulation (p = 0.0067), islets exposed to high glucose for 48 h were desensitised and unresponsive to short term glucose-stimulation with respect to insulin secretion (p = 0.32). Moreover, the exposure of human islets to 19 mM glucose resulted in significantly altered expression of eight genes (FDR<5%), with five of these (GLRA1, RASD1, VAC14, SLCO5A1, CHRNA5) also exhibiting changes in DNA methylation (p < 0.05). A gene set enrichment analysis of the expression data showed significant enrichment of e.g. TGF-beta signalling pathway, Notch signalling pathway and SNARE interactions in vesicular transport; these pathways are of relevance for islet function and possibly also diabetes. We also found increased DNA methylation of CpG sites annotated to PDX1 in human islets exposed to 19 mM glucose for 48 h. Finally, we could functionally validate a role for Glra1 in insulin secretion.

CONCLUSION

Our data demonstrate that high glucose levels affect human pancreatic islet gene expression and several of these genes also exhibit epigenetic changes. This might contribute to the impaired insulin secretion seen in T2D.

Use of additives, scaffolds and extracellular matrix components for improvement of human pancreatic islet outcomes in vitro: A systematic review

Pancreatic islet transplantation is an established treatment to restore insulin independence in type 1 diabetic patients. Its success rates have increased lately based on improvements in immunosuppressive therapies and on islet isolation and culture. It is known that the quality and quantity of viable transplanted islets are crucial for the achievement of insulin independence and some studies have shown that a significant number of islets are lost during culture time. Thus, in an effort to improve islet yield during culture period, researchers have tested a variety of additives in culture media as well as alternative culture devices, such as scaffolds. However, due to the use of different categories of additives or devices, it is difficult to draw a conclusion on the benefits of these strategies. Therefore, the aim of this systematic review was to summarize the results of studies that described the use of medium additives, scaffolds or extracellular matrix (ECM) components during human pancreatic islets culture. PubMed and Embase repositories were searched. Of 5083 articles retrieved, a total of 37 articles fulfilled the eligibility criteria and were included in the review. After data extraction, articles were grouped as follows: 1) "antiapoptotic/anti-inflammatory/antioxidant," 2) "hormone," 3) "sulphonylureas," 4) "serum supplements," and 5) "scaffolds or ECM components." The effects of the reviewed additives, ECM or scaffolds on islet viability, apoptosis and function (glucose-stimulated insulin secretion - GSIS) were heterogeneous, making any major conclusion hard to sustain. Overall, some "antiapoptotic/anti-inflammatory/antioxidant" additives decreased apoptosis and improved GSIS. Moreover, islet culture with ECM components or scaffolds increased GSIS. More studies are needed to define the real impact of these strategies in improving islet transplantation outcomes.

Cold Exposure Improves the Anti-diabetic Effect of T0901317 in Streptozotocin-Induced Diabetic Mice

Activation of liver X receptors (LXRs) can improve glucose tolerance in insulin-independent diabetes, however, whether similar effects can be achieved in insulin-dependent diabetes remains unclear. Here, we evaluated the anti-diabetic activity of T0901317, a potent agonist of LXRs, in diabetic mice induced by streptozotocin, and our data demonstrate that T0901317 is most effective when combined with cold treatment of animals. Treatment with T0901317 improved glucose tolerance of diabetic mice, which was associated with repressed expression of key genes involved in hepatic gluconeogenesis such as Pepck and G6p. Combined treatment by T0901317 and cold exposure reduced transcription of gluconeogenic genes to similar levels. Intriguingly, combined treatment greatly increased expression of Ucp1, Cidea, Dio2, and Elvol3 predominantly in the inguinal white adipose tissue, consequently leading to browning of this fat pad, and resulting in further improvement of glucose tolerance which was associated with increased protein levels of UCP1 and GLUT4. Collectively, these results suggest that browning of white adipose tissue via cold exposure in combination with activation of liver X receptors is an alternative and effective strategy to manage insulin-dependent diabetes.

Effects of palmitate on genome-wide mRNA expression and DNA methylation patterns in human pancreatic islets

BACKGROUND

Circulating free fatty acids are often elevated in patients with type 2 diabetes (T2D) and obese individuals. Chronic exposure to high levels of saturated fatty acids has detrimental effects on islet function and insulin secretion. Altered gene expression and epigenetics may contribute to T2D and obesity. However, there is limited information on whether fatty acids alter the genome-wide transcriptome profile in conjunction with DNA methylation patterns in human pancreatic islets. To dissect the molecular mechanisms linking lipotoxicity to impaired insulin secretion, we investigated the effects of a 48 h palmitate treatment in vitro on genome-wide mRNA expression and DNA methylation patterns in human pancreatic islets.

METHODS

Genome-wide mRNA expression was analyzed using Affymetrix GeneChip(®) Human Gene 1.0 ST whole transcript-based array (n = 13) and genome-wide DNA methylation was analyzed using Infinium HumanMethylation450K BeadChip (n = 13) in human pancreatic islets exposed to palmitate or control media for 48 h. A non-parametric paired Wilcoxon statistical test was used to analyze mRNA expression. Apoptosis was measured using Apo-ONE(®) Homogeneous Caspase-3/7 Assay (n = 4).

RESULTS

While glucose-stimulated insulin secretion was decreased, there was no significant effect on apoptosis in human islets exposed to palmitate. We identified 1,860 differentially expressed genes in palmitate-treated human islets. These include candidate genes for T2D, such as TCF7L2, GLIS3, HNF1B and SLC30A8. Additionally, genes in glycolysis/gluconeogenesis, pyruvate metabolism, fatty acid metabolism, glutathione metabolism and one carbon pool by folate were differentially expressed in palmitate-treated human islets. Palmitate treatment altered the global DNA methylation level and DNA methylation levels of CpG island shelves and shores, 5'UTR, 3'UTR and gene body regions in human islets. Moreover, 290 genes with differential expression had a corresponding change in DNA methylation, for example, TCF7L2 and GLIS3. Importantly, out of the genes differentially expressed due to palmitate treatment in human islets, 67 were also associated with BMI and 37 were differentially expressed in islets from T2D patients.

CONCLUSION

Our study demonstrates that palmitate treatment of human pancreatic islets gives rise to epigenetic modifications that together with altered gene expression may contribute to impaired insulin secretion and T2D.

Platelet-activating factor downregulates the expression of liver X receptor-α and its target genes in human neutrophils

Liver X receptors (LXRs) are ligand-activated members of the nuclear receptor superfamily that regulate the expression of genes involved in lipid metabolism and inflammation, although their role in inflammation and immunity is less well known. It has been reported that oxysterols/LXRs may act as anti-inflammatory molecules, although opposite actions have also been reported. In this study, we investigated the effect of platelet-activating factor (PAF), a proinflammatory molecule, on LXRα signalling in human neutrophils. We found that PAF exerted an inhibitory effect on mRNA expression of TO901317-induced LXRα, ATP-binding cassette transporter A1, ATP-binding cassette transporter G1, and sterol response element binding protein 1c. This negative action was mediated by the PAF receptor, and was dependent on the release of reactive oxygen species elicited by PAF, as it was enhanced by pro-oxidant treatment and reversed by antioxidants. Current data also support the idea that PAF induces phosphorylation of the LXRα molecule in an extracellular signal-regulated kinase 1/2-mediated fashion. These results suggest that a possible mechanism by which PAF exerts its proinflammatory effect is through the downregulation of LXRα and its related genes, which supports the notion that LXRα ligands exert a modulatory role in the neutrophil-mediated inflammatory response.

The effect of hepatic progenitor cells on experimental hepatocellular carcinoma in the regenerating liver

OBJECTIVE

Liver regeneration following hepatectomy can stimulate the growth of hepatocellular carcinoma (HCC), and major hepatectomy can be associated with activation of hepatic progenitor cells (HPCs). The aim of this study was to evaluate how HPCs influence the malignant potential of tumor cells in vitro and HCC tumor growth after surgery in a rodent model.

MATERIAL AND METHODS

Hepatoma cells (JM1) were cultured with conditioned medium (CM) from syngeneic HPCs (WB-F344). Growth rate, resistance to Adriamycin, and expression patterns for invasiveness and stemness were compared with naïve JM1. Microscopic HCC tumors from naïve JM1 or JM1 cultured with CM were inoculated in Fischer 344 rats undergoing 70% hepatectomy with or without simultaneous infusion of WB-F344. Tumor growth and invasiveness-related factors were compared. Buffalo rats were induced with Morris hepatoma cells. Liver tissue from both in vivo models was examined with regard to activation of cells with progenitor-like phenotype.

RESULTS

Co-culture with CM resulted in an increased resistance to Adriamycin and enhanced expressions of α-FP, MMP9, ABCG2, CD133, and SOX2, as well as the activation of ERK, AKT, WNT, and TGF-β1 pathways. Tumor size and metastases were significantly higher in groups with co-cultured cells or HPCs infusion. After 70% hepatectomy and tumor implantation, cells positive for α-FP, CK19, and CD133 were found, thus suggesting a progenitor-like phenotype in the setting of epithelial-mesenchymal transition.

CONCLUSION

HPCs have a marked effect on HCC cells in vitro and appear to stimulate the growth and malignant potential of experimental HCC tumors.

Polymorphisms of genes involved in polycyclic aromatic hydrocarbons' biotransformation and atherosclerosis

Polycyclic aromatic hydrocarbons (PAHs) are among the most prevalent environmental pollutants and result from the incomplete combustion of hydrocarbons (coal and gasoline, fossil fuel combustion, byproducts of industrial processing, natural emission, cigarette smoking, etc.). The first phase of xenobiotic biotransformation in the PAH metabolism includes activities of cytochrome P450 from the CYP1 family and microsomal epoxide hydrolase. The products of this biotransformation are reactive oxygen species that are transformed in the second phase through the formation of conjugates with glutathione, glucuronate or sulphates. PAH exposure may lead to PAH-DNA adduct formation or induce an inflammatory atherosclerotic plaque phenotype. Several genetic polymorphisms of genes encoded for enzymes involved in PAH biotransformation have been proven to lead to the development of diseases. Enzyme CYP P450 1A1, which is encoded by the CYP1A1 gene, is vital in the monooxygenation of lipofilic substrates, while GSTM1 and GSTT1 are the most abundant isophorms that conjugate and neutralize oxygen products. Some single nucleotide polymorphisms of the CYP1A1 gene as well as the deletion polymorphisms of GSTT1 and GSTM1 may alter the final specific cellular inflammatory respond. Occupational exposure or conditions from the living environment can contribute to the production of PAH metabolites with adverse effects on human health. The aim of this study was to obtain data on biotransformation and atherosclerosis, as well as data on the gene polymorphisms involved in biotransformation, in order to better study gene expression and further elucidate the interaction between genes and the environment.

Liver X receptor biology and pharmacology: new pathways, challenges and opportunities

Nuclear receptors (NRs) are master regulators of transcriptional programs that integrate the homeostatic control of almost all biological processes. Their direct mode of ligand regulation and genome interaction is at the core of modern pharmacology. The two liver X receptors LXRα and LXRβ are among the emerging newer drug targets within the NR family. LXRs are best known as nuclear oxysterol receptors and physiological regulators of lipid and cholesterol metabolism that also act in an anti-inflammatory way. Because LXRs control diverse pathways in development, reproduction, metabolism, immunity and inflammation, they have potential as therapeutic targets for diseases as diverse as lipid disorders, atherosclerosis, chronic inflammation, autoimmunity, cancer and neurodegenerative diseases. Recent insights into LXR signaling suggest future targeting strategies aiming at increasing LXR subtype and pathway selectivity. This review discusses the current status of our understanding of LXR biology and pharmacology, with an emphasis on the molecular aspects of LXR signaling that constitute the potential of LXRs as drug targets.

Liver X receptor agonist T0901317 induced liver perturbation in zebrafish: histological, gene set enrichment and expression analyses

BACKGROUND

Liver X receptor (LXR), a ligand-activated transcription factor, regulates important biological processes. It has been associated with pathology and proposed as a therapeutic target. The zebrafish is a new vertebrate model for disease modeling, drug and toxicity screening and will be interesting to test for its potential for LXR-related studies.

METHODS

Adult male fish were exposed to LXR agonist T0901317 at 20, 200 and 2000nM for 96h and the livers were sampled for histological, microarray and qRT-PCR analyses.

RESULTS

Histological analysis suggests dose-dependent perturbation of carbohydrate and lipid metabolisms by T0901317 in the liver, which lead to hepatocyte swelling and cell death. Microarray data revealed several conserved effects of T0901317 with mammalian models, including up-regulation of LXR-targeted genes, modulation of biological pathways associated with proteasome, cell death, extracellular matrix and adhesions, maturity onset diabetes of the young and lipid beta oxidation. Interestingly, this study identified the complement and coagulation systems as down-regulated by T0901317 for the first time, potentially via transcriptional repression by LXR activation. qRT-PCR validated the expression of 16 representative genes, confirming activation of LXR signaling and down-regulation of these biological pathways by T0901317 which could be linked to the anti-thrombogenic, anti-atherogenic and anti-inflammatory actions, as well as metabolic disruptions via LXR activation.

CONCLUSION AND GENERAL SIGNIFICANCE

Our study underscores the potential of using zebrafish model coupled with transcriptomic analysis to capture pharmacological and toxicological or pathological events induced by LXR modulators.

Liver X receptor agonists augment human islet function through activation of anaplerotic pathways and glycerolipid/free fatty acid cycling

Recent studies in rodent models suggest that liver X receptors (LXRs) may play an important role in the maintenance of glucose homeostasis and islet function. To date, however, no studies have comprehensively examined the role of LXRs in human islet biology. Human islets were isolated from non-diabetic donors and incubated in the presence or absence of two synthetic LXR agonists, TO-901317 and GW3965, under conditions of low and high glucose. LXR agonist treatment enhanced both basal and stimulated insulin secretion, which corresponded to an increase in the expression of genes involved in anaplerosis and reverse cholesterol transport. Furthermore, enzyme activity of pyruvate carboxylase, a key regulator of pyruvate cycling and anaplerotic flux, was also increased. Whereas LXR agonist treatment up-regulated known downstream targets involved in lipogenesis, we observed no increase in the accumulation of intra-islet triglyceride at the dose of agonist used in our study. Moreover, LXR activation increased expression of the genes encoding hormone-sensitive lipase and adipose triglyceride lipase, two enzymes involved in lipolysis and glycerolipid/free fatty acid cycling. Chronically, insulin gene expression was increased after treatment with TO-901317, and this was accompanied by increased Pdx-1 nuclear protein levels and enhanced Pdx-1 binding to the insulin promoter. In conclusion, our data suggest that LXR agonists have a direct effect on the islet to augment insulin secretion and expression, actions that should be considered either as therapeutic or unintended side effects, as these agents are developed for clinical use.